Nanocrystals

Abstract

The present invention provides the use of a lead (IV)-containing compound for the preparation of a chalcogenide nanocrystal of lead, and a method of manufacturing a broadband chalcogenide nanocrystal of lead in a low-cost, size-controllable and scalable process comprising contacting a lead (IV)-containing compound with an organic acid and a chalcogen-containing agent.

Description

[0001] This patent application is a divisional application of the patent application with application number 2020800240263, application date March 25, 2020, and invention name “Nanocrystals”. Technical Field

[0003] The present invention generally relates to lead chalcogenide nanocrystals. In particular, the present invention relates to a method for making lead chalcogenide nanocrystals using lead (IV) containing compounds. The present invention also extends to the lead chalcogenide nanocrystals obtained by the method and the uses of the lead chalcogenide nanocrystals. Background Art

[0004] Nanocrystals can be used for a wide range of applications, for example because the optical properties of nanocrystals can be fine-tuned to provide desired properties. The optical properties (e.g., light absorption and emission characteristics) of nanocrystals can be fine-tuned by controlling the size of the nanocrystals. The largest nanocrystals produce the longest wavelength (and the lowest frequency), while the smallest nanocrystals produce shorter wavelengths (and higher frequencies). The size of the nanocrystals can be controlled by the method for making nanocrystals. This possibility of fine-tuning the optical properties of nanocrystals by controlling the size of the nanocrystals makes nanocrystals suitable for a wide range of applications, including (e.g.) photodetectors, sensors, solar cells, bioimaging and biosensing, photovoltaics, displays, lighting, security and anti-counterfeiting, batteries, wired high-speed communications, quantum dot (QD) lasers, photocatalysts, spectrometers, injectable compositions, field effect transistors, light emitting diodes, lasers, photonic or optical switching devices, hydrogen manufacturing, and metamaterials.

[0005] Lead nanocrystals are known, and various methods for making lead nanocrystals are also known. For example, Hines et al. disclose a method for preparing lead sulfide nanocrystals having a band gap tunable throughout the near infrared (e.g., 800 nm to 1800 nm) in Adv. Mater. 2003, 15, No. 21, 1844-1849. Lead sulfide nanocrystals can be prepared by reacting lead (II) oxide (PbO) with oleic acid to form lead oleate, and then reacting the lead oleate with bis (trimethylsilyl) sulfide. However, the starting material lead (II) oxide is very expensive, and it was found that the reaction described by Hines et al. was difficult to control on a large scale. Therefore, the method disclosed by Hines et al. is not suitable for large-scale production of lead nanocrystals.

[0006] Cademartiri et al., J. Phys. Chem. B., vol. 110, no. 2, 2006, 671-

[0007] 673 discloses a method for preparing lead sulfide nanocrystals, wherein lead chloride (PbCl2) reacts with oleylamine and elemental sulfur. The nanocrystals obtained by this method are difficult to purify and exhibit a limited peak absorption of 1245nm to 1625nm. The residual lead chloride remaining on the lead sulfide nanocrystals is usually precipitated over a long period of time, making it difficult to manufacture high-purity lead sulfide nanocrystals from lead chloride. Therefore, the method disclosed by Cademartiri et al. is not suitable for large-scale production of pure and highly monodispersed lead sulfide nanocrystals.

[0008] Hendricks et al. disclose a method for preparing lead sulfide nanocrystals in Science, 2015, 348, 1226-1230, wherein lead oleate reacts with reactive disubstituted thiourea. The lead sulfide nanocrystals prepared by this method exhibit an absorption peak of 850nm to 1800nm. Since it controls the size (and absorption) of the nanocrystals by changing the side chain of the thiourea reactant, this method is difficult to carry out on a large scale.

[0009] Thus, although several methods are known for making lead chalcogenide nanocrystals, these methods do not allow for the pre-control of the crystal size and therefore do not allow for fine tuning of the optical properties of the nanocrystals. The known methods also generally do not provide nanocrystals that exhibit a broad absorption range. Furthermore, the known methods are not suitable for large-scale (e.g., commercially available) preparation of lead chalcogenide nanocrystals.

[0010] Therefore, there is a need to find alternative methods for preparing lead chalcogenide nanocrystals that can be used on a large scale (e.g., commercially available) and / or that can pre-control the size of the prepared nanocrystals to enable fine-tuning of the optical properties of the nanocrystals. There is also a need to find methods that can provide lead chalcogenide nanocrystals that exhibit a wide absorption range. It is believed that such methods will provide lead chalcogenide nanocrystals that are suitable for a wide range of applications. Summary of the invention

[0011] According to a first aspect of the present invention, there is provided a use of a lead (IV)-containing compound for preparing lead chalcogenide nanocrystals or a lead chalcogenide nanocrystal composition.

[0012] According to a second aspect of the present invention, there is provided use of lead (II, IV) oxide to prepare lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions.

[0013] According to a third aspect of the present invention, there is provided a method for preparing lead chalcogenide nanocrystals or a lead chalcogenide nanocrystal composition, the method comprising contacting a lead (IV)-containing compound with an organic acid and a chalcogen-containing reagent.

[0014] According to a fourth aspect of the present invention, there is provided a method for preparing lead chalcogenide nanocrystals or a lead chalcogenide nanocrystal composition, the method comprising contacting lead (II, IV) oxide with an organic acid and a chalcogen-containing reagent.

[0015] According to a fifth aspect of the present invention, there is provided a composition of lead chalcogenide nanocrystals obtained by the method according to the third or fourth aspect of the present invention.

[0016] According to a sixth aspect of the present invention, there is provided a film comprising a composition of nanocrystals according to the fifth aspect of the present invention.

[0017] According to a seventh aspect of the present invention, a system or composition is provided, such as a photodetector, a sensor, a solar cell, a bioimaging or biosensing composition, a photovoltaic system, a display, a battery, a laser, a photocatalyst, a spectrometer, an injectable composition, a field effect transistor, a light-emitting diode, a photonic or optical switching device or a metamaterial comprising a composition according to the fifth aspect of the present invention.

[0018] According to an eighth aspect of the present invention, there is provided a lead chalcogenide nanocrystal composition, wherein the average particle size of the nanocrystals ranges from 2 nm to 20 nm and the relative size dispersion is less than 25%.

[0019] The nanocrystalline composition according to the eighth aspect of the present invention preferably exhibits an absorption wavelength range of 500 nm to 4500 nm, preferably suitably in the range of 500 nm to 2400 nm.

[0020] The nanocrystalline composition according to the eighth aspect of the present invention preferably exhibits an emission wavelength in the range of 600 nm to 4500 nm, preferably suitably in the range of 600 nm to 2500 nm.

[0021] The nanocrystalline composition according to the eighth aspect of the present invention preferably exhibits an absorption full width at half maximum (FWHM) value of less than 250nm, preferably less than 230nm, preferably less than 130nm, preferably less than 110nm. Preferably, the FWHM range is in the range of 10nm to 250nm, preferably 20nm to 220nm, preferably 50nm to 150nm, preferably 75nm to 115nm, preferably 80nm to 110nm.

[0022] The nanocrystalline composition according to the eighth aspect of the present invention preferably exhibits an emission full width at half maximum (FWHM) value of less than 250 nm, preferably less than 230 nm, preferably less than 150 nm.

[0023] Preferably, the FWHM range is in the range of 10 nm to 250 nm, preferably 20 nm to 220 nm, preferably 30 nm to 150 nm, preferably 40 nm to 110 nm.

[0024] The nanocrystalline composition according to the eighth aspect of the invention preferably exhibits a quantum yield (QY) value greater than 10%, preferably greater than 20%, preferably greater than 40%, preferably greater than 50%.

[0025] According to the first to eighth aspects of the present invention, it is preferred that the lead chalcogenide nanocrystals or the lead chalcogenide nanocrystal composition comprises PbS, PbSe, PbTe or a mixture thereof, more preferably PbS or PbSe, most preferably PbS. DETAILED DESCRIPTION

[0026] When describing aspects of the present invention, the terms used are to be interpreted in accordance with the following definitions, unless the context dictates otherwise.

[0027] Unless the context clearly dictates otherwise, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include both singular and plural referents. For example, "a nanocrystal" refers to one nanocrystal or more than one nanocrystal. For example, "a lead (IV) compound" refers to one lead (IV) compound or more than one lead (IV) compound. When used with inclusive language, reference to a number includes combinations including or greater than the number.

[0028] As used herein, the terms "comprising", "comprises" and "comprised of" are synonymous with "including", "includes" or "containing".

[0029] ("containing", "contains") is synonymous and is inclusive or open-ended and does not exclude additional unlisted components, elements or method steps. The term "comprising"

[0030] The terms “comprising,” “comprises,” and “comprised of” also include the term “consisting of.”

[0031] As used herein, when the term "and / or" is used in a list of two or more items, it means that any one of the listed items can be used alone, or any combination of two or more of the listed items can be used. For example, if a list is described as including groups A, B, and / or C, the list can include only A; only B; only C; include a combination of A and B; include a combination of A and C, include a combination of B and C; or include a combination of A, B, and C.

[0032] As used herein, unless expressly stated otherwise, all numbers such as numbers expressing values, ranges, quantities, percentages, etc. may be considered to be preceded by the word "about", even if the term does not expressly appear.

[0033] When referring to measurable values ​​such as parameters, amounts, time intervals, etc., the term "about" as used herein means that the value includes the standard deviation of error for the device or method used to determine the value. The term "about" is intended to include variations of + / -10% or less, + / -5% or less, or + / -0.1% or less of the specific value, as long as these variations are suitable for implementation in the present disclosure. It should be understood that the value itself to which the modifier "about" refers is also specifically disclosed.

[0034] Numerical ranges expressed by endpoints include all integers and, where appropriate, fractions within the range (e.g., when referring to (e.g.) multiple elements, 1 to 5 may include 1, 2, 3, 4, and when referring to (e.g.) measured values, 1 to 5 may also include 1.5, 2, 2.75, and 3.80). The expression of endpoints also includes the endpoint values ​​themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range described herein is intended to include all subranges contained therein.

[0035] Unless otherwise defined, all terms used in this disclosure, including technical and scientific terms, have the meanings commonly understood by those of ordinary skill in the art to which the disclosure belongs. By way of further guidance, definitions of terms used in the specification are included to better understand the teachings of the present disclosure. All publications cited herein are incorporated herein by reference.

[0036] Unless otherwise defined, the term "composition" as used herein can be open or closed. For example, a "composition" includes a specific material, i.e., nanocrystals, and further non-specific materials, or can be composed of (i.e.) a specific material that substantially excludes non-specific materials.

[0037] The pertinent features of the present invention will now be described.

[0038] use

[0039] According to a first aspect, the present invention provides the use of a lead (IV) compound to prepare lead chalcogenide nanocrystals or a composition of lead chalcogenide nanocrystals.

[0040] As used herein, the term "lead (IV)-containing compound" refers to any compound that includes lead in an oxidation state of +4. Any suitable such compound may be used. Examples of suitable lead (IV)-containing compounds include, but are not limited to, lead (II, IV) oxide (i.e., Pb3O4) and lead (IV) oxide (i.e., PbO2).

[0041] Suitably, the lead (IV) containing compound may comprise lead (II, IV) oxide or lead (IV) oxide, or a combination thereof Suitably, the lead (IV) containing compound may comprise lead (II, IV) oxide.

[0042] The use of lead (II, IV) oxide is advantageous because it is a highly reactive and inexpensive material that can be readily used in large-scale (eg commercial) processes, ie industrial-scale manufacturing processes.

[0043] As used herein, the term "chalcogenide" refers to a compound comprising at least one chalcogen and at least one positively charged element. As used herein, the term "chalcogen" refers to a Group 16 element. For example, a "chalcogenide" may include a compound comprising an oxide, sulfide, selenide, telluride, or polonide and at least one positively charged element or cation. A "lead chalcogenide" is a compound comprising an oxide, sulfide, selenide, telluride, or polonide and at least one lead cation.

[0044] As used herein, the term "nanocrystal" refers to a crystalline particle having at least one dimension measuring less than 100 nanometers (nm).

[0045] Lead chalcogenide nanocrystals may contain or consist of quantum dots (QDs). As used herein, the term "quantum dots" used herein refers to semiconductor nanocrystals that exhibit quantum confinement effects that allow them to mimic the properties of atoms. Quantum dots may also be referred to as zero-dimensional nanocrystals.

[0046] According to a second aspect, the present invention provides the use of lead (II, IV) oxide to prepare lead chalcogenide nanocrystals.

[0047] Suitably, the lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared ranges, suitably in the range of 500nm to 4500nm, preferably suitably in the range of 500nm to 2400nm.

[0048] Suitably, the lead sulphide nanocrystals or lead sulphide nanocrystal compositions prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared range, suitably in the range of 500nm to 2400nm.

[0049] Suitably, the lead selenide nanocrystals or lead selenide nanocrystal compositions prepared from the lead (IV) containing compound exhibit absorption in the visible and near infrared range, suitably in the range of 800 nm to 4500 nm.

[0050] Suitably, the lead telluride nanocrystals or lead telluride nanocrystal compositions prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared range, suitably in the range of 500 nm to 2400 nm.

[0051] Suitably, the lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions prepared from lead (IV) containing compounds exhibit emission in the visible and near infrared range, suitably in the range of 600nm to 4500nm, preferably suitably in the range of 600nm to 2500nm.

[0052] Suitably, the lead sulphide nanocrystals or lead sulphide nanocrystal compositions prepared from the lead (IV) containing compound exhibit emission in the visible and near infrared range, suitably in the range of 600 nm to 2500 nm.

[0053] Suitably, the lead selenide nanocrystals or lead selenide nanocrystal compositions prepared from the lead (IV) containing compound exhibit emission in the visible and near infrared range, suitably in the range of 900 nm to 4500 nm.

[0054] Suitably, the lead telluride nanocrystals or lead telluride nanocrystal compositions prepared from lead (IV) containing compounds exhibit emission in the visible and near infrared range, suitably in the range of 600 nm to 2500 nm.

[0055] method

[0056] According to a third aspect, the present invention provides a method for preparing lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions, the method comprising contacting a lead (IV)-containing compound with an organic acid and a chalcogen-containing reagent.

[0057] A fourth aspect of the present invention provides a method for preparing lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions, the method comprising contacting lead (II, IV) oxide with an organic acid and a chalcogen-containing reagent.

[0058] The method is suitable for preparing a plurality of lead chalcogenide nanocrystals, ie, a nanocrystal composition. The lead chalcogenide nanocrystals prepared by the method of the present invention may include quantum dots (ie, crystalline quantum dots).

[0059] Various aspects of the methods of the invention, such as the specific reagents and / or reaction conditions, can be varied to provide lead chalcogenide nanocrystals of a desired size to achieve desired optical properties such as desired absorption and emission (e.g., for a particular use of the nanocrystals).

[0060] For example, the reagents used in the method (particularly the chalcogen-containing reagents) can be varied to provide lead chalcogenide nanocrystals of a desired size to achieve desired optical properties such as absorption and emission as desired (eg, for a particular use of the nanocrystals).

[0061] For example, the reaction conditions of the method can be varied to provide lead chalcogenide nanocrystals of a desired size to achieve desired optical properties such as absorption and emission as desired (eg, for a particular use of the nanocrystals).

[0062] In other words, the uses and methods of the present invention can be used to prepare lead chalcogenide nanocrystals with size-tunable optical properties.Examples of reagents and / or reaction conditions that can be varied are discussed herein.

[0063] The method of the present invention can include the step of selecting a specific reagent to control the size of the prepared nanocrystals, i.e., to prepare nanocrystals with desired optical properties. For example, the reagent that can be selected to control the size of the prepared nanocrystals can be a specific chalcogen-containing reagent.

[0064] The method of the present invention can include changing the reaction conditions to control the size of the prepared nanocrystal, that is, to prepare the step of nanocrystal with desired optical properties. For example, the reaction conditions including one or more of the following can be changed to control the size of the prepared nanocrystal:

[0065] (i) solvent type;

[0066] (ii) the amount of solvent;

[0067] (iii) organic acid type;

[0068] (iv) the amount of organic acid;

[0069] (v) the method of adding reactants (especially chalcogen-containing reagents);

[0070] (vi) reaction temperature;

[0071] (vii) reaction time;

[0072] (viii) the ratio of Pb to the chalcogen-containing reagent; and

[0073] (ix) Addition of a second solvent.

[0074] By varying the reaction conditions to control the size of the prepared nanocrystals, the optical properties (absorption and emission) can be varied and fine-tuned to the desired properties. This provides a method for fine-tuning the size and optical properties (absorption and emission) of nanocrystals.

[0075] Suitably, the methods of the invention provide lead chalcogenide nanocrystals and compositions thereof that exhibit absorption in the visible and near infrared ranges, for example in the range of about 500nm to 4500nm, preferably suitably in the range of 500nm to 2400nm. The specific absorption exhibited can be selected by varying the specific reagents and / or reaction conditions used as discussed herein. Suitably, lead sulfide nanocrystals prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared ranges, suitably in the range of 500nm to 2400nm. Suitably, lead selenide nanocrystals prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared ranges, suitably in the range of 800nm ​​to 4500nm. Suitably, lead telluride nanocrystals prepared from lead (IV) containing compounds exhibit absorption in the visible and near infrared ranges, suitably in the range of 500nm to 2400nm.

[0076] Suitably, the methods of the present invention provide lead chalcogenide nanocrystals and compositions thereof that exhibit emission in the visible and near infrared ranges, for example in the range of about 600nm to 4500nm, preferably suitably in the range of 600nm to 2500nm. The specific emission exhibited can be selected by varying the specific reagents and / or reaction conditions used as discussed herein. Suitably, lead sulfide nanocrystals prepared from lead (IV) containing compounds exhibit emission in the visible and near infrared ranges, suitably in the range of 600nm to 2500nm. Suitably, lead selenide nanocrystals prepared from lead (IV) containing compounds exhibit emission in the visible and near infrared ranges, suitably in the range of 900nm to 4500nm. Suitably, lead telluride nanocrystals prepared from lead (IV) containing compounds exhibit emission in the visible and near infrared ranges, suitably in the range of 600nm to 2500nm.

[0077] Suitably, for the above purposes, any suitable lead (IV)-containing compound may be used in the method of the present invention. Suitably, the lead (IV)-containing compound may include lead (II, IV) oxide or lead (IV) oxide, or a combination thereof. Suitably, the lead (IV)-containing compound may include lead (II, IV) oxide.

[0078] The term "organic acid" as used herein refers to an organic compound having acidic properties. The term "organic compound" as used herein refers to a compound in which one or more carbon atoms are covalently bonded to atoms of other elements, most commonly hydrogen, oxygen and / or nitrogen.

[0079] Any suitable organic acid can be used in the method of the present invention. Suitably, the organic acid comprises a carboxylic acid, such as a fatty acid (e.g. a saturated or unsaturated fatty acid, suitably an unsaturated fatty acid). The example of a suitable carboxylic acid comprises a C4 to C28 fatty acid, such as a C12-C22 fatty acid. Suitably, the organic acid may comprise oleic acid.

[0080] Suitably, the organic acid comprises a fatty acid, preferably oleic acid.

[0081] As used herein, the term "chalcogen-containing reagent" refers to a reagent comprising at least one chalcogen, i.e., at least one Group 16 element or an anion thereof. Any suitable chalcogen-containing reagent can be used in the method of the present invention. For example, the chalcogen-containing reagent can be selected from reagents containing oxygen, sulfur, selenium and tellurium (e.g., reagents containing sulfur, selenium and tellurium, in particular reagents containing sulfur or selenium) and mixtures thereof.

[0082] Suitably, the chalcogen-containing reagent may include a chalcogen-containing compound or an elemental chalcogen, and mixtures thereof. For example, the chalcogen-containing reagent may include a chalcogen-containing compound. For example, the chalcogen-containing reagent may include an elemental chalcogen.

[0083] Suitable chalcogen-containing compounds may include oxygen, sulfur, selenium or tellurium atoms, or combinations thereof, and atoms of at least one other suitable element. More suitably, chalcogen-containing compounds may include sulfur, selenium or tellurium atoms, or combinations thereof (preferably sulfur or selenium atoms), and atoms of at least one other suitable element.

[0084] Suitably, the chalcogen-containing compound may comprise an ionic compound comprising an oxygen, sulfur, selenium or tellurium anion, or a combination thereof, and at least one suitable cation. More suitably, the chalcogen-containing ionic compound may comprise a sulfur, selenium or tellurium anion, or a combination thereof (preferably a sulfur or selenium anion), and at least one suitable cation.

[0085] Examples of suitable oxygen-containing reagents include oxygen.

[0086] Examples of suitable sulfur-containing reagents include bis(trialkylsilyl)sulfide compounds (e.g., bis(trimethylsilyl)sulfide, bis(triethylsilyl)sulfide and bis(tripropylsilyl)sulfide, particularly bis(trimethylsilyl)sulfide), thioacetamide, tri-n-octylphosphine sulfide, tributylphosphine sulfide, (alkyl-substituted, phenyl)thiourea compounds (e.g., N,N'-disubstituted and N,N,N'-trisubstituted thioureas), alkyl-substituted thioamide compounds and elemental sulfur.

[0087] Thioacetamide is an inexpensive reagent with low toxicity, which makes it particularly suitable for large-scale use.

[0088] Examples of suitable selenium-containing compounds include bis(trimethylsilyl)selenide, tri-n-octylphosphine selenide (TOPSe), and tributylphosphine selenide.

[0089] It is also preferred to use certain phosphine-containing reagents because these reagents can form Se precursors that are more reactive than TOPSe. These precursors play an important role in maintaining high PbSe supersaturation, which is crucial for promoting nucleation, growth and controlling the size distribution of QDs and making the reaction conditions mild. Examples of preferred phosphine-containing reagents include diphenylphosphine selenide (DPP), o-xylylphosphine selenide (DOTP) and diphenylphosphine oxide selenide (DPPO).

[0090] Examples of suitable tellurium-containing compounds include tri-n-octylphosphine telluride.

[0091] For example, the methods of the invention can include contacting lead (II, IV) oxide with a fatty acid and a chalcogen-containing reagent.

[0092] For example, the methods of the invention can include contacting lead (II, IV) oxide with oleic acid and a chalcogen-containing reagent.

[0093] For example, the methods of the invention can include contacting lead (II, IV) oxide with a fatty acid and a chalcogen-containing compound.

[0094] For example, the methods of the invention can include contacting lead (II, IV) oxide with oleic acid and a chalcogen-containing compound.

[0095] For example, the methods of the invention can include contacting lead (II, IV) oxide with a fatty acid and an oxygen-, sulfur-, selenium-, or tellurium-containing (eg, sulfur-, selenium-, or tellurium-containing, particularly sulfur- or selenium-containing) reagent.

[0096] For example, the methods of the invention can include contacting lead (II, IV) oxide with oleic acid and a reagent containing oxygen, sulfur, selenium, or tellurium (eg, containing sulfur, selenium, or tellurium, particularly containing sulfur or selenium).

[0097] For example, the methods of the invention can include contacting lead (II, IV) oxide with a fatty acid and an oxygen-, sulfur-, selenium-, or tellurium-containing (eg, sulfur-, selenium-, or tellurium-containing, particularly sulfur- or selenium-containing) compound.

[0098] For example, the method of the invention can include contacting lead (II, IV) oxide with oleic acid and an oxygen-, sulfur-, selenium-, or tellurium-containing (eg, sulfur-, selenium-, or tellurium-containing, particularly sulfur- or selenium-containing) compound.

[0099] Reference to contacting a lead (IV)-containing compound with an organic acid and a chalcogen-containing reagent refers to bringing these reagents together in a manner that enables them to react, ie, to produce lead chalcogenide nanocrystals and / or combinations thereof.

[0100] Suitably, the lead (IV)-containing compound is contacted with an organic acid to make a lead salt, and the lead salt is contacted with a chalcogen-containing reagent. In other words, the lead (IV)-containing compound is contacted with an organic acid and reacts with the organic acid to form a lead salt. The lead salt so formed is then reacted with a chalcogen-containing reagent to form lead chalcogenide nanocrystals and / or compositions thereof. Although it is generally not necessary to do so, the lead salt may be separated prior to reacting the lead salt with the chalcogen-containing reagent. Carrying out the process without separating the lead salt provides the advantage of carrying out the process in a one-pot synthesis, which enables the process to be easily scaled up.

[0101] The formation of the lead salt as described above may be monitored in any suitable manner, for example visually by a colour change as the lead salt forms.

[0102] The lead (IV)-containing compound, the organic acid and the chalcogen-containing reagent may be contacted (or reacted) in any suitable manner, typically by mixing in a suitable reaction vessel.

[0103] Generally, it is believed that a lead (IV)-containing compound is reacted with an organic acid to form a lead salt, which is then reacted with a chalcogen-containing reagent to form lead chalcogenide nanocrystals and / or combinations thereof.

[0104] Usually, lead (IV) compound can be contacted with the organic acid of molar excess.For example, the scope of the mol ratio of lead atom and organic acid (in lead (IV) compound) can be 1:1.5 to 1:200, for example 1:1.5 to 1:60.It is believed that the mol ratio of lead atom and organic acid (in lead (IV) compound) can be selected to obtain the required nanocrystal size, and therefore obtain the required absorption.Usually, the higher the amount of organic acid used, the larger the nanocrystal formed.

[0105] Typically, the lead salt can be contacted with the chalcogen-containing reagent in an amount of lead atoms in molar excess relative to the chalcogen atoms. For example, the molar ratio of lead atoms to chalcogen atoms can range from 0.9:1 to 50:1; for example, 1.5:1 to 30:1, for example, 1.5:1 to 25:1. It is believed that the molar ratio of lead atoms (in the lead salt) to chalcogen atoms (in the chalcogen-containing reagent) can be selected to obtain highly monodisperse nanocrystals over a wide range of sizes, and thus obtain the desired narrow absorption peak over a wider range. Typically, the higher the amount of lead atoms used, the more highly monodisperse nanocrystals are formed over a wider absorption range.

[0106] Typically, the lead (IV) compound and the organic acid are mixed in a suitable solvent until the reaction (i.e., the formation of the lead salt) is substantially complete and a lead salt solution in the solvent is formed. The chalcogen-containing reagent can then be added to the lead salt solution and reacted to form lead chalcogenide nanocrystals and / or combinations thereof. The chalcogen-containing reagent can be added with or without a solvent.

[0107] The lead salt and the chalcogen-containing reagent may be contacted in any suitable manner. Suitably, the lead salt and the chalcogen-containing reagent may be mixed together, for example, in the presence of a suitable solvent. For example, a solution of the chalcogen-containing reagent in a suitable solvent may be added to a solution of the lead salt in a suitable solvent (preferably the same solvent). Alternatively, the chalcogen-containing reagent may be (for example) directly added to a solution of the lead salt in a suitable solvent. Addition of the chalcogen-containing reagent may be performed in one step or in multiple steps. For example, the chalcogen-containing reagent may be added to the lead salt in two or more times, for example, in two additions. It is believed that the manner in which the chalcogen-containing reagent is added may be used to change the size of the nanocrystals formed, and thus fine-tune the optical properties of the nanocrystals. Typically, addition of the chalcogen-containing reagent in multiple steps provides larger nanocrystals (i.e., compared to a single step addition).

[0108] The method of the present invention may also include adding a second solvent immediately after adding the chalcogen-containing reagent to the lead salt (i.e., to quickly quench the reaction). The second solvent is typically an organic solvent, such as a polar solvent (e.g., acetone, methanol, or ethanol) or a non-polar solvent (e.g., hexane).

[0109] The method of the present invention can be carried out at any suitable temperature. For example, the lead (IV) compound can be contacted with the organic acid at any suitable temperature, i.e., at any suitable temperature at which the reaction occurs. The specific temperature at which the reaction occurs may depend on the specific lead (IV) compound and the organic acid being reacted. A suitable temperature range may be 120°C to 250°C, such as 120°C to 240°C, such as 180°C to 240°C, such as 180°C to 230°C.

[0110] For example, when the lead (IV)-containing compound comprises lead (II, IV) oxide and the organic acid comprises oleic acid, the temperature range at which these compounds react (i.e., to form a lead salt) may be 120°C to 250°C, suitably 120°C to 240°C, suitably 180°C to 240°C, suitably 180°C to 230°C.

[0111] The lead salt may be contacted with the chalcogen-containing reagent at any suitable temperature, i.e., at any suitable temperature at which the reaction occurs. The specific temperature at which the reaction occurs may depend, inter alia, on the specific lead salt and the chalcogen-containing reagent being reacted. Suitable temperature ranges may be 20° C. to 300° C. or 20° C. to 180° C. It is believed that the selection of a specific reaction temperature may be used to alter the size of the nanocrystals formed to fine-tune their optical properties as desired. Typically, increasing the temperature at which the lead salt is contacted / reacted with the chalcogen-containing reagent provides larger nanocrystals.

[0112] The temperature at which the lead (IV) compound is contacted with the organic acid may be the same as or different from the temperature at which the lead salt is contacted with the chalcogenide-containing reagent. Suitably, the temperature at which the lead (IV) compound is contacted with the organic acid may be higher than the temperature at which the resulting lead salt is contacted with the chalcogenide-containing reagent. For example, a temperature of 150° C. to 300° C. may be used to contact the resulting lead salt with the chalcogenide-containing reagent to improve the quality of the quantum dots.

[0113] Suitably, the lead salt may be contacted with the chalcogen-containing reagent at a temperature of 20°C to 150°C, such as 30°C to 100°C, such as 30°C to 60°C, such as 20°C to 60°C, such as about 40°C. Such a reaction temperature may be appropriate when the chalcogen-containing reagent is bis(trimethylsilyl)sulfide, such as when bis(trimethylsilyl)sulfide is contacted with lead oleate. Such low temperature conditions have advantages in use, especially for large-scale manufacturing.

[0114] For example, when the lead salt comprises lead oleate and the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, the temperature range of these reactions can be 20°C to 180°C, such as 20°C to 55°C, preferably about 40°C. Such methods wherein the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide can provide lead chalcogenide nanocrystals that exhibit absorption in the visible and near infrared ranges, such as in the range of about 500nm to 2400nm, such as in the range of about 530nm to 2400nm, such as in the range of about 530nm to 1600nm. Such methods wherein the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide can provide lead chalcogenide nanocrystals that exhibit emission in the visible and near infrared ranges, such as in the range of about 600nm to 2500nm, such as in the range of about 630nm to 2500nm, such as in the range of about 630nm to 1700nm.

[0115] Suitably, the lead salt may be contacted with the chalcogen-containing reagent at a temperature of 50°C to 300°C, such as 50°C to 150°C. Such a reaction temperature may be appropriate when the chalcogen-containing reagent comprises thioacetamide, such as when thioacetamide is contacted with lead oleate. Such a method in which the chalcogen-containing reagent comprises thioacetamide may provide lead chalcogenide nanocrystals that exhibit absorption in the visible and near infrared ranges, such as in the range of about 500nm to 2400nm, such as 500nm to 1700nm. Such a method in which the chalcogen-containing reagent comprises thioacetamide may provide lead chalcogenide nanocrystals that exhibit emission in the visible and near infrared ranges, such as in the range of about 600nm to 2500nm, such as 600nm to 1800nm.

[0116] Suitably, the lead salt may be contacted with the chalcogen-containing reagent at a temperature of 50°C to 300°C, such as 80°C to 150°C. Such a reaction temperature may be appropriate when the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe), such as when TOPSe is contacted with lead oleate in the presence of diphenylphosphine (DPP). Such a method in which the chalcogen-containing reagent comprises TOPSe in the presence of DPP may provide lead chalcogenide nanocrystals that exhibit absorption in the visible and near infrared ranges, such as in the range of about 800nm ​​to 4500nm, such as in the range of about 900nm to 4200nm, such as in the range of about 1100nm to 4100nm. Such a method in which the chalcogen-containing reagent comprises TOPSe may provide lead chalcogenide nanocrystals that exhibit emission in the visible and near infrared ranges, such as in the range of about 900nm to 4500nm, such as in the range of about 1000nm to 4300nm, such as in the range of about 1200nm to 4100nm.

[0117] The method of the present invention can be carried out in the presence of a solvent. Any suitable solvent can be used. Suitably, the solvent is a solvent that does not form a coordination complex with lead. Suitably, the solvent is an organic solvent, such as a non-polar solvent or a polar solvent, or a mixture thereof. Examples of suitable solvents include C4-C28 organic solvents such as octadecene, or polar solvents such as dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide, tetrahydrofuran. Typically, the same solvent is used for the reaction of the lead (IV) compound with the organic acid and for the reaction of the resulting lead salt with the chalcogen-containing reagent. This simplifies the method of the present invention, making it particularly suitable for large-scale use.

[0118] For example, the lead (IV) compound may be contacted with an organic acid in the presence of a suitable solvent. Suitably, the solvent is a non-polar solvent or a polar solvent, or a mixture thereof. Examples of suitable solvents include C4-C22 organic solvents, such as octadecene.

[0119] For example, the lead salt obtained can be contacted with a chalcogen-containing reagent in the presence of a suitable solvent. Suitably, the solvent is a non-polar solvent or a polar solvent, or a mixture thereof. Examples of suitable solvents include C4-C22 organic solvents, such as octadecene.

[0120] The amount of solvent used can be selected according to the specific reagent used and / or other reaction conditions adopted. Generally, the concentration of lead (IV) compound in the solvent (at the beginning of the reaction) can range from 0.005mmol / ml to 0.10mmol / ml. Generally, the concentration of lead atoms in the solvent (at the beginning of the reaction) can range from 0.015mmol / ml to 0.30mmol / ml. Generally, the concentration of organic acid in the solvent (at the beginning of the reaction) can range from 0.0075mmol / ml to 10mmol / ml, such as 0.1mmol / ml to 2mmol / ml. It is believed that the amount of solvent can affect the size of the lead chalcogenide nanocrystals finally formed, so the amount of solvent selected for use in the method can help to fine-tune their optical properties. For example, it is believed that reducing the amount of solvent can generally result in the formation of larger nanocrystals.

[0121] Suitably, the process of the invention is carried out in an inert atmosphere.Any suitable inert atmosphere may be used, for example nitrogen or argon.

[0122] Suitably, lead (IV) compound can be contacted with organic acid for a necessary period of time to complete the preparation of lead salt. Suitable reaction times will depend on employed specific reagent and reaction conditions. Typical reaction time range can be (for example) 10 minutes to 2 hours, for example 15 minutes to 2 hours.

[0123] Suitably, the lead salt and the chalcogen-containing reagent may be contacted for a period of time necessary to complete the preparation of lead chalcogenide nanocrystals. The appropriate reaction time will depend on the specific reagents and reaction conditions used. Typical reaction times may be, for example, 15 minutes to 2 hours, such as 30 minutes to 2 hours.

[0124] The method of the present invention may include:

[0125] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0126] forming a second solution, the second solution being a solution of a chalcogen-containing reagent (e.g., bis(trimethylsilyl)sulfide) in a second solvent;

[0127] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0128] The temperature of the first solution is lowered to a low temperature ranging from 20°C to 100°C.

[0129] adding the second solution to the first solution at a low temperature to produce a reaction mixture;

[0130] The reaction mixture is maintained at a temperature of 20°C to 300°C for a predetermined length of time.

[0131] The method of the present invention may include:

[0132] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0133] forming a second solution, the second solution being a solution of a chalcogen-containing reagent (e.g., bis(trimethylsilyl)sulfide) in a second solvent;

[0134] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0135] The temperature of the first solution is lowered to a low temperature ranging from 20°C to 60°C.

[0136] adding the second solution to the first solution at a low temperature to produce a reaction mixture;

[0137] The reaction mixture is maintained at a temperature of 20°C to 60°C for a predetermined length of time.

[0138] The method of the present invention may include:

[0139] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0140] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0141] providing the first solution at a second temperature ranging from 50°C to 100°C;

[0142] adding a chalcogen-containing reagent (e.g., thioacetamide) to the first solution at a second temperature to produce a reaction mixture;

[0143] The reaction mixture is maintained at a temperature of 50°C to 300°C for a predetermined length of time.

[0144] The method of the present invention may include:

[0145] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0146] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0147] providing the first solution at a second temperature ranging from 50°C to 150°C;

[0148] adding a chalcogen-containing reagent (e.g., thioacetamide) to the first solution at a second temperature to produce a reaction mixture;

[0149] The reaction mixture is maintained at a temperature of 50°C to 150°C for a predetermined length of time.

[0150] The method of the present invention may include:

[0151] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0152] forming a second solution of a chalcogen-containing reagent (e.g., tri-n-octylphosphine selenide (TOPSe)) in a second solvent in the presence of diphenylphosphine (DPP);

[0153] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0154] The temperature of the first solution is lowered to a low temperature ranging from 20°C to 100°C.

[0155] adding the second solution to the first solution at a low temperature to produce a reaction mixture;

[0156] The reaction mixture is maintained at a temperature of 20°C to 300°C for a predetermined length of time.

[0157] The method of the present invention may include:

[0158] forming a first solution comprising a lead (IV) compound and an organic acid in a first solvent;

[0159] forming a second solution, the second solution being a solution of a chalcogen-containing reagent (e.g., tri-n-octylphosphine selenide (TOPSe)) in a second solvent in the presence of diphenylphosphine (DPP);

[0160] heating the first solution to a first temperature in a range of 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time;

[0161] The temperature of the first solution is lowered to a low temperature ranging from 20°C to 100°C.

[0162] adding the second solution to the first solution at a low temperature to produce a reaction mixture;

[0163] The reaction mixture is maintained at a temperature of 50°C to 180°C for a predetermined length of time.

[0164] The method of the present invention may also include monitoring an optical property (i.e., an optical property of a solution of a reaction mixture, such as a reactant) to monitor the progress of the nanocrystal production. The optical property may be a UV-visible-near infrared absorption spectrum. The method may include the step of stopping the reaction when the value of the optical property corresponds to the desired size and / or size distribution of the lead chalcogenide nanocrystals.

[0165] The method of the present invention may further comprise separating the lead chalcogenide nanocrystals from the reaction mixture. The lead chalcogenide nanocrystals may be separated using any suitable method.

[0166] The method of the present invention may include quenching the reaction mixture, for example by adding a quenching solvent to the reaction mixture. Any suitable quenching solvent may be used, such as acetone, methanol, ethanol or hexane. The method of the present invention may also include isolating the lead chalcogenide nanoparticles.

[0167] For example, lead chalcogenide nanocrystals can be precipitated from the reaction mixture using a suitable solvent such as a polar solvent (eg, acetone, methanol, or ethanol).The separation step can be performed in an inert atmosphere or in air.

[0168] An example of the method of the present invention is shown in Fig.13 and Fig.15 middle. Fig.13 and Fig.15A method of preparing a first solution is shown, wherein Pb3O4 is mixed with oleic acid in octadecene (to form lead oleate salt). The first solution is mixed with an octadecene solution of bis(trimethylsilyl) sulfide at a temperature of room temperature (e.g., 20°C) to 60°C, or the first solution is mixed with thioacetamide (with or without solvent) at a temperature of 50°C to 300°C, or the first solution is mixed with an octadecene solution of tri-n-octylphosphine selenide (TOPSe) in the presence of diphenylphosphine (DPP) at a temperature of 50°C to 300°C to provide the desired nanocrystals.

[0169] An example of the method of the present invention is shown in Fig.14 . Fig.14 Step 1 of preparing solution 1 (e.g., a solution comprising a lead (IV)-containing compound and an organic acid in a first solvent such as octadecene) and step 2 of preparing solution 2 (e.g., a solution of a chalcogen-containing reagent in a second solvent such as octadecene) are shown. Fig.14 The method shown includes step 3 of rapidly injecting solution 2 into solution 1 at a predetermined temperature (e.g., an appropriate temperature discussed herein), step 4 of maintaining the temperature of the mixture produced in step 3 at a predetermined temperature for a period of time until a desired particle size is reached, step 5 of terminating / quenching the reaction, and step 6 of purifying the resulting nanoparticles.

[0170] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that the amount of organic acid (e.g., oleic acid) greatly affects the size of the prepared nanocrystals. Generally, the more organic acid is introduced, the larger the size of the prepared nanocrystals. For example, by only increasing the amount of oleic acid by 27.5 times (all other reagents and conditions being the same), the peak absorption of the nanocrystals was observed to be red-shifted from 652 nm to 1220 nm.

[0171] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that the peak absorption of the nanocrystals is further red-shifted from 1120 nm to 1304 nm by multi-step addition of bis(trimethylsilyl)sulfide.

[0172] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that multi-step additions of the lead(IV)-containing compound and / or bis(trimethylsilyl)sulfide generally produce larger nanocrystals.

[0173] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that increasing the temperature of the reaction of bis(trimethylsilyl)sulfide with the lead salt from 40°C to 60°C generally provides larger nanocrystals. The peak absorption of the nanocrystals is observed to be red-shifted from a reference value of 652nm to 986nm.

[0174] When the chalcogen-containing reagent includes bis(trimethylsilyl)sulfide, it is believed that the introduction of acetone, alcohol or water can produce ultra-small size nanocrystals. It was observed that after the injection of bis(trimethylsilyl)sulfide into the lead salt, the peak absorption of the nanocrystals was blue-shifted by 24nm by the rapid addition of a small amount of acetone.

[0175] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that the rapid introduction of cold hexane after injection of bis(trimethylsilyl)sulfide results in the formation of small nanocrystals.A blue shift from 652 nm to 533 nm was observed.

[0176] When the chalcogen-containing reagent comprises bis(trimethylsilyl) sulfide, it is believed that decreasing the concentration of lead oleate by increasing the amount of solvent (eg, octadecene) results in the formation of smaller nanocrystals and the observation of a 40 nm blue shift.

[0177] When the chalcogen-containing reagent comprises bis(trimethylsilyl)sulfide, it is believed that any combination of the above method steps can be used to produce a wide range of nanocrystals at temperatures between 20°C and 60°C (i.e., for the reaction of bis(trimethylsilyl)sulfide with a lead salt).

[0178] When the chalcogen-containing reagent comprises thioacetamide, the process can be simplified in that it is acceptable to simply add the thioacetamide to the reaction (ie, without first dissolving the thioacetamide in a solvent) or to add a solution of the thioacetamide to a solvent or mixture of solvents.

[0179] When the chalcogen-containing reagent comprises thioacetamide, it is believed that the amount of organic acid (eg, oleic acid) greatly affects the size of the nanocrystals produced, such that the more organic acid used, the larger the size of the nanocrystals produced.

[0180] When the chalcogen-containing reagent comprises thioacetamide, it is believed that increasing the temperature of the reaction of thioacetamide with the lead salt (e.g., to a temperature of about 85°C) greatly affects the size of the nanocrystals produced, such that the higher the temperature used, the larger the size of the nanocrystals produced.

[0181] When the chalcogen-containing reagent comprises thioacetamide, it is believed that decreasing the concentration of the lead salt (eg, lead oleate) in the solvent, ie, by increasing the amount of solvent, can provide smaller nanocrystals.

[0182] When the chalcogen-containing reagent comprises thioacetamide, it is believed that the introduction of acetone, alcohol, or water can result in ultra-small-sized nanocrystals.

[0183] When the chalcogen-containing reagent comprises thioacetamide, it is believed that the introduction of cold hexanes quickly after injection of the thioacetamide results in the formation of small nanocrystals.

[0184] When the chalcogen-containing reagent comprises thioacetamide, it is believed that any combination of the above method steps can be used to produce a wide range of nanocrystals at temperatures of 50°C to 300°C, suitably 50°C to 150°C (i.e., for the reaction of thioacetamide with a lead salt).

[0185] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that the amount of organic acid (such as oleic acid) greatly affects the size of the prepared nanocrystals, such that the more organic acid used, the larger the size of the prepared nanocrystals.

[0186] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that multi-step addition of TOPSe generally produces larger nanocrystals.

[0187] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that the multi-step addition of the lead(IV)-containing compound and / or TOPSe generally produces larger nanocrystals.

[0188] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that increasing the temperature at which TOPSe reacts with the lead salt greatly affects the size of the nanocrystals produced, such that the higher the temperature used, the larger the size of the nanocrystals produced.

[0189] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that the introduction of acetone, alcohol, water or mixtures thereof can produce ultra-small-sized nanocrystals, ie, can reduce the size compared to reactions without the solvent.

[0190] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that the rapid introduction of cold hexane after injection of the TOPSe solution results in the formation of small nanocrystals.

[0191] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that reducing the concentration of lead oleate by increasing the amount of solvent (e.g., octadecene) allows for the formation of smaller nanocrystals, i.e., a reduction in size compared to reactions using less solvent.

[0192] When the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) in the presence of DPP, it is believed that any combination of the above method steps can be used to produce a wide range of nanocrystals at temperatures between 50°C and 300°C (i.e., for the reaction of TOPSe with a lead salt).

[0193] Lead chalcogenide nanocrystals are produced according to the method of the present invention. Suitably, the nanocrystals may comprise quantum dots (ie crystalline quantum dots).

[0194] Some specific synthetic strategies are provided below:

[0195] For the preparation of large PbS nanocrystals using Pb3O4 at 40 °C, it was found that:

[0196] 1) The amount of oleic acid (OA) greatly affects the size of PbS nanocrystals. The more OA is introduced, the larger the size of the prepared PbS nanocrystals. For example, by increasing the amount of OA by 16 times, the peak absorption of PbS nanocrystals was observed to be red-shifted from 652nm to 1168nm.

[0197] 2) By multi-step addition of (TMS)2S, the peak absorption of PbS nanocrystals was observed to further red-shift from 1168 nm to 1304 nm.

[0198] 3) Multi-step addition of both lead and sulfur precursors also helps to make large PbS quantum dots (QDs).

[0199] 4) Raising the temperature to 60°C, which is still low enough to maintain better reaction control over injection and reaction mixing, enabling the production of large PbS QDs. It was observed that the peak absorption of PbS nanocrystals can be red-shifted from the reference value of 1220nm to 1426nm.

[0200] 5) The introduction of other sulfur precursors such as thioacetamide (TAA) or elemental S or tri-n-octylphosphine sulfide or tributylphosphine sulfide or alkyl-substituted thiourea precursors can effectively prepare large PbS nanoparticles.

[0201] In addition to the above five methods, partial and full combinations of the above five synthetic strategies can effectively produce large PbS nanocrystals at low temperatures (ie, about 40° C.).

[0202] For the preparation of small PbS nanocrystals using Pb3O4 at 40 °C, it was found that:

[0203] 1) The amount of oleic acid (OA) greatly affects the size of PbS nanocrystals. The less OA, the smaller the PbS nanocrystals produced. It was found that when the ratio of OA to lead was reduced to 2:1, PbS nanocrystals with a peak wavelength of 652nm were obtained.

[0204] 2) When the temperature is lowered from 40°C to room temperature, a blue shift of about 50 nm can be observed.

[0205] 3) The introduction of acetone, alcohol or water can produce ultra-small-sized PbS nanocrystals. It was observed that after the sulfur precursor was injected into lead oleate, the peak absorption of PbS nanocrystals was blue-shifted by about 100nm by adding a small amount of acetone.

[0206] 4) Introducing cold hexane after injection of the sulfur precursor produced small PbS nanocrystals. A blue shift from 652 nm to 533 nm was observed.

[0207] 5) Reducing the concentration of lead oleate by increasing the amount of ODE helps to obtain small PbS nanocrystals, and a blue shift of 50 nm is observed.

[0208] In addition to the above five methods, partial and complete combinations of the above five synthetic strategies for making smaller PbS nanocrystals and the opposite methods for making larger PbS nanocrystals can form an effective method for making smaller PbS nanocrystals at low temperature (ie, about 40° C.).

[0209] At the same time, low-cost and low-toxic TAA is used to replace the expensive, toxic and extremely smelly (TMS)2S precursor to make PbS nanocrystals. It was found that the threshold temperature of the TAA reaction is about 50°C, and the higher the temperature used, the larger the PbS nanocrystals made. In addition, the amount of oleic acid can affect the size of PbS, and it was found that the greater the amount of OA applied, the larger the PbS nanocrystals obtained.

[0210] Therefore, the present invention enables the use of (TMS)2S and TAA agents to obtain PbS QDs operating at low temperatures (eg, 40°C) in the visible and NIR ranges.

[0211] It is believed that the above strategy is also applicable to tuning the particle size and absorption and emission wavelength of PbSe nanocrystals. In addition, it is believed that the feed molar ratio of lead to chalcogenide (e.g., selenide) and the reaction time effectively control the particle size of the resulting nanocrystals. For example, a high ratio of lead to chalcogenide generally results in smaller nanocrystal size, while a long reaction time results in larger nanocrystal size.

[0212] Nanocrystals / Quantum Dots

[0213] The present invention provides one or more lead chalcogenide nanocrystals (preferably a plurality, ie, a combination) obtained by the above method.

[0214] Suitably, the lead chalcogenide nanocrystals exhibit absorption in the visible and near infrared range, such as in the range of about 500nm to 4500nm, such as in the range of about 500nm to 2400nm, such as in the range of about 530nm to 2400nm, such as in the range of about 530nm to 1600nm.

[0215] Suitably, the lead chalcogenide nanocrystals exhibit emission in the visible and near infrared range, for example in the range of about 600nm to 4500nm, for example about 600nm to 2500nm, for example about 630nm to 2500nm, for example about 630nm to 1700nm.

[0216] The lead chalcogenide nanocrystal composition according to the present invention comprises or consists of nanocrystals having an average particle size ranging from 2 nm to 22 nm, preferably from 5 nm to 20 nm, and a relative size dispersion of less than 25%. Preferably, the nanocrystals have an average particle size ranging from 2 nm to 17 nm, and a relative size dispersion of less than 22%. Preferably, the nanocrystals have an average particle size ranging from 2 nm to 10 nm, and a relative size dispersion of less than 20%.

[0217] Preferably, the PbS nanocrystal composition according to the present invention comprises or consists of nanocrystals having an average particle size ranging from 2 nm to 10 nm and a relative size dispersion of less than 25%, preferably less than 20%.

[0218] The PbSe nanocrystal composition according to the present invention comprises nanocrystals having an average particle size ranging from 2 nm to 17 nm and a relative size dispersion of less than 25%, preferably less than 22%, or the composition consists of the above nanocrystals.

[0219] The lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably comprises lead chalcogenide nanocrystals having an average particle size ranging from 2 nm to 20 nm, preferably from 2 nm to 17 nm, preferably from 2 nm to 10 nm.

[0220] The lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably contains greater than 0.001 wt. %, preferably greater than 0.01 wt. %, preferably greater than 0.1 wt. %, preferably greater than 1 wt. %, preferably greater than 5 wt. % of lead chalcogenide nanocrystals.

[0221] In some applications, the lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably contains greater than 5 weight %, preferably greater than 30 weight %, preferably greater than 75 weight %, preferably greater than 90 weight %, preferably greater than 95 weight % of lead chalcogenide nanocrystals.

[0222] In one embodiment, the lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention consists of lead chalcogenide nanocrystals.

[0223] The remainder of the composition that is not lead chalcogenide nanocrystals may be support materials, such as solvents, additives, inorganic ligands, organic ligands, or reaction byproducts.

[0224] The present invention also provides a composition of lead chalcogenide nanocrystals directly obtained by the above method.

[0225] The present invention also provides a composition of lead chalcogenide nanocrystals obtainable by the above method.

[0226] The composition of lead chalcogenide nanocrystals may include one or more quantum dots (ie, crystalline quantum dots). The present invention provides a composition of lead chalcogenide quantum dots obtained by the above method.

[0227] The present invention also provides a composition of lead chalcogenide quantum dots directly obtained by the above method.

[0228] The present invention also provides a composition of lead chalcogenide quantum dots obtainable by the above method.

[0229] Lead chalcogenide nanocrystals (e.g., lead chalcogenide quantum dots) and compositions, films, systems, or components comprising the lead chalcogenide nanocrystals can be used for any appropriate purpose. For example, lead chalcogenide nanocrystals and compositions thereon can be used to provide or be used in photodetectors, sensors, solar cells, bioimaging or biosensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injectable compositions, field effect transistors, light emitting diodes, photonic or optical switching devices or metamaterials, thermoelectric (cooling) and energy (high temperature electricity) generation applications, fiber amplifiers, lasers, optical gain media, fiber optic communications, high speed communications, telecommunications, infrared LEDs and lasers, electroluminescent devices.

[0230] Lead chalcogenide nanocrystal compositions (e.g., lead chalcogenide quantum dots) can also be used for IR sensing and photodetectors. For example, lead chalcogenide nanocrystals (e.g., lead chalcogenide quantum dots) can be used as light absorbers in 3D cameras and 3D time-of-flight camera sensors in mobile phones and consumer, automotive, medical, industrial, defense, and aerospace applications.

[0231] Lead chalcogenide nanocrystal compositions (e.g., lead chalcogenide quantum dots) can also be used in bioimaging and biosensing applications. For example, lead chalcogenide nanocrystals (e.g., lead chalcogenide quantum dots) can be used as biomarkers or biotags in in vitro and ex vivo applications.

[0232] Lead chalcogenide nanocrystal compositions (eg, lead chalcogenide quantum dots) may also be used in wired high-speed communication devices, night vision devices, and solar energy conversion.

[0233] The present invention provides films comprising the lead chalcogenide nanocrystal compositions of the present invention.

[0234] The present invention provides systems or components comprising the lead chalcogenide nanocrystal compositions of the present invention, such as photodetectors, sensors, solar cells, bioimaging or biosensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injectable compositions, field effect transistors, light emitting diodes, photonic or optical switching devices or metamaterials, thermoelectric (cooling) and energy (high temperature electricity) generation applications.

[0235] The present invention provides biomarkers or biotags, bioimaging and labeling (in vitro and in vivo) comprising the lead chalcogenide nanocrystals of the present invention.

[0236] The method of the present invention allows the nanocrystals of the present invention to have excellent full width at half maximum (FWHM) values. FWHM refers to the width of a light signal at half of its maximum intensity. This measurement gives the bandwidth of a light source operating at 50% capacity.

[0237] The emission properties of the nanocrystals of the present invention are both chemically dependent and size dependent. They generally exhibit an emission function in the shape of a Gaussian curve. Lower intensities may result in wider spectral bandwidths and less pure color performance on the screen. In order to determine the FWHM, the difference between the low wavelength point and the high wavelength point at half the maximum spectral intensity must be calculated. The narrower FWHM of the present invention provides a higher signal-to-noise ratio and has a more accurately tuned absorption wavelength. In essence, a narrower bandwidth is converted into a purer color with a higher efficiency level.

[0238] For example, the method of the present invention can produce a maximum absorption wavelength (λ 最大 ) is 500nm to 1000nm, preferably 600nm to 975nm, preferably 700nm to 775nm and the emission wavelength or photoluminescence (PL) is 600nm to 1200nm, preferably 700nm to 1100nm, preferably 800nm ​​to 950nm. The composition according to the eighth aspect of the present invention can be made to have an absorption FWHM of less than 130nm, preferably less than 120nm, such as about 110nm, and an emission FWHM of less than 130nm, preferably less than 120nm, such as about 110nm. These properties can be provided by a nanocrystal composition with a relative size dispersion of less than 20%.

[0239] Due to the method used by the present invention, the nanocrystals of the composition according to the eighth aspect of the present invention have good relative size dispersion. Relative size dispersion is a measure of the variation in the particle size of the nanocrystals. The relative size dispersion is determined by measuring the particle size of a particular batch of nanoparticles and determining the variance relative to the average size. This can be expressed as a specific average size x plus or minus the range of particle size. For example, the present invention can produce nanocrystals with a maximum absorption wavelength of 950nm and an emission peak at 1060±5nm. The size of these particles is 3.10±0.52 (determined by transmission electron microscopy (TEM)). This produces a relative size dispersion of 16.8% ((0.52 / 3.10)×100).

[0240] Typically, the method of the invention enables the production of nanoparticle compositions according to the eighth aspect of the invention having a relative size dispersity (determined by TEM) of less than 25%, preferably less than 22%, preferably less than 20%.

[0241] In a preferred embodiment of the present invention, the molar ratio of lead atoms to chalcogen atoms in the nanocrystal composition according to the eighth aspect of the present invention is in the range of 1.2: 1 to 4: 1, preferably 1.6: 1 to 3: 1. This preferred range can be achieved for each of PbS, PbSe and PbTe nanocrystals.

[0242] These ratios of lead atoms to chalcogen atoms are associated with the low relative size dispersion exhibited by the nanocrystals of the present invention. Typically, the relative size dispersion of the nanocrystal composition having a lead atom to chalcogen atom molar ratio in the range of 1.2:1 to 4:1 according to the eighth aspect of the present invention is less than 20%, such as less than 18%, such as between 10% and 17%.

[0243] In general, a higher Pb to S ratio in lead-sulfur nanocrystal compositions is associated with larger nanocrystal sizes and longer λ of the PbS nanocrystals. 最大 In general, a lower Pb to Se ratio (or an increase in the Se molar ratio) in a lead-selenium nanocrystal composition is associated with larger nanocrystal size and longer λ 最大 Related.

[0244] The molar ratio of lead atoms to chalcogen atoms was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0245] Generally, the PbS nanocrystal composition according to the eighth aspect of the present invention has a maximum absorption wavelength (λ 最大 ) and their average particle size show a proportional correlation, i.e., larger points show longer λ 最大 The effect of nanoparticle size on the λ 最大 Similar trends are observed in the correlations. However,最大 When the PbSe nanocrystals are the same, they are usually smaller than PbS. 最大 =1314nm) and PbSe(λ 最大 =2046nm) and their particle size determination bar graphs are shown in Figure 8a and Figure 8b as well as Fig.20a and Fig.20b middle.

[0246] Preferred features of the fourth to seventh aspects are as defined for the first, second and third aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0247] For a better understanding of the invention, and to show how exemplary embodiments of the invention may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0248] Figure 1 shows the powder XRD pattern of the PbS nanocrystals prepared according to Example 1;

[0249] Figure 2 shows the absorption spectrum of PbS nanocrystals prepared in toluene in Example 1;

[0250] Figure 3 shows the absorption spectra of PbS nanocrystals obtained with different amounts of oleic acid in Example 2;

[0251] Figure 4 shows the absorption spectra of PbS nanocrystals obtained at 40°C or 60°C in Example 3;

[0252] Figure 5 shows the absorption spectra of PbS nanocrystals obtained by single or multiple additions of (TMS)2S in Example 4;

[0253] Figure 6 shows the absorption spectra of PbS nanocrystals obtained with different amounts of ODE in Example 5;

[0254] Figure 7 shows the absorption spectrum of PbS nanocrystals obtained using TAA and (TMS)2S in Example 6;

[0255] Figure 8a and Figure 8b The TEM image of PbS nanocrystals in Example 6 is shown (λ 最大

[0256] =1314nm) and histogram of particles measured by TEM;

[0257] Fig. 9shows the absorption spectra of PbS nanocrystals obtained with and without the addition of acetone in Example 7;

[0258] Fig.10 shows the absorption spectra of PbS nanocrystals obtained with and without the addition of hexane in Example 8;

[0259] Fig.11 shows the absorption spectra of PbS nanocrystals obtained using different amounts of oleic acid and different reaction temperatures in Example 9;

[0260] Fig.12 The absorption spectra of the PbS nanocrystals and thin film sample solutions prepared as in Example 10 are shown;

[0261] Fig.13 An embodiment of a specific method of the present invention is shown;

[0262] Fig.14 An embodiment of a specific method of the present invention is shown;

[0263] Fig.15 A scheme for synthesizing PbSe nanocrystals using Pb3O4 and TOPSe is shown;

[0264] Fig.16 The powder XRD pattern of the PbSe nanocrystals prepared in Example 11 is shown.

[0265] Fig.17 The absorption spectrum of the PbSe nanocrystals prepared in Example 11 is shown.

[0266] Fig.18 Absorption spectra of PbSe nanocrystals demonstrating the broad spectral tunability of PbSe nanocrystals obtained from different reaction conditions as prepared in Example 11 are shown.

[0267] Fig.19 TEM images of PbSe nanocrystals prepared under different conditions in Example 11 are shown (λ 最大 =1926nm).

[0268] Fig.20a and Fig.20b The colloidal PbSe nanocrystals (λ 最大 =2046 nm) and histogram of the particles determined by TEM. The PbSe dots are highly crystalline and free of stacking faults and lattice defects.

[0269] Fig.21a and Figure 21b The PbS nanocrystals (λ最大 =950nm, PL = 1060 ± 5nm) and PbSe (λ 最大 =1000nm, PL=1100±5nm) absorption and emission spectra.

[0270] Example

[0271] Several examples and comparative examples are described below to illustrate the method according to the present invention.

[0272] Although specific embodiments of the present invention have been described below for purposes of illustration, it will be apparent to those skilled in the art that numerous changes may be made to the details of the invention without departing from the invention as defined in the appended claims.

[0273] Unless otherwise indicated, all parts and percentages in the following examples and throughout the specification are parts by weight or percentage by weight, respectively.

[0274] Absorption spectra were obtained on a JASCO V-770 UV-Visible / NIR spectrometer, which can provide measurements in the wavelength range of 400 nm to 3200 nm.

[0275] Example 1: Synthesis of lead sulfide (PbS) nanocrystals using Pb3O4 and (TMS)2S

[0276] 0.19g Pb3O4, 0.6ml oleic acid and 7ml octadecene (ODE) were loaded into a three-necked flask, evacuated and kept at 180°C for 30 minutes under N2 atmosphere to produce a lead oleate solution. After forming a clear lead oleate solution, the temperature was reduced to 40°C. 45μl of 4ml ODE solution of bis(trimethylsilyl) sulfide ((TMS)2S) was rapidly injected. Over the next 5 minutes, the solution changed from light yellow to light brown and then to dark brown, indicating controlled nucleation. The reaction was kept at 40°C for 60 minutes (monitored by UV-visible-NIR spectroscopy) and then slowly cooled to room temperature. Then 20ml of distilled acetone was added to the reaction mixture. PbS nanocrystals were precipitated by centrifugation, dispersed in toluene, and precipitated again by a combination of acetone and centrifugation. Finally, the nanocrystals were dispersed in toluene. The purification step was carried out in air.

[0277] The PbS nanocrystals prepared in Example 1 were characterized by powder XRD and EDX measurements.

[0278] XRD samples were prepared by drop casting particles from a toluene solution onto the end of a microscope slide until a relatively thick, opaque film was formed. The film was then analyzed using a Panalytical X'Pert PRO MPD instrument.

[0279] EDX samples were prepared by drop casting particles from toluene solutions onto SEM specimen posts covered with carbon-based adhesive tabs. Toluene was allowed to evaporate prior to analysis. Samples were analyzed on a Philips / FEI XL30ESEM equipped with an Oxford Instruments Energy 250 energy dispersive spectrometer system.

[0280] Figure 1 The powder XRD pattern of PbS nanocrystals prepared according to Example 1 is shown. Figure 1 The XRD pattern shown confirms that the PbS nanocrystals produced in Example 1 have a rock salt structure.

[0281] EDX measurement is shown in Table 1, and it was confirmed that the prepared nanocrystals contained lead and sulfur.

[0282] Table 1

[0283]

[0284] The absorption spectrum of the PbS nanocrystals prepared in toluene in Example 1 was obtained, and the results are shown in Figure 2 .

[0285] Example 2: Synthesis of PbS nanocrystals using Pb3O4 and (TMS)2S with different amounts of oleic acid

[0286] The above synthesis in Example 1 was repeated using oleic acid in an amount of 0.6 ml and oleic acid in an amount of 14.4 ml.

[0287] Figure 3 Absorption spectra of the resulting nanocrystals are shown (where the solid line corresponds to 0.6 ml of oleic acid; the dashed line corresponds to 14.4 ml of oleic acid), showing that different amounts of oleic acid provide crystals of different sizes.

[0288] Figure 3 It is shown that larger PbS nanocrystals are obtained when the amount of oleic acid used is 14.4 ml compared to the amount of oleic acid being 0.6 ml.

[0289] Example 3: Synthesis of PbS nanocrystals using Pb3O4 and (TMS)2S at 60°C

[0290] The above synthesis in Example 1 was repeated except that the reaction temperature of the lead salt and bis(trimethylsilyl)sulfide ((TMS)2S) was changed from 40°C to 60°C.

[0291] The absorption spectra of the nanocrystals obtained at 40°C and 60°C are shown in Figure 4 (where the solid line corresponds to the reaction at 40°C; the dashed line corresponds to the reaction at 60°C), which shows that different temperatures provide crystals of different sizes.

[0292] Figure 4It is shown that larger PbS nanocrystals are obtained when the reaction temperature of the lead salt with the chalcogen-containing reagent is increased.

[0293] Example 4: Synthesis of PbS nanocrystals using Pb3O4 and (TMS)2S via multi-step (TMS)2S addition

[0294] 0.19g Pb3O4, 9.6ml oleic acid and 7ml octadecene (ODE) were loaded into a three-necked flask, evacuated and kept at 180°C for 30 minutes under N2 atmosphere to produce a lead oleate solution. After forming a clear lead oleate solution, the temperature was reduced to 40°C. 90μl of 4ml ODE solution of bis(trimethylsilyl) sulfide ((TMS)2S) was rapidly injected. The reaction was kept at 40°C for 60 minutes and then slowly cooled to room temperature. Then 20ml of distilled acetone was added to the reaction mixture. PbS nanocrystals were precipitated by centrifugation, dispersed in toluene, and precipitated again by a combination of acetone and centrifugation. Finally, the nanocrystals were dispersed in toluene. The purification step was carried out in air.

[0295] The above process was repeated except that the ODE solution of bis(trimethylsilyl)sulfide (TMS) was divided into two equal parts and each part was added to the reaction mixture separately with an interval of 15 minutes between each injection. The reaction was completed within 30 minutes after the last injection.

[0296] Figure 5 The absorption spectra of nanocrystals obtained by single or multiple additions of (TMS)2S are shown (where the solid line corresponds to the reaction of single addition of (TMS)2S; and the dashed line corresponds to the reaction of two additions of (TMS)2S), indicating that different (TMS)2S addition methods provide crystals of different sizes.

[0297] Figure 5 It is shown that larger PbS nanocrystals are obtained when (TMS)2S is added by double addition compared to by single addition.

[0298] Example 5: Synthesis of PbS nanocrystals using Pb3O4 and (TMS)2S with different amounts of ODE

[0299] 0.19g Pb3O4, 9.6ml oleic acid and 7ml octadecene (ODE) were loaded into a three-necked flask, evacuated and kept at 180°C for 30 minutes under N2 atmosphere to produce a lead oleate solution. After forming a clear lead oleate solution, the temperature was reduced to 40°C. 45μl of 4ml ODE solution of bis(trimethylsilyl) sulfide ((TMS)2S) was rapidly injected. The reaction was kept at 40°C for 60 minutes and then slowly cooled to room temperature. Then 20ml of distilled acetone was added to the reaction mixture. PbS nanocrystals were precipitated by centrifugation, dispersed in toluene, and precipitated again by a combination of acetone and centrifugation. Finally, the nanocrystals were dispersed in toluene. The purification step was carried out in air.

[0300] The above procedure was repeated except that the amount of ODE used to dilute Pb3O4 and oleic acid before adding (TMS)2S to the lead oleate solution was changed from 7 ml to 21 ml.

[0301] The absorption spectra of the nanocrystals obtained with different amounts of ODE are shown in Figure 6 (where the solid line corresponds to the reaction using 21 ml of ODE; the dashed line corresponds to the reaction using 7 ml of ODE), which indicates that different amounts of ODE provide crystals of different sizes.

[0302] Figure 6 It is shown that smaller PbS nanocrystals are obtained when the amount of ODE used is increased.

[0303] Example 6: Synthesis of PbS nanocrystals using Pb3O4 and thioacetamide (TAA)

[0304] The synthesis in Example 1 above was repeated except that the same molar amount of thioacetamide (TAA) was used instead of (TMS)2S. The thioacetamide can be added to the lead oleate as a powder, or the thioacetamide can be dissolved in a solvent such as acetone, DMF or THF before injection. The reaction mixture was then heated to 50°C and maintained at this temperature for 1 hour or heated to 90°C and maintained at this temperature for 20 minutes.

[0305] The absorption spectra of nanocrystals obtained using TAA and (TMS)2S are shown in Figure 7 (The solid line corresponds to the reaction using (TMS)2S; the dashed line corresponds to the reaction using TAA), indicating that different reagents provide crystals of different sizes.

[0306] Figure 7 It is shown that larger PbS nanocrystals are obtained when TAA is used instead of (TMS)2S.

[0307] Figure 8a and Figure 8bTEM images of PbS nanocrystals and a histogram of particles measured by TEM are shown. PbS nanocrystals with a maximum absorption of 1314 nm were obtained when TAA was used instead of (TMS)2S.

[0308] As shown below, Table 2 shows the maximum absorption wavelength, size and composition of PbS nanocrystals obtained when TAA is used to replace (TMS)2S. Increasing the ratio of Pb to S increases the maximum absorption wavelength of PbS dots;

[0309] Table 2

[0310]

[0311] The absorption FWHM of these nanocrystals is about 100 nm. For example, a nanocrystal that exhibits a maximum absorption of 950 nm has a FWHM of 105 nm.

[0312] Example 7: Synthesis of PBS nanocrystals using Pb3O4 and (TMS)2S by adding acetone during the reaction

[0313] The above synthesis in Example 1 was repeated except that within 10 seconds after the ODE solution of (TMS)2S was added to the lead oleate solution, 5 ml of acetone was quickly injected into the solution.

[0314] The absorption spectra of the nanocrystals obtained with and without the addition of acetone are shown in Fig. 9 (where the solid line corresponds to the reaction with the addition of acetone; the dashed line corresponds to the reaction without the addition of acetone, ie according to Example 1), which indicates that different reagents provide crystals of different sizes.

[0315] Fig. 9 It is shown that compared to Example 1, smaller PbS nanocrystals are obtained when acetone is added.

[0316] Example 8: Synthesis of PBS nanocrystals using Pb3O4 and (TMS)2S, quenched by cold hexane during the reaction

[0317] The above synthesis in Example 1 was repeated except that cold hexane was quickly injected into the solution within 1.5 minutes after the (TMS)2S ODE solution was added to the lead oleate solution.

[0318] The absorption spectra of the nanocrystals obtained with and without the addition of hexane are shown in Fig.10 (where the solid line corresponds to the reaction with added hexane; the dashed line corresponds to the reaction without added hexane, ie according to Example 1), which indicates that different reagents provide crystals of different sizes.

[0319] Fig.10 It is shown that compared to Example 1, smaller PbS nanocrystals are obtained when hexane is added.

[0320] Example 9: Synthesis of PbS nanocrystals using thioacetamide (TAA)

[0321] 0.35g Pb3O4, 1ml oleic acid and 5ml octadecene (ODE) are loaded into a three-necked flask, evacuated and kept at 180°C for 30 minutes under N2 atmosphere to produce a lead oleate solution. After forming a clear lead oleate solution, the temperature is lowered to room temperature. 40mg TAA is directly loaded into the flask, and the reaction mixture is heated to 50°C and kept at this temperature for 60 minutes. The reaction mixture is then slowly cooled to room temperature. Then 20ml of distilled acetone is added to the reaction mixture. PbS nanocrystals are precipitated by centrifugation, dispersed in toluene, and precipitated again by a combination of acetone and centrifugation. Finally, the nanocrystals are dispersed in toluene. Purification steps are carried out in air.

[0322] The above method was then repeated, except that the amount of oleic acid and the reaction temperature of lead oleate and TAA were as follows:

[0323]

[0324]

[0325] The broad absorption spectrum of the PbS nanocrystals obtained in Example 9 is shown in Fig.11 , where the spectra from left to right correspond to the reaction with 1 ml oleic acid at 50°C; the reaction with 1.4 ml oleic acid at 50°C; the reaction with 1.4 ml oleic acid at 70°C and the reaction with 1.4 ml oleic acid at 85°C. The spectra show that different reaction conditions and different amounts of oleic acid provide PbS nanocrystals of different sizes.

[0326] Example 10: Comparison of PbS nanocrystal solution and drop cast films

[0327] The above synthesis of Example 1 was repeated. Thin film samples were prepared by drop casting particles from toluene solution onto a glass slide. Toluene was evaporated prior to analysis.

[0328] The solution and thin film absorption spectra of PbS nanocrystals are shown in Fig.12 (The solid line corresponds to the nanocrystal solution; the dashed line corresponds to the thin film sample.) The absorption peaks of both the solution and the film are very similar and overlap well, indicating that their electronic states have not changed and no self-assembly has occurred after droplet casting.

[0329] Example 11: Synthesis of lead selenide (PbSe) nanocrystals using Pb3O4 and TOPSe

[0330] 1.5 g of lead oleate (wherein the molar ratio of Pb to OA is 1:4) and 3.9 ml of octadecene (ODE) were charged into a three-necked round-bottom flask, then degassed by three vacuum / nitrogen cycles and kept at 80 ° C for 30 minutes under N2 atmosphere. 3.6 g of TOPSe (wherein the molar ratio of TOP to Se is 2:1) was quickly injected. After the temperature of the reaction mixture returned to 80 ° C, 0.06 ml of DPP was quickly injected. After the addition of DPP, the color of the reaction mixture immediately changed from light brown to dark brown, indicating that nucleation of PbSe nanocrystals occurred. The occurrence of nucleation is an important initial step in the formation of PbSe nanocrystals and allows the PbSe nanocrystals to further grow to the desired size. The reaction solution was then rapidly heated from 80 ° C to 150 ° C, aliquots were taken at different temperatures, rapidly cooled to room temperature (20 ° C) and kept under N2 before analysis. To purify the PbSe nanocrystals, the aliquot and the final reaction mixture were diluted with hexane (1:1 by volume), and then acetone was added (hexane / acetone volume ratio was 1:3). The PbSe nanocrystals were precipitated by centrifugation, redispersed in hexane, and precipitated again by a combination of acetone and centrifugation. The purification steps were performed in air.

[0331] The PbSe nanocrystals prepared in Example 11 were characterized using UV-Vis-NIR spectroscopy, XRD, TEM, and ICP-OES.

[0332] For absorbance, PbSe nanocrystals were dispersed in either tetrachloroethylene or hexane, and their absorbance was monitored using a Jasco V-770 UV-VIS / NIR spectrometer.

[0333] XRD samples were prepared by drop casting PbSe nanoparticles dispersed in hexane onto a microscope slide until a relatively thick, opaque film was formed. The film was then analyzed using a Bruker D2 Phaser instrument.

[0334] TEM samples were prepared by drop casting of PbSe nanoparticles dispersed in hexane onto a copper grid. The solvent was evaporated before analysis. Samples were analyzed on a FEI Titan G2 80-200 kV (S-) ChemiSTEM instrument.

[0335] Fig.15 A scheme for the synthesis of PbSe nanocrystals using Pb3O4 and TOPSe is shown.

[0336] Fig.16 The powder XRD pattern of PbSe nanocrystals prepared according to Example 11 is shown. Fig.16 The XRD pattern shown confirms that the cubic phase PbSe nanocrystals prepared in Example 11 are obtained.

[0337] Fig.17 Shown are absorption spectra of PbSe nanocrystals prepared according to Example 11. The spectra correspond from left to right to reaction temperatures of 90°C, 100°C, and 110°C.

[0338] Table 3 shows the maximum absorption wavelength, size and composition of PbSe nanocrystals. Lower Pb to Se ratios (or an increase in Se molar ratio) result in larger particles and longer maximum wavelengths.

[0339] Table 3

[0340]

[0341] The absorption FWHMs of these nanocrystals are approximately 98, 87, and 100, respectively.

[0342] The molar ratio of lead atoms (in the lead (IV) containing compound) to the organic acid can be varied to obtain the desired nanocrystal size and maximum absorption wavelength as shown in the synthesis of PbS nanocrystals. This parameter can be applied to the synthesis of PbSe, but for simplicity, a fixed molar ratio of lead to oleic acid is used.

[0343] Different Pb:Se molar ratios were also used for PbSe synthesis. The amount of TOPSe ranged from 1.8 g to 12.15 g, corresponding to Pb:Se molar ratios of 1:4 to 1:27.

[0344] Fig.18 The broad spectral tunability of PbSe nanocrystals obtained from different reaction conditions is shown. The spectra show that the maximum absorption wavelength of PbSe nanocrystals can be controlled by using different Pb:Se ratios and different reaction temperatures.

[0345] Fig.19 TEM images of PbSe nanocrystals (λ 最大 =1926nm).

[0346] Fig.20a and Fig.20b shows that PbSe nanocrystals (λ 最大 =2046 nm) and histogram of the particles measured by TEM. The PbSe dots are highly crystalline and free of stacking faults and lattice defects.

[0347] Fig.21a and Figure 21b The PbS nanocrystals (λ 最大 =950nm, PL = 1060 ± 5nm) and PbSe (λ 最大=1000nm, PL =1100±5nm). These spots were excited with 808nm laser.

[0348] Table 4 shows the maximum absorption wavelength, photoluminescence peak, emission FWHM and quantum yield (QY) of some PbS and PbSe nanocrystals.

[0349] The photoluminescence quantum yield (PLQY) and full width at half maximum (FWHM) of some PbS and PbSe nanocrystals are shown in Table 4.

[0350] Table 4

[0351]

[0352] PLQY data were recorded and analyzed according to the method of de Mello, JC, Wttmann, HF & Friend, RH. An improved experimental determination of external photoluminescence quantum efficiency. Adv. Mater. 1997, 9(3), 230-232; doi: 10.1002 / adma.19970090308.

[0353] Before preparing aliquots of PLQY, aliquots of each sample prepared were used to record spectra outside the integrating sphere to determine the initial absorbance. 1 ml of each sample in a glass cuvette was placed in a Prolite LabsphereSpectrafect integrating sphere. The sample was excited with one of the THOR laboratory M9-A64-0200 laser diodes at 1064 nm or the THOR laboratory L808P200 laser diodes at 808 nm. The optical powers of the 808 nm and 1064 nm beams were 125 mW and 165 mW, respectively. Before entering the integrating sphere, each beam was directly passed through an optical chopper operating at 173 Hz. The emission from the sphere was gathered by a Bentham TMc300 monochromator, and then the emission from the sphere was detected by a Newport 818-IG photodiode. A lock-in amplifier was used, using the chopper frequency as a reference, to collect signals from the photodiode. PLQY was determined by recording the scattered laser radiation and emitted photoluminescence of the sample, wherein the sample was placed in both the inside and outside of the excitation beam by a rotating base. A bottle of sample solvent was also recorded and its contribution to the signal removed. All data were corrected for the spectral response of the system by measuring illumination from a Bentham IL1 halogen lamp of known spectral intensity introduced into an empty integrating sphere.

Claims

1. Use of lead (IV)-containing compounds for preparing lead chalcogenide nanocrystals.

2. The use according to claim 1, wherein the lead (IV)-containing compound comprises lead (II, IV) oxide.

3. Use according to claim 1 or 2, wherein the lead chalcogenide nanocrystals exhibit absorption in the range of 500 nm to 4500 nm, preferably 500 nm to 2400 nm.

4. A method for making lead chalcogenide nanocrystals, the method comprising contacting a lead (IV) containing compound with an organic acid and a chalcogen containing reagent.

5. The method of claim 4, wherein the lead (IV) containing compound comprises lead (II, IV) oxide.

6. The method of claim 4 or 5, wherein the lead (IV)-containing compound is contacted with the organic acid to produce a lead salt, and the lead salt is contacted with the chalcogen-containing reagent.

7. The process according to any one of claims 4 to 6, carried out in the presence of a solvent, preferably wherein the solvent comprises a non-polar solvent such as octadecene, or a polar solvent such as DMF, NMP, DMAc, THF, acetone.

8. The method according to any one of claims 4 to 7, comprising: forming a first solution, wherein the first solution is a solution of the lead (IV) containing compound and an organic acid in a first solvent; forming a second solution, wherein the second solution is a solution of the chalcogen-containing reagent in a second solvent; heating the first solution to a first temperature ranging from 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time; reducing the temperature of the first solution to a low temperature ranging from 20°C to 100°C; adding the second solution to the first solution at the low temperature to produce a reaction mixture; The reaction mixture is maintained at a temperature of 20°C to 300°C for a predetermined length of time.

9. The method according to any one of claims 4 to 7, comprising: forming a first solution, wherein the first solution is a solution of the lead (IV) containing compound and an organic acid in a first solvent; heating the first solution to a first temperature ranging from 120° C. to 250° C., and maintaining the first solution at the first temperature for a predetermined length of time; providing the first solution at a second temperature ranging from 50°C to 150°C; adding the chalcogen-containing reagent to the first solution at the second temperature to produce a reaction mixture; The reaction mixture is maintained at a temperature of 50°C to 300°C for a predetermined length of time.

10. The method of claim 8 or 9, further comprising quenching the reaction mixture, for example by adding a quenching solvent to the reaction mixture.

11. The method of any one of claims 8 to 10, further comprising purifying the lead chalcogenide nanoparticles.

12. The method according to any one of claims 4 to 11, wherein the organic acid is a fatty acid, preferably oleic acid.

13. The method according to any one of claims 4 to 12, wherein the chalcogen-containing reagent is selected from reagents containing oxygen, sulfur, selenium and tellurium, and mixtures thereof.

14. The method of claim 8, wherein the chalcogen-containing reagent comprises bis(trimethylsilyl) sulfide.

15. The method of claim 9, wherein the chalcogen-containing reagent comprises thioacetamide.

16. The method of claim 9, wherein the chalcogen-containing reagent comprises tri-n-octylphosphine selenide (TOPSe) and diphenylphosphine (DPP).

17. The process according to claim 6 or 7, wherein the lead salt is contacted with the chalcogen-containing reagent at a temperature of 20 to 100°C, preferably 30 to 60°C.

18. The process according to claim 6 or 7, wherein the lead salt is contacted with the chalcogen-containing reagent at a temperature of 50°C to 300°C, preferably 50°C to 180°C.

19. A method according to any one of claims 4 to 18, comprising the step of varying reaction conditions to control the size of the prepared nanocrystals.

20. The method according to claim 19, wherein the reaction conditions to be changed include one or more of the following: (i) solvent type; (ii) the amount of solvent; (iii) organic acid type; (iv) the amount of organic acid; (v) the method of adding the reactants (especially the chalcogen-containing reagent); (vi) reaction temperature; (vii) Response time (viii) the ratio of Pb to the chalcogen-containing reagent; and (ix) Addition of a second solvent.

21. A method according to any one of claims 4 to 20, comprising monitoring optical properties to monitor the manufacturing process of the nanocrystals.

22. The method of claim 21, wherein the optical property is UV-Vis-NIR absorption spectrum.

23. The use or method of any preceding claim, wherein the nanocrystals comprise quantum dots.

24. One or more (preferably a plurality) lead chalcogenide nanocrystals obtained by the method according to any one of claims 4 to 22.

25. A lead chalcogenide nanocrystalline composition obtained by the method according to any one of claims 4 to 22.

26. A lead chalcogenide nanocrystal composition comprising nanocrystals having an average particle size ranging from 2 nm to 20 nm and a relative size dispersion of less than 25%.

27. The lead chalcogenide nanocrystalline composition of claim 26, exhibiting absorption in the range of about 500 nm to about 4500 nm, preferably about 500 nm to about 2400 nm, such as about 530 nm to 2400 nm, such as about 530 nm to 1600 nm.

28. The lead chalcogenide nanocrystalline composition of claim 26 or 27, exhibiting emission in the range of 600 nm to 4500 nm, preferably 600 nm to 2500 nm.

29. The lead chalcogenide nanocrystalline composition of any one of claims 26 to 28, exhibiting an absorption full width at half maximum (FWHM) value of less than 250 nm, preferably less than 230 nm, preferably less than 130 nm, preferably less than 110 nm, and an emission full width at half maximum (FWHM) value of less than 250 nm, preferably less than 230 nm, preferably less than 150 nm, preferably less than 110 nm.

30. The lead chalcogenide nanocrystalline composition of any one of claims 26 to 29, exhibiting a quantum yield (QY) greater than 10%, preferably greater than 20%, preferably greater than 40%, preferably greater than 50%.

Images