Lead sulfide nanocrystals, methods of making and uses thereof

Abstract

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

Description

Technical Field

[0001] This invention relates primarily to lead chalcogenide nanocrystals. In particular, this invention relates to a method for producing lead chalcogenide nanocrystals using lead (IV) compounds. The invention also extends to the lead chalcogenide nanocrystals obtained by said method and the uses of said lead chalcogenide nanocrystals. Background Technology

[0002] Nanocrystals can be used in a wide range of applications, for example, because their optical properties can be fine-tuned to provide desired characteristics. The optical properties of nanocrystals, such as light absorption and emission characteristics, can be fine-tuned by controlling their size. The largest nanocrystals produce the longest wavelengths (and lowest frequencies), while the smallest nanocrystals produce shorter wavelengths (and higher frequencies). The size of nanocrystals can be controlled through their manufacturing methods. This ability to fine-tune the optical properties of nanocrystals by controlling their size makes them suitable for a wide range of applications, including, for example, photodetectors, sensors, solar cells, bioimaging and biosensing, photovoltaics, displays, lighting, security and 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 production, and metamaterials.

[0003] Lead nanocrystals are known, as are various methods for producing them. For example, Hines et al., Adv. Mater. 2003, 15, No. 21, 1844-1849, disclose a method for preparing lead sulfide nanocrystals having a tunable band gap throughout the near-infrared range (e.g., 800 to 1800 nm). Lead sulfide nanocrystals can be prepared by reacting lead(II) oxide (PbO) with oleic acid to form lead oleate, followed by reaction with a bis(trimethylsilyl)sulfide. However, the reaction described by Hines et al. has been found to be 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.

[0004] Cademartiri et al., J. Phys. Chem. B., Vol. 110, No. 2, 2006, 671-673, disclose 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 limited peak absorption from 1245 nm to 1625 nm. Residual lead chloride remaining on the lead sulfide nanocrystals usually precipitates over time, making it difficult to produce 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 monodisperse lead sulfide nanocrystals.

[0005] Hendricks et al., Science, 2015, 348, 1226-1230, disclose a method for preparing lead sulfide nanocrystals, wherein lead oleate reacts with a reactive disubstituted thiourea. The lead sulfide nanocrystals prepared by this method exhibit absorption peaks in the range of 850 nm to 1800 nm. The method is complex to implement on a large scale because the size (and absorption) of the nanocrystals is controlled by altering the side chains of the thiourea reactants.

[0006] Liu et al., "Reduction of lead dioxide with oxalic acid to prepare lead oxide as the positive material for lead batteries", RAS Adv., 2016, 6, 108513-108522, disclosed the reduction of lead (IV) to prepare lead oxide (II) as an anode material for lead-acid batteries.

[0007] Therefore, although several methods for producing lead chalcogenide nanocrystals are known, these methods cannot control the crystal size in real time, thus preventing fine-tuning of the nanocrystals' optical properties. Known methods also generally cannot produce nanocrystals exhibiting a wide absorption range. Furthermore, these known methods are not suitable for the large-scale (e.g., commercially viable) preparation of lead chalcogenide nanocrystals.

[0008] Therefore, it is desirable to find alternative methods for preparing lead chalcogenide nanocrystals that can be used on a large (e.g., commercially useful) scale and / or that allow for on-the-fly control of the size of the prepared nanocrystals to enable fine-tuning of their optical properties. It is also desirable to provide methods for preparing lead chalcogenide nanocrystals exhibiting a wide absorption range. Such methods are believed to provide lead chalcogenide nanocrystals suitable for a wide range of applications. Summary of the Invention

[0009] According to a first aspect of the invention, use is provided for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals using a lead (IV) compound as a starting material, wherein lead (IV) comprises at least 50 mol%, preferably greater than 75 mol%, preferably greater than 90 mol%, and preferably greater than 95 mol% of all lead present in the lead compound starting material. Preferably, lead (II) oxide is absent from the starting material. Preferably, lead (II) compounds are absent from the starting material.

[0010] According to a second aspect of the invention, use is provided for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals using lead(IV) as a starting material, wherein the molar ratio of the present lead(IV) to any lead(II) is greater than 1:1, preferably greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, preferably greater than 10:1, and preferably greater than 20:1. Preferably, lead(II) is absent from the starting material. Preferably, lead(II)-containing compounds are absent from the starting material.

[0011] According to a third aspect of the invention, a method for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals is provided, the method comprising contacting a lead (IV) compound starting material with an organic acid and a chalcogenide-containing reagent, wherein the molar ratio of the lead (IV) compound to any present lead (II) compound is greater than 1:1, preferably greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, preferably greater than 10:1, preferably greater than 20:1. Preferably, lead (II) oxide is absent from the starting material. Preferably, lead (II) compounds are absent from the starting material.

[0012] According to a fourth aspect of the present invention, a method for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals is provided, the method comprising contacting lead oxide (IV) as a starting material with an organic acid and a chalcogenide-containing reagent, wherein the molar ratio of lead oxide (IV) to lead oxide (II) is greater than 1:1, preferably greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, preferably greater than 10:1, and preferably greater than 20:1. Preferably, lead oxide (II) is absent from the starting material. Preferably, lead (II)-containing compounds are absent from the starting material.

[0013] According to a fifth aspect of the invention, a composition of lead chalcogenide nanocrystals obtained by a method according to a third or fourth aspect of the invention is provided.

[0014] According to a sixth aspect of the present invention, a film comprising a nanocrystalline composition according to a fifth aspect of the present invention is provided.

[0015] According to a seventh aspect of the invention, a system or composition is provided, such as a photodetector, sensor, solar cell, bioimaging or biosensing composition, photovoltaic system, display, battery, laser, photocatalyst, spectrometer, injectable composition, field-effect transistor, light-emitting diode, photonic or optical switching device, or metamaterial comprising a composition according to a fifth aspect of the invention.

[0016] According to an eighth aspect of the invention, a lead chalcogenide nanocrystal composition is provided, the nanocrystals having an average particle size greater than 5 nm, preferably in the range of 6 nm to 25 nm, in the range of 7 nm to 20 nm, preferably in the range of 8 nm to 15 nm, and a relative size dispersion of less than 25%, preferably less than 15%, preferably less than 10%.

[0017] The nanocrystalline composition according to the eighth aspect of the invention preferably exhibits an absorption wavelength in the range of 500 nm to 4500 nm, preferably suitably in the range of 500 nm to 2400 nm, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm.

[0018] The nanocrystal composition according to the eighth aspect of the 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, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm.

[0019] The nanocrystalline composition according to the eighth aspect of the invention preferably exhibits an absorption full width at half maximum (FWHM) value of less than 150 nm, more preferably less than 130 nm, more preferably less than 115 nm, and more preferably less than 105 nm. Preferably, the FWHM ranges from 75 nm to 150 nm, more preferably from 80 nm to 130 nm, more preferably from 85 nm to 110 nm, and more preferably from 90 nm to 105 nm.

[0020] The nanocrystalline composition according to the eighth aspect of the invention preferably exhibits an emission full width at half maximum (FWHM) value of less than 150 nm, more preferably less than 130 nm, more preferably less than 115 nm, and more preferably less than 105 nm. Preferably, the FWHM ranges from 75 nm to 150 nm, more preferably from 80 nm to 130 nm, more preferably from 85 nm to 110 nm, and more preferably from 90 nm to 105 nm.

[0021] The nanocrystal composition according to the eighth aspect of the present invention preferably exhibits a quantum yield (QY) value greater than 10%, more preferably greater than 20%, more preferably greater than 40%, and more preferably greater than 50%.

[0022] According to the first to eighth aspects of the present invention, the preferred lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions include PbS, PbSe, PbTe or mixtures thereof, more preferably PbS or PbSe, and most preferably PbS.

[0023] Surprisingly, the method of the present invention is capable of producing nanocrystals and compositions with improved electronic properties than those produced using mixed lead (II,IV) starting materials (particularly Pb3O4), such as those disclosed in co-pending application PCT / EP20201058346, filed March 25, 2020, the teachings of which are incorporated herein by reference. This is surprising because, at comparable absorption wavelengths, the nanocrystals of the present invention exhibit a better P / V ratio (peak-to-valley ratio).

[0024] Equally surprising is that the method of the present invention is able to produce nanocrystals that primarily exhibit a cubic structure and also display high crystallinity. This has never been observed before in lead chalcogenide nanocrystals and may contribute to improving the structural characteristics of the p / v ratio.

[0025] illustrate

[0026] In describing various aspects of the invention, the terminology used should be interpreted according to the following definitions, unless the context otherwise requires.

[0027] As used in the specification and appended claims, the singular forms “a,” “an,” and “the” include both singular and plural references, unless the context clearly specifies otherwise. For example, “nanocrystal” refers to one or more nanocrystals. For example, “lead (IV) compound” refers to one or more lead (IV) compounds. When used with language containing such language, references to numbers include compositions that contain the number or more of the number.

[0028] As used herein, the terms “comprising, comprises, comprised of” are synonymous with “including, includes” or “containing, contain”, and are inclusive or open-ended, not excluding additional, unlisted members, elements, or method steps. The terms “comprising, comprises, and comprised of” also include the term “consisting of”.

[0029] As used herein, the term "and / or" when used in a list of two or more items means that any one of the listed items can be used alone, or can be any combination of the two or more listed items. For example, if a list is described as including groups A, B, and / or C, then the list can: include A alone; include B alone; include C alone; include a combination of A and B; include a combination of A and C, and a combination of B and C; or include a combination of A, B, and C.

[0030] As used herein, unless otherwise expressly stated, all numbers (e.g., numbers representing values, ranges, percentage quantities) may be interpreted as beginning with the word “about” even if they do not appear explicitly in the terminology used herein.

[0031] When referring to measurable values ​​such as parameters, quantities, time intervals, etc., the term "about" as used herein indicates that the value includes the standard deviation of the error of the equipment or method used to determine the value. The term "about" means a variation of + / -10% or less, + / -5% or less, or + / -0.1% or less of the specified value, provided that such variation is suitable for implementation in this disclosure. It should be understood that the value referred to by the modifier "about" is itself specifically disclosed.

[0032] The numerical range represented by the endpoints includes all integers, as well as fractions included in the range where appropriate (e.g., when multiple elements are involved, 1 to 5 may include 1, 2, 3, 4, and when measurements are involved, it may also include 1.5, 2, 2.75, and 3.80). The description of the endpoints also includes the endpoint values ​​themselves (e.g., 1.0 to 5.0 includes 1.0 and 5.0). Any numerical range described herein is intended to include all subranges contained therein.

[0033] Unless otherwise defined, all terms used in this disclosure, including technical and scientific terms, shall have the meanings commonly understood by one of ordinary skill in the art to which this disclosure pertains. Further guidance, including definitions of terms used in the specification, is provided to better understand the teachings of this disclosure. All publications cited herein are incorporated by reference.

[0034] As used herein, unless otherwise defined, the term "composition" can be open-ended or closed-ended. For example, "composition" includes specified materials, i.e., nanocrystals, as well as unspecified materials, or may consist of specified materials, i.e., substantially excluding unspecified materials.

[0035] The appropriate features of the invention will now be described.

[0036] use

[0037] According to a first aspect, the present invention provides the use of lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals prepared from lead (IV) compounds.

[0038] As used herein, the term "lead (IV) compound" refers to any compound comprising lead in an oxidation state of +4. Any suitable such compound may be used. A suitable lead (IV) compound is preferably lead (IV) oxide (i.e., PbO2). Preferably, the content of any lead (II) compound in the starting material is less than 50% by weight, preferably less than 25% by weight, preferably less than 10% by weight, preferably less than 10% by weight, and preferably less than 1% by weight.

[0039] Appropriately, lead (IV) compounds consist of lead (IV) oxide or are mainly composed of lead (IV) oxide.

[0040] The use of lead oxide (IV) is advantageous because it is a highly reactive and inexpensive material that can be readily used in large-scale (e.g., commercial) processes, i.e., in industrial-scale production. It is also surprising that the nanocrystals of this invention can be prepared by the method claimed in this application. It appears to operate through a mechanism different from other reactions that primarily use Pb(II) or a mixture of Pb(II,IV) reagents.

[0041] The size-dependent shape, surface elemental composition, and crystal facets of quantum dots (QDs) are particularly important because they play a crucial role in determining their chemical reactivity, band levels, and ligand coordination chemistry. They influence the formation of colloidal quantum dot (CQD) films, which ultimately control the electrical properties of CQD optoelectronic devices. The size, shape, and surface composition of quantum dots can be controlled through synthesis or post-synthesis surface modification. By selecting appropriate synthesis conditions and precursors, the shape and surface of colloidal quantum dots can be customized to meet the requirements of high-quality film formation for optoelectronic devices. In this invention, the morphology of nanoparticles derived from Pb(IV) is clearly different from that of Pb(II) or mixed Pb(II,IV) reagents, which we believe is due to the use of lead(IV) precursors / reaction mechanisms. It is speculated that the cubic structure of the nanocrystals will possess unprecedented optical / electrical properties.

[0042] As used herein, the term "chalcogenide" refers to a chemical compound containing at least one chalcogen element and at least one positively charged element. As used herein, the term "chalcogen element" refers to elements of Group 16. For example, "chalcogenide" can include compounds containing oxides, sulfides, selenides, tellurides, or polonides, and at least one positively charged element or cation. "Lead chalcogenide" is a chemical compound containing oxides, sulfides, selenides, tellurides, or polonides, and at least one lead cation.

[0043] As used in this article, the term "nanocrystal" refers to crystal particles having at least one size measurement of less than 100 nm.

[0044] Lead chalcogenide nanocrystals can comprise or consist of quantum dots (QDs). As used herein, the term "quantum dot" refers to a semiconductor nanocrystal that exhibits a quantum confinement effect, which allows it to mimic the properties of atoms. Quantum dots can also be referred to as zero-dimensional nanocrystals.

[0045] According to a second aspect, the present invention provides the use of lead chalcogenide nanocrystals prepared from lead oxide (IV).

[0046] Suitably, lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitably in the range of 500 nm to 4500 nm, preferably suitably in the range of 500 nm to 2400 nm, preferably suitably in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm. In a preferred embodiment, lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals prepared from lead (IV) compounds exhibit absorption greater than 1300 nm.

[0047] Suitable lead sulfide nanocrystals or compositions of lead sulfide nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitablely in the range of 500 nm to 2400 nm, preferably suitablely in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm.

[0048] Suitable lead selenide nanocrystals or compositions of lead selenide nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitablely in the range of 800 nm to 4500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm.

[0049] Suitable lead telluride nanocrystals or compositions of lead telluride nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitablely in the range of 500 nm to 2400 nm, preferably suitablely in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm.

[0050] Suitable lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 600 nm to 4500 nm, preferably suitablely in the range of 600 nm to 2500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm.

[0051] Preferably, the lead sulfide nanocrystals or compositions of lead sulfide nanocrystals prepared from lead (IV) compounds exhibit the maximum absorption wavelength (λ). max The absorption is greater than 1300nm, preferably in the range of 1350nm to 2500nm, more preferably in the range of 1400nm to 1750nm, and more preferably in the range of 1450nm to 1600nm.

[0052] Suitable lead sulfide nanocrystals or compositions of lead sulfide nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 600 nm to 2500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0053] Suitable lead selenide nanocrystals or compositions of lead selenide nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 900 nm to 4500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0054] Suitable lead telluride nanocrystal compositions or lead telluride nanocrystal compositions prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 600 nm to 2500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0055] method

[0056] According to a third aspect, the present invention provides a method for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals, the method comprising contacting a lead (IV) compound with an organic acid and a chalcogenide-containing reagent, wherein the molar ratio of the present lead (IV) compound to any lead (II) compound is greater than 1:1, preferably greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, preferably greater than 10:1, and preferably greater than 20:1. Preferably, lead (II) oxide is absent from the starting material. Preferably, lead (II) compounds are absent from the starting material.

[0057] A fourth aspect of the present invention provides a method for preparing lead chalcogenide nanocrystals or compositions of lead chalcogenide nanocrystals, the method comprising contacting lead oxide (IV) with an organic acid and a chalcogenide-containing reagent, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 1:1, preferably greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, preferably greater than 10:1, and preferably greater than 20:1. Preferably, lead oxide (II) is absent from the starting materials. Preferably, the starting materials do not contain lead (II) compounds.

[0058] The method appropriately prepares various lead chalcogenide nanocrystals, i.e., nanocrystal compositions. Lead chalcogenide nanocrystals prepared by the method of the present invention may include quantum dots (i.e., crystalline quantum dots).

[0059] Various aspects of the method of the present invention (e.g., specific reagents and / or reaction conditions) can be modified to provide lead chalcogenide nanocrystals of desired size, thereby achieving desired optical properties, such as desired absorption and emission (e.g., for the specific use of the nanocrystals).

[0060] For example, the reagents used in the method (especially those containing chalcogens) can be changed to provide lead chalcogenide nanocrystals of the desired size, thereby obtaining the desired optical properties, such as the desired absorption and emission (e.g., for the specific use of the nanocrystals).

[0061] For example, the reaction conditions of the method can be modified to provide lead chalcogenide nanocrystals of the desired size, thereby obtaining the desired optical properties, such as the desired absorption and emission (e.g., for the specific use of the nanocrystals).

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

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

[0064] The method of the present invention may include steps of improving reaction conditions to control the size of the prepared nanocrystals, i.e., to prepare nanocrystals with desired optical properties. For example, to control the size of the prepared nanocrystals, reaction conditions including one or more of the following may be improved:

[0065] (i) Solvent type;

[0066] (ii) Solvent quantity;

[0067] (iii) Organic acid types;

[0068] (iv) Amount of organic acids;

[0069] (v) The method of adding reactants (especially reagents containing chalcogens);

[0070] (vi) Reaction temperature;

[0071] (vii) The ratio of lead to reagents containing chalcogens; and

[0072] (viii) Addition of a secondary solvent.

[0073] By modifying the reaction conditions to control the size of the prepared nanocrystals, the optical properties (absorption and emission) can be improved and fine-tuned to the desired characteristics. This provides a method for fine-tuning the size and optical properties (absorption and emission) of nanocrystals.

[0074] Suitably, the method of the present invention provides lead chalcogenide nanocrystals and compositions thereof that exhibit absorption in the visible and near-infrared range, for example, in the range of about 500 nm to 4500 nm, preferably suitably in the range of 500 nm to 2400 nm, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm. The specific absorption exhibited can be selected by changing the specific reagents and / or reaction conditions used as discussed herein. Suitably, lead sulfide nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitably in the range of 500 nm to 2400 nm, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm. Suitablely, lead selenide nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitablely in the range of 800 nm to 4500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm. Suitablely, lead telluride nanocrystals prepared from lead (IV) compounds exhibit absorption in the visible and near-infrared range, suitablely in the range of 500 nm to 2400 nm, preferably in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0075] Suitably, the method of the present invention provides lead chalcogenide nanocrystals and compositions thereof that exhibit emission in the visible and near-infrared range, for example, in the range of about 600 nm to 4500 nm, preferably suitably in the range of 600 nm to 2500 nm, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm. The specific emission exhibited can be selected by changing the specific reagents and / or reaction conditions used as discussed herein. Suitably, lead sulfide nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitably in the range of 600 nm to 2500 nm, preferably suitably in the range of 950 nm to 1600 nm, and preferably in the range of 1350 nm to 1600 nm. Suitablely, lead selenide nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 900 nm to 4500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm. Suitablely, lead telluride nanocrystals prepared from lead (IV) compounds exhibit emission in the visible and near-infrared range, suitablely in the range of 600 nm to 2500 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0076] Suitablely, any suitable lead (IV) compound can be used in the methods of the present invention for the purposes discussed above. Suitablely, the lead (IV) compound consists of or is substantially composed of lead (IV) oxide.

[0077] As used herein, the term "organic acid" refers to an organic compound that has acidic properties. As used herein, the term "organic compound" refers to a chemical compound in which one or more carbon atoms are covalently bonded to atoms of other elements, most commonly hydrogen, oxygen, and / or nitrogen.

[0078] Any suitable organic acid may be used in the methods of the present invention. Suitablely, the organic acid includes carboxylic acids, such as fatty acids (e.g., saturated or unsaturated fatty acids, suitably unsaturated fatty acids). Examples of suitable carboxylic acids include C4 to C28 (e.g., C12-C22) fatty acids. Suitablely, the organic acid may include oleic acid.

[0079] Appropriately, organic acids include fatty acids, preferably oleic acid.

[0080] As used herein, the term "chalcogenide-containing reagent" refers to a reagent containing at least one chalcogenide element (i.e., at least one Group 16 element or its anion). Any suitable chalcogenide-containing reagent can be used in the methods of the present invention. For example, chalcogenide-containing reagents can be selected from reagents containing oxygen, sulfur, selenium, and tellurium (such as reagents containing sulfur, selenium, and tellurium, particularly reagents containing sulfur or selenium) and mixtures thereof.

[0081] Suitable reagents containing chalcogens may include compounds or elemental chalcogens, as well as mixtures thereof. For example, reagents containing chalcogens may include compounds or elemental chalcogens.

[0082] Suitable chalcogenide compounds may include oxygen, sulfur, selenium, or tellurium atoms, or combinations thereof, and at least one suitable atom of another element. More preferably, chalcogenide compounds may include sulfur, selenium, or tellurium atoms, or combinations thereof (preferably sulfur or selenium atoms), and at least one suitable atom of another element.

[0083] Suitablely, chalcogenide-containing compounds include ionic compounds comprising oxygen, sulfur, selenium, or tellurium anions or combinations thereof, and at least one suitable cation. More preferably, chalcogenide-containing ionic compounds may comprise sulfur, selenium, or tellurium anions or combinations thereof (preferably sulfur or selenium anions), and at least one suitable cation.

[0084] Examples of suitable oxygen-containing reagents include oxygen.

[0085] Examples of suitable sulfur-containing reagents include bis(trialkylsilyl)sulfide compounds (such as bis(trimethylsilyl)sulfide, bis(triethylsilyl)sulfide and bis(tripropylsilyl)sulfide, especially bis(trimethylsilyl)sulfide), thioacetamides, tri-n-octylphosphine sulfide, tributylphosphine sulfide, (alkyl-substituted, phenyl)thiourea compounds (such as N,N'-disubstituted and N,N,N'-trisubstituted thioureas), alkyl-substituted thioamide compounds and elemental sulfur.

[0086] Thioacetamide is an inexpensive reagent with low toxicity, making it particularly suitable for large-scale use.

[0087] Suitable examples of selenium-containing compounds include bis(trimethylsilyl)selenide, tri-n-octylphosphine selenide (TOPSe), and tributylphosphine selenide.

[0088] Certain phosphine-containing reagents are preferred because they can form Se precursors with higher reactivity 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 quantum dots, as well as allowing for mild reaction conditions. Examples of preferred phosphine-containing reagents include diphenylphosphine selenide (DPP), di-o-tolylphosphine selenide (DOTP), and diphenylphosphine oxide selenide (DPPO).

[0089] Suitable examples of tellurium-containing compounds include tri-n-octylphosphine telluride.

[0090] In all the embodiments, methods, uses and various aspects of the invention described below, the lead (IV) compound or lead (IV) oxide preferably comprises at least 50 mol% of all lead present in the lead compound starting material, preferably more than 75 mol%, preferably more than 90 mol%, and more preferably more than 95 mol%.

[0091] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with a fatty acid and a reagent containing a chalcogenide. Preferably, the starting material does not contain lead (II) compounds.

[0092] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with oleic acid and a reagent containing a chalcogenide. Preferably, the starting material does not contain lead (II) compounds.

[0093] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with a fatty acid and a compound containing a chalcogenide. Preferably, the starting material does not contain lead (II) compounds.

[0094] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with oleic acid and a chalcogenide compound. Preferably, the starting material does not contain a lead (II) compound.

[0095] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with a fatty acid and a reagent containing oxygen, sulfur, selenium, or tellurium (e.g., sulfur-, selenium-, or tellurium-containing, particularly sulfur- or selenium-containing). Preferably, the starting material does not contain lead (II) compounds.

[0096] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with oleic acid and a reagent containing oxygen, sulfur, selenium, or tellurium (e.g., sulfur-, selenium-, or tellurium-containing, particularly sulfur- or selenium-containing). Preferably, the starting material does not contain lead (II) compounds.

[0097] For example, the method of the present invention may include contacting a lead oxide (IV) starting material with a fatty acid and a compound containing oxygen, sulfur, selenium, or tellurium (e.g., sulfur-, selenium-, or tellurium-containing compounds, especially sulfur- or selenium-containing compounds). Preferably, the starting material does not contain lead (II) compounds.

[0098] For example, the method of the present invention may include contacting lead oxide (IV) starting material with oleic acid and a compound containing oxygen, sulfur, selenium, or tellurium (e.g., sulfur-, selenium-, or tellurium-containing compounds, especially sulfur- or selenium-containing compounds). Preferably, the starting material does not contain lead (II) compounds.

[0099] When referring to contacting lead (IV) compound starting materials with organic acids and chalcogenide reagents, it means bringing these reagents together in a manner that enables them to react, i.e., to prepare lead chalcogenide nanocrystals and / or combinations thereof. Preferably, the starting materials do not contain lead (II) compounds.

[0100] Suitable, a lead (IV) compound starting material is contacted with an organic acid to produce a lead salt, and said lead salt is then contacted with a chalcogenide reagent. In other words, the lead (IV) compound is contacted with and reacts with an organic acid to form a lead salt. The lead salt thus formed then reacts with a chalcogenide reagent to form one (or more) lead chalcogenide nanocrystals and / or combinations thereof. The lead salt can be separated before reacting with the chalcogenide reagent, but this is generally not necessary. Carrying the method without separating the lead salt has the advantage of carrying it out as a "one-pot" synthesis, which makes the method easy to scale up.

[0101] The formation of lead salts as described above can be monitored by any suitable means, such as by visually observing color changes during lead salt formation.

[0102] Lead (IV) compounds, organic acids, and reagents containing chalcogens can come into contact (or react) in any suitable manner, usually by mixing in a suitable reaction vessel.

[0103] It is generally believed that lead (IV) compounds react with organic acids to form lead salts, which then react with reagents containing chalcogens to form one or more lead chalcogen compound nanocrystals and / or combinations thereof.

[0104] Typically, lead (IV) compounds can be contacted with a molar excess of organic acid. For example, the molar ratio of lead atoms (in lead (IV) compounds) to organic acid can range from 1:1.5 to 1:200, such as 1:1.5 to 1:60. It is thought that the molar ratio of lead atoms (in lead (IV) compounds) to organic acid can be selected to obtain the desired nanocrystal size, thereby achieving the desired absorption. Generally, the higher the amount of organic acid used, the larger the nanocrystals formed.

[0105] Typically, lead salts can be contacted with reagents containing chalcogenides, in an amount such that there is a molar excess of lead atoms relative to the chalcogenide atoms. For example, the molar ratio of lead atoms to chalcogenide atoms can range from 0.9:1 to 50:1; such as 1.5:1 to 30:1, or 1.5:1 to 25:1. It is thought that the molar ratio of lead atoms (in the lead salt) to chalcogenide atoms (in the chalcogenide-containing reagent) can be chosen to achieve highly monodisperse nanocrystals over a wide size range, and thus obtain the desired narrow absorption peak over a wide range. Generally, the higher the amount of lead atoms, the wider the absorption range of the highly monodisperse nanocrystals formed.

[0106] Typically, a lead (IV) compound and an 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 is formed in the solvent. A chalcogenide reagent can then be added to the lead salt solution and reacted to form lead chalcogenide nanocrystals and / or combinations thereof. The chalcogenide reagent can be added with or without a solvent.

[0107] The lead salt and the chalcogenide reagent can be brought into contact in any suitable manner. Suitablely, the lead salt and the chalcogenide reagent can be mixed together, for example, in the presence of a suitable solvent. For example, a solution of the chalcogenide reagent in a suitable solvent can be added to a lead salt solution in a suitable solvent (preferably the same solvent). Alternatively, the chalcogenide reagent can be added directly to the lead salt solution in a suitable solvent, for example. The addition of the chalcogenide reagent can be carried out in one or more steps. For example, the chalcogenide reagent can be added to the lead salt in two or more parts, for example, in two parts. It is thought that the manner of adding the chalcogenide reagent can be used to change the size of the produced nanocrystals and thereby fine-tune the optical properties of the nanocrystals. Generally, adding the chalcogenide reagent in multiple steps can provide larger nanocrystals (i.e., compared to single-step addition).

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

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

[0110] Lead salts can contact chalcogenide reagents at any suitable temperature, i.e., at any suitable temperature at which the reaction occurs. The specific temperature at which this reaction occurs may depend particularly on the specific lead salt and chalcogenide reagent being reacted. Suitable temperatures can range from 20°C to 300°C or from 20°C to 180°C. It is thought that the choice of a specific reaction temperature can be used to modify the size of the formed nanocrystals, thereby fine-tuning their optical properties as needed. Generally, increasing the contact / reaction temperature of the lead salt and chalcogenide reagent yields larger nanocrystals.

[0111] The contact temperature between the lead (IV) compound and the organic acid can be the same as or different from the contact temperature between the lead salt and the chalcogenide reagent. Suitablely, the contact temperature between the lead (IV) compound and the organic acid can be higher than the contact temperature between the resulting lead salt and the chalcogenide reagent. For example, a temperature of 150°C to 300°C can be used to contact the resulting lead salt with the chalcogenide reagent to improve the quality of the quantum dots.

[0112] Suitable lead salts can be contacted with chalcogenide-containing reagents at temperatures ranging from 20°C to 150°C, for example, 30°C to 100°C, 30°C to 60°C, 20°C to 60°C, or about 40°C. This reaction temperature may be suitable when the chalcogenide-containing reagent is a bis(trimethylsilyl) sulfide, for example, when bis(trimethylsilyl) sulfide is contacted with lead oleate. These low-temperature conditions are advantageous in use, particularly in large-scale production.

[0113] For example, when the lead salt includes lead oleate and the chalcogenide-containing reagent includes bis(trimethylsilyl)sulfide, the reaction temperature can be in the range of 20°C to 180°C, for example, 20°C to 55°C, preferably about 40°C. In this method, the chalcogenide-containing reagent includes bis(trimethylsilyl)sulfide, which can provide lead chalcogenide nanocrystals exhibiting absorption in the visible and near-infrared ranges, for example, in the range of about 500 nm to 4500 nm, for example, in the range of about 500 nm to 2400 nm, for example, about 530 nm to 2400 nm, for example, about 530 nm to 1450 nm. The chalcogenide-containing reagents in this method include bis(trimethylsilyl) sulfides, which can provide chalcogenide nanocrystals that exhibit emission of lead in the visible and near-infrared range, for example in the range of about 600 nm to 4500 nm, for example 600 nm to 2500 nm, for example about 630 nm to 2500 nm, for example about 630 nm to 1550 nm.

[0114] Suitablely, lead salts can be contacted with chalcogenide-containing reagents at temperatures ranging from 50°C to 300°C, for example, from 50°C to 150°C. Such a reaction temperature may be suitable when the chalcogenide-containing reagent includes thioacetamide, for example, when thioacetamide is contacted with lead oleate. This method, in which the chalcogenide-containing reagent includes thioacetamide, can provide chalcogenide nanocrystals of lead exhibiting absorption in the visible and near-infrared range, for example, in the range of about 500 nm to 2400 nm, or for example, in the range of 500 nm to 1700 nm. Similarly, this method, in which the chalcogenide-containing reagent includes thioacetamide, can provide chalcogenide nanocrystals of lead exhibiting emission in the visible and near-infrared range, for example, in the range of about 600 nm to 2500 nm, or for example, in the range of 600 nm to 1800 nm.

[0115] 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 one that does not form a coordination complex with lead. Suitably, the solvent is an organic solvent, such as a nonpolar 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 lead (IV) compounds with organic acids, and for the reaction of the resulting lead salts with reagents containing chalcogens. This simplifies the method and makes it particularly suitable for large-scale use.

[0116] For example, lead (IV) compounds can be contacted with organic acids in the presence of a suitable solvent. Suitablely, the solvent is a nonpolar solvent, a polar solvent, or a mixture thereof. Examples of suitable solvents include C4-C22 organic solvents, such as octadecene.

[0117] For example, the resulting lead salt can be contacted with a chalcogenide-containing reagent in the presence of a suitable solvent. Suitablely, the solvent is a nonpolar solvent, a polar solvent, or a mixture thereof. Examples of suitable solvents include C4-C22 organic solvents, such as octadecene.

[0118] The amount of solvent used can be selected based on the specific reagents used and / or other reaction conditions of the application. Typically, the concentration of lead (IV) compounds in the solvent (at the start of the reaction) is in the range of 0.005 mmol / ml to 0.10 mmol / ml. Typically, the concentration of lead atoms in the solvent (at the start of the reaction) is in the range of 0.015 mmol / ml to 0.30 mmol / ml. Typically, the concentration of organic acids in the solvent (at the start of the reaction) is in the range of 0.0075 mmol / ml to 10 mmol / ml, for example, 0.1 mmol / ml to 2 mmol / ml. It is believed that the amount of solvent may affect the size of the final lead chalcogenide nanocrystals formed; therefore, selecting the amount of solvent used in the method may help to fine-tune its optical properties. For example, it is believed that reducing the amount of solvent generally results in the formation of larger nanocrystals.

[0119] Suitablely, the method of the present invention is carried out in an inert atmosphere. Any suitable inert atmosphere can be used, such as nitrogen or argon.

[0120] Appropriately, lead (IV) compounds can be contacted with organic acids for a required period of time to achieve the preparation of lead salts. The suitable reaction time will depend on the specific reagents and reaction conditions used. For example, typical reaction times can range from 5 minutes to 2 hours, such as 7 minutes to 2 hours.

[0121] Appropriately, lead salts can be contacted with chalcogenide-containing reagents for a specified period of time to achieve the preparation of lead chalcogenide nanocrystals. The suitable reaction time will depend on the specific reagents and reaction conditions used. For example, typical reaction times can range from 5 minutes to 2 hours, such as 30 minutes to 2 hours.

[0122] The method of the present invention may include:

[0123] A first solution containing lead (IV) compound and organic acid is formed in a first solvent;

[0124] A second solution of a reagent containing chalcogen elements (e.g., bis(trimethylsilyl) sulfide) is formed in a second solvent;

[0125] The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is held at the first temperature for a predetermined period of time.

[0126] The temperature of the first solution was lowered to a comparison temperature in the range of 20°C to 100°C;

[0127] The second solution is added to the first solution at a comparative temperature to produce a reaction mixture;

[0128] The reaction mixture is kept at a temperature of 20°C to 300°C for a predetermined period of time.

[0129] The method of the present invention may include:

[0130] A first solution containing lead (IV) compound and organic acid is formed in a first solvent;

[0131] A second solution of a reagent containing chalcogen elements (e.g., bis(trimethylsilyl) sulfide) is formed in a second solvent;

[0132] The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is held at the first temperature for a predetermined period of time.

[0133] The temperature of the first solution was lowered to a comparison temperature in the range of 20°C to 60°C;

[0134] The second solution is added to the first solution at a comparative temperature to produce a reaction mixture;

[0135] The reaction mixture is kept at a temperature of 20°C to 60°C for a predetermined period of time.

[0136] The method of the present invention may include:

[0137] A first solution containing lead (IV) compound and organic acid is formed in a first solvent;

[0138] The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is held at the first temperature for a predetermined period of time.

[0139] Provide a first solution at a second temperature in the range of 50°C to 100°C;

[0140] A reagent containing chalcogens (e.g., thioacetamide) is added to the first solution at a second temperature to produce a reaction mixture;

[0141] The reaction mixture is kept at a temperature of 50°C to 300°C for a predetermined period of time.

[0142] The method of the present invention may include:

[0143] A first solution containing lead (IV) compound and organic acid is formed in a first solvent;

[0144] The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is held at the first temperature for a predetermined period of time.

[0145] Provide a first solution at a second temperature in the range of 50°C to 150°C;

[0146] A reagent containing chalcogens (e.g., thioacetamide) is added to the first solution at a second temperature to produce a reaction mixture;

[0147] The reaction mixture is kept at a temperature of 50°C to 150°C for a predetermined period of time.

[0148] The method of the present invention may further include monitoring optical properties (i.e., the optical properties of the reaction mixture, such as a solution of reactants) to monitor the production progress of the nanocrystals. The optical properties may be ultraviolet-visible-near-infrared absorption spectra. The method may include a step of stopping the reaction when the values ​​of the optical properties correspond to the desired size and / or size distribution of the lead chalcogenide nanocrystals.

[0149] The method of the present invention may further include separating lead chalcogenide nanocrystals from the reaction mixture. Any suitable method can be used to separate lead chalcogenide nanocrystals.

[0150] 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, such as acetone, methanol, ethanol, or hexane, may be used. The method of the present invention may also include separating lead chalcogenide nanoparticles.

[0151] For example, lead chalcogenide nanocrystals can be precipitated from the reaction mixture using a suitable solvent, such as a polar solvent (e.g., acetone, methanol, or ethanol). The separation step can be performed under an inert atmosphere or in air.

[0152] When the reagent containing chalcogenides includes bis(trimethylsilyl) sulfides, the amount of organic acid (e.g., oleic acid) is considered to significantly affect the size of the prepared nanocrystals. Generally, the more organic acid introduced, the larger the size of the prepared nanocrystals.

[0153] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfides, it is believed that the multi-step addition of lead (IV) compounds and / or bis(trimethylsilyl) sulfides generally produces larger nanocrystals.

[0154] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfide, it is believed that increasing the reaction temperature of bis(trimethylsilyl) sulfide with lead salt from 40°C to 60°C usually yields larger nanocrystals.

[0155] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfides, it is believed that the introduction of acetone, alcohols, or water can lead to the formation of ultra-small nanocrystals.

[0156] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfide, it is believed that rapidly introducing cold hexane after injecting bis(trimethylsilyl) sulfide will lead to the formation of small nanocrystals.

[0157] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfides, it is believed that reducing the concentration of lead oleate by increasing the amount of solvent (e.g., octadecene) will lead to the formation of smaller nanocrystals.

[0158] When the reagent containing chalcogens includes bis(trimethylsilyl) sulfide, any combination of the above method steps is considered suitable for producing a wide range of nanocrystals at temperatures from 20°C to 60°C (i.e., for the reaction of bis(trimethylsilyl) sulfide with lead salt).

[0159] When the reagent containing chalcogens includes thioacetamide, the method can be simplified because thioacetamide can be simply loaded into the reaction (i.e., without first dissolving thioacetamide in a solvent) or the thioacetamide solution can be loaded into a solvent or solvent mixture.

[0160] When the reagent containing chalcogens includes thioacetamide, it is believed that the amount of organic acid (such as oleic acid) greatly affects the size of the prepared nanocrystals, so that the more organic acid used, the larger the size of the prepared nanocrystals.

[0161] When the reagent containing chalcogens includes thioacetamide, it is believed that increasing the reaction temperature of thioacetamide with lead salt (e.g., increasing it to about 85°C) greatly affects the size of the prepared nanocrystals, so that the higher the temperature used, the larger the size of the prepared nanocrystals.

[0162] When the reagent containing chalcogens includes thioacetamide, it is believed that reducing the concentration of lead salt (such as lead oleate) in the solvent, i.e., increasing the amount of solvent, can provide smaller nanocrystals.

[0163] When the reagent containing chalcogens includes thioacetamide, it is believed that the introduction of acetone, alcohol, or water can lead to the formation of ultra-small nanocrystals.

[0164] When the reagent containing chalcogens includes thioacetamide, it is believed that rapidly introducing cold hexane after the injection of thioacetamide will lead to the formation of small nanocrystals.

[0165] When the reagent containing chalcogens includes thioacetamide, any combination of the above method steps is considered to be usable for producing a wide range of nanocrystals at temperatures from 50°C to 300°C (i.e., for the reaction of thioacetamide with lead salts), suitably from 50°C to 150°C.

[0166] The method of the present invention produces lead chalcogenide nanocrystals. Suitably, the nanocrystals may include quantum dots (i.e., crystalline quantum dots).

[0167] Meanwhile, low-cost and less toxic TAA was used to replace the expensive, toxic, and extremely odorous (TMS)₂S precursor in the preparation of PbS nanocrystals. The threshold temperature for the TAA reaction was found to be approximately 50°C, and higher temperatures resulted in larger PbS nanocrystals. Similarly, the amount of oleic acid affected the size of PbS, and it was found that greater amounts of OA yielded larger PbS nanocrystals.

[0168] Therefore, the present invention enables the use of TAA reagents to obtain PbS quantum dots that operate in the visible light range.

[0169] Nanocrystals / Quantum Dots

[0170] The present invention provides one or more (preferably multiple, i.e., a combination) lead chalcogenide nanocrystals obtained by the above method.

[0171] Suitablely, lead chalcogenide nanocrystals exhibit absorption in the visible and near-infrared range, for example in the range of about 500 nm to 4500 nm, for example in the range of about 500 nm to 2400 nm, for example in the range of about 530 nm to 2400 nm, for example in the range of about 530 nm to 1450 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0172] Suitablely, lead chalcogenide nanocrystals exhibit emission in the visible and near-infrared range, for example in the range of about 600 nm to 4500 nm, for example in the range of about 600 nm to 2500 nm, for example in the range of about 630 nm to 2500 nm, for example in the range of about 630 nm to 1550 nm, preferably suitablely in the range of 950 nm to 1600 nm, and more preferably in the range of 1350 nm to 1600 nm.

[0173] The lead chalcogenide nanocrystal composition of the present invention comprises, or is composed of, nanocrystals with an average particle size greater than 5 nm, preferably in the range of 6 nm to 22 nm, more preferably 7 nm to 20 nm, and a relative size dispersion of less than 25%, preferably less than 20%, more preferably less than 10%. Preferably, the nanocrystals have an average particle size in the range of 8 nm to 17 nm and a relative size dispersion of less than 20%. Preferably, the nanocrystals have an average particle size in the range of 9 nm to 15 nm and a relative size dispersion of less than 15%.

[0174] Preferably, the PbS nanocrystal composition according to the present invention comprises, or is composed of, nanocrystals having an average particle size in the range of 6 nm to 15 nm, and having a relative size dispersion of less than 20%, preferably less than 10%.

[0175] The PbSe nanocrystal composition of the present invention comprises, or is composed of, nanocrystals in which the average particle size is in the range of 2 nm to 17 nm, preferably 6 nm to 15 nm, and the relative size dispersion of the nanocrystals is less than 25%, preferably less than 20%.

[0176] The lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably contains lead chalcogenide nanocrystals, wherein the average particle size of the lead chalcogenide nanocrystals is in the range of 6 nm to 20 nm, preferably 7 nm to 17 nm, and more preferably 8 nm to 15 nm.

[0177] The lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably contains more than 0.001% by weight of lead chalcogenide nanocrystals, more preferably more than 0.01% by weight, more preferably more than 0.1% by weight, more preferably more than 1% by weight, and more preferably more than 5% by weight.

[0178] In some applications, the lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention preferably contains more than 5% by weight of lead chalcogenide nanocrystals, more than 30% by weight, more than 75% by weight, more than 90% by weight, and more than 95% by weight.

[0179] In one embodiment, the lead chalcogenide nanocrystal composition according to the eighth aspect of the present invention comprises lead chalcogenide nanocrystals.

[0180] The remainder of the composition, which is not a lead chalcogenide nanocrystal, may be a carrier material, such as a solvent, additive, inorganic ligand, organic ligand, or reaction byproduct.

[0181] The present invention also provides a composition of lead chalcogenide nanocrystals obtained directly by the above method.

[0182] The present invention also provides a composition of lead chalcogenide nanocrystals that can be obtained by the above method.

[0183] The composition of lead chalcogenide nanocrystals may include one or more quantum dots (i.e., crystalline quantum dots). This invention provides a composition of lead chalcogenide quantum dots obtained by the method described above.

[0184] The present invention also provides a composition of lead chalcogenide quantum dots obtained directly by the above method.

[0185] The present invention also provides compositions of lead chalcogenide quantum dots that can be obtained by the above method.

[0186] Lead chalcogenide nanocrystals (e.g., lead chalcogenide quantum dots) and compositions, films, systems, or components containing said lead chalcogenide nanocrystals can be used for any suitable purpose. For example, lead chalcogenide nanocrystals and compositions thereof can be used to provide or for use 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 power) generation applications, fiber optic amplifiers, lasers, optical gain media, fiber optic communications, high-speed communications, telecommunications, infrared LEDs and lasers, and electroluminescent devices.

[0187] Lead chalcogenide nanocrystal compositions (e.g., lead chalcogenide quantum dots) can also be used in infrared sensing and photodetectors. For example, lead chalcogenide nanocrystals (e.g., lead chalcogenide quantum dots) can be used as light absorbers in 3D camera sensors and 3D time-of-flight camera sensors for mobile and consumer, automotive, medical, industrial, defense, and aerospace applications.

[0188] 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.

[0189] Lead chalcogenide nanocrystal compositions (such as lead chalcogenide quantum dots) can also be used in wired, high-speed communication devices, night vision devices, and solar energy conversion.

[0190] The present invention provides a membrane comprising a chalcogenide nanocrystal composition of lead according to the present invention.

[0191] This invention provides a system or component comprising a chalcogenide nanocrystal composition of lead of the present invention, such as a photodetector, sensor, solar cell, bioimaging or biosensing composition, photovoltaic system, display, battery, laser, photocatalyst, spectrometer, injectable composition, field-effect transistor, light-emitting diode, photonic or optical switching device or metamaterial, thermoelectric (cooling) and energy (high-temperature power) generation application.

[0192] This invention provides a biolabeling or biotag, bioimaging, and labeling (in vitro and in vivo) of chalcogenide lead nanocrystals of this invention.

[0193] The method of this invention enables the nanocrystals of this invention to possess an excellent full width at half maximum (FWHM) value. FWHM refers to the width of the optical signal at half its maximum intensity. This metric provides the bandwidth of a light source operating at 50% capacity.

[0194] The emission properties of the nanocrystals of this invention depend on both their chemical properties and size. They typically exhibit an emission function with a Gaussian curve shape. Lower intensity may result in a wider spectral bandwidth and less pure color representation on screen. To determine the FWHM, the difference between the low-wavelength and high-wavelength points must be calculated at half the maximum spectral intensity. The narrower FWHM of this invention provides a higher signal-to-noise ratio and allows for more precise tuning of the absorption wavelength. Essentially, a narrower bandwidth translates to purer colors and higher efficiency levels.

[0195] For example, the method of the present invention can produce nanocrystals whose maximum absorption wavelength (λ) is... max The wavelength of the light emission (FWHM) is greater than 1300 nm, preferably in the range of 1350 nm to 2500 nm, preferably 1400 nm to 1750 nm, and preferably 1450 nm to 1600 nm, and the emission wavelength or photoluminescence (PL) is in the range of 1200 nm to 2500 nm, preferably 1300 nm to 2000 nm, and preferably 1350 nm to 1750 nm. The composition according to the eighth aspect of the invention can produce an absorption FWHM of less than 120 nm, preferably less than 110 nm, for example, about 100 nm, and can produce an emission FWHM of less than 120 nm, preferably less than 110 nm, for example, about 110 nm. These properties can be provided by a nanocrystalline composition having a relative size dispersion of less than 20%, preferably less than 15%, and preferably less than 10%.

[0196] Due to the method used in this invention, the nanocrystals of the composition according to the eighth aspect of this invention exhibit good relative size dispersion. Relative size dispersion is a measure of the variation in the size of nanocrystal particles. It is determined by measuring the particle size of a specific batch of nanoparticles and determining the variance of the average size. This can be expressed as a specific average size x, plus or minus the range of particle sizes.

[0197] Typically, the method of the present invention is capable of producing the nanoparticle composition according to the eighth aspect of the present invention, wherein the relative size dispersion (determined by TEM) is less than 25%, preferably less than 22%, preferably less than 20%, and preferably less than 15%.

[0198] In a preferred embodiment of the invention, the molar ratio of lead atoms to chalcogenide atoms in the nanocrystalline composition according to the eighth aspect of the 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 type of PbS, PbSe, and PbTe nanocrystal.

[0199] These ratios of lead atoms to chalcogenide atoms are related to the low relative size dispersion exhibited by the nanocrystals of the present invention. Typically, the nanocrystal compositions according to the eighth aspect of the present invention have a molar ratio of lead atoms to chalcogenide atoms in the range of 1.2:1 to 4:1, and have a relative size dispersion of less than 20%, for example less than 18%, for example between 10% and 17%.

[0200] Typically, a higher Pb to S ratio in lead-sulfur nanocrystal compositions is associated with larger nanocrystal sizes and a longer λ value for the PbS point. max Relatedly, a lower Pb to Se ratio (or an increased Se molar ratio) in lead-selenium nanocrystal compositions is associated with larger nanocrystal sizes and longer λ. max Related.

[0201] The molar ratio of lead atoms to chalcogenide atoms was measured using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0202] Typically, the PbS nanocrystal composition according to the eighth aspect of the present invention exhibits a maximum absorption wavelength (λ). max The proportional correlation between the particle size and its average particle size, i.e., larger points exhibit longer λ. max For PbSe nanocrystals, it can be observed that the nanoparticle size is related to λ. max A similar trend in correlation. However, at the same λ... max PbSe nanocrystals are typically smaller than PbS. PbS(λ) max =1314nm) and PbSe(λ max TEM image (2046 nm).

[0203] The preferred features of the fourth to seventh aspects are as defined with respect to the first, second and third aspects. Attached Figure Description

[0204] To better understand the invention and to show how its exemplary embodiments can be implemented to produce effects, reference will be made only to the accompanying diagrams, in which:

[0205] Figure 1 The absorption spectra of PbS nanocrystals using PbO2 as the lead source and multiple additions of (TMS)2S are shown.

[0206] Figure 2TEM images of PS nanocrystals prepared from a PbO2 lead source with an FWHM of 89 nm are shown at different magnifications. In the lead(IV)-based nanocrystals, a cubic structure predominates, and the nanoparticles exhibit high crystallinity.

[0207] Figure 3 The absorption spectra of PbS nanocrystals using Pb3O4 as the lead source and multiple additions of (TMS)2S are shown.

[0208] Figure 4 TEM images of PS nanocrystals prepared from a Pb3O4 lead source at different magnifications are shown, FWHM = 94 nm. In the lead-based (II,IV)PbS nanocrystals, spherical structures are dominant, and the nanoparticles exhibit high crystallinity.

[0209] Figure 5 The absorption spectra of PbS nanocrystals using PbO as the lead source and multiple additions of (TMS)₂S are shown.

[0210] Figure 6 TEM images of PS nanocrystals prepared using PbO as the lead source are shown at different magnifications, FWHM = 91 nm. In the lead(II)-based PbS nanocrystals, spherical or rounded-edge structures are dominant, and the nanoparticles exhibit high crystallinity.

[0211] Figure 7 The absorption spectra of PbS nanocrystals in hexane stored under light-free, air-free, and room-temperature conditions are shown as a function of time. A significant blue shift was observed in the nanocrystals after 42 days of storage, indicating their participation in the oxidation reaction.

[0212] Figure 8 The absorption spectra of PbS nanocrystals treated with ammonium chloride in hexane showed no change over storage time, even in darkness, in air, and at room temperature. This indicates that the surface lead atoms of the nanocrystals are covalently bonded to halides, protecting the nanocrystals from (photo)oxidation.

[0213] Figure 9 The maximum absorption wavelength (λ) of the PbS nanocrystalline film is shown when heated at different temperatures. The nanocrystals were prepared using Pb(II), Pb(IV), and Pb(II,IV) lead sources and multiple additions of (TMS)₂S. No blue shift was observed when the film was heated to 180 °C in air, indicating that the Pb(IV) and Pb(II,IV)-based PbS nanocrystals exhibit thermal stability comparable to that of Pb(II)-based PbS nanocrystals.

[0214] Figure 10The freewheeling height (FWHM) of PbS nanocrystalline films at different heating temperatures is shown. Nanocrystals were prepared using Pb(II), Pb(IV), and Pb(II,IV) lead sources with multiple additions of (TMS)₂S. No significant FWHM broadening was observed in any of the films when heated to 120 °C in air, indicating that the thermal stability of Pb(IV) and Pb(II,IV)-based PbS nanocrystals is comparable to that of Pb(II)-based PbS nanocrystals.

[0215] Figure 11 HRTEM images of PbS quantum dots made from lead(II) oxide precursors are shown. The quantum dots appear in a truncated octahedral crystal. The (002), (111), and (-111) crystal planes are visible.

[0216] Figure 12 HRTEM images of PbS quantum dots made from lead oxide (IV) precursors are shown. The quantum dots appear in truncated octahedral (major) and cubic octahedral (minor) crystals. The (002), (111), and (022) crystal faces are visible in the truncated octahedral crystals, while the (002) crystal face appears in the cubic octahedral crystals. Detailed Implementation

[0217] example

[0218] Several embodiments and comparative examples are described below to illustrate the method described according to this disclosure.

[0219] While specific embodiments of the invention have been described below for illustrative purposes, it will be apparent to those skilled in the art that many changes may be made to the details of the invention without departing from the invention as defined in the appended claims.

[0220] Unless otherwise stated, all parts and percentages in the following examples and throughout the specification are parts by weight or weight percentages.

[0221] Absorption spectra of colloidal quantum dots or quantum dot films were obtained on a JASCO V-770 UV-Vis / NIR spectrometer, which can provide measurements at wavelengths from 400 nm to 3200 nm.

[0222] Cu Kai X-ray diffractometer was used on a Panalytical X'Pert PRO MPD diffractometer. XRD data were collected at room temperature within the range of 10 < 2 q < 90°. In each case, a few drops of dispersed sample were placed on a glass microscope slide and allowed to evaporate. Data were analyzed using Rigaku SmartLab Studio II software, and searches and matches were performed using the Crystallographic Open Database.

[0223] TEM and high-resolution transmission electron microscopy (HRTEM) images were obtained using a FEI Talos F200X microscope equipped with an X-FEG electron source. The experiments were conducted using an accelerating voltage of 200 kV and a beam current of approximately 5 nA. Images were recorded using a FEICETA 4k x 4k CMOS camera. In each case, a few drops of quantum dots dispersed in a solvent were placed on a carbon-coated copper grid and allowed to evaporate. Samples were used as is or treated with acetone followed by methanol to remove unwanted organic material before imaging.

[0224] ICP-OES data were obtained on an Agilent 720 ICP-OES system. The dispersions of nanocrystals in toluene were added to water and heated to evaporate the solvent. The solids were then digested and retained in aqua regia (2HCl:1HNO3). The mixture was then brought to volume in volumetric flasks and diluted as needed to run within our ICP calibration range. Samples were calibrated separately for Pb and S. The certified calibration CRM solution containing Pb was a 28-element mixed standard solution from Fisher Scientific's SPEX CertiPrep, and the certified calibration CRM solution containing S was a multi-element standard solution labeled CCS-5 supplied by Inorganic Ventures. Both Pb & S calibrators were run at concentrations of 0.5 ppm and 10 ppm.

[0225] Material

[0226] PbO (99.999% trace metal-based, Sigma-Aldrich), Pb3O4 (99%, Sigma-Aldrich), PbO2 (99.998% trace metal-based, Sigma-Aldrich), hexamethyldisilazane ((TMS)2S, synthetic grade, Sigma-Aldrich), oleic acid (OA, 90%, Fisher Scientific).

[0227] Thioacetamide (TAA, ≥99%, Sigma-Aldrich), trioctylphosphine (TOP, 97%, Sigma-Aldrich), Se, octadecene (ODE, 90%, Fisher Scientific), diphenylphosphine (DPP, 98%, Sigma-Aldrich). NaCl (99.5%, Fisher Scientific), NaI (≥99%, Sigma-Aldrich), NH4Cl (99.99% trace metal-based, Sigma-Aldrich). All solvents (hexane, acetone, methanol) were purchased from Fisher Scientific.

[0228] Example 1: Synthesis of lead sulfide (PbS) nanocrystals using Pb(IV) oxide (PbO2) and multiple additions of (TMS)2S.

[0229] 1.25 g (5.23 mmol Pb) PbO2 and 10 mL oleic acid (28.40 mmol) were added to a 50 mL three-necked round-bottom flask. The mixture was degassed under vacuum and then maintained at 250 °C under a nitrogen atmosphere for 60 min to produce a lead (IV) oleate solution. After a clear brown oleate solution was formed, the temperature was lowered to about 40 °C, and the 1.08 g (0.56 mmol Pb) of lead (IV) oleate solution used was added to a 100 mL three-necked round-bottom flask containing 13.50 mL of pre-degassed octadecene (ODE). The mixture was further degassed under vacuum at 90 °C for 30 min and maintained at 100 °C under a nitrogen atmosphere. 0.8 mL of the first (TMS)2S stock solution in the degassed ODE ((TMS)2S: ODE equals 1 / 8 v / v) was then injected. After reacting at 100°C for 7 min, 0.8 mL of a second (TMS)₂S stock solution was added to the degassed ODE ((TMS)₂S: ODE = 1 / 12 v / v). The reaction mixture changed from light brown to dark brown over the next few minutes, indicating the formation and growth of nanocrystals. Then, 0.8 mL of the second (TMS)₂S stock solution was added every 5 min until the target absorption wavelength was obtained. The reaction was then cooled to room temperature (20°C to 30°C), and the PbS nanocrystals were purified by precipitation and redispersion in four times their volume of acetone and hexane, respectively. The nanocrystals were then redispersed in the desired solvent, such as n-hexane, n-octane, or toluene.

[0230] Figure 1 The absorption spectra of PbS nanocrystals using PbO2 as the lead source and with multiple additions of (TMS)2S are shown. Table 1 summarizes their maximum absorption, FWHM, and peak-to-valley ratio.

[0231] 1541 89 5.3

[0232] Figure 2 TEM images of PS nanocrystals prepared using a PbO2 lead source at different magnifications are shown, λ = 1541 nm, FWHM = 89 nm. The cubic structure is dominant in the lead(IV)-based nanocrystals, which also exhibit high crystallinity.

[0233] Reference Example 2: PbS nanocrystals were synthesized using Pb(II,IV) oxide (Pb3O4) and multiple additions of (TMS)2S.

[0234] 2.4 g (10.50 mmol Pb)Pb₃O₄ and 20 mL (56.70 mmol) oleic acid were added to a 50 mL three-necked round-bottom flask. The mixture was degassed under vacuum and then maintained at 230 °C under a nitrogen atmosphere for 60 min to produce lead oleate (II, IV) solutions. After forming a clear, light brown oleate solution, the temperature was lowered to approximately 40 °C, and 1.07 g (0.556 mmol) of the used lead oleate (IV) solution was added to a 100 mL three-necked round-bottom flask containing 13.50 mL of pre-degassed octadecene (ODE). The mixture was further degassed under vacuum at 90 °C for 30 min and maintained at 100 °C under a nitrogen atmosphere. 0.8 mL of the first (TMS)₂S stock solution was injected into the degassed ODE ((TMS)₂S: ODE equals 1 / 8 v / v). After reacting at 100°C for 7 min, 0.8 mL of a second (TMS)₂S stock solution was added to the degassed ODE ((TMS)₂S: ODE = 1 / 12 v / v). The reaction mixture changed from light brown to dark brown over the next few minutes, indicating the formation and growth of nanocrystals. Then, 0.8 mL of the second (TMS)₂S stock solution was added every 5 min until the target absorption wavelength was obtained. The reaction was then cooled to room temperature (20°C to 30°C), and the PbS nanocrystals were purified by precipitation and redispersion in available (four times their volume) acetone and hexane, respectively. The nanocrystals were then redispersed in the desired solvent, such as n-hexane, n-octane, or toluene.

[0235] Figure 3 The absorption spectra of PbS nanocrystals using Pb3O4 as the lead source and with multiple additions of (TMS)2S are shown. Table 2 summarizes their maximum absorption, FWHM, and peak-to-valley ratio.

[0236] 1549 94 4.76 1556 92 4.88

[0237] It can be seen that, compared with Pb3O4, PbS nanocrystals produced using PbO2 exhibit a higher P / V ratio at similar absorption wavelengths. Similarly, the FWHM value of PbS nanocrystals produced using PbO2 is lower than the corresponding FWHM value of PbS nanocrystals produced using Pb3O4.

[0238] Figure 4 TEM images of PS nanocrystals prepared using Pb3O4 as the lead source are shown at different magnifications, λ = 1549 nm, FWHM = 94 nm. The lead(II,IV)-based nanocrystals exhibit a predominantly near-spherical or rounded-edge structure and also display high crystallinity.

[0239] Reference Example 3: Synthesis of PbS nanocrystals using Pb(II) oxide (PbO) and multiple additions (TMS)2s.

[0240] 1.17 g (5.24 mmol Pb)Pb₃O₄ and 20 mL of oleic acid (28.40 mmol) were added to a 50 mL three-necked round-bottom flask. The mixture was degassed under vacuum and then maintained at 150 °C under a nitrogen atmosphere for 60 min to produce a lead oleate solution. After a clear, light brown oleate solution was formed, the temperature was lowered to approximately 40 °C, and 1.07 g (0.556 mmol) of the used lead (IV) oleate solution was added to a 100 mL three-necked round-bottom flask containing 13.50 mL of pre-degassed octadecene (ODE). The mixture was further degassed under vacuum at 90 °C for 30 min and maintained at 100 °C under a nitrogen atmosphere. 0.8 mL of the first (TMS)₂S stock solution was injected into the degassed ODE ((TMS)₂S: ODE equals 1 / 8 v / v). After reacting at 100°C for 7 min, 0.8 mL of a second (TMS)₂S stock solution was added to the degassed ODE ((TMS)₂S:ODE = 1 / 12 v / v). The reaction mixture changed from light brown to dark brown over the next few minutes, indicating the formation and growth of nanocrystals. Then, 0.8 mL of the second (TMS)₂S stock solution was added every 5 min until the target absorption wavelength was obtained. The reaction was then cooled to room temperature (20°C to 30°C), and the PbS nanocrystals were purified by precipitation and redispersion in available (four times the volume) acetone / methanol and hexane, respectively. The nanocrystals were then redispersed in the desired solvent, such as n-hexane, n-octane, or toluene.

[0241] Figure 5 The absorption spectra of PbS nanocrystals using PbO as the lead source and multiple additions of (TMS)₂S are shown.

[0242] Table 3 summarizes their maximum absorption, FWHM, and peak-to-valley ratio.

[0243] 1514 92 5.00

[0244] Similar to PbS nanocrystals produced using Pb3O4, PbS nanocrystals produced using PbO exhibit a lower P / V ratio at similar absorption wavelengths compared to PbS nanocrystals produced using PbO2. Likewise, the FWHM value of PbS nanocrystals produced using PbO2 is lower than the corresponding FWHM value produced using PbO.

[0245] Figure 6 TEM images of PS nanocrystals using PbO as the lead source are shown at different magnifications. Near-spherical or rounded-edge structures dominate in the lead(II)-based nanocrystals, which also exhibit high crystallinity.

[0246] Example 4: Surface passivation of PbS nanocrystals with halide salts and storage stability of the resulting colloidal PbS quantum dots.

[0247] The process is summarized as Scheme 1, which describes the use of Pb(IV) oxide as a lead source and a surface passivation reaction to prepare PbS nanocrystals.

[0248] The surface of PbS nanocrystals was treated with different halide salts to improve their storage stability and thermal stability.

[0249] PbS nanocrystals were synthesized as described in Example 1 above. The typical steps of the surface passivation reaction are as follows: After the PbS nanocrystals reached the desired absorption wavelength, the reaction mixture was rapidly cooled to 60°C, and while stirring under nitrogen, 1 mL of 0.19 M halide salts, such as NaCl, NaI, or NH4Cl, in degassed methanol was added dropwise to the reaction mixture containing 1.07 g of lead oleate (0.556 mmol Pb). The passivation reaction could proceed for 30 to 60 minutes, and the resulting nanocrystals were purified using acetone and methanol as non-solvents. The obtained solid was dispersed in a desired solvent, such as n-octane. The resulting dispersion may require further centrifugation to remove unwanted solid (excess salt) precipitate. Compared to untreated PbS nanocrystals, halide-treated nanocrystals typically exhibit a redshift of approximately 50 nm (see Table 4).

[0250] Table 4: Dispersion stability of untreated and halide-treated PbS nanocrystals in air and at room temperature.

[0251]

[0252] Figure 7 and Figure 8The absorption spectra of PbS nanocrystals dispersed in hexane and stored in air at room temperature (20 °C), including untreated and NH4Cl-treated nanocrystals, are shown.

[0253] Table 4 compares the stability of PbS nanocrystals with and without halide salt passivation. Without halide salt passivation, PbS nanocrystals showed a 96 nm blue shift after 42 days of storage in air and at room temperature, indicating that the nanocrystals were affected by oxidation. In contrast, halide-passivated PbS nanocrystals showed only a 6 nm blue shift after the same storage conditions and time.

[0254] Example 5: Film formation and thermal stability of PbS nanocrystals

[0255] The synthesis described in Example 1 above was repeated. As shown in Example 4, the surface of the PbS nanocrystals was passivated with halides. PbS films were prepared by spin-coating a dispersion of PbS nanocrystals in n-hexane, n-octane, or toluene onto a glass slide.

[0256] To conduct thermal stability studies, spin-coated films with thicknesses in the range of 200 nm were heated on hot plates in air at different temperatures, and their absorption wavelengths and FWHM were monitored. Figure 9 and Figure 10 The changes in membrane absorption wavelength and FWHM of PbS prepared using lead(II), lead(IV), and lead(II,IV) as lead sources and (TMS)S are shown.

[0257] Example 6 - Synthesis of PbS quantum dots

[0258] 6.1-PbS quantum dots of lead(II) oxide

[0259] Lead oxide (PbO) (0.1723 g, 0.772 mmol) was loaded into a 3-necked RBF equipped with a magnetic stir bar and a condenser. The system was evacuated and placed under N2 on a Schlenk production line, with triple vacuum circulation. Oleic acid (1.465 mL, 4.15 mmol) was then injected into the flask and degassed three times at room temperature, with 10-minute intervals between each degaussing step. The temperature was then increased to form lead oleate, which began to form at 115 °C. The temperature was further increased to 150 °C and held for 15 minutes to complete the reaction. 20 mL of dry, degassed octadecene (ODE) was then injected into the lead oleate solution, and the temperature was stabilized at 100 °C for 30 minutes. 1.18 mL of a solution of 0.093 M (TMS)₂S in ODE was then immediately injected into the lead oleate solution. The solution was observed to turn black 40 seconds after injection. Seven minutes later, 1.28 mL of 0.033 M (TMS)₂S in ODE was immediately injected into the lead oleate solution. After another 5 minutes, the reaction was quenched in an ice-water bath, and the reaction flask was then sealed and purged into a glove box. An aliquot of 12.5 mL of the reaction solution was combined with 30 mL of anhydrous IPA and centrifuged (4.5 K, 3 min) to precipitate the product. The precipitates were combined in anhydrous hexane (~5 mL) and anhydrous IPA (10 mL) was added before centrifugation (4.5 K, 3 min). IPA washing was repeated before dissolving the precipitates in anhydrous octane (5 mL). A final centrifugation was performed to remove insoluble precipitates, and the supernatant containing the purified product was stored in a glove box under N₂.

[0260] 6.2 – PbS quantum dots from lead(IV) oxide

[0261] PbO2 (0.1847 g, 0.772 mmol) was loaded into a 3-necked RBF equipped with a magnetic stir bar and a condenser. The system was evacuated and placed under N2 on the Schlenk production line, with triple vacuum circulation. Oleic acid (1.465 mL, 4.15 mmol) was then injected into the flask and degassed three times at room temperature, with the vacuum maintained for 10 minutes at intervals. The temperature was then increased to form lead oleate, which began to form at 200 °C. The temperature was further increased to 220 °C and held for 15 minutes to complete the reaction. 20 mL of dried, degassed octadecene-1-ene (ODE) was then injected into the lead oleate solution, and the temperature was stabilized at 100 °C for 30 minutes. 1.18 mL of a solution of 0.093 M (TMS)₂S in ODE was then immediately injected into the lead oleate solution. The solution was observed to turn black 40 seconds after injection. After 7 minutes, 1.28 mL of 0.033 M (TMS)₂S in ODE was immediately added to the lead oleate solution. After another 5 minutes, 0.15 mL of 0.033 M (TMS)₂S in ODE was immediately added to the lead oleate solution. After 3 minutes, the reaction was quenched in an ice-water bath, then the reaction flask was sealed and purged into a glove box. An aliquot of 12.5 mL of the reaction solution was combined with anhydrous IPA (30 mL) and centrifuged (4.5 K, 3 min) to precipitate the product. The precipitates were combined in anhydrous hexane (~5 mL) and anhydrous IPA (10 mL) was added before centrifugation (4.5 K, 3 min). IPA washing was repeated before dissolving the precipitate in anhydrous octane (5 mL). A final centrifugation was performed to remove insoluble precipitates, and the supernatant containing the purified product was stored in a glove box under N₂.

[0262] 6.3 Characterization of Examples 6.1 and 6.2

[0263] Absorption spectra of PbS quantum dots were obtained on a JASCO V-770 UV-Vis / NIR spectrometer, which can provide measurements in the wavelength range of 400 nm to 3200 nm.

[0264] High-resolution transmission electron microscopy (HRTEM) characterization was performed on a FEI (Thermo Fisher) Talos FX200A transmission electron microscope equipped with a high-brightness electron source (200 kV super-X field emission gun - FEG). Images from the TEM characterization were recorded using a CETATM16M (4096 x 4096 pixels) CMOS camera. Atomic-resolution images of the nanoparticles were obtained in the microscope's high-resolution transmission electron microscopy (HRTEM) mode, revealing the lattice fringes of the nanocrystals. The TEM images were analyzed using Gatan Digital Micrograph 2.3, and crystal orientation analysis was performed using CrysTbox.

[0265] As shown in Table 5, PbS CQDs with similar maximum absorption wavelengths (~1330 nm to 1340 nm) and band gaps (0.92 eV to 0.93 eV) were synthesized using different lead oxide precursors (according to Example 6).

[0266] Table 5. Peak absorption wavelengths and band gaps of quantum dots prepared from lead oxide (II) and lead oxide (IV).

[0267] Lead(II)-based PbS quantum dots 1330 0.93 Lead(IV) oxide-based PbS quantum dots 1340 0.92

[0268] The shape of PbS colloidal quantum dots (CQDs) changes from octahedral to cubic as their size (or absorption wavelength) increases. Smaller PbS CQDs (<3 nm; Eg > 1.3 eV) exhibit an octahedral shape dominated by the (111) crystal facet. As the CQD size increases, the (100) crystal facet is expected to gradually form, transforming the octahedron with only (111) shaped crystal faces into (111) and (100) truncated octahedra and cubic octahedra. The (111) crystal facet is lead-rich and polar, while the (100) crystal facet has lower surface energy and is nonpolar. HRTEM images of PbS CQDs prepared from lead(II) and lead(IV) are shown in [images / images]. Figure 11 and Figure 12 middle.

[0269] It should be noted that the (200) and (002) crystal planes are in group (100) with a plane spacing of ca0.29 nm, and the (022) crystal plane is in group (110). The plane spacing of the (111) and (-111) crystal planes is approximately 0.35 nm.

[0270] like Figure 11As shown, PbS CQD made from the lead(II) oxide precursor of the present invention is a truncated octahedral crystal with visible (002), (111), and (-111) crystal faces. PbS-CQD made from lead(IV) shows a significantly higher proportion of cubic octahedrons as the predominant shape. Figure 12 AD). The (002) and (111) crystal planes are dominant, while the (022) crystal plane is sometimes visible in the cubic octahedral crystals of lead(IV)PbSCQD.

[0271] Compared to truncated octahedral crystals based solely on lead(II) points, lead(IV)PbS CQDs with a larger proportion of cubic octahedrons should have a higher nonpolar area and a lower surface energy (100) crystal plane. At similar maximum absorption wavelengths and band gaps as lead(II)CQDs, the increased (100) crystal plane area of ​​lead(IV)CQDs leads to a higher packing density of CQDs via (100)-(100) coupling, thereby improving charge transport in films including the CDQs. Indeed, Sargent et al. reported that hole mobility and time response in PbS photodetectors can be improved through surface modification to make the (100) crystal plane dominant to increase coupling. [1] By directly measuring the plane-dependent electrical properties of n-type large PbS nanocrystals, Tan and colleagues reported that both the (110) and (100) planes exhibit high conductivity, while the (111) plane remains non-conductive even at 5V. [2] These results demonstrate that lead(IV)PbS CQD offers better charge transport and results in higher performance, particularly in optoelectronic devices, compared to lead(II)-based PbS.

[0272] In summary, the nanocrystals and nanocrystal compositions of the present invention exhibit several improved electrical properties compared to equivalent nanocrystals and nanocrystal compositions made from Pb(II) and Pb(II,IV) reagents. The nanocrystals also possess a different morphology compared to prior art materials made from Pb(II) and Pb(II,IV) reagents. Other properties (such as stability) are at least as good as those of equivalent nanocrystals and nanocrystal compositions made from Pb(II) and Pb(II,IV) reagents.

[0273] References:

[0274] 1.Biondi et al.Facet-Oriented Coupling Enables Fast and SensitiveColloidal Quantum Dot Photodectectors Adv.Mater 2021,33,2101056;https: / / doi.10.1002 / adma.202101056

[0275] 2.Tan et al,Facet-dependent electrical conductivity properties of PbSnanocrystals,2016;https: / / doi.org / 10.1021 / acs.chemmater.6b00274。

Claims

1. A method for manufacturing lead chalcogenide nanocrystals having a cubic structure, the nanocrystals having a particle size greater than 5 nm, the method comprising contacting a lead oxide (IV) starting material with a fatty acid and a chalcogenide-containing reagent, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 1:

1. Lead oxide (IV) is contacted with fatty acids to produce lead salts, and then the lead salts are contacted with a reagent containing chalcogens. The method described herein is carried out in the presence of an organic solvent under an inert atmosphere.

2. The method according to claim 1, wherein the chalcogenide-containing reagent is a phosphine-containing reagent selected from the list of substances comprising: diphenylphosphine selenide, di-o-tolylphosphine selenide, and diphenylphosphine oxide selenide.

3. The method according to claim 1, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 2:

1.

4. The method according to claim 1, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 3:

1.

5. The method of claim 1, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 5:

1.

6. The method of claim 1, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 10:

1.

7. The method of claim 1, wherein the molar ratio of the present lead oxide (IV) to any lead oxide (II) is greater than 20:

1.

8. The method according to claim 1, wherein the starting material does not contain lead(II) compounds.

9. The method according to claim 1, wherein the organic solvent comprises a nonpolar solvent or a polar solvent.

10. The method according to claim 9, wherein the nonpolar solvent is octadecene.

11. The method of claim 9, wherein the polar solvent is selected from DMF, NMP, DMAc, THF and acetone.

12. The method according to claim 1, comprising: A first solution of lead oxide (IV) and fatty acids is formed in a first solvent; A second solution of the reagent containing chalcogen elements is formed in the second solvent; The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is maintained at the first temperature for a predetermined period of time. The temperature of the first solution was lowered to a comparative temperature in the range of 20°C to 100°C; The second solution is added to the first solution at the comparative temperature to produce a reaction mixture; The reaction mixture is kept at a temperature of 20°C to 300°C for a predetermined period of time.

13. The method of claim 1, further comprising: A first solution of lead oxide (IV) and fatty acids is formed in a first solvent; The first solution is heated to a first temperature in the range of 120°C to 250°C, and the first solution is kept at the first temperature for a predetermined period of time. The first solution is provided at a second temperature in the range of 50°C to 150°C; A reagent containing chalcogen elements is added to the first solution at the second temperature to produce a reaction mixture; The reaction mixture is kept at a temperature of 50°C to 300°C for a predetermined period of time.

14. The method according to claim 12 or 13 further comprises quenching the reaction mixture.

15. The method of claim 14, wherein the reaction mixture is quenched by adding a quenching solvent to the reaction mixture.

16. The method of claim 12 or 13 further comprises chalcogenide nanoparticles for purifying lead.

17. The method according to claim 1, wherein the fatty acid is oleic acid.

18. The method according to claim 1, wherein the chalcogenide-containing reagent is selected from reagents containing oxygen, sulfur, selenium and tellurium and mixtures thereof.

19. The method of claim 12, wherein the chalcogenide-containing reagent comprises bis(trimethylsilyl) sulfide.

20. The method of claim 13, wherein the chalcogenide-containing reagent comprises thioacetamide.

21. The method according to claim 1, wherein the lead salt is contacted with the reagent containing the chalcogenide element at a temperature of 20°C to 100°C.

22. The method of claim 21, wherein the lead salt is contacted with the reagent containing the chalcogenide element at a temperature of 30°C to 60°C.

23. The method according to claim 1, wherein the lead salt is contacted with the reagent containing the chalcogenide element at a temperature of 50°C to 300°C.

24. The method of claim 23, wherein the lead salt is contacted with the reagent containing the chalcogenide element at a temperature of 50°C to 150°C.

25. The method of claim 1, further comprising the step of improving reaction conditions to control the size of the prepared nanocrystals, wherein the reaction conditions to be improved include one or more of the following: (i) Solvent type; (ii) Solvent quantity; (iii) Organic acid type; (iv) The amount of organic acids; (v) Method of adding reactants; (vi) Reaction temperature; (vii) The ratio of lead to reagents containing chalcogens; and (viii) Addition of secondary solvent.

26. The method according to claim 25, wherein the reactant is a reagent containing a chalcogenide.

27. The method of claim 1, further comprising monitoring optical properties to monitor the production progress of the nanocrystals.

28. The method of claim 27, wherein the optical property is an ultraviolet-visible-near-infrared absorption spectrum.

29. The method of claim 1, wherein the nanocrystal comprises a quantum dot.

Images