Method for making quantum rods with controllable emission wavelength

Abstract

The invention provides a method for manufacturing a quantum rod, comprising: preparing a Cd-precursor; preparing an S-precursor and a CdSe seed; preparing a Zn-precursor; mixing the S-precursor and the CdSe seed with the Cd-precursor in a reaction mixture; adding a Zn-precursor to the reaction mixture; stopping the reaction; and performing a purification process to obtain the quantum rod.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 761,853, filed on April 10, 2018, the contents of which are incorporated herein by reference. Background Art

[0003] Due to the many applications of semiconductor nanoparticles (SNPs), such as in photonics, displays, microelectronics, photovoltaics and bioluminescent imaging, the demand for semiconductor nanoparticles with luminescence in the visible spectrum is increasing. Due to the small size, electronic properties and the possibility of chemical modification of semiconductor nanoparticles, SNPs can be used as controllable "artificial" atoms with characteristics that meet the specific requirements of various technical applications. Using appropriately surface-modified colloidal nanoparticles, SNPs can be tightly packed or embedded in different types of inorganic and organic matrices. In addition, SNPs can be assembled in tightly packed ordered or disordered arrays.

[0004] Interest in semiconductor nanocrystals with narrow band gaps has increased significantly in recent years, mainly due to their increasing applications in information displays, solar cells, optoelectronics (e.g., lasers, optical modulators, photodetectors, and photoelectric conversion devices), large-format and inexpensive microelectronics, bioimaging systems, biosensors, etc. Products based on quantum dot (QD) technology (e.g., displays, lasers, light-emitting diodes (LEDs), and substrates for portable cameras, etc.) have been introduced into the global market.

[0005] Despite the relatively high cost of mass production of SNPs relative to mass-produced organic dyes and inorganic bulk semiconductors, luminescent SNPs are often the preferred materials for photonic and lighting applications because SNPs offer precisely controllable emission and absorption spectra that are not achievable with inorganic bulk or epitaxially grown semiconductors and organic molecules. Additionally, the advantages of luminescent SNPs over organic molecules lie in the long-term stability of their spectral properties and the tuning of the emission range without significant changes in the material composition, whereas the generation of different colors using organic dyes requires completely different compounds and syntheses that have different color stabilities, resulting in color changes over time.

[0006] Quantum rods (QRs) are luminescent SNPs of elongated shape, which offer additional advantages over QDs in properties such as emission of linearly polarized light, large extinction coefficients, and high luminescence quantum yields. In particular, QRs arranged in parallel in a film can be used as enhancement films (EFs) for display backlight applications in liquid crystal displays (LCDs) and replace quantum dot enhancement films (QDEFs) that are very common in the prior art. Due to polarized emission, QRs can not only increase the color gamut of LCDs, but also significantly improve their overall optical efficiency. These advantageous quantum rods are also highly desirable in LEDs that act as on-chip light converters or utilize the electroluminescent effect. However, a serious limitation to the widespread application of QRs in the prior art is the difficulty in precise control and reproducibility of the emission wavelength in their synthesis, especially in the case of QRs emitting in the green spectral range (515-560 nm). In the prior art, there is no reliable method to synthesize quantum rods with emission in the visible spectral range below 540 nm. However, for a good color gamut, the "green" color should be controlled by λ em The emission is 520-525 nm, and bright “blue” QRs emitting in the 450-470 nm range are also needed for display and LED applications.

[0007] In the prior art, "green" QRs can be made based on a seeding method, in which seeds (usually CdSe QDs) are synthesized in a separate step before the shell growth. In the next step, the CdSe seeds are covered with a CdS shell. The emission wavelength of the QRs thus obtained increases with the increase of the seed size, and therefore, the emission wavelength of the QRs shows a great dependence on the initial seed size. Therefore, the seed size required for the preparation of "green" rods must not exceed 2.3nm. Here, the main challenge is to limit the seed size to be small enough so that the synthesized QRs have λ in the subsequent steps. 发射 (λ em ) < 560 nm. Since the reaction time of such small seeds is very short (typically a few seconds at 320°C to 380°C after injection of the Se precursor), it is difficult to interrupt the reaction quickly enough to prevent their further growth. Special techniques have been explored, such as rapid cooling of the reaction mixture in an acetone / 2-propanol bath or injection of cold low-boiling solvents, however, these methods are not yet efficient enough and it is still difficult to accurately and reliably control the size of the seeds when the diameter is less than 3 nm. Therefore, the λ of the “green” QR emThe reproducibility is also very low. In addition, the problem is further exacerbated in the next step (i.e. CdS shell formation), which also shows a very fast evolution of the spectrum when the CdS shell starts to grow around the CdSe seed crystal. Typically, a very large red shift (≥50nm) occurs during the first minute of the synthesis, and then the emission gradually moves further into the red range during 7-10 minutes. Therefore, it is also difficult to stop the reaction accurately when the emission wavelength reaches the desired value in this step, and the reproducibility is also very limited due to this additional reason.

[0008] Additional efforts have been made to try to control the λ of seeded core-shell QRs. em , but these approaches have not been successful. For example, methods based on limiting reaction rates are not effective for QR synthesis, because low-temperature synthesis of seeds or subsequent QRs leads to poor crystallinity of the obtained nanoparticles, which in turn greatly deteriorates the luminescent properties of the QRs. In addition, methods based on diluting reaction solutions or using elemental precursors with lower reactivity than Cd alkylphosphonates cannot lead to the formation of nanoparticles with rod-like shapes, because both concentration and reactivity have been shown to be key prerequisites for shape control during the growth of anisotropic semiconductor nanoparticles.

[0009] Recently, it was reported that the addition of [Zn] to the reaction mixture during the growth of QRs resulted in a small hypochromic shift in the emission wavelength of the prepared gradient alloy nanoparticles after reaching a certain maximum. However, despite the introduction of very high amounts of [Zn] (Zn / Cd molar ratio not less than 4) in the synthesis, the blue shift reported during the synthesis did not exceed 10 nm in the best case. In addition, there are no key details about the QR synthesis, such as the number of seeds, the ratio between sulfur, trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), hexylphosphonic acid (HPA) and hexadecylphosphonic acid (HDPA), and the details of the reaction method. Therefore, this method for quantum rod synthesis cannot be considered reproducible.

[0010] Another approach to introduce Zn into the seed quantum rod composition is the synthesis of core / double-shell CdSe / CdS / ZnS semiconductor rods. Although in this case a significant increase in quantum efficiency was observed after treatment with Zn(C2H5)2, this approach does not lead to any "blue" shift and improvement in emission control. In addition, this approach requires special precautions, since diethylzinc and dimethylcadmium used as metal precursors are very toxic and pyrophoric. Summary of the invention

[0011] In an exemplary embodiment, the present invention provides a method for manufacturing a quantum rod. The method includes: preparing a Cd-precursor; preparing an S-precursor and a CdSe seed; preparing a Zn-precursor; mixing the S-precursor and the CdSe seed with the Cd-precursor in a reaction mixture; adding the Zn-precursor to the reaction mixture; stopping the reaction; and performing a purification process to obtain a quantum rod.

[0012] In another exemplary embodiment, the present invention provides a method for manufacturing a blue-shifted quantum rod. The method includes: preparing a quantum rod including a CdSe seed and a CdS shell; blue-shifting the emission wavelength of the prepared quantum rod by reacting the prepared quantum rod with a Zn-precursor and an S-precursor; stopping the reaction; and performing a purification process to obtain the blue-shifted quantum rod.

[0013] In yet another exemplary embodiment, the present invention provides a quantum rod. The quantum rod comprises: a seed; and a shell. The composition of the seed and the shell includes Cd, Zn, S and / or Se. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 An exemplary general scheme for fabricating quantum rods with a high degree of control over the emission wavelength of the quantum rods is shown.

[0015] Figure 2 The emission anisotropy of a quantum rod with a rod-in-rod structure (top three curves) and a quantum rod with a rod-in-dot structure (bottom three curves) is shown.

[0016] Figure 3 An exemplary process of manufacturing a Zn-doped quantum rod according to an exemplary embodiment of the present invention is shown.

[0017] Figure 4 The results of Example 1 ( Figure 4 Part a) and Example 2 ( Figure 4 b) Evolution of the emission spectrum of the quantum rod during the synthesis. The arrow indicates the "blue" shift of the emission during the synthesis.

[0018] Figure 5 According to Example 1 ( Figure 5 Part a), Example 2 ( Figure 5 Part b) and Example 3 ( Figure 5 Part c) Dynamics of the emission spectrum evolution.

[0019] Figure 6 It shows that Pr3( Figure 6 Part a), the final product of Example 1 ( Figure 6 Part b), the final product of Example 2 ( Figure 6 Part c), Pr2 (of Example 3) Figure 6 Part d), Pr11 ( Figure 6 Part e) and the final product of Example 3 ( Figure 6 Part f) Transmission electron microscopy (TEM) image of the quantum rods obtained after purification.

[0020] Figure 7 The purification of Pr3 from Example 1 ( Figure 7 Parts a and b), the final product of Example 1 ( Figure 7 Parts c and d) and the final product of Example 2 ( Figure 7 Size distribution of the nanoparticles obtained by purification of parts e and f).

[0021] Figure 8 Shown are the results of thermogravimetric analysis (TGA) performed on the final purified product from Example 1. The 801 curve corresponds to the mass loss and the 802 curve corresponds to the mass loss derivative.

[0022] Fig. 9 It shows that there is no Zn-precursor ( Fig. 9 a) and having a Zn-precursor ( Fig. 9 Comparison of the “green” QR obtained in part b).

[0023] Fig.10 An exemplary laboratory setup for synthesizing quantum rods is shown. The laboratory setup includes an electronic thermal controller (left), a heating source and a magnetic stirrer (bottom), a condenser collector with an inert gas / vacuum supply (top), and a glass syringe with a stainless steel needle (right).

[0024] Figures 11A-11D The evolution of the luminescence spectra at different thermal levels for the Zn-rich quantum rod (corresponding to Pr11 of Example 3) and the Cd-rich quantum rod (corresponding to Pr3 of Example 3) is shown ( Figures 11A-11B ), temperature dependence of the integrated emission intensity ( Fig. 11C ) and the temperature dependence of FWHM ( Fig.11D ). DETAILED DESCRIPTION

[0025] Exemplary embodiments of the present invention provide a method for manufacturing quantum rods that are more reliable in emission wavelength control than prior art. Exemplary embodiments of the present invention also provide an efficient, detailed, convenient and reproducible method for producing quantum rods with precise control of emission wavelength over a wide range.

[0026] In an exemplary embodiment, the present invention provides a method for preparing core-shell semiconductor nanoparticles (also referred to as "quantum rods") of elongated shape characterized by a very large (e.g., up to 100 nm or more) blue shift in emission wavelength during synthesis, and wherein the synthesis is slow and gradual enough to allow the reaction to be within the desired value λ of the shift. em The method is convenient and reproducible, and provides very uniform quantum rods with low size distribution, high quantum yield, and enhanced stability relative to the environment (with [Zn] treatment). The method enables the synthesis of "true" green (≤530nm) and blue (≤470nm) emitting quantum rods, which are highly desirable for display and LED applications.

[0027] Exemplary embodiments of the present invention will be discussed in more detail herein, including, for example, the amount of reagents / solvents, compositions, methods of adding Zn-precursors, and methods of separating / purifying quantum rods. It should be understood that these exemplary embodiments are merely exemplary and non-restrictive, and that one of ordinary skill in the art can derive other embodiments based thereon without departing from the principles of the present invention.

[0028] In an exemplary embodiment, the present invention provides a method of making quantum rods with precisely controllable emission wavelengths. The method includes: preparing a Cd-precursor for shell growth; preparing a stock solution of an S-precursor and CdSe seeds, the stock solutions of the S-precursor and CdSe seeds being one solution or as separate solutions; preparing a Zn-precursor of the general formula Zn(RCOO)2; initiating the reaction in a suitable solvent (i.e., a solvent that dissolves the reactants) by rapidly injecting (e.g., a continuous injection completed in less than a few seconds) a combined mixture of the S-precursor and seeds or first injecting a separate seed solution and then injecting the S-precursor solution into a reaction mixture with the prepared Cd-precursor at an elevated temperature for initiating shell growth (e.g., >300°C to initiate the growth of CdS material); adding a Zn-precursor of the general formula Zn(RCOO)2 (e.g., in solid form) or a solution thereof to the reaction mixture one or more times; further adding an S-precursor one or more times when a large blue shift (>35nm) and / or an increase in the reaction rate is required; stopping the reaction when the desired emission performance is achieved; and performing a purification procedure.

[0029] In another exemplary embodiment, in the general formula of the Zn-precursor, R is an alkyl C n H 2n+1 , where n is in the range of 0 to 30.

[0030] In another exemplary embodiment, in the general formula of the Zn-precursor, R is a carbon chain containing two or more double bonds or triple bonds and having a total length of 5 to 22 carbon atoms. For example, R can be an alkenyl group A-CH=CH-B- wherein A is independently a hydrogen (H) atom or an alkyl group C n H 2n +1-, wherein n is 0 to 16, and B is absent or is an alkylene group -(CH2) n -where n is 0 to 16.

[0031] In another exemplary embodiment, in the general formula of the Zn-precursor, R is a branched alkyl or alkenyl group or a branched carbon chain containing two or more double bonds or triple bonds and having a total length of 5 to 22 carbon atoms.

[0032] In another exemplary embodiment, the Zn-precursor is a separate compound.

[0033] In another exemplary embodiment, the Zn-precursor is a mixture of various organic compounds.

[0034] In another exemplary embodiment, the Cd-precursor is prepared from a Cd-containing derivative and an alkylphosphonic acid. For example, the Cd-precursor can be prepared from CdO and an alkylphosphonic acid in a molar ratio, wherein the amount of Cd to total phosphonic acid is 1:2 in a solvent having a high boiling point (e.g., >300° C.). In another example, the Cd-precursor can be prepared from CdO and a CdO having the general formula C n H 2n+1 Preparation of alkylphosphonic acids of PO3H2 wherein n is in the range of 6 to 18.

[0035] In another exemplary embodiment, the S-precursor is prepared separately by dissolving elemental sulfur in a suitable solvent. In one example, a suitable solvent can be a heavy alkane (C 14 -C 22 ), 1-octadecene, trialkylphosphines, trialkylphosphine oxides and glicerole trialkanoates and combinations thereof.

[0036] In another exemplary embodiment, the Zn-precursor is a zinc salt solution or a mixture thereof with a high boiling point solvent. In one example, the high boiling point solvent is a heavy alkane (C 14 -C 22 ), 1-octadecene, trialkylphosphine, trialkylphosphine oxide, trienoic acid trienoate alone or in different combinations thereof.

[0037] In another exemplary embodiment, the Zn-precursor is a solution of zinc oleate in 1-octadecene.

[0038] In another exemplary embodiment, the Zn-precursor is added to the reaction mixture after initiation of the CdS shell growth.

[0039] In another exemplary embodiment, the Zn-precursor is added to the reaction mixture in the range of 1 second to 1000 minutes after initiation of the CdS shell growth.

[0040] In another exemplary embodiment, wherein after the Zn-precursor is added, the reaction is allowed to proceed for a duration of 1 minute to 10,000 minutes before terminating the reaction.

[0041] In another exemplary embodiment, the Zn / Cd feed ratio is 0.1 to 10.

[0042] In another exemplary embodiment, the emission wavelength of the resulting quantum rods is shifted to shorter wavelengths during synthesis in the range of 10-150 nm.

[0043] Figure 1 shows the method for manufacturing a Cd x Zn 1-x An exemplary general scheme for quantum rods with S shells (where x is in the range of 0 to 0.99) with a high degree of control over the emission wavelength of the quantum rods. In particular, Figure 1 An exemplary process for obtaining two types of core-shell quantum rods (dots in rods (top) and rods in rods (bottom)) is shown. One of ordinary skill in the art will appreciate that two types of seeds (dots and rods) can be obtained according to known methods, and that these seeds are covered with organic ligands (e.g., alkyl phosphonic acids, trioctylphosphine oxide, alkyl amines, long-chain carboxylic acids, etc.) and can form stable colloids in non-polar organic solvents (e.g., toluene, chloroform, hexane, octadecene).

[0044] refer to Figure 1 :

[0045] AlkPO3H2 is a single compound or a mixture of different alkylphosphoric acids;

[0046] Alk is an alkyl group CH3-(CH2) n -, wherein n is 2 to 20, preferably 3 to 18, more preferably 6 to 16;

[0047] x is the atomic index of the [Cd] atom in the stoichiometric formula of the shell material and is from 0 to 0.99, preferably from 0.95 to 0.05, more preferably from 0.75 to 0.25;

[0048] Alk3PS and Alk3PSe are trialkylphosphine sulfide and trialkylphosphine selenide, respectively;

[0049] L is the average length of the quantum rods and is from 10 nm to 100 nm, preferably from 15 nm to 80 nm, more preferably from 20 nm to 50 nm;

[0050] d is the average diameter of the quantum rods and is 3 nm to 15 nm, preferably 4 nm to 10 nm, more preferably 5 nm to 8 nm;

[0051] The shape of the quantum rod is schematically depicted. It is understood that different shapes such as ellipsoids, cylinders, etc. are also possible, but the condition L>d must be met;

[0052] The Zn-precursor is a source of [Zn] atoms and may be a derivative of a zinc carboxylate of the general formula Zn(RCOO)2, wherein R is:

[0053] Alkyl CH3-(CH2) n -, where n is 0-30 (or 0-18);

[0054] Alkenyl A-CH=CH-B-, wherein A is independently a hydrogen atom or an alkyl CH3-(CH2) n -, wherein n is 0 to 16, and B is absent or is an alkylene group -(CH2) n -, where n is 0 to 16;

[0055] A carbon chain containing more than two double or triple bonds and having a total length of 5 to 22 carbon atoms; or

[0056] A branched alkyl or alkenyl group or a branched carbon chain containing two or more double or triple bonds and having a total length of 5 to 22 carbon atoms.

[0057] The Zn-precursor is a single compound or a mixture with other organic compounds (which may be low melting point organic compounds, or may be aliphatic, aromatic or long chain olefins and / or long chain alkyl carboxylic acids and / or alkenyl carboxylic acids).

[0058] It should be understood that in the case where x=0, the CdZnS shell may be referred to as a ZnS shell.

[0059] like Figure 2 As shown in , rod-in-rod nanoparticles show a higher degree of emission anisotropy relative to rod-in-dot nanoparticles.

[0060] Figure 3 An exemplary process for fabricating Zn-doped quantum rods according to an exemplary embodiment of the present invention is shown.

[0061] In step 301, a Cd precursor for shell growth is prepared. For example, in a solvent with a high boiling point, the Cd precursor can be prepared from CdO and an alkylphosphonic acid of appropriate length, wherein the molar ratio of the amount of Cd to the total phosphoric acid is not less than 1:2. For example, a coordinated high boiling point solvent such as trioctylphosphine oxide can be used.

[0062] In step 302, stock solutions of S-precursor and CdSe seeds are prepared as one stock solution, or stock solutions of S-precursor and CdSe seeds are prepared as separate solutions. The stock solution of S-precursor can be prepared by dissolving elemental sulfur in a suitable high boiling point solvent (such as a long chain alkane (C 14 -C 22 ), 1-octadecene or trioctylphosphine). In an exemplary embodiment, trioctylphosphine may be preferred because the trioctylphosphine sulfide formed has appropriate reactivity with cadmium alkylphosphonates to form CdS shells in an elongated shape. CdSe seeds can be added to a stock solution of the S-precursor or prepared separately by dissolving CdSe seeds in a suitable solvent.

[0063] It should be understood that with respect to steps 301 and 302, the amounts of CdO, phosphonic acid, solvent, sulfur, and seed may be varied while still achieving good results in preparing quantum rods according to exemplary embodiments (see, e.g., Examples 1-3 discussed below).

[0064] In step 303, a Zn precursor is prepared. The Zn precursor can be prepared in different ways.

[0065] In an exemplary embodiment, the Zn-precursor is a solution of a zinc salt in an organic solvent. It can be prepared from ZnO and a carboxylic acid by heating the two reactants in an organic solvent at >300° C. in an inert atmosphere for several hours. Examples of zinc salts and organic solvents are zinc oleate and 1-octadecene.

[0066] In another exemplary embodiment, the Zn-precursor is a zinc salt that is separated from a solution prepared from ZnO and a carboxylic acid by heating the two reactants in an organic solvent at >300°C in an inert atmosphere for several hours. The separation step can be performed by filtering the reaction mixture at room temperature, or by evaporating the organic solvent in a vacuum. The separated zinc salt can be dissolved in an organic solvent for the synthesis of quantum rods, or can be used in solid form.

[0067] In another exemplary embodiment, the Zn-precursor is a zinc salt obtained by an exchange reaction between a Zn salt of a low-boiling carboxylic acid (eg, zinc acetate) and a high-boiling carboxylic acid (eg, oleic acid or stearic acid).

[0068] The concentration of the Zn salt in the solution may vary. Exemplary concentrations of the Zn salt in the solution may be 0.1-5.0 mmol / g, or may be 0.2-1.0 mmol / g.

[0069] In step 304, the seeds and S-precursor are rapidly injected with Cd-precursor at high temperature (>300°C) to induce the growth of elongated CdS shells on the CdSe seeds. In case of using separate seed solutions and S-precursor, the seed solution is injected first and then the S-precursor solution is injected.

[0070] In step 305, a Zn-precursor is added to the reaction mixture after the seeds and S-precursor are injected. Additional S-precursor may also be added to the reaction in step 305. Adding the Zn-precursor to the reaction mixture containing the CdSe / CdS quantum rods may be performed in a single step or in multiple steps. Adding the S-precursor to the reaction mixture containing the CdSe / CdS quantum rods may also be performed in a single step or in multiple steps.

[0071] In an exemplary embodiment, the Zn-precursor is added to the reaction mixture immediately after the injection of the seed and S-precursor. In another exemplary embodiment, the Zn-precursor is added a period of time after the injection (e.g., in the range of 1 second to 180 minutes after the injection).

[0072] The rate and duration of adding the Zn-precursor may vary. An addition rate of the Zn-precursor that minimizes temperature excursions may be preferred, for example, the Zn-precursor may be added at a slow rate over a duration of 1-20 minutes.

[0073] The amount of Zn-precursor added in step 305 can vary. However, it should be noted that according to an exemplary embodiment of the present invention, a small amount of Zn can result in a significant blue shift in absorption. For example, as demonstrated with respect to Examples 1-3 discussed below, a Zn / Cd molar ratio of 1.57 results in a blue shift of 24 nm and 27 nm, respectively. In the case of synthesizing blue light-emitting quantum rods, the Zn / Cd molar ratio is about 4.57, which results in a blue shift of 102 nm.

[0074] Immediately after the S-precursor and seeds are injected at step 304, the emission wavelength begins to shift toward longer wavelengths at a faster rate. The shift toward longer wavelengths then slows, and after a certain amount of Zn-precursor (about 1 equivalent of Cd) is added, the emission wavelength begins to slowly shift toward shorter wavelengths. This shift to shorter wavelengths (also called a "blue shift") can be large (e.g., 10-150 nm) and occurs slowly enough for the probe to measure the emission wavelength and quench the reaction at step 306 when the emission wavelength reaches the desired emission wavelength. With respect to Examples 1-3 and in Figure 4-5 The aforementioned principle is described in .

[0075] The Zn-precursor can be added to the reaction mixture containing CdS / CdS quantum rods in a single step or multiple steps. The addition of Zn-precursor to the reaction mixture containing CdSe / CdS quantum rods provides a blue shift of about 30-40nm. The multiple additions of Zn-precursor cause the further blue shift of the emission wavelength to exceed 30nm until about 50nm. In addition, the addition of S-precursor increases the blue shift to about 100nm (see Example 3, multiple additions of Zn-precursor and S-precursor). The addition of Zn-precursor or S-precursor can be carried out in any combination.

[0076] Utilizing Zn-precursors during the synthesis of quantum rods also leads to increased luminescence quantum yield due to improved CdS shell crystallinity by reducing the amount of charge / exciton surface traps (as shown in Example 1 discussed below).

[0077] During the Zn addition, the particle size and shape did not change significantly ( Figure 6 Part a and Figure 6 Compare part c of Figure 6 Part D and Figure 6 ef is compared with the Figure 7 Part ab and Figure 7 ), but the emission blue shift occurs.

[0078] At step 306, after the desired emission properties of the quantum rod are achieved, the reaction is quenched, for example, by cooling (eg, by adding a cold solvent to the reaction mixture and / or by removing a heating source).

[0079] The time of terminating the reaction can vary according to the desired properties of the final product. In an exemplary embodiment, the reaction is terminated immediately after adding the Zn-precursor. In other exemplary embodiments, after adding the Zn-precursor, the reaction is allowed to proceed, so as to further blue-shift the emission wavelength to the desired emission wavelength. In another exemplary embodiment, the reaction is terminated after repeatedly adding the Zn-precursor or after repeatedly adding the Zn-precursor and the S-precursor. The reaction time can vary, for example, according to reaction conditions and seed size, 30-120 minutes may be required after adding the Zn-precursor, to reach the desired blue-shift of the emission wavelength of 10-30nm. In other exemplary embodiments, according to the reaction rate, a blue shift of up to about 450nm can occur in 16-20 hours, and the reaction rate can be controlled by the amount of the Zn-precursor and the S-precursor added.

[0080] In step 307, the final product (e.g., quantum rod) is purified by one or more precipitation-redispersion sequences. For precipitation, polar solvents (e.g., alcohols, ketones, etc.) can be used. The solvent used for precipitation should be fully mixed with the reaction solvent and can dissolve organic impurities, raw materials and other contaminants. For separating the quantum rods from the mixture, centrifugation or filtration can be used. After separation, the quantum rods are then dissolved in a weakly polar solvent (e.g., aromatic and aliphatic hydrocarbons, chlorinated alkanes, etc.), which results in a solution of quantum rods. The latter can be purified again (to remove contaminants that may still be present) by performing another precipitation step and another centrifugation (or filtration) procedure. Ultrasonic treatment can be used to accelerate the dissolution process of the reaction product.

[0081] The final separation of quantum rods from the reaction mixture can be carried out by conventional precipitation / dissolution steps. For example, the reaction mixture can be diluted with toluene or other suitable weakly polar solvents (benzene, chlorobenzene, etc.), and polar solvents (such as methanol, ethanol, acetone) can be added to precipitate the quantum rods. The quantum rods can be collected by filtration or centrifugation, or they can be further washed with a suitable solvent (such as toluene, benzene, chlorobenzene, etc.), and then the quantum rod precipitate is precipitated and collected.

[0082] In another exemplary alternative embodiment, instead of adding the Zn-precursor to the reaction mixture in step 305, the CdSe / CdS quantum rods can be separated from the reaction mixture after step 304, dissolved in an appropriate high boiling point solvent (e.g., TOPO, ODE, TOP) and further treated with Zn-precursors and S-precursors. The obtained CdSe / CdS quantum rods can be dissolved in a high boiling point solvent, degassed by flushing with an inert gas, heated to a temperature above 270°C (preferably above 300°C or above 340°C), and a Zn-precursor can be added. In order to increase the blue shift and / or reaction rate, an S-precursor can be added before or after the addition of the Zn-precursor. Multiple additions of the Zn-precursor and the S-precursor can be performed.

[0083] In an alternative exemplary embodiment, the already prepared CdSe / CdS quantum rods obtained by any other method can be treated with Zn-precursors and / or S-precursors to control the "blue" shift of the emission wavelength. In this case, the process will start with the already prepared CdSe / CdS quantum rods, and then with Zn-precursors (and additional S-precursors) in the reaction mixture and / or by injecting Zn-precursors (and additional S-precursors) into the reaction mixture containing CdSe / CdS quantum rods.

[0084] Figure 3 The results of the method provide a highly uniform final product of quantum rods (see e.g. Figure 6-7), the quantum rod is stabilized by an organic ligand shell and contains almost no impurities. The quantum rod can be dissolved in a non-polar organic solvent.

[0085] The method disclosed herein provides high reproducibility in terms of emission wavelength, shape and size of the quantum rods manufactured. Compared with quantum rods without Zn doping, the quantum rods according to the aforementioned exemplary embodiments have better thermal / chemical stability. The method makes it possible to synthesize quantum rods that emit in the entire visible spectrum (including the complete blue and green regions), which is not achievable by other colloidal methods (i.e., those methods without Zn-precursors) for making seeded high-brightness luminescent quantum rods.

[0086] Exemplary products that may be realized by the method include:

[0087] 1. Quantum rod with rod midpoint structure, which has Cd y Zn 1-y Se seeds and Cd x Zn 1-x S-shell, where y is in the range of 0 to 1 and x is in the range of 0 to 0.99; and

[0088] 2. Quantum rods with rod-in-rod structure, which have Cd y Zn 1-y Se seeds and Cd x Zn 1-x S-shell, where y is in the range of 0 to 1 and x is in the range of 0 to 0.99.

[0089] In the initial stage of adding the Zn-precursor, the addition of Zn affects only the shell, resulting in a gradual decrease in Cd and an increase in Zn in the shell composition, which corresponds to a gradual change in the index x from 1 (no Zn in the shell) to 0 (all Cd is replaced by Zn). As the reaction proceeds, the CdSe seeds may also be affected by the addition of Zn, resulting in a decrease in the initial CdSe seed size or a decrease in Cd and an increase in Zn in the seed composition, which corresponds to a gradual change in the index y from 1 (no Zn in the seed) to 0 (all Cd is replaced by Zn in the seed).

[0090] Figures 11A-11D The enhanced thermal stability of the photoluminescence of the Zn-doped quantum rods obtained by the exemplary embodiments of the present invention is shown. It can be clearly seen that the quantum rods treated with the Zn-precursor show stable PL characteristics up to 200°C compared to the quantum rods not treated with the Zn-precursor, which is very desirable for LED applications (e.g., for on-chip structures where the temperature can approach 150°C or higher). The obtained quantum rods are generally more uniform in size and aspect ratio (see Fig. 9In addition, the exchange of Cd for Zn is more favorable from an environmental and market perspective in terms of the lower toxicity of the resulting material.

[0091] The following examples (Examples 1-3) further illustrate exemplary embodiments of the present invention and demonstrate exemplary advantages achieved thereby. It should be understood that the following examples are exemplary and should not be construed as limiting the scope of the present invention.

[0092] As combined with Example 1 and Figure 8 It was demonstrated that exemplary embodiments of the present invention were able to achieve a mass loss of no more than 20%, which is a typical mass fraction of organic ligands for CdSe / CdS quantum rods.

[0093] As further demonstrated in conjunction with Examples 1-2, exemplary embodiments of the present invention can achieve a coefficient of variance (COV) (defined as COV = (standard deviation / mean size) * 100%) of less than 10%, which advantageously provides a narrow particle size distribution.

[0094] In combination with Examples 1-3, it is further demonstrated that according to an exemplary embodiment of the present invention, the amount of Zn-precursor (Zn / Cd ratio) required for a significant gradual "blue shift" of the emission wavelength during synthesis can be relatively small. Increasing the amount of Zn-precursor added will increase the "blue" shift of the emission wavelength, which is due to the greater degree of replacement of Cd and Zn atoms in the composition of the quantum rods.

[0095] In addition to Examples 1-3, a control product was produced using the same reaction conditions as for the CdSe / CdS production (including ratios between reagents, temperature, same seeds, concentrations, volumes, laboratory settings as in Example 1, etc.), but without the addition of Zn-precursor. In this synthesis, the reaction was terminated when the emission wavelength reached approximately the same value as the final product in Example 1. Fig. 9 As can be seen from the TEM and the figure, compared with QR ( Fig. 9 Part a) is almost the same as Example 1 ( Fig. 9 The QRs of part b) have the same emission wavelength, but with shorter size (average 13 nm vs. average 26 nm) and larger size distribution (12% COV vs. 8% COV). This shows that the addition of the Zn-precursor allows the preparation of more uniform QRs with emission in the green and blue spectral range.

[0096] Example

[0097] The following examples further illustrate the present invention.

[0098] Example 1

[0099] Example 1 provides an example of the synthesis of a Zn-precursor and the use of the Zn-precursor to control the synthesis of core-shell quantum rods.

[0100] In a preliminary step, the Zn-precursor is prepared as follows. Under vigorous stirring, a mixture of ZnO (Meryer, 99%, 3.22 g, 123 mmol), oleic acid (Sigma, 85%, 71.1 g, 252 mmol) and 1-octadecene (Sigma, 90%, 100 ml) is degassed under reduced pressure at 130° C. for 90 min: the sequence of pumping out and filling with inert gas (nitrogen) is repeated for a total of five cycles. The mixture is then heated to 310° C., maintained for 1 hour, and then cooled to 95° C. At this temperature, the water formed during the reaction is removed from the reaction mixture under reduced pressure (10-20 mbar). During the evacuation, the mixture is slowly heated to 170° C. (1 hour) under vigorous stirring, and then the sequence of pumping out and filling with inert gas (nitrogen) is repeated again for five cycles. The mixture is heated to 320° C. under vigorous stirring, and the reaction is allowed to proceed until all white solids are dissolved (8 hours). The solution (S1) is cooled to ambient temperature and used as is without further purification. The yield of the final mixture was 103.1 g, the concentration of [Zn] was calculated to be 0.4 mmol / g, and the density d≈0.8 g / ml. The solution solidified after long-term storage at room temperature, but melted upon slight heating (about 40°C).

[0101] CdSe seeds were synthesized according to well-known protocols, such as that of U.S. Pat. No. 6,872,249. After injection of the Se precursor, the synthesis was terminated within 5 seconds. The seeds from the reaction mixture were precipitated with methanol (Tol:MeOH 1:1 by volume), washed once by dissolving in toluene and precipitating with methanol (1:1 ratio). The precipitate was collected by centrifugation, dissolved in toluene, filtered through a 0.2 μm PTFE filter, and the toluene was blown out by nitrogen vapor. The yield of the solid product was 134 mg. The emission spectrum of the resulting nanoparticles is shown in Figure 4 In part a, λ max =504 nm. The solid product obtained was dissolved in 6.6 ml TOP to form a clear solution (S2) with a concentration of 20.25 mg / ml. The solution was stored in the dark under nitrogen.

[0102] Similar to the synthesis of zinc oleate described above, CdO (Meryer, 99%, 90 mg, 0.7 mmol), hexadecylphosphonic acid (99.95%, 265 mg, 0.86 mmol), hexylphosphonic acid (99.5%, 80 mg, 0.48 mmol) and trioctylphosphine oxide (Stream, 90%, 3.0 g, 7.8 mmol) were degassed. The suspension was then heated to 340°C under vigorous stirring, at which point it became a transparent colorless solution (S3). At this temperature, trioctylphosphine (Stream, 97%, 1 ml) was rapidly injected. In a separate flask, sulfur (84 mg, 2.6 mmol) was dissolved in trioctylphosphine (1.6 ml) under vigorous stirring, to which solution S2 (400 mkl) was added to obtain a sulfur solution. The combined solution was rapidly injected into S3 at 375°C to initiate the growth of an elongated CdS shell around the CdSe seeds. This corresponds to the start of the reaction time countdown.

[0103] The probe was removed to measure the emission wavelength of the nanoparticles at different times during the synthesis (see Figure 4 Part a and Table 1 below). For example, Figure 4 As shown in part a and in Table 1 below, the first probe (Pr1: 160 seconds) was taken out 2 minutes and 40 seconds after the reaction time counter started. Starting from 3 minutes after the reaction time counter started (when the temperature stabilized after injection), solution S1 (3.5 g, 4.4 ml) was gradually added dropwise at the same temperature of 370°C over 30 minutes. The second and third probes (Pr2 and Pr3, respectively) were taken out at 18 minutes and 35 minutes. The TEM image and size distribution of the quantum rods corresponding to the third probe Pr3 are shown in Figure 6 Part a and Figure 7 The dimensions of the quantum rod corresponding to the third probe Pr3 are as follows: 27.2nm (SD = 1.7nm) × 5.3nm (SD = 0.45nm); the coefficients of variance COV of length and width are 6% and 8% respectively; aspect ratio = 5.1. The reaction was further allowed to proceed for 90 minutes. The fourth probe Pr4, the fifth probe Pr5 and the sixth probe Pr6 were taken out at 68 minutes, 95 minutes and 120 minutes. The probe emission spectra obtained are as follows Figure 4 As shown in part a.

[0104] The synthesis is terminated by removing the heating source. Then 10 ml of toluene is added at 180 ° C. After cooling to room temperature, the product is precipitated with 10 ml of ethanol, collected by centrifugation and washed once by redispersion in toluene (8 ml, ultrasonic treatment for 10 minutes), and then precipitated with ethanol (8 ml, centrifugation). The solid product obtained is then redispersed in toluene (5 ml) and centrifuged (4000 rpm, 10 minutes). The solution is collected, filtered through a 0.2 μm PTFE filter, and purged with a nitrogen stream at 60 ° C.

[0105] Yield: 120 mg. According to TGA data, the inorganic part of the product accounts for 82% of the product, such as Figure 8 The volatile fraction (18%) is consistent with the typical mass fraction of organic ligands on the surface of quantum rods. The TEM images and size distribution of the obtained nanorods are shown in Figure 6 Part b and Figure 7 The size of the obtained quantum rod is: 26.1nm (SD = 2.1nm) × 5.2nm (SD = 0.54nm); COV of length and width are 8% and 10% respectively; aspect ratio = 5.0. The quantum yield (measured using an integrating sphere) is 59%. For comparison, the second probe Pr2 and the third probe Pr3 were treated in the same manner (precipitation, washing, redispersion and drying) and the quantum yields were measured (52% and 56%, respectively).

[0106] The evolution of the emission wavelength of the nanoparticles during the synthesis of Example 1 is also shown in Tables 1 and Figure 5 In part a:

[0107] Table 1

[0108] Probe Time, seconds <![CDATA[λ max ,nm]]> Pr1 160 558 Pr2 1080 567 Pr3 2100 573 Pr4 4080 558 Pr5 5700 554 Pr6 7200 549

[0109] Example 2

[0110] Example 2 provides an example of controlled synthesis of core-shell quantum rods using a Zn-precursor, where a 25 nm "blue" shift occurs.

[0111] CdSe quantum dot seeds were synthesized similarly to that described in Example 1, except that the reaction was terminated immediately after the injection of the Se precursor. The CdSe seeds were purified in the same manner to prepare a solution with a concentration of 20.25 mg / ml (S4). The photoluminescence spectrum of the obtained nanoparticles was max = has an emission maximum at 473 nm.

[0112] Using 200 μL of S4 instead of S3, the controlled synthesis of quantum rods was performed similarly as described in Example 1. Regarding Example 2, a mixture of S4 and S-precursor was used to initiate CdS shell growth in a similar manner as discussed above with respect to Example 1. Then, starting from the 5th minute from the start of the reaction, S1 was gradually added over 25 minutes.

[0113] The probe was taken out to measure the emission wavelength of the nanoparticles formed at different points during the synthesis (Pr1: 2 minutes, Pr2: 8 minutes, Pr3: 20 minutes, Pr4: 36 minutes, Pr5: 75 minutes), and the results are shown in Table 2 below. Figure 4 Part b and Figure 5 The reaction was terminated at 76 minutes and the product was isolated similarly to that described in Example 1.

[0114] Yield: 115 mg. The TEM images and size distribution of the obtained nanorods are shown in Figure 6 Part C and Figure 7 The dimensions of the quantum rod are: 79.4 nm (SD = 4.7 nm) × 5.3 nm (SD = 0.55 nm); COV of length and width are 6% and 10% respectively; aspect ratio = 15.0.

[0115] The evolution of the emission wavelength of the nanoparticles during the synthesis of Example 2 is also shown in Tables 2 and Figure 5 Part b.

[0116] Table 2

[0117] Probe Time, seconds <![CDATA[λ max ,nm]]> Pr1 120 542 Pr2 480 556 Pr3 1200 548 Pr4 4080 537 Pr5 5700 527

[0118] Example 3

[0119] Example 3 provides an example of the controlled synthesis of core-shell quantum rods emitting in the blue spectral range using multiple injections of Zn-precursors and additional injections of S-precursors with a large (>100 nm) "blue" shift.

[0120] CdSe quantum dot seeds were synthesized in a similar manner as discussed above with respect to Example 1, except that the reaction was terminated 15 seconds after the injection of the Se precursor. The CdSe seeds were purified in the same manner to prepare a solution with a concentration of 16.52 mg / ml (S5). The photoluminescence spectrum of the resulting nanoparticles was max The emission maximum is at 519 nm.

[0121] 350 μL of S5 was used instead of S3 to carry out controlled synthesis of quantum rods in a manner similar to that discussed above with respect to Example 1. With respect to Example 3, a mixture of S5 and S-precursors was used to induce CdS shell growth in a manner similar to that discussed above with respect to Example 1. Then, starting from the 5th minute after the start of the reaction, S1 was gradually added over a duration of 20 minutes. The following zinc precursor additions were carried out at 32 minutes (1 ml), 38 minutes (0.5 ml), 46 minutes (0.5 ml), 52 minutes (0.5 ml), 70 minutes (0.5 ml), 93 minutes (1 ml), 125 minutes (1 ml), 180 minutes (0.5 ml), 210 minutes (0.5 ml), 300 minutes (2 ml), 690 minutes (1 ml), 845 minutes (1 ml). The following additions of S-precursor (S1) were performed at 300 min (0.4 ml), 465 min (0.2 ml), 580 min (0.2 ml), 780 min (0.2 ml), 870 min (0.2 ml). Each addition meant that the solution was injected at an average rate of 0.2 ml / min. The probe was taken out to measure the emission wavelength of the nanoparticles formed at different points during the synthesis (Pr1: 3 min, Pr2: 13 min, Pr3: 24 min, Pr4: 38 min, Pr5: 51 min, Pr6: 95 min, Pr7: 120 min, Pr8: 167 min, Pr9: 222 min, Pr10: 268 min, Pr11: 298 min, Pr12: 350 min, Pr13: 394 min, Pr14: 454 min, Pr15: 520 min, Pr16: 570 min, Pr17: 685 min, Pr18: 745 min, Pr19: 835 min, Pr20: 950 min), the results of which are shown in Tables 3 and 4 below. Figure 5 The reaction was terminated at 950 minutes and the product was isolated in a similar manner as discussed above with respect to Example 1. The yield was 100 mg. TEM images of the resulting quantum rods and the quantum rods isolated from Pr3 and Pr11 are shown in Figure 6 The temperature dependence of the photoluminescence intensity and FWHM of the quantum rods isolated from Pr11 (rich in Zn) compared with the quantum rods isolated from Pr3 (rich in Cd) is shown in Figures 11A-11D middle.

[0122] Table 3

[0123]

[0124]

[0125] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference as if each reference were individually and specifically indicated to be fully set forth herein.

[0126] The use of the terms "one" and "an" and "the" and "at least one" and similar indicators in the context of describing the present invention (particularly in the context of the following claims) will be interpreted as covering the singular and plural unless otherwise specified herein or explicitly contradicted by the context. The use of the term "at least one" followed by a list of one or more items (e.g., "at least one of A and B") should be interpreted as indicating any combination of one item (A or B) selected from the listed items or two or more of the listed items (A and B), unless otherwise specified herein or explicitly contradicted by the context. Unless otherwise specified, the terms "comprising", "having", "including" and "containing" should be interpreted as open terms (i.e., meaning "including but not limited to"). Unless otherwise specified herein, the description of the numerical range herein is intended only to be used as a shorthand method of individually referring to each individual value falling within the range, and each individual value is incorporated into this specification as if it were individually quoted herein. Unless otherwise specified herein or the context is clearly contradictory, all methods described herein can be performed in any suitable order. Unless otherwise stated, the use of any and all examples or exemplary language (e.g., "such as") provided herein is intended only to better illustrate the present invention and is not intended to limit the scope of the present invention. No language in the specification should be construed as indicating that any non-claimed element is essential to the practice of the present invention.

[0127] Preferred embodiments of the present invention are described herein, including the best mode of implementing the present invention known to the inventor. After reading the foregoing description, variations of those preferred embodiments may become apparent to those of ordinary skill in the art. The inventor expects that skilled technicians will appropriately adopt these variations, and the inventor hopes that the present invention will be implemented in a manner different from that specifically described herein. Therefore, the present invention includes all modifications and equivalents of the subject matter described in the appended claims as allowed by applicable law. In addition, unless otherwise specified herein or the context is clearly contradictory, the present invention encompasses any combination of all possible variations of the above-mentioned elements.

Claims

1. A method for manufacturing a quantum rod, comprising: preparing Cd-precursor; preparing S-precursor and CdSe seeds; Preparation of Zn-precursor; mixing the S-precursor and the CdSe seeds with the Cd-precursor in a reaction mixture; adding the Zn-precursor to the reaction mixture; Stop the reaction; as well as A purification process is performed to obtain the quantum rod, which includes a seed and a shell, wherein the seed is Cd y Zn 1- y Se seeds, wherein y is in the range of 0.01 and 1; and the shell is Cd x Zn 1-x S shell, where x is in the range of 0 to 0.99, The addition of the Zn-precursor leads to a blue shift in the emission wavelength, and the quantum rod has a thermally stable emission integrated intensity in the temperature range of 0 to 200°C.

2. The method of claim 1, wherein the method further comprises adding additional S-precursor to the reaction mixture.

3. The method of claim 2, wherein the additional S-precursor is added to the reaction mixture in multiple steps. The method according to claim 1 , wherein the blue shift is in the range of 10 nm to 150 nm. The method according to claim 1 , wherein the emission wavelength of the quantum rod is less than or equal to 530 nm. The method according to claim 1 , wherein the emission wavelength of the quantum rod is less than or equal to 470 nm.

7. The method of claim 1, wherein the S-precursor and the CdSe seeds are prepared as a combined stock solution.

8. The method of claim 1, wherein the S-precursor and the CdSe seeds are prepared as separate stock solutions.

9. The method according to claim 1, wherein mixing the S-precursor and the CdSe seeds with the Cd-precursor comprises injecting the S-precursor and the CdSe seeds into a reaction mixture containing the Cd-precursor to initiate a reaction between the Cd-precursor and the CdSe seeds and the S-precursor.

10. The method of claim 9, wherein the reaction mixture comprises a solvent at a temperature above 300°C.

11. The method according to claim 1, wherein the Zn-precursor has the general formula Zn(RCOO)2.

12. The method according to claim 11, wherein R is an alkyl C n H 2n+1 , wherein n is in the range of 0 to 30; or wherein R is a branched alkyl group or a branched alkenyl group, or a branched carbon chain containing two or more double bonds or triple bonds and having a total length of 5 to 22 carbon atoms.

13. The method according to claim 1, wherein the Zn-precursor is a single compound or a mixture of organic compounds.

14. The method of claim 1, wherein the Zn-precursor comprises a zinc salt or zinc oleate.

15. The method of claim 1, wherein adding a Zn-precursor to the reaction mixture comprises adding the Zn-precursor to the reaction mixture in multiple steps.

16. The method of claim 1, wherein the purification process comprises one or more precipitation-redispersion sequences.

17. A method for manufacturing a blue-shifted quantum rod, comprising: preparing a quantum rod including a CdSe seed and a CdS shell; The emission wavelength of the prepared quantum rod is blue-shifted by reacting the prepared quantum rod with a Zn-precursor and an S-precursor; Stop the reaction; and A purification process is performed to obtain the blue-shifted quantum rod, which comprises a seed and a shell, wherein the seed is Cd y Zn 1-y Se seeds, wherein y is in the range of 0.01 and 1; and the shell is Cd x Zn 1-x S shell, where x is in the range of 0 to 0.99, The blue-shifted quantum rod has a thermally stable emission integrated intensity within a temperature range of 0 to 200°C. The method according to claim 17 , wherein the emission wavelength of the blue-shifted quantum rod is less than or equal to 530 nm.

19. A quantum rod prepared by the method of claims 1-18, comprising: seed; and shell; wherein the composition of the seed and the shell comprises Cd, Zn, S and / or Se, and wherein the quantum rod has a thermally stable emission integrated intensity in the temperature range of 0 to 200°C; Wherein the seeds are Cd y Zn 1-y Se seeds, wherein y is in the range of 0.01 and 1; and the shell is Cd x Zn 1-x S-shell, where x is in the range of 0 to 0.99.

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