Quantum dot shell synthesis

Abstract

The present invention relates to the synthesis of core / shell / shell quantum dots, and in particular to a novel shell synthesis method.

Description

[Technical Field]

[0001] The present invention relates to the synthesis of core / shell / shell quantum dots, and in particular to a novel shell synthesis method. [Background technology]

[0002] Core / shell / shell quantum dots have the property of absorbing blue (and UV) light and emitting it at longer wavelengths, e.g., as green or red light. They can be made into efficient luminescent materials whose emission color can be tuned by varying the crystal size, making them applicable as downconverter materials in lighting and LED displays. A particularly interesting sub-application field is microLED displays, where every pixel contains a blue, green, and red emitting source (so-called self-luminous screens) and pixel sizes are reduced to less than 10 μm. At this length scale, these quantum dots offer a clear advantage over conventional downconverting materials or native green and red emitting materials due to their higher efficiency.

[0003] The first QDs incorporated into commercial displays were those containing cadmium selenide (CdSe), a direct-gap semiconductor whose emission can be tuned across the entire visible range by varying the size of the CdSe crystals. However, due to strict restrictions on the use of cadmium in consumer products, Cd-based QDs are generally considered unsuitable, and a transition from Cd-based QDs to Cd-free alternatives such as indium phosphide (InP) QDs has begun. The photothermal instability of InP-based QDs is addressed by their core / shell / shell structure.

[0004] In the case of metal S / Se shell layers, the synthesis of the shell relies on the reaction of metal carboxylates with tertiary phosphine sulfides / selenides. However, this reaction is slow and often not robust due to the presence of impurities in commercially available secondary phosphine sulfides / selenides. This leads to undesirable optical properties (low PLQY) and makes the process difficult to upscale. Therefore, there is a need in the art for a fast and robust shell synthesis that leads to core / shell / shell quantum dots with excellent optical properties (high PLQY). Summary of the Invention

[0005] In one aspect, the method comprises the steps of: (a) A core of a binary, ternary, or quaternary material containing the following elements: - one or more first core elements selected from the group consisting of In, Ga, and Al, and - preparing the core comprising one or more second core elements selected from the group consisting of P, As, and Sb; (b) forming a first layer on the core by contacting the core with a mixture comprising a metal precursor, a secondary phosphine selenide, and a tertiary phosphine selenide; (c) forming a second layer on the first layer by contacting the product of step (b) with a mixture comprising a metal precursor, a secondary phosphine sulfide, and a tertiary phosphine sulfide. The present invention provides a method for preparing quantum dots, comprising:

[0006] Such a method may be referred to as a method according to the invention or a method of the invention as described herein. Quantum dots prepared via the method according to the present invention are (semi)spherical nanoparticles comprising a core, a first layer on the core, and a second layer on the first layer. Such quantum dots are sometimes referred to as core / shell / shell quantum dots. It is understood that quantum dots are different from quantum rods, which are elongated semiconductor nanoparticles.

[0007] Core / shell / shell quantum dots can be represented by core / first layer / second layer, e.g., InP / ZnSe / Zn 1-x CD x S is an InP core (i.e., a core comprising or consisting essentially of InP), a ZnSe first layer (i.e., a first layer comprising or consisting essentially of ZnSe), and a Zn 1-x CD x In another example, InP / Zn(S,Se) / ZnS refers to a quantum dot comprising an InP core, a Zn(S,Se) first layer (i.e., a first layer comprising or consisting essentially of a Zn, S, and Se alloy, where the molar ratio between Zn and S+Se is essentially 1), and a ZnS second layer. In this context, the terminology AB or ABC core, layer, or shell refers to a core, layer, or shell comprising or consisting essentially of AB or ABC, respectively.

[0008] The composition of the quantum dots, core, first layer, and second layer (i.e., the elements contained therein and their molar ratios) can be determined by EDX (energy dispersive X-ray spectroscopy) on an ensemble of quantum dots. In the context of this application, quantum dots are capable of absorbing and emitting electromagnetic radiation, the wavelength of the emitted radiation being higher than the wavelength of the absorbed radiation. Preferably, the absorbed radiation is in the visible spectrum ("visible light").

[0009] The advantage of the method according to the present invention is that quantum dots with good optical properties, i.e., high photoluminescence, can be obtained through a robust, fast, and high-yield reaction at a relatively low temperature (e.g., 240°C), which means that the method is cost-effective. Furthermore, the method allows good control over the shell thickness. A suitable measure of photoluminescence is the "photoluminescence quantum yield" (PLQY), which is the ratio of the number of emitted photons that can be collected to the number of photons absorbed by the quantum dot. This PLQY is sometimes referred to as internal PLQY, in contrast to external PLQY, which is defined as the ratio of the total number of emitted photons to the number of photons provided to the quantum dot. Unless explicitly stated, PLQY herein refers to internal PLQY. [Brief explanation of the drawings]

[0010] [Figure 1] Mass-corrected absorbance (a.u.) at various wavelengths of InP / ZnSe quantum dots synthesized by using tertiary phosphine only (short-dashed line), 85% tertiary phosphine + 15% secondary phosphine (long-dashed line), and 50% tertiary phosphine + 50% secondary phosphine (solid line). [Figure 2] Mass-corrected absorbance (a.u.) at various wavelengths of InP / ZnSe / ZnS quantum dots synthesized by using tertiary phosphine only (short-dashed line), 85% tertiary phosphine + 15% secondary phosphine (long-dashed line), and 50% tertiary phosphine + 50% secondary phosphine (solid line). [Figure 3] Absolute PLQY values ​​(circles) of InP / ZnSe / ZnS quantum dots obtained by synthesis using tertiary phosphine only, 85% tertiary phosphine + 15% secondary phosphine, and 50% tertiary phosphine + 50% secondary phosphine, as well as their chemical yields (triangles). [Figure 4] Absolute PLQY values ​​(circles) and full width at half maximum (FWHM, triangles) of InP / ZnSe / ZnS quantum dots obtained by synthesis using tertiary phosphine only, 85% tertiary phosphine + 15% secondary phosphine, and 50% tertiary phosphine + 50% secondary phosphine. DETAILED DESCRIPTION OF THE INVENTION

[0011] In certain embodiments, methods according to the invention result in quantum dots having a PLQY of at least 85%, at least 85.5%, at least 86%, at least 86.5%, at least 87%, at least 87.5%, at least 88%, at least 88.5%, at least 89%, at least 89.5%, at least 90%, at least 90.5%, at least 91%, at least 91.5%, at least 92%, at least 92.5%, at least 93%, at least 93.5%, at least 94%, at least 94.5%, at least 95%, at least 95.5%, at least 96%, at least 96.5%, at least 97%, at least 97.5%, at least 98%, at least 98.5%, at least 99%, or at least 99.5%. The method according to the present invention is also robust, fast, and provides high yields. Methods in the art for preparing core / shell / shell quantum dots often rely solely on tertiary phosphine selenides and sulfides during the formation of the first and second layers, respectively. Without being bound by this theory, due to the relatively low reactivity of these species, these methods are prone to the presence of (slightly more reactive) impurities in the phosphines, resulting in significant batch-to-batch and intra-batch variations in the shell composition and, therefore, properties such as photoluminescence. Such impurities are unavoidable in commercial sources. Furthermore, the relative inertness of tertiary phosphines leads to slow reactions and low yields.

[0012] The present invention circumvents this problem by including more reactive secondary phosphine selenides and sulfides in addition to less reactive tertiary phosphine selenides and sulfides, resulting in a more robust (i.e., more uniform) synthesis that is more amenable to scale-up, has a higher overall yield, is faster (at relatively low temperatures such as 240°C), and is more cost-effective. Higher yields at relatively low temperatures have the economic benefit of being more cost-effective. Robustness means that the results of the method are less affected or not significantly affected by the presence of impurities or small variations in reaction conditions. The reactive impurities in the tertiary phosphines are overwhelmed by the presence of reactive secondary phosphines. Without being bound by this theory, the secondary phosphines serve as reactive species during the formation of the first and second shells, respectively, while the tertiary phosphines act as reservoirs of selenide and sulfide for reaction, respectively. It is understood that this combination of reactive secondary species and non-reactive tertiary species acting as sulfide / selenide reservoirs may depend on a series of equilibrium reactions not further discussed herein.

[0013] The presence of a more reactive phosphine in the reaction also makes it feasible to use relatively less reactive metal precursors (e.g., long-chain metal carboxylates containing more than five carbon atoms) and to have controlled second layer synthesis, which often has a slow rate and requires high temperatures or long reaction times in the absence of a secondary phosphine. It will be understood that application of the methods according to the present invention will generally result in a plurality of quantum dots. Whenever reference is made to the properties of a single quantum dot, reference is preferably made to the average value of the properties over a plurality of quantum dots. The average may be a number-weighted average or a mass-weighted average.

[0014] In some embodiments, the first and second layers are (hemi)spherical layers arranged concentrically around the core. In some embodiments, the first layer surrounds the core and the second layer surrounds the second layer. In some embodiments, the first and second layers are solid layers. In some embodiments, the quantum dots have a diameter of 5 to 30 nm, up to 29 nm, up to 28 nm, up to 27 nm, up to 26 nm, up to 25 nm, up to 24 nm, up to 23 nm, up to 22 nm, up to 21 nm, up to 20 nm, up to 19 nm, up to 18 nm, up to 17 nm, up to 16 nm, up to 15 nm, up to 14 nm, up to 13 nm, up to 12 nm, up to 11 nm, up to 10 nm, up to 9.5 nm, up to 9 nm, up to 8.5 nm, up to 8 nm. In some embodiments, the quantum dots have a diameter of 6 to 30 nm, 29 nm, 28 nm, 27 nm, 26 nm, 25 nm, 24 nm, 23 nm, 22 nm, 21 nm, 20 nm, 19 nm, 18 nm, 17 nm, 16 nm, 15 nm, 14 nm, 13 nm, 12 nm, 11 nm, 10 nm, 9.5 nm, 9 nm, 8.5 nm, 8 nm. Quantum dots with an average diameter in this range can provide good optical properties for down-conversion, since the absorption coefficient at the wavelength corresponding to the pump light strongly exceeds the absorption coefficient at the wavelength corresponding to the quantum dot emission.

[0015] The core is a (hemi-)spherical semiconductor nanocrystal that, due to quantum mechanical effects, has optical and electronic properties that are distinct from larger particles of the same material. The core can be considered a quantum dot in its own right, although it is not a core / shell / shell quantum dot. The core is (is made from) a binary, ternary, or quaternary material (or compound). Binary, ternary, or quaternary materials are materials composed of two, three, or four different elements, respectively. It is understood that the order of elements in the formula of a ternary or quaternary material is a matter of convention and has no effect on the composition of the material.

[0016] In some embodiments, the binary, ternary, or quaternary material is a binary or ternary material. In certain embodiments, the binary, ternary, or quaternary material is InP, InGaP, InAs, InSb, or InSbAs. In certain embodiments, the binary material is InP, InAs, InSb, GaP, GaAs, GaSb, AlP, AlAs, or AlSb. In certain embodiments, the ternary material is InPAs, InPSb, InAsSb, GaPAs, GaPSb, GaAsSb, AlPAs, AlPSb, AlAsSb, InGaP, InGaAs, InGaSb, InAlP, InAlAs, InAlSb, GaAlP, GaAlAs, or GaAlSb.

[0017] In some embodiments, the ternary material is InGaP or InSbAs. In an embodiment, the quaternary material is InPAsSb, GaPAsSb, AlPAsSb, InGaPAs, InGaPSb, InGaAsSb, InAlPAs, InAlPSb, InAlAsSb, GaAlPAs, GaAlPSb, GaAlAsSb, InGaAlP, InGaAlAs, or InGaAlSb. In one embodiment, the binary, ternary, or quaternary material is InP. Such cores, when 2 nm to 4 nm in diameter, emit light in the visible spectrum upon illumination with blue (and UV) light, making them highly attractive for downconverter applications.

[0018] The preparation of the core in step (a) of the method according to the present invention can be carried out by any commonly known technique. For example, but not limited to, the core can be synthesized by mixing each halide of the first core element with a metal halide, preferably zinc halide, and injecting the resulting mixture with a precursor of the second core element, preferably at a temperature of 150°C to 250°C, more preferably at a temperature of 150°C to 200°C. As an example, an InP core can be synthesized by mixing InCl3 and ZnCl2 in oleylamine and injecting a phosphor precursor (e.g., tris(diethylamino)phosphine) at high temperature (180°C).

[0019] In one embodiment, the preparation of the core in step (a) of the method according to the invention is a colloidal synthesis. In some embodiments, the core has a diameter of 1 to 5 nm, preferably 1.5 to 4.5 nm, and more preferably 2 to 4 nm. Suitable core diameters allow the quantum dots to emit light in the visible spectrum upon irradiation with blue (and UV) light. In certain embodiments, the yield of step (a) involved in the methods according to the invention is at least 90%, at least 90.5%, at least 91%, at least 91.5%, at least 92%, at least 92.5%, at least 93%, at least 93.5%, at least 94%, at least 94.5%, at least 95%, at least 95.5%, at least 96%, at least 96.5%, at least 97%, at least 97.5%, at least 98%, at least 98.5%, at least 99%, or at least 99.5%.

[0020] The first layer, also referred to as the first shell, inner shell, or inner layer, is formed during step (b) of the method according to the invention by contacting the core with a mixture comprising a metal precursor, a secondary phosphine selenide, and a tertiary phosphine selenide. While the first layer is beneficial in producing quantum dots, it is not expected to have a significant effect on the optical properties of the quantum dots, as it creates a barrier that is thin enough to obtain high-speed transport by tunneling of charge carriers between the second layer and the core. Secondary phosphine selenides have the general structure R 1 R 2 P-Se, where R 1 and R 2 is an organic moiety, preferably P and R 1 with, and R 2 Each bond between is formally a single phosphorus-carbon bond.

[0021] In some embodiments, R 1 and R 2 is a hydrocarbon moiety. Preferably, R 1 and R 2 is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl, or cycloalkynyl. More preferably, R 1 and R 2 is independently alkyl, cycloalkyl, or aryl. In some embodiments, R 1 and R 2 is C 2~10Preferably, R 1 and R2 independently represents C 2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl, or C 3-10 More preferably, R 1 and R 2 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl.

[0022] In some embodiments, R 1 and R 2 is C 2~6 Preferably, R 1 and R 2 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl, or C 3-6 More preferably, R 1 and R 2 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl. In some embodiments, R 1 and R 2 is the same as P's R 1 =R 2 The double substitution by may be by any group as defined above. In some embodiments, R 1 and R 2 P and R are different. 1 and R 2 Asymmetric substitution with may be by any two non-identical groups as defined above.

[0023] In certain embodiments, the secondary phosphine selenide is diphenylphosphine selenide, di-2-norbornylphosphine selenide, di-iso-butylphosphine selenide, di-tert-butylphosphine selenide, dicyclopentylphosphine selenide, dicyclohexylphosphine selenide, or 9-phosphabicyclononane selenide. In some embodiments, the secondary phosphine selenide is diphenylphosphine selenide. Aryl is defined herein as a single-bonded aromatic hydrocarbon moiety. xy A moiety is defined herein as a moiety having a total number of carbon atoms from x to y inclusive.

[0024] Tertiary phosphine selenides have the general structure R 3 R 4 R 5 With P=Se, where R 3 , R 4 , and R 5 is an organic moiety, preferably P and R 3 With, R 4 with, and R 5 Each bond between is formally a single phosphorus-carbon bond. In some embodiments, R 3 , R 4 , and R 5 is a hydrocarbon moiety. Preferably, R 3 , R 4 , and R 5 is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl, or cycloalkynyl. More preferably, R 3 , R 4 , and R 5 is independently alkyl, cycloalkyl, or aryl. In some embodiments, R 3 , R 4 , and R 5 is C 2-10 Preferably, R3 , R 4 , and R 5 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl or C 3-10 More preferably, R 3 , R 4 , and R 5 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl.

[0025] In some embodiments, R 3 , R 4 , and R 5 is C 2-6 Preferably, R 3 , R 4 , and R 5 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl or C 3-6 More preferably, R 3 , R 4 , and R 5 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl. In some embodiments, R 3 , R 4 , and R 5 is the same as P's R 3 =R 4 =R 5 The triple substitution by may be by any group as defined above. In some embodiments, R 3 , R 4, and R 5 is different. P's R 3 , R 4 , and R 5 Asymmetric substitution by may be by any three non-identical groups as defined above.

[0026] In certain embodiments, the tertiary phosphine selenide is tri-n-octylphosphine selenide, triethylphosphine selenide, tri-n-propylphosphine selenide, tri-n-butylphosphine selenide, triisobutylphosphine selenide, tri-n-hexylphosphine selenide, di-tert-butyl(n-butyl)phosphine selenide, or triphenylphosphine selenide. In some embodiments, the tertiary phosphine selenide is tri-n-octylphosphine selenide. In an embodiment, the mixture used in step (b) of the method according to the present invention comprises a secondary phosphine selenide and a tertiary phosphine selenide as well as a secondary phosphine sulfide and a tertiary phosphine sulfide. Preferably, the secondary phosphine sulfide and the tertiary phosphine sulfide may be as described in any embodiment below in the context of the second layer.

[0027] In some embodiments, the first shell is Zn(Se,S) or ZnSe 1-x S xwhere x is the molar ratio between the number of sulfur atoms and the total number of sulfur and selenide atoms. Such a first shell can be obtained by adding a secondary phosphine sulfide and a tertiary phosphine sulfide in addition to a secondary phosphine selenide and a tertiary phosphine selenide to the mixture used in step (b) of the method according to the invention. Preferably, x is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0. 4, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.7 5, 0.76, 0.77, 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or more. Alternatively, x can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 4, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.7 5, 0.76, 0.77, 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or less.

[0028] In certain embodiments, the metal precursor used in step (b) of the method according to the present invention is a metal carboxylate or a metal thiolate. In one embodiment, the metal precursor used in step (b) of the method according to the present invention is a metal C 10-22 Carboxylate, preferably C 10-22 Zinc carboxylate or C 10-22 Cadmium carboxylate, more preferably C 10-22 It is a zinc carboxylate. In the context of the present invention, a metal thiolate is any organic compound in which a metal ion is formally bound or complexed to a negatively charged sulfur atom, thus MSR or M, where M is the metal, S is the sulfur atom, and R is any organic moiety. +- For example, the metal thiolate can be, without limitation, a metal thiocarboxylate, a metal dithiocarboxylate, a metal thiocarbamate, or a metal dithiocarbamate.

[0029] In certain embodiments, the metal precursor used in step (b) of the method according to the present invention is a metal dithiocarbamate or metal thiocarbamate, preferably zinc dithiocarbamate, zinc thiocarbamate, cadmium dithiocarbamate, or zinc thiocarbamate, more preferably zinc dithiocarbamate or cadmium dithiocarbamate. Preferably, the dithiocarbamate is a dialkyldithiocarbamate and / or the thiocarbamate is an alkylthiocarbamate, wherein each alkyl group is independently selected from the group consisting of C 1-10 Alkyl, preferably C 2-5 In certain embodiments, the metal precursor used in step (b) of the method according to the present invention is a metal dithiocarbamate, preferably zinc dithiocarbamate or cadmium dithiocarbamate, more preferably zinc dithiocarbamate. Preferably, the dithiocarbamate is a dialkyldithiocarbamate, wherein each alkyl group is independently selected from the group consisting of C 1-10 Alkyl, preferably C 2-5 It is preferably alkyl, more preferably ethyl.

[0030] In one embodiment, the metal precursor used in step (b) of the method according to the present invention is zinc diethyldithiocarbamate. In one embodiment, the metal precursor used in step (b) of the method according to the present invention is a metal oleate, stearate, or myristate, preferably zinc oleate, cadmium oleate, zinc stearate, cadmium stearate, zinc myristate, or cadmium myristate, more preferably zinc oleate, zinc stearate, or zinc myristate.

[0031] In an alternative embodiment, the metal precursor used in step (b) of the method according to the invention is C 2-6 Carboxylate, preferably C 2-6Zinc carboxylate, or C 2-6 In one embodiment, the metal precursor used in step (b) of the method according to the present invention is C 2-4 Carboxylate, preferably C 2-4 Zinc carboxylate, or C 2-4 In one embodiment, the metal precursor used in step (b) of the method according to the present invention is C 2-3 Carboxylate, preferably C 2-3 Zinc carboxylate, or C 2-3 In one embodiment, the metal precursor used in step (b) of the method according to the present invention is an acetate, preferably zinc acetate or cadmium acetate.

[0032] In some embodiments, the metal precursor used in step (b) of the method according to the present invention is a zinc or cadmium precursor, preferably a zinc or cadmium carboxylate or thiolate. In some preferred embodiments, the metal precursor is a zinc precursor, preferably a zinc carboxylate or thiolate. The identity of the metal determines the composition of the first layer. For example, if a zinc precursor is used, the first layer comprises or consists essentially of ZnSe, where Zn comes from the zinc precursor and Se comes from secondary and tertiary phosphine selenides. As another example, by using a mixture of zinc and cadmium precursors, a first shell comprising or consisting essentially of a Zn, Cd, and Se alloy is obtained. In this context, Zn 1-x CD x The notation Se refers to the composition of the first shell in which the molar ratio Cd / (Cd+Zn) is x, which is determined by and preferably (essentially) equal to the molar ratio Cd / (Cd+Zn) in the mixture of zinc precursor and cadmium precursor used in step (b) of the method according to the invention.

[0033] In one embodiment, the metal precursor used in step (b) of the method according to the present invention is zinc oleate. In one embodiment, the metal precursor used in step (b) of the method according to the invention is a mixture of zinc and cadmium precursors, preferably a mixture of zinc and cadmium carboxylates, more preferably C 10-22 Zinc carboxylate and C 10-22 and cadmium carboxylate, even more preferably a mixture of zinc oleate and zinc zinc oleate, or zinc stearate and cadmium stearate, or zinc myristate or cadmium myristate, and most preferably a mixture of zinc oleate and cadmium oleate.

[0034] In one embodiment, the metal precursor used in step (b) of the method according to the invention is a mixture of zinc and cadmium precursors, preferably a mixture of zinc and cadmium carboxylates as defined above, in which the molar ratio Cd / (Cd+Zn) (i.e., the mole fraction of Cd) in the mixture is between 0.001 and 1.0, more preferably from 0.02 to 0.2, and most preferably from 0.025 to 0.133. In an alternative embodiment, the metal precursor used in step (b) of the method according to the invention is not or does not comprise a cadmium precursor, preferably the metal precursor is a (pure) zinc precursor, preferably a (pure) zinc carboxylate or zinc thiolate.

[0035] In one embodiment, the molar ratio of the number of molecules of secondary phosphine selenide on the one hand to the total number of molecules of secondary phosphine selenide and tertiary phosphine selenide on the other hand in the mixture used in step (b) of the process according to the invention is from 1% to 90%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 55%, from 1% to 50%, from 1% to 45%, from 1% to 40%, from 1% to 35%, from 1% to 30%. , 1% to 25%, 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, 5% to 90%, 10% to 90%, 15% to 90%, 20% to 90%, 25% to 90%, 30% to 90%, 35% to 90%, 40% to 90%, 45% to 90%, 50% to 90%, 55% to 90%, 60% to 90%, 65% to 90%, 70% to 90%, 75% to 90%, 80% to 90%, 85% to 90%, 5% to Up to 5%, 10% to 20%, 15% to 25%, 20% to 30%, 25% to 35%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, 50% to 60%, 55% to 65%, 60% to 70%, 65% to 75%, 70% to 80%, 75% to 85%, 80% to 90%, 85% to 95%, 5% to 25%, 10% to 30%, 15% to 35%, 20% to 40%, 25% to 45%, 30% to 50%, 35% to 55%, 40% to 60%, 45% to 65%, 50% to 70%, 55% to 75%, 60% to 80%, 65% to 85%, 70% to 90%, 75% to 95%, 5% to 35%, 10% to 40%, 15% to 45%, 20% to 50%, 25% to 55%, 30% to 60%, 35% to 65%, 40% to 70%, 45% to 75%, 50% to 80%, 55% to 85%, 60% to 90%, 65% to 95%.

[0036] In certain embodiments, the mixture used in step (b) of the method according to the invention comprises secondary phosphine selenide and tertiary phosphine selenide as well as secondary phosphine sulfide and tertiary phosphine sulfide.Preferably, the molar ratio of the number of molecules of secondary phosphine sulfide, on the one hand, to the total number of molecules of secondary and tertiary phosphine sulfide, on the other hand, in the mixture used in step (b) of the process according to the invention is from 1% to 90%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 55%, from 1% to 50%, from 1% to 45%, from 1% to 40%, from 1% to 35%, from 1% to 30%, from 1% to Up to 25%, 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, 5% to 90%, 10% to 90%, 15% to 90%, 20% to 90%, 25% to 90%, 30% to 90%, 35% to 90%, 40% to 90%, 45% to 90%, 50% to 90%, 55% to 90%, 60% to 90%, 65% to 90%, 70% to 90%, 75% to 90%, 80% to 90%, 85% to 90%, 5% to 15%, 10% to 20%, 15% to 25%, 20% to 30%, 25% to 35%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, 50% to 60%, 55% to 65%, 60% to 70%, 65% to 75%, 70% to 80%, 75% to 85%, 80% to 90%, 85% to 95%, 5% to 25%, 10% to 30%, 15% to 35%, 20% to 40%, 25% to 45%, 30% to 50%, 35 % to 55%, 40% to 60%, 45% to 65%, 50% to 70%, 55% to 75%, 60% to 80%, 65% to 85%, 70% to 90%, 75% to 95%, 5% to 35%, 10% to 40%, 15% to 45%, 20% to 50%, 25% to 55%, 30% to 60%, 35% to 65%, 40% to 70%, 45% to 75%, 50% to 80%, 55% to 85%, 60% to 90%, 65% to 95%.

[0037] In one embodiment, the mixture used in step (b) of the method according to the present invention contains secondary phosphine selenide and tertiary phosphine selenide as well as secondary phosphine sulfide and tertiary phosphine sulfide. Preferably, the molar ratio of the total number of molecules of secondary phosphine sulfide and secondary phosphine selenide on the one hand to the total number of molecules of secondary phosphine sulfide, secondary phosphine selenide, tertiary phosphine sulfide, and tertiary phosphine selenide on the other hand in the mixture used in step (b) of the method according to the present invention is from 1% to 90%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 85%, from 1% to 80%, from 1% to 85%, from 1% to 80%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 85 ... % to 55%, 1% to 50%, 1% to 45%, 1% to 40%, 1% to 35%, 1% to 30%, 1% to 25%, 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, 5% to 90%, 10% to 90%, 15% to 90%, 20% to 90%, 25% to 90%, 30% to 90%, 35% to 90%, 40% to 90%, 45% to 90%, 50% to 90%, 55% to 90% From 60% to 90%, 65% to 90%, 70% to 90%, 75% to 90%, 80% to 90%, 85% to 90%, 5% to 15%, 10% to 20%, 15% to 25%, 20% to 30%, 25% to 35%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, 50% to 60%, 55% to 65%, 60% to 70%, 65% to 75%, 70% to 80%, 75% to Up to 85%, 80% to 90%, 85% to 95%, 5% to 25%, 10% to 30%, 15% to 35%, 20% to 40%, 25% to 45%, 30% to 50%, 35% to 55%, 40% to 60%, 45% to 65%, 50% to 70%, 55% to 75%, 60% to 80%, 65% to 85%, 70% to 90%, 75% to 95%, 5% to 35%, 10% to 40%, 15% to 45%,20% to 50%, 25% to 55%, 30% to 60%, 35% to 65%, 40% to 70%, 45% to 75%, 50% to 80%, 55% to 85%, 60% to 90%, 65% to 95%.

[0038] In some embodiments, the molar ratio between the number of Se atoms and the total number of Zn and Cd atoms in the first layer is 0.50 to 1.50, 0.55 to 1.45, 0.60 to 1.40, 0.65 to 1.35, 0.70 to 1.30, 0.75 to 1.25, 0.80 to 1.20, 0.85 to 1.15, 0.90 to 1.10, 0.95 to 1.05, 0.96 to 1.04, 0.97 to 1.03, 0.98 to 1.02, or 0.99 to 1.01. This ratio can be determined by EDX (energy dispersive X-ray spectroscopy) on a population of quantum dots. In certain additional embodiments, the molar ratio between the total number of Se and S atoms, on the one hand, and the total number of Zn and Cd atoms, on the other hand, contained in the first layer is from 0.50 to 1.50, from 0.55 to 1.45, from 0.60 to 1.40, from 0.65 to 1.35, from 0.70 to 1.30, from 0.75 to 1.25, from 0.80 to 1.20, from 0.85 to 1.15, from 0.90 to 1.10, from 0.95 to 1.05, from 0.96 to 1.04, from 0.97 to 1.03, from 0.98 to 1.02, or from 0.99 to 1.01.

[0039] In one embodiment, the first layer has a thickness of up to 1.0 nm, preferably 0.1 nm to 0.9 nm, and more preferably 0.2 nm to 0.8 nm. The first layer prevents the growth of the second layer (e.g., CdSe) on the core (e.g., InP). This effect is achieved, and the optimal thickness of the first layer is within this range to achieve good optical properties for down-conversion. An additional advantage of the methods of the present invention is that they provide good control over shell thickness, particularly the thickness of the first layer. In certain embodiments, the standard deviation for the thickness of the first layer in a population of quantum dots prepared by the methods of the present invention is 0.10 or less, preferably 0.05 or less, and more preferably 0.025 or less.

[0040] In an embodiment, the yield of step (b) comprised in the process according to the invention is at least 60%, at least 60.5%, at least 61%, at least 61.5%, at least 62%, at least 62.5%, at least 63%, at least 63.5%, at least 64%, at least 64.5%, at least 65%, at least 65.5%, at least 66%, at least 66.5%, at least 67%, at least 67.5%, at least 68%, at least 68.5%, at least 69%, at least 69.5%, at least 70%, at least 70.5%, at least 71%, at least 71.5%, at least 72%, at least 72.5%, at least 73%, at least 73.5%, at least 74%, at least 74.5%, at least 75%, at least 75.5%, at least 76%, at least 76.5%, at least 77%, at least 77.5%, at least 78%, at least 78.5%, at least 79%, at least 79.5%, at least 80%, at least 80.5%, at least 81%, at least 81.5%, at least 82%, at least 82.5%, at least 83%, at least 83.5%, at least 84%, at least 84.5%, or at least 85%. As explained above, an advantage of the method according to the present invention is that a high yield can be obtained during the synthesis of the first layer. In some embodiments, the secondary phosphine selenide in the mixture used in step (b) of the method according to the present invention is generated in situ after adding the secondary phosphine and selenium to the mixture used in step (b).

[0041] In one embodiment, the secondary phosphine selenide in the mixture used in step (b) of the process according to the invention is added neat, in crystalline form, to the mixture used in step (b). In one embodiment, the mixture used in step (b) of the method according to the present invention contains secondary phosphine sulfide and tertiary phosphine sulfide in addition to secondary phosphine selenide and tertiary phosphine selenide. Preferably, the secondary phosphine sulfide is generated in situ after adding the secondary phosphine and sulfur to the mixture used in step (b). Alternatively, the secondary phosphine is added as is in crystalline form to the mixture used in step (b).

[0042] The second layer, which may also be referred to as a second shell, outer shell, or outer layer, is formed during step (c) of the method according to the present invention by contacting the core with a mixture containing a metal precursor, a secondary phosphine sulfide, and a tertiary phosphine sulfide. Forming a high-quality second layer is crucial for obtaining quantum dots with a high photoluminescence quantum yield (PLQY).

[0043] Secondary phosphine sulfides have the general structure R 6 R 7 PS, where R 6 and R 7 are organic moieties, preferably P and R, respectively. 6 and R 7 The bond between is formally a single phosphorus-carbon bond. In some embodiments, R 6 and R 7 is a hydrocarbon moiety. Preferably, R 6 and R 7 is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl, or cycloalkynyl. More preferably, R 6 and R 7 is independently alkyl, cycloalkyl, or aryl. In some embodiments, R6 and R 7 is C 2-10 Preferably, R 6 and R 7 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl, or C 3-10 More preferably, R 6 and R 7 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl.

[0044] In some embodiments, R 6 and R 7 is C 2-6 Preferably, R 6 and R 7 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl, or C 3-6 More preferably, R 6 and R 7 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl. In some embodiments, R 6 and R 7 is the same as P's R 1 =R 2 The double substitution by may be by any group as defined above. In some embodiments, R 6 and R 7 is different. P's R 6 and R 7Asymmetric substitution by may be by any two non-identical groups as defined above.

[0045] In certain embodiments, the secondary phosphine sulfide is diphenylphosphine sulfide, di-2-norbornylphosphine sulfide, di-iso-butylphosphine sulfide, di-tert-butylphosphine sulfide, dicyclopentylphosphine sulfide, dicyclohexylphosphine sulfide, or 9-phosphabicyclononane sulfide. In some embodiments, the secondary phosphine sulfide is diphenylphosphine sulfide.

[0046] Tertiary phosphine sulfides have the general structure R 8 R 9 R 10 With P=S, where R 8 , R 9 , and R 10 is an organic moiety, preferably P and R 8 , R 9 , and R 10 The bond between each is formally a single phosphorus-carbon bond. In some embodiments, R 8 , R 9 , and R 10 is a hydrocarbon moiety. Preferably, R 8 , R 9 , and R 10 is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl, or cycloalkynyl. More preferably, R 8 , R 9 , and R 10 is independently alkyl, cycloalkyl, or aryl.

[0047] In some embodiments, R 8 , R 9 , and R 10 is C 2-10 Preferably, R 8 , R 9 , and R 10 independently, C2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl, or C 3-10 More preferably, R 8 , R 9 , and R 10 independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl. In some embodiments, R 8 , R 9 , and R 10 is C 2-6 Preferably, R 8 , R 9 , and R 10 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl, or C 3-6 More preferably, R 8 , R 9 , and R 10 independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl.

[0048] In some embodiments, R 8 , R 9 , and R 8 is the same as P's R 8 =R 9 =R 10 The triple substitution by may be by any group as defined above. In some embodiments, R 8 , R 9 , and R 10 P's R 8 , R 9, and R 10 Asymmetric substitution by may be by any three non-identical groups as defined above. In certain embodiments, the tertiary phosphine sulfide is tri-n-octylphosphine sulfide (TOP-S), triethylphosphine sulfide, tri-n-propylphosphine sulfide, tri-n-butylphosphine sulfide, triisobutylphosphine sulfide, tri-n-hexylphosphine sulfide, or di-tert-butyl(n-butyl)phosphine sulfide.

[0049] In some embodiments, the tertiary phosphine sulfide is tri-n-octylphosphine sulfide (TOP-S). In certain embodiments, the metal precursor used in step (c) of the method according to the present invention is a metal carboxylate or a metal thiolate. In one embodiment, the metal precursor used in step (c) of the method according to the present invention is a metal C 10-22 Carboxylate, preferably zinc C 10-22 Carboxylate or Cadmium C 10-22 Carboxylate, more preferably zinc C 10-22 It is a carboxylate.

[0050] In certain embodiments, the metal precursor used in step (c) of the method according to the present invention is a metal dithiocarbamate or metal thiocarbamate, preferably zinc dithiocarbamate, zinc thiocarbamate, cadmium dithiocarbamate, or zinc thiocarbamate, more preferably zinc dithiocarbamate or cadmium dithiocarbamate. Preferably, the dithiocarbamate is a dialkyldithiocarbamate and / or the thiocarbamate is an alkylthiocarbamate, wherein each alkyl group is independently selected from the group consisting of C 1-10 Alkyl, preferably C 2-5 It is alkyl, more preferably ethyl. In certain embodiments, the metal precursor used in step (c) of the method according to the present invention is a metal dithiocarbamate, preferably zinc dithiocarbamate or cadmium dithiocarbamate, more preferably zinc dithiocarbamate. Preferably, the dithiocarbamate is a dialkyldithiocarbamate, where each alkyl group is independently C 1-10 Alkyl, preferably C 2-5 It is preferably alkyl, more preferably ethyl.

[0051] In one embodiment, the metal precursor used in step (c) of the method according to the present invention is zinc diethyldithiocarbamate. In an embodiment, the metal precursor used in step (c) of the method according to the present invention is a metal oleate, stearate, or myristate, preferably zinc oleate, cadmium oleate, zinc stearate, cadmium stearate, zinc myristate, or cadmium myristate, more preferably zinc oleate, zinc stearate, or zinc myristate.

[0052] In an alternative embodiment, the metal precursor used in step (c) of the process according to the invention is C 2-6 Carboxylate, preferably C 2-6 Zinc carboxylate, or C 2-6 In one embodiment, the metal precursor used in step (c) of the method according to the present invention is C 2-4 Carboxylate, preferably C 2-4 Zinc carboxylate, or C 2-4 In one embodiment, the metal precursor used in step (c) of the method according to the present invention is C 2-3 Carboxylate, preferably C 2-3 Zinc carboxylate, or C 2-3 In one embodiment, the metal precursor used in step (c) of the method according to the present invention is an acetate, preferably zinc acetate or cadmium acetate.

[0053] In some embodiments, the metal precursor used in step (c) of the method according to the present invention is a zinc or cadmium precursor, preferably a zinc or cadmium carboxylate or thiolate. In some preferred embodiments, the metal precursor is a zinc precursor, preferably a zinc carboxylate or thiolate. The identity of the metal determines the composition of the second layer. For example, if a zinc precursor is used, the second layer comprises or (essentially) consists of ZnS, where Zn originates from the zinc precursor and S originates from secondary and tertiary phosphine sulfides. As another example, by using a mixture of a zinc precursor and a cadmium precursor, a second shell is obtained that comprises or (essentially) consists of an alloy of Zn, Cd, and S. In this context, the notation Zn 1-x CD x S refers to the composition of the second shell in which the molar ratio Cd / (Cd+Zn) is x, which is determined by and preferably (essentially) equal to the molar ratio Cd / (Cd+Zn) in the mixture of zinc precursor and cadmium precursor used in step (c) of the method according to the invention.

[0054] In one embodiment, the metal precursor used in step (c) of the method according to the present invention is zinc oleate. In one embodiment, the metal precursor used in step (c) of the method according to the invention is a mixture of zinc and cadmium precursors, preferably a mixture of zinc and cadmium carboxylates, preferably C 10-22 Zinc carboxylate and C 10-22 and cadmium carboxylate, more preferably a mixture of zinc oleate and zinc zinc oleate, or zinc stearate and cadmium stearate, or zinc myristate or cadmium myristate, and most preferably a mixture of zinc oleate and cadmium oleate.

[0055] In one embodiment, the metal precursor used in step (c) of the method according to the invention is a mixture of zinc and cadmium precursors, preferably a mixture of zinc and cadmium carboxylates as defined above, in which the molar ratio Cd / (Cd+Zn) (i.e., the molar fraction of Cd) in the mixture is between 0.001 and 1.0, preferably from 0.02 to 0.2, more preferably from 0.025 to 0.133. In an alternative embodiment, the metal precursor used in step (c) of the method according to the invention is not or does not comprise a cadmium precursor, preferably the metal precursor is a (pure) zinc precursor, preferably a (pure) zinc carboxylate or zinc thiolate.

[0056] In an embodiment, the molar ratio of the number of molecules of secondary phosphine sulfide, on the one hand, to the total number of molecules of secondary phosphine sulfide and tertiary phosphine sulfide, on the other hand, in the mixture used in step (c) of the process according to the invention is from 1% to 90%, from 1% to 85%, from 1% to 80%, from 1% to 75%, from 1% to 70%, from 1% to 65%, from 1% to 60%, from 1% to 55%, from 1% to 50%, from 1% to 45%, from 1% to 40%, from 1% to 35%, from 1% to 30%, from 1% to 5 ...0%, from 1% to 50%, from 1% to 50%, from 1% to 50%, from 1% to 50%, from 1% to 50%, from 1% to 60%, from 1% to 65%, from 1% to 50%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 65%, from 1% to 50%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% to 60%, from 1% to 50%, from 1% % to 25%, 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, 5% to 90%, 10% to 90%, 15% to 90%, 20% to 90%, 25% to 90%, 30% to 90%, 35% to 90%, 40% to 90%, 45% to 90%, 50% to 90%, 55% to 90%, 60% to 90%, 65% to 90%, 70% to 90%, 75% to 90%, 80% to 90%, 85% to 90%, 5% to 15%, 1 0% to 20%, 15% to 25%, 20% to 30%, 25% to 35%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, 50% to 60%, 55% to 65%, 60% to 70%, 65% to 75%, 70% to 80%, 75% to 85%, 80% to 90%, 85% to 95%, 5% to 25%, 10% to 30%, 15% to 35%, 20% to 40%, 25% to 45%, 30% to 50%, 3 5% to 55%, 40% to 60%, 45% to 65%, 50% to 70%, 55% to 75%, 60% to 80%, 65% to 85%, 70% to 90%, 75% to 95%, 5% to 35%, 10% to 40%, 15% to 45%, 20% to 50%, 25% to 55%, 30% to 60%, 35% to 65%, 40% to 70%, 45% to 75%, 50% to 80%, 55% to 85%, 60% to 90%, 65% to 95%.

[0057] In some embodiments, the molar ratio between the number of S atoms and the total number of Zn and Cd atoms contained in the second layer is 0.50 to 1.50, 0.55 to 1.45, 0.60 to 1.40, 0.65 to 1.35, 0.70 to 1.30, 0.75 to 1.25, 0.80 to 1.20, 0.85 to 1.15, 0.90 to 1.10, 0.95 to 1.05, 0.96 to 1.04, 0.97 to 1.03, 0.98 to 1.02, or 0.99 to 1.01. This ratio can be determined by EDX (energy dispersive X-ray spectroscopy) on a population of quantum dots. In one embodiment, the second layer has a thickness of up to 10 nm, preferably between 1 nm and 10 nm.

[0058] In some embodiments, the ratio of the volume of the second layer to the volume of the core is from 10 to 50, from 15 to 45, from 15 to 40, from 15 to 35, from 15 to 30, or from 15 to 25. If the volume of the second layer, and therefore the volume of the quantum dots, increases, the absorption per quantum dot also increases. An additional advantage of the methods of the present invention is that they provide good control over shell thickness, particularly the thickness of the second layer. In certain embodiments, the standard deviation for the thickness of the second layer in a population of quantum dots prepared by the methods of the present invention is 0.10 or less, preferably 0.05 or less, and more preferably 0.025 or less.

[0059] In an embodiment, the yield of step (c) comprised in the process according to the invention is at least 60%, at least 60.5%, at least 61%, at least 61.5%, at least 62%, at least 62.5%, at least 63%, at least 63.5%, at least 64%, at least 64.5%, at least 65%, at least 65.5%, at least 66%, at least 66.5%, at least 67%, at least 67.5%, at least 68%, at least 68.5%, at least 69%, at least 69.5%, at least 70%, at least 70.5%, at least 71%, at least 71.5%, at least 72%, at least 72.5%, at least 73%, at least 73.5%, at least 74%, at least 74.5%, at least 75%, at least 75.5%, at least 76%, at least 76.5%, at least 77%, at least 77.5%, at least 78%, at least 78.5%, at least 79%, at least 79.5%, at least 80%, at least 80.5%, at least 81%, at least 81.5%, at least 82%, at least 82.5%, at least 83%, at least 83.5%, at least 84%, at least 84.5%, or at least 85%. As explained above, an advantage of the method according to the invention is that a high yield can be obtained during the synthesis of the second layer.

[0060] In certain embodiments, the secondary phosphine sulfide in the mixture used in step (c) of the process according to the invention is generated in situ after adding the secondary phosphine and sulfur to the mixture used in step (c). In certain embodiments, the secondary phosphine sulfide in the mixture used in step (c) of the process according to the invention is added neat, in crystalline form, to the mixture used in step (c). In certain embodiments, the secondary phosphine selenide and secondary phosphine sulfide have the same general structure R 2 , where X is S or Se. 1 sec R 2 sec In these embodiments, R 1 =R 6=R 1 sec and R 2 =R 7 =R 2 sec where R 1 , R 2 , R 6 , and R 7 is defined above.

[0061] In some embodiments, R 1 sec and R 2 sec is a hydrocarbon moiety. Preferably, R 1 sec and R 2 sec is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl, or cycloalkynyl. More preferably, R 1 sec and R 2 sec is independently alkyl, cycloalkyl, or aryl. In some embodiments, R 1 sec and R 2 sec is C 2-10 Preferably, R 1 sec and R 2 sec independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl, or C 3-10 More preferably, R 1 sec and R 2 sec independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl.

[0062] In some embodiments, R 1 sec and R 2 sec is C 2-6 Preferably, R 1 sec and R 2 sec independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl, or C 3-6 More preferably, R 1 sec and R 2 sec independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl. In some embodiments, R 1 sec and R 2 sec are the same. R 1 sec =R 2 sec The double substitution of P by may be substitution by any group as defined above. In some embodiments, R 1 and R 2 It is different from P's R 1 sec and R 2 sec Asymmetric substitution by may be by any two non-identical groups, as defined above.

[0063] In certain embodiments, the secondary phosphine contained in the secondary phosphine selenides and sulfides is diphenylphosphine (DPP), di-2-norbornylphosphine, di-iso-butylphosphine, di-tert-butylphosphine, dicyclopentylphosphine, dicyclohexylphosphine, or 9-phosphabicyclononane. In certain embodiments, the secondary phosphine contained in the secondary phosphine selenides and sulfides is diphenylphosphine (DPP).

[0064] In certain embodiments, tertiary phosphine selenides and tertiary phosphine sulfides have the same general structure R 1 tert R 2 tert R 2 tert In some of these embodiments, R 3 =R 8 =R 1 tert , R 4 =R 9 =R 2 tert , and R 5 =R 10 =R 3 tert where R 3 , R 4 , R 5 , R 8 , R 9 , and R 10 is defined above. In some embodiments, R 1 tert , R 2 tert , and R 3 tert is a hydrocarbon moiety. Preferably, R 1 tert , R 2 tert , and R 3 tert is independently alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, alkynyl or cycloalkynyl. More preferably, R 1 tert , R 2 tert , and R 3 tert is independently alkyl, cycloalkyl, or aryl.

[0065] In some embodiments, R 1 tert , R 2 tert , and R 3 tert is C 2-10 Preferably, R 1 tert , R 2 tert , and R 3 tert independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, C 3-10 Aryl, C 2-10 Alkenyl, C 3-10 Cycloalkenyl, C 2-10 Alkynyl, or C 3-10 More preferably, R 1 tert , R 2 tert , and R 3 tert independently, C 2-10 Alkyl, C 3-10 Cycloalkyl, or C 3-10 It is aryl. In some embodiments, R 1 tert , R 2 tert , and R 3 tert is C 2-6 Preferably, R 1 tert , R 2 tert , and R 3 tert independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, C 3-6 Aryl, C 2-6 Alkenyl, C 3-6 Cycloalkenyl, C 2-6 Alkynyl, or C 3-6 More preferably, R 1 tert , R 2 tert , and R3 tert independently, C 2-6 Alkyl, C 3-6 Cycloalkyl, or C 3-6 It is aryl.

[0066] In some embodiments, R 1 tert , R 2 tert , and R 3 tert is the same as P's R 1 tert =R 2 tert =R 3 tert The triple substitution by may be by any group as defined above. In some embodiments, R 1 tert , R 2 tert , and R 3 tert is different. P's R 1 tert , R 2 tert , and R 3 tert Asymmetric substitution by may be by any three non-identical groups as defined above. In certain embodiments, the tertiary phosphine contained in the tertiary phosphine selenides and sulfides is tri-n-octylphosphine (TOP), triethylphosphine, tri-n-propylphosphine, tri-n-butylphosphine, triisobutylphosphine, tri-n-hexylphosphine, or di-tert-butyl(n-butyl)phosphine. In certain embodiments, the tertiary phosphine contained in the tertiary phosphine selenides and sulfides is tri-n-octylphosphine (TOP).

[0067] In certain embodiments, the metal precursors used in step (b) and step (c) of the method according to the present invention are both metal carboxylates or metal thiolates. In one embodiment, the metal precursors used in steps (b) and (c) of the method according to the invention are both metal C 10-22 Carboxylate, preferably C 10-22 Zinc carboxylate or C 10-22 Cadmium carboxylate, more preferably C 10-22 It is a zinc carboxylate. In certain embodiments, the metal precursors used in steps (b) and (c) of the method according to the present invention are both metal dithiocarbamate or metal thiocarbamate, preferably zinc dithiocarbamate, zinc thiocarbamate, cadmium dithiocarbamate, or zinc thiocarbamate, more preferably zinc thiocarbamate or cadmium dithiocarbamate. Preferably, the dithiocarbamate is a dialkyldithiocarbamate and / or the thiocarbamate is an alkylthiocarbamate, wherein each alkyl group is independently selected from the group consisting of C 1-10 Alkyl, preferably C 2-5 It is alkyl, more preferably ethyl.

[0068] In certain embodiments, the metal precursors used in steps (b) and (c) of the method according to the present invention are both metal dithiocarbamate salts, preferably zinc dithiocarbamate or cadmium dithiocarbamate, more preferably zinc dithiocarbamate. Preferably, the dithiocarbamate salt is a dialkyldithiocarbamate, where each alkyl group is independently selected from the group consisting of C 1-10 Alkyl, preferably C 2-5 It is preferably alkyl, more preferably ethyl. In certain embodiments, the metal precursors used in steps (b) and (c) of the method according to the present invention are both zinc diethyldithiocarbamate. In one embodiment, the metal precursors used in steps (b) and (c) of the method according to the present invention are both metal oleates, stearates, or myristates, preferably zinc oleate, cadmium oleate, zinc stearate, cadmium stearate, zinc myristate, or cadmium myristate, more preferably zinc oleate, zinc stearate, or zinc myristate.

[0069] In some embodiments, the metal precursors used in steps (b) and (c) of the method according to the invention are zinc or cadmium precursors, preferably zinc precursors. In some embodiments, the metal precursors used in steps (b) and (c) of the method according to the invention are both zinc or cadmium carboxylates, preferably zinc carboxylates. In some embodiments, the metal precursors used in steps (b) and (c) of the method according to the invention are both zinc thiolate or cadmium thiolate, preferably zinc thiolate. In certain embodiments, the metal precursors used in steps (b) and (c) of the method according to the present invention are both zinc oleate.

[0070] In one embodiment, the metal precursor used in steps (b) and (c) of the method according to the invention is a mixture of both zinc and cadmium precursors, preferably a mixture of zinc and cadmium carboxylates, more preferably zinc C 10-22 Carboxylate and Cadmium C 10-22 A mixture of carboxylates is even more preferred, a mixture of zinc oleate and cadmium oleate, or zinc stearate and cadmium stearate, or zinc myristate or cadmium chamyristate, and most preferred is a mixture of zinc oleate and cadmium oleate. In one embodiment, the metal precursors used in steps (b) and (c) of the method according to the invention are both mixtures of zinc and cadmium precursors, preferably mixtures of zinc and cadmium carboxylates as defined above, with the molar ratio Cd / (Cd+Zn) in each of these mixtures being between 0.001 and 1.0, more preferably from 0.02 to 0.2, and most preferably from 0.025 to 0.133.

[0071] In certain embodiments, the metal precursor used in step (b) of the process according to the invention is a zinc precursor, preferably a zinc carboxylate, and the metal carboxylate used in step (c) of the process according to the invention is a mixture of a zinc precursor and a cadmium precursor, preferably a mixture of a zinc carboxylate and a cadmium carboxylate. In these embodiments, the precursor is preferably C 10-22 The Cd / (Cd+Zn) molar ratio in the mixture is preferably from 0.001 to 1.0, more preferably from 0.02 to 0.2, more preferably from 0.025 to 0.133. In one embodiment, the core is InP, the metal precursor used in step (b) is a zinc carboxylate, preferably zinc oleate, and the metal precursor used in step (c) is a mixture of a zinc carboxylate and a cadmium carboxylate, preferably zinc oleate and cadmium oleate, preferably in a mixture with a molar ratio of Cd / (Cd+Zn) of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InP / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S.

[0072] This type of InP / ZnSe / ZnS quantum dots is highly efficient and narrow emitter in the visible spectrum, making it useful, for example, as luminescence downconverters in LED displays. In one embodiment, the core is InGaP, the metal precursor used in step (b) is a zinc carboxylate, preferably zinc oleate, and the metal precursor used in step (c) is a mixture of a zinc carboxylate and a cadmium carboxylate, preferably zinc oleate and cadmium oleate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InGaP / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S.

[0073] In one embodiment, the core is InAs, the metal precursor used in step (b) is a zinc carboxylate, preferably zinc oleate, and the metal precursor used in step (c) is a mixture of a zinc carboxylate and a cadmium carboxylate, preferably zinc oleate and cadmium oleate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InPAs / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S. In one embodiment, the core is InSb, the metal precursor used in step (b) is a zinc carboxylate, preferably zinc oleate, and the metal precursor used in step (c) is a mixture of a zinc carboxylate and a cadmium carboxylate, preferably zinc oleate and cadmium oleate, preferably in a mixture with a molar ratio of Cd / (Cd+Zn) of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InPSb / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S.

[0074] In one embodiment, the core is InSbAs, the metal precursor used in step (b) is a zinc carboxylate, preferably zinc oleate, and the metal precursor used in step (c) is a mixture of a zinc carboxylate and a cadmium carboxylate, preferably zinc oleate and cadmium oleate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InSbAs / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S. In one embodiment, the core is InP, the metal precursor used in step (b) is zinc thiolate, and the metal precursor used in step (c) is a mixture of zinc thiolate and cadmium thiolate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InP / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD xIt can be represented by S.

[0075] In one embodiment, the core is InGaP, the metal precursor used in step (b) is a thiolate, and the metal precursor used in step (c) is a mixture of zinc thiolate and cadmium thiolate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InGaP / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S. In one embodiment, the core is InAs, the metal precursor used in step (b) is zinc thiolate, and the metal precursor used in step (c) is a mixture of zinc thiolate and cadmium thiolate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InPAs / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S.

[0076] In one embodiment, the core is InSb, the metal precursor used in step (b) is zinc thiolate, and the metal precursor used in step (c) is a mixture of zinc thiolate and cadmium thiolate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InPSb / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S. In one embodiment, the core is InSbAs, the metal precursor used in step (b) is zinc thiolate, and the metal precursor used in step (c) is a mixture of zinc thiolate and cadmium thiolate, preferably with a molar ratio of Cd / (Cd+Zn) in the mixture of 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. The resulting quantum dots are InSbAs / ZnSe / Zn, where x is preferably 0.001 to 1.0, 0.02 to 0.2, or 0.025 to 0.133. 1-x CD x It can be represented by S.

[0077] In some embodiments, the method of the present invention includes a step (d) of forming a ligand layer on the second layer. Quantum dots prepared via such a method result in quantum dots that include a core, a first layer on the core, a second layer on the first layer, and a ligand layer on the second layer. The ligand layer may also be referred to as a ligand shell, a third shell or layer, or an outer shell or layer. In some embodiments, the first layer, second layer, and third layer are (hemi)spherical layers arranged concentrically around the core. In some embodiments, the first layer surrounds the core, the second layer surrounds the second layer, and the ligand layer surrounds the second layer.

[0078] In certain embodiments, the ligand layer comprises an organic compound. Preferably, the ligand layer consists essentially of one or more organic compounds. In this context, the organic compounds may be referred to as organic ligands. It is understood that the organic compound may be an organic moiety bound to another layer, preferably the second layer, contained in the quantum dot. For example, a ligand layer containing a thiol may mean that the -SH moiety of the thiol binds to ZnS contained in the second layer. Therefore, the number of organic compounds or ligands contained in the ligand layer includes the number of organic moieties bound to other layers.

[0079] In some embodiments, the ligand layer comprises from 10 to 2000, from 10 to 1900, from 10 to 1800, from 10 to 1700, from 10 to 1600, from 10 to 1500, from 10 to 1400, from 10 to 1300, from 10 to 1200, from 10 to 1100, from 10 to 1000, from 10 to 900, from 10 to 800, from 10 to 700, from 10 to 600, from 10 to 500, from 10 to 400, from 10 to 300 organics, from 50 to 800, from 100 to 700, from 150 to 600, or from 200 to 500 organic ligands (per quantum dot). In some embodiments, the ligand layer comprises oleylamine.

[0080] In an embodiment, the method according to the present invention comprises steps (b) and / or (c) at a temperature between 180°C and 350°C, between 180°C and 340°C, between 180°C and 330°C, between 180°C and 320°C, between 180°C and 310°C, between 180°C and 300°C, between 180°C and 290°C, between 180°C and 280°C, between 180°C and 270°C, between 180°C and 260°C, between 180°C and 250°C, between 190°C and 350°C, between 190°C and 340°C. , 190℃ to 330℃, 190℃ to 320℃, 190℃ to 310℃, 190℃ to 300℃, 190℃ to 290℃, 190℃ to 280℃, 190℃ to 270℃, 190℃ to 260℃, 190℃ to 250℃, 200℃ to 350℃, 200℃ to 340℃, 200℃ to 330℃, 200℃ to 320℃, 200℃ to 310℃, 200℃ to 300℃, 200℃ to 290℃, 200℃ to 2 Up to 80°C, 200°C to 270°C, 200°C to 260°C, 200°C to 250°C, 210°C to 350°C, 210°C to 340°C, 210°C to 330°C, 210°C to 320°C, 210°C to 310°C, 210°C to 300°C, 210°C to 290°C, 210°C to 280°C, 210°C to 270°C, 210°C to 260°C, 210°C to 250°C, 220°C to 350°C, 220°C to 340°C, 22 The process may be carried out at a temperature of from 0°C to 330°C, from 220°C to 320°C, from 220°C to 310°C, from 220°C to 300°C, from 220°C to 290°C, from 220°C to 280°C, from 220°C to 270°C, from 220°C to 260°C, from 220°C to 250°C, from 230°C to 350°C, from 230°C to 340°C, from 230°C to 330°C, from 230°C to 320°C, from 230°C to 310°C, from 230°C to 300°C, from 230°C to 290°C, from 230°C to 280°C, from 230°C to 270°C, from 230°C to 260°C, or from 230°C to 250°C.

[0081] In certain embodiments, step (b) included in the method according to the present invention has a reaction time of 5 to 60 minutes, 5 to 55 minutes, 5 to 50 minutes, 5 to 45 minutes, 5 to 40 minutes, 10 to 60 minutes, 10 to 55 minutes, 10 to 50 minutes, 10 to 45 minutes, 10 to 40 minutes, 20 to 60 minutes, 20 to 55 minutes, 20 to 50 minutes, 20 to 45 minutes, or 20 to 40 minutes. In certain embodiments, the step (c) included in the method according to the present invention has a reaction time of 1 to 30 minutes, 1 to 25 minutes, 1 to 20 minutes, 5 to 30 minutes, 5 to 25 minutes, or 5 to 20 minutes.

[0082] In one embodiment: - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 1 to 30 minutes; or - the process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes and step (c) having a reaction time of 1 to 30 minutes; or - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 5 to 20 minutes; or The process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes, and the process according to the invention comprises step (c) having a reaction time of 5 to 20 minutes.

[0083] In one embodiment: - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 1 to 30 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 350°C; or - the process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes and step (c) having a reaction time of 1 to 30 minutes, step (b) and / or step (c) being carried out at a temperature of 200°C to 350°C; or - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 350°C; or - the process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes and step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 350°C; or - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 1 to 30 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 300°C; or - the process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes and step (c) having a reaction time of 1 to 30 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 300°C; or - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 300°C; or The process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes, and the process according to the invention comprises step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 300°C. - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 1 to 30 minutes, step (b) and / or step (c) being carried out at a temperature of 200°C to 250°C; or - the process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes and step (c) having a reaction time of 1 to 30 minutes, step (b) and / or step (c) being carried out at a temperature of 200°C to 250°C; or - the process according to the invention comprises step (b) having a reaction time of 15 to 45 minutes and step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 200°C to 250°C; or The process according to the invention comprises step (b) having a reaction time of 20 to 40 minutes, and the process according to the invention comprises step (c) having a reaction time of 5 to 20 minutes, and step (b) and / or step (c) being carried out at a temperature of 300°C to 250°C.

[0084] In a further aspect, the present invention provides quantum dots obtained, obtainable or prepared by any method according to the invention as described herein, such quantum dots may be referred to as quantum dots according to the invention. In a further aspect, the present invention provides a polymer film comprising quantum dots according to the present invention, which retain their advantageous properties even when embedded in a solid layer of polymer film, such a polymer film may be referred to as a polymer film according to the present invention.

[0085] In a further aspect, the present invention provides a luminescence downconverter for downconverting optical frequencies, comprising a quantum dot according to the present invention or a polymer film according to the present invention. Within the context of this specification, a luminescence downconverter is a device capable of converting light having a high frequency into light having a lower frequency (i.e., downconversion). The properties of the quantum dots according to the present invention are particularly advantageous for downconversion. In a further aspect, the present invention provides a method for preparing a luminescence downconverter, the method comprising a method for preparing a quantum dot according to the present invention.

[0086] In this document and its claims, the verb "comprise" and its conjugations are used in an open-ended sense, meaning that the items following the word are included, but items not specifically mentioned are not excluded. Additionally, the verb "consisting of" may be replaced with "consisting essentially of," meaning that the product, assay device, each corresponding method, or use as defined herein may include additional components, each corresponding additional step, other than those specifically identified, without altering the inherent characteristics of the invention. Additionally, the reference of an element by the indefinite article "a" or "an" does not exclude the possibility that a plurality of elements is present, unless the context clearly requires only one element. Thus, the indefinite article "a" or "an" normally means "at least one." All patents and publications cited herein are incorporated by reference in their entirety.

[0087] The present invention will now be explained in more detail by means of a number of examples, which should not be construed as limiting the scope of the invention. The invention is not limited to the implementations described in the illustrative cases. The invention also extends to the combination of each of the means described above, independently of each other.

[0088] Example 1 - InP / ZnSe / ZnS synthesis InP synthesis InP cores are synthesized by mixing InCl3 and ZnCl2 in oleylamine and injecting a phosphor precursor (eg, tris(diethylamino)phosphine) at high temperature (180°C).

[0089] InP / ZnSe synthesis Addition of 5 mol% DPP to the selenium-saturated (2.24 M) TOP-Se precursor prior to injection leads to quantum dots with higher photoluminescence quantum yields (PLQY) than those synthesized without the addition of DPP to TOP-Se. In both cases, the same InP nanocrystals are used as cores, and the same synthesis conditions and amounts are maintained.

[0090] Figure 1 shows an example of the evolution of quantum dot emission properties during synthesis. QDs synthesized with DPP added to the TOP-Se precursor exhibit an overall higher relative PLQY than QDs synthesized without DPP. When DPP is used, the PLQY increases sixfold at the end of ZnSe shell growth. For reproducibility purposes, absolute PLQY measurements were performed from another synthesis under the same conditions (and with the addition of DPP-ZnSe), and the same trend of high, stable PL increasing during the reaction was observed. Figure 1 (right) shows the absolute PLQY values ​​at these points. At this point, a PLQY of 40-60% is observed for InP / ZnSe. This is a significant increase from InP / ZnSe synthesized without DPP, which had an estimated PLQY in the range of 5-15%. Shell growth is complete in 30 minutes.

[0091] InP / ZnSe / ZnS synthesis Growth of ZnS on the outer shell is more difficult than that of ZnSe. Using TOP-S and Zn oleate as precursors at 300 °C does not provide evidence of ZnS shell growth. Figure 2 shows the absorption and emission spectra and peak parameters for an aliquot taken during the formation of hypothetical ZnS on InP / ZnSe quantum dots. No growth is observed in the absorption spectrum, and no significant changes in the emission peaks are observed. The growth of ZnS can be achieved by increasing the reactivity of one of the precursors using either a more reactive Zn carboxylate (e.g., acetate) or a more reactive phosphine (e.g., DPP, diphenylphosphine). DPP reacts with sulfur to form a white precipitate, DPP- (diphenylphosphine sulfide). DPP-S can be dissolved in TOP-S, and in these experiments, a 15 mol% DPP-S / TOP-S solution is used for the synthesis. The results, shown in Figure 2, show a significant increase in PL (photoluminescence).

[0092] Fully Synthetic Finally, we were able to synthesize high-QY InP / ZnSe / ZnS quantum dots by integrating three previous results: DPP in TOP-Se for a brighter ZnSe shell, and DPP-S in TOP-S for the formation of a ZnS shell with Zn oleate. Figure 5 summarizes the absolute quantum yield measurements for ZnSe, ZnS, and the purification steps in the final synthesis. The resulting QDs exhibit PLQYs of 90–95% at the final synthesis stage. The final chemical yields of S and Se in the ZnS and ZnSe shells with the addition of DPP are 85% and 75%, respectively. During the purification steps using various anti-solvents (ethanol and acetone), the PLQY remains above 90% and shows a slight increase towards 100%.

Claims

1. 1. A method for preparing quantum dots, comprising the steps of: (a) A core of a binary, ternary, or quaternary material containing the following elements: - one or more first core elements selected from the group consisting of In, Ga, and Al, and - one or more second core elements selected from the group consisting of P, As, and Sb; preparing the core comprising: (b) forming a first layer on the core by contacting the core with a mixture comprising a metal precursor, a secondary phosphine selenide, and a tertiary phosphine selenide; (c) forming a second layer on the first layer by contacting the product of step (b) with a mixture comprising a metal precursor, a secondary phosphine sulfide, and a tertiary phosphine sulfide. The method comprising:

2. 2. The method of claim 1, wherein one of the first core elements is In, and preferably the binary, ternary, or quaternary material is InP, InGaP, InAs, InSb, or InSbAs.

3. 3. The method of claim 1, wherein the secondary phosphine selenide is diphenylphosphine selenide, di-2-norbornylphosphine selenide, di-isobutylphosphine selenide, di-tert-butylphosphine selenide, dicyclopentylphosphine selenide, dicyclohexylphosphine selenide, or 9-phosphabicyclononane selenide.

4. The method according to any one of claims 1 to 3, wherein the tertiary phosphine selenide is a trialkylphosphine selenide.

5. 5. The method of claim 4, wherein the trialkylphosphine selenide is tri-n-octylphosphine selenide (TOP-Se).

6. 6. The method of claim 1, wherein the second phosphine selenide is a trialkylphosphine sulfide.

7. 7. The method of claim 6, wherein the trialkylphosphine selenide is tri-n-octylphosphine sulfide (TOP-S).

8. The method according to any one of claims 1 to 7, wherein the metal used in step (b) and / or step (c) is zinc or cadmium, preferably zinc.

9. 9. The method according to any one of claims 1 to 8, wherein the metal carboxylate used in step (b) and / or step (c) is a metal carboxylate or a metal thiolate, preferably a metal oleate, a metal stearate or a metal myristate.

10. A method according to any one of claims 1 to 9, wherein step (b) and / or step (c) is carried out at a temperature of from 200°C to 350°C, preferably from 200°C to 300°C.

11. The method according to any one of claims 1 to 10, wherein step (b) has a reaction time of from 15 to 45 minutes, preferably from 20 to 40 minutes.

12. The method according to any one of claims 1 to 11, wherein step (c) has a reaction time of from 1 to 30 minutes, preferably from 5 to 20 minutes.

13. 13. The method according to any one of claims 1 to 12, wherein the molar ratio between diphenylphosphine selenide and the second phosphine selenide is from 40% to 60%.

14. 14. The process according to any one of claims 1 to 13, wherein the molar ratio between diphenylphosphine sulfide and the second phosphine sulfide is from 40% to 60%.

15. Quantum dots obtainable by the method according to any one of claims 1 to 14.

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