WO2019081404A1

WO2019081404A1 - Quantum dots based on indium phosphide

Info

Publication number: WO2019081404A1
Application number: PCT/EP2018/078845
Authority: WO
Inventors: David MOCATTA; Amir Holtzman
Original assignee: Merck Patent Gmbh
Priority date: 2017-10-24
Filing date: 2018-10-22
Publication date: 2019-05-02
Also published as: TW201930556A

Abstract

The present invention relates to quantum dots (QD) based on indium phosphide (InP), a method for the preparation of said quantum dots, optical medium and an optical device.

Description

Quantum dots based on indium phosphide

Field of the invention

Background Art

Quantum dots are known in the prior arts. Quantum dots (QD) are a class of materials that offer various promising applications in fields related to light emission and absorption, e.g. in fields such as in-vivo imaging, light- emitting device manufacture, photodetection and solar energy conversion. For example, quantum dots may find application in transistors, solar cells, LEDs, diode lasers, medical imaging, quantum computing and a variety of other fields. Furthermore, QDs emitting in the visible electromagnetic spectrum may be of particular interest for lighting and display applications, e.g. for high brightness LEDs. A quantum dot may be sufficiently small to exhibit distinct quantum mechanical properties. A single QD can for example contain about 100 to even 100000 atoms, having a diameter that ranges from about 10 to 50 or more atoms, e.g. a diameter in the range of about 2 to about 10 nanometers. For example, three-dimensional confinement of the nanocrystal exciton states can be achieved, such that intermediate properties are obtained between those of the bulk material and discrete molecules. Therefore, the characteristics of a quantum dot may be closely related to its size and shape, e.g. the band gap, which determines the frequency range of emitted light, may be inversely related to its size. Monodisperse ensembles of QDs may feature a narrow, size-tunable emission spectrum, while also being particularly suitable for solution-based processing. Colloidal synthesis of nanocrystals may comprise the synthesis from precursor compounds in a solution. When heating the solution, the decomposed precursors form monomers that nucleate. Known QDs obtainable by colloidal synthesis may comprise binary compounds, such as lead sulfide, lead selenide, cadmium selenide, cadmium sulfide, indium arsenide and indium phosphide, or ternary compounds such as cadmium selenide sulfide. Particular nanocrystals known in the art may involve cadmium chalcogenide based materials where especially CdSe QDs synthesis is a fully mastered process. Such nanocrystal can be easily manufactured due to the simplicity of their synthesis, and may have a high optical quality.

However, cadmium is a toxic heavy element which may be subject to legal restrictions, e.g. by the EU OHS directive. Consequently, the use of such materials in large amounts is preferably avoided. Furthermore, the high toxicity may limit the applicability of cadmium chalcogenide based materials, e.g. in in-vivo imaging. In addition to a low toxicity, a cost-efficient production at an industrial scale can also be considered highly

advantageous when scaling the use of nanocrystals from an academic setting to commercial product applications.

Cadmium-free alternatives for manufacturing quantum dots are known in the art, such as CulnS2 and InP. Particularly indium phosphide (InP) QDs are known that have emission characteristics similar to CdSe QDs, while advantageously having a lower toxicity. Methods for colloidally

manufacturing InP nanocrystals are known in the art.

US 2015/0083969 A1 discloses an lnP/ZnS(F) core/shell nanocrystal particle. WO 2016/146719 A1 mentions a method for synthesizing nanoparticles by mixing a first precursor material comprising a first compound comprising a halide moiety and a metal or a metalloid, a second precursor material comprising a second compound comprising a polyatomic nonmetal, and a solvent and by heating up the mixture. US 8679543 B2 describes a coated InP/ZnS core /shell nanocrystal.

D. Gary et al, JACS, 2016, 138, 1510-1513, describes single-crystal and electronic structure of a 1 .3nm Indium Phosphide nanoclusters (Magic- Sized nanoclusters) and a method for preparation of thereof.

D.Gary et al., Chem. Mater., 2015, 27, 1432-1441 , discloses InP quantum dots via magic sized cluster intermediates exhibiting no light emission.

J. Ning, U. Banin, ChemComm, 2017, 53, 2626-2629 describes Magic Size InP and InAs clusters, synthesis of thereof and shelling. A light emission was observed from InP/ZnS core/shell nanocrystals.

D. Gary et al, ChemComm, 2016, 00, 161 discloses a reaction scheme between ln37P2o(O2CR)si and primary amine.

Quantum dots obtainable according to prior art documents could be used. However, it is a permanent desire to improve the features of these quantum dots. Therefore, it is an object of embodiments of the present invention to provide quantum dots having improved color purity and efficiency.

It is an object of embodiments of the present invention to provide an efficient and/or cheap method for production of improved quantum dots.

The above objective is accomplished by quantum dots and a method for producing the same according to the present invention. Summary of the invention Surprisingly, the inventors have found that quantum dots (QD) based on indium phosphide (InP) exhibiting a peak maximum in the

photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of at most 35 nm measured at 25°C using a toluene solution solves one or more of the problems mentioned above. Preferably said method of the present invention solves all the problems mentioned above at the same time.

In another aspect, the present invention relates to a method for preparing QD being based on InP.

In another aspect, the present invention also relates to QD being obtainable by a method for preparing QD.

In another aspect, the present invention further relates to composition comprising QD being based on InP.

In another aspect, the present invention also relates to an optical medium comprising QD being based on InP.

Detailed description of the invention

The present invention provides quantum dots (QD) based on indium phosphide (InP) characterized in that the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of at most 35 nm measured at 25°C using a toluene solution. Quantum dots (QD) are well known in the art as described above.

Conventionally QD are a nanosized light emitting semiconductor material. According to the present invention, the term "nanosized" means the size in between 0,1 nm and 999 nm.

Thus, according to the present invention, the term ^"a nanosized light emitting semiconductor material^" is taken to mean that the light emitting material which size of the overall diameter is in the range from 0.5 nm to 999 nm. And in case of the material has elongated shape, the length of the overall structures of the light emitting material is in the range from 0.5 nm to 999 nm.

According to the present invention, the term "nano sized" means the size of the semiconductor material itself without ligands or another surface modification, which can show the quantum size effect.

According to the present invention, a type of shape of the core of the nanosized light emitting material, and shape of the nanosized light emitting material to be synthesized are not particularly limited.

For examples, spherical shaped, elongated shaped, star shaped, polyhedron shaped, pyramidal shaped, tetrapod shaped, tetrahedron shaped, platelet shaped, cone shaped, and irregular shaped nanosized light emitting materials can be synthesized.

The present QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of at most 35 nm preferably at most 30 nm, more preferably at most 25 nm, even more preferably at most 20 nm measured at 25°C using a toluene solution. Preferably, the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of preferably at least 8 nm, more preferably at least 10 nm, even more preferably at least 15 nm measured at 25°C using a toluene.

In a preferred embodiment, the QD preferably exhibit a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) in the range of 8 nm to 35 nm, preferably 10 nm to 30, more preferably at least 15 nm to 25 nm, measured at 25°C using a toluene.

Preferably, the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength in the range of 402 to 600 nm and a full width half maximum (FWHM) of at most 35 nm, preferably at most 30 nm, more preferably at most 25 nm, even more preferably at most 20 nm measured at 25°C using a toluene solution.

Preferably, the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength in the range of 402 to 600 nm and a full width half maximum (FWHM) of preferably at least 8 nm, more preferably at least 10 nm, even more preferably at least 15 nm measured at 25°C using a toluene.

In a preferred embodiment, the QD preferably exhibit a peak maximum in the photoluminescence spectrum at a wavelength in the range of 402 to 600 nm and a full width half maximum (FWHM) in the range of 8 nm to 35 nm, preferably 10 nm to 30, more preferably at least 15 nm to 25 nm, measured at 25°C using a toluene. Preferably, the data concerning the peak maximum in the

photoluminescence is obtained using a toluene solution of quantum material with an optical density (OD) of 0.09 at the excitation wavelength of 350nm on a Jasco FP-8300 spectrophotometer. The FWHM of full -width- half-maximum is the width of the exciton peak measured at half the maximum emission counts. Preferably, the determination of the full width half maximum (FWHM) is made with an appropriate data base preferably comprising at least 10, more preferably at least 20 and even more preferably at least 50 data points. The determination is preferably performed by using LabVIEW Software

(LabVIEW 2017; May 2017) with the following Vis (Virtual Instrument): 1 . 'Peak detector' for finding center wavelength and y-value (counts).

The following parameters are preferably used: width: 10, threshold: maximum value of input data divided by 5.

2. Dividing the counts (y-value) at the center wavelength value (see item 1 ) by 2 giving the y-value for the half-width of the peak. The two points having this half-width y-value were found and the difference between their two wavelength values were taken to give the FWHM parameter.

Preferably, present QD exhibit a ratio of the peak maximum to the peak minimum in the absorption spectrum of at least 5, more preferably at least 5.5, even more preferably at least 6, even more preferably at least 7 and even more preferably of at least 8.5. In a further preferred embodiment, present QD exhibit a ratio of the peak maximum to the peak minimum in the absorption spectrum in the range of 5.5 to 15, more preferably in the range of 6 to 9 and even more preferably of 7 to 9 measured, most preferably in the range of 8 to 9. The ratio of the peak maximum to the peak minimum is measured using a toluene solution in a quartz 1 cm path length cuvette with an optical density (OD) of 0.09 at 350nm on a Shimadzu UV-1800 spectrophotometer at 25°C. The ratio of the peak maximum to the peak minimum is the ratio of the OD of the first exciton peak and the trough on the lower wavelength side of that peak. Preferably, the ratio of the peak maximum to the peak minimum in the absorption spectrum is related to the first exciton peak. Preferably, the peak maximum of the present QD is at a wavelength above 385 nm, more preferably above 390 nm. Preferably, the QD exhibit a peak maximum in the absorption spectrum at a wavelength in the range of 390 to 400 nm. According to the present invention, the QD are based on indium phosphide (InP). Therefore, the present QD comprise a considerable amount of InP. Preferably, the QD comprise a centre area of InP. More preferably, the centre area of InP comprises a diameter in the range of 0.8 to 5.0 nm, preferably 0.9 nm to 3.0 nm, more preferably 1 .0 to 1 .5 nm. The size of the particles can be obtained by methods well known in the art. The particle size distribution is preferably assessed with Gatan Digital Micrograph software using images obtained from High Resolution Transmission Electron Microscopy (HRTEM) and provided as arithmetic mean (number average).

The sample preparation for performing the HRTEM can be performed by any conventional method. Preferably, the sample is purified before the measurement. E.g. 0.2ml of the crude sample is dissolved in 0.2ml of chloroform; 1 .6ml of acetone is then added and the mixture is precipitated by centrifuge (5 minutes, 5Krpm). Then the precipitant is dissolved in 0.5ml of chloroform, and 30uL from this solution is dropped on a Cu/C TEM grid with ultrathin amorphous carbon layer. The grid is dried in vacuum at 80°C for 1 .5h to remove the residues of the solvent as well as possible organic residues.

HRTEM and/or other TEM measurements are preferably carried out on a Tecnai F20 G2 machine equipped with EDAX Energy Dispersive X-Ray Spectrometer. in a preferred embodiment, the QD are based on magic sized clusters comprising indium phosphide, more preferably the QD are based on magic sized clusters essentially consisting of indium phosphide (MSC InP). Magic sized clusters (MSC) are well known in the art. MSC have a well-defined composition and exhibit remarkable thermodynamic stability relative to similar sizes. In a further embodiment, the Quantum Dots (QD) based on Indium

Phosphide (InP) comprises a high amount of InP, preferably the QD comprise at least 50 % by weight, more preferably 70 % by weight and even more preferably at least 90 % by weight InP as semiconducting material. InP means a material comprising In and P independent on the ratio of these materials. As mentioned above and below the QD may comprise a ligand. The amount of ligand is not considered as component in order to determine the amount of InP.

Preferably, the QD are based on a nanocrystal core, which consists solely of fused 6-membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo-tetrahedral arrangement. The nanocrystal core preferably have the formula [ln₂i P2o]³⁺, [ln₄₂P4o]⁶⁺, [InesPeo]^9*, [ln₈4P8o]¹²⁺, [ln₉₅P9o]¹⁵⁺, [ln₃iP₃o]³⁺, [Ιη₄ιΡ₄₀]³⁺, [Ιη₅ι Ρ₅ο]³⁺, [Ιη₆ιΡ₆ο]³⁺, [ln₇iP₇o]³⁺,

[Ιη8ΐ Ρδο]³⁺, [lngi P9o]³⁺. In this preferred embodiment the subset of atoms preferably possesses a C2 rotation axis that bisects two phosphorus atoms and a single indium atom located at the center of the particle, and measures approximately 1 .3 nm ^χ 1 .0 nm ^χ 1 .0 nm. A dihedral angle of 160 ± 3° is consistent along the longest straight In-P. The average In-P bond length in the [ln₂i P2o]³⁺. core is 2.528 A (min 2.479 A, max 2.624 A), and the average P- In-P bond angle is 109.2° (min 97.7°, max 1 19.9°).

Preferably, an additional 16 indium atoms are singly bound to this core through surface-exposed phosphorus atoms, with an average bond length of 2.482 A (min 2.450 A, max 2.515 A). Preferably, the sum of the single- bond covalent radii for In and P is 2.53 A and it is preferably inferred that the bonding in the inorganic core of this cluster may be best viewed as covalent in nature, with differences in bond lengths between In-P in the core and In-P at the surface arising from internal strain. The structure is preferably assessed using single-crystal X-ray diffraction at 25°C as well known in the art. (see J. Am. Chem. Soc. 2016, 138, 1510-1513). It should be noted that the core of the present QD may comprise additional InP or areas having another structure. Preferably, the area comprising the preferred structure as mentioned above is at least 30% by volume, more preferably at least 50% by volume and even more preferably at least 70 % by volume.

In some embodiments of the present invention, the QD preferably have a relative quantum yield of at least 1 .5%, more preferably at least 2.5% and even more preferably at least 3% measured by calculating the ratio of the emission counts of the QD and the known dye quinine bisulfate (CAS 549- 56-4) and multiplying by the known QY of the dye (55%) measured at 25°C.

The relative quantum yield is preferably calculated using absorbance and emission spectrum (excited at 350 nm), obtained using Shimadzu UV-1800 and Jasco FP-8300 spectrophotometer, using the following formula, with quinine bisulfate dye in ethanol is used as a reference, with a quantum yield of 55%

QY = QYref

ref wherein the symbols have the following meaning

QY = Quantum Yield of the sample

QYref = Quantum Yield of the reference/standard

n = the refractive index of the sample solvent (especially ethanol) n_ref = the refractive index of the reference

I = the integral of the sample emission intensity as measured on the

Jasco. Calculated as \\ dv with I intensity, v =wavelength.

A = is the percentage absorbance of the sample. The percentage of the sampling light that the sample absorbs. Iref = the integral of the reference emission intensity as measured on the Jasco. Calculated as Jl dv with I intensity, v =wavelength.

Aref = is the percentage absorbance of the reference. The

percentage of the sampling light that the reference absorbs.

The absorbance and emission spectrum is achieved at a temperature of about 25°C.

In some embodiments of the present invention, the surface of the quantum dots can be over coated with one or more kinds of surface ligands.

Without wishing to be bound by theory it is believed that such a surface ligands may lead to disperse the nanosized material in a solvent more easily. In addition, the surface ligand may improve the features of the quantum dots such as efficiency, wavelength of the peak maximum and full width half maximum (FWHM).

In some embodiments of the present invention, the QD preferably comprise a ligand.

The surface ligands in common use include phosphines and phosphine oxides such as Trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), and Tributylphosphine (TBP); phosphonic acids such as

Dodecylphosphonic acid (DDPA), Tetradecylphosphonic acid (TDPA), Octadecylphosphonic acid (ODPA), and Hexylphosphonic acid (HPA); amines such as Oleylamine, Dedecyl amine (DDA), Tetradecyl amine (TDA), Hexadecyl amine (HDA), and Octadecyl amine (ODA), Oleylamine (OLA), alkenes, such as 1 -Octadecene (ODE), thiols such as hexadecane thiol and hexane thiol; mercapto carboxylic acids such as mercapto propionic acid and mercaptoundecanoicacid; carboxylic acids such as oleic acid, stearic acid, myristic acid; acetic acid and a combination of any of these. Polyethylenimine (PEI) also can be used preferably. The ligands mentioned above, especially the acids, can be used in acidic form and/or as a salt. The person skilled in the art will be aware that the ligand will bind to the core in an appropriate manner, e.g. the acids may get deprotonated.

Examples of surface ligands have been described in, for example, the laid- open international patent application No. WO 2012/059931 A. Preferably, the QD comprise a carboxylate ligand, more preferably a carboxylate ligand having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms, even more preferably a carboxylate ligand selected from the group consisting of myristate, palmitate, laurate, stearate, oleate; and/or a phosphorus containing ligand, such as phosphine ligands, preferably alkyl phosphine ligands having 3 to 108 carbon atoms, phosphine oxide ligands, preferably alkyl phosphine oxide having 3 to 108 carbon atoms and/or phosphonate ligands, more preferably an alkyl phosphonate ligand having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group even more preferably a phosphonate ligand selected from the group consisting of octadecylphosphonate, dodecylphosphonate,

tetradecylphosphonate, hexadecylphosphonate; and/or amines, preferably primary or secondary amines having 1 -36 carbon atoms, preferably 6 to 30.

In view of the ligands mentioned above, phosphonate ligands are preferred, such as Dodecylphosphonate, Tetradecylphosphonate,

Octadecylphosphonate, and Hexylphosphonate; According to a special embodiment, the quantum dots may comprise a core / shell structure. Consequently, the QD may comprise a shell of a

semiconductor. According to the present invention, the term ^"core / shell structure^" means the structure having a core part and at least one shell part covering said core.

In some embodiments of the present invention, a quantum dot shell may comprise a shell of a semiconductor material comprising ll-VI, lll-V, or IV-VI semiconductors, or a combination of any of these. In some embodiments, as a combination, ternary or quaternary materials of II, III, IV, V, VI materials of the periodic table can be used.

For example, CdSe/CdS, CdSeS/CdZnS, CdSeS/CdS/ZnS, ZnSe/CdS, CdSe/ZnS, InP/ZnS, InP/ZnSe, InP/ZnSe/ZnS, InZnP/ZnS, InZnPS/ ZnS, InZnP/ZnSe/ZnS, ZnSe/CdS, ZnSe/ZnS or combination of any of these, can be used preferably. Preferably, the semiconducting material does not comprise Cd, more preferably the semiconducting material of the shell comprises ZnS and/or ZnSe. In an embodiment of the invention, the shell preferably has a thickness in the range of 0.3nm to 20nm, preferably 0.3nm to 10nm, measured by taking images on a 120kV TEM and measuring the diameter of the quantum material for a sample of more than 50 particles and provided as arithmetic mean (number average). The measurement is preferably performed using imageJ software or the software mentioned above. Preferably, the shell thickness is calculated by subtracting the shelled particle thickness from the literature value of the MSCs e. g. 1 .0 or 1 .3nm. Furthermore, the particle size of the shelled particles can be determined as mentioned above before shelling.

In some embodiments of the invention, the size of the overall structures of the quantum dots, is from 1 nm to 100 nm, more preferably, it is from 1 nm to 30 nm, even more preferably, it is from 2 nm to 15 nm. The size is measured according to the method mentioned above and is based on the arithmetic mean (number average).

A further subject matter of the present invention is a method for preparing quantum dots (QD) being based on indium phosphide (InP), characterized by preparing magic size cluster (MSC) of InP (MSC InP). Preferably, the method provides quantum dots (QD) based on indium phosphide (InP) exhibiting a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of at most 35 nm measured at 25° using a toluene solution. In addition thereto, the method provides the preferred embodiments of the quantum dots (QD) of the present invention as mentioned above and below.

In a preferred embodiment of the present invention, the preparation method of quantum dots (QD) preferably comprises a quenching step, wherein the quenching step more preferably includes a lowering of the temperature of a reaction mixture by at least 130 °C, preferably at least 150°C within a period of time less than 2 seconds, preferably less than 1 second. These data can be measured with any conventional method and is based on the average temperature decrease.

Preferably, the quenching step is performed by adding a solvent to the reaction mixture. More preferably, the solvent being added to the reaction mixture exhibits a temperature below 100 °C, more preferably below 50 °C, even more preferably below 30 °C, most preferably below 10 °C. Using the present method, it is possible to assess the temperature decrease based the temperature of the reaction mixture, the temperature of the solvent being added thereto, the volume of the reaction mixture, the power output of the heating element, the volume of the solvent being added thereto and the time span during which the solvent being added to the reaction mixture. Furthermore, the temperature of any device being in contact with the reaction mixture may have an influence to the data mentioned above, e. g. the temperature and power output of the heating mantle if used. Preferably, the volume ratio of the reaction mixture to the solvent being added to the reaction mixture is in the range of 4:1 to 1 :4 preferably 2:1 to 1 :2.

The magic size cluster (MSC) can be prepared by any method known in the art. Preferably, the preparation of the MSC InP is achieved by a reaction mixture comprising a phosphorus precursor being selected from the group consisting of organic phosphine compounds, preferably alkylsilyl phosphine compounds having 1 to 3 silicon atoms preferably alkylsilyl phosphine compounds having 1 to 30 carbon atoms, preferably 1 to 10 carbon atoms, even more preferably 1 to 4 carbon atoms, most preferably 1 or 2 carbon atoms in the alkyl groups or aryl silyl phosphine compounds, preferably aryl silyl phosphine compounds having 1 -3 silicon atoms preferably aryl silyl phosphine compounds having 6 to 30 carbon atoms, preferably 6 to 18 carbon atoms, even more preferably 6 to 12 carbon atoms, most preferably 6 or 10 carbon atoms in the aryl groups.

In addition to a phosphorus precursor, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising an indium precursor preferably being selected from the group consisting of indium carboxylates, more preferably indium carboxylates having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 16 carbon atoms.

The indium carboxylate is preferably selected from the group consisting of indium myristate, indium laurate, indium palmitate, indium stearate and indium oleate. Preferably, the phosphorous precursor comprises

tris(trimethylsilyl)phosphine and similar materials having an aryl, and/or alkyl group instead of the methyl unit, such as tris(triphenylsilyl)phosphine, tris(triethylsilyl)phosphine, tris(diphenylmethylsilyl)phosphine,

tris(phenyldimethylsilyl)phosphine, tris(triphenylsilyl)phosphine,

tris(triethylsilyl)phosphine, tris(diethylmethylsilyl)phosphine,

tris(ethyldimethylsilyl)phosphine.

In a specific embodiment, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising a phosphorus precursor and an indium precursor being different to the phosphorus precursor and the molar ratio of the phosphorus precursor to the indium precursor in the range of 1 :3 to 1 :1 , preferably 1 :2.5 to 1 :1 .

The preparation of the MSC InP is preferably achieved using a solvent. The solvent is not specifically restricted. Preferably, the solvent is selected from aldehydes, ketones, ethers, esters, amides, sulfur compounds,

hydrocarbons, halogenated hydrocarbons (e.g. chlorinated hydrocarbons), , unsaturated and saturated, aromatic or heteroaromatic hydrocarbons, halogenated aromatic or heteroaromatic hydrocarbons and/or, preferably cyclic hydrocarbons, terpenes, ketones, ethers and esters. More preferably, the solvent is selected from hydrocarbons, unsaturated and saturated, aromatic hydrocarbons, cyclic hydrocarbons, terpenes. Preferably a non- coordinating solvent is used.

Preferably, an alkane, more preferably a squalane is used as a solvent. Preferably, an alkane having 6 to 46 carbon atoms, more preferably 8 to 40 carbon atoms, even more preferably 12 to 34 carbon atoms, most preferably 16 to 30 carbon atoms is used as a solvent.

In some embodiments of the present invention, said another compound is a solvent selected from one or more members of the group consisting of squalene, squalane, heptadecane, octadecane, octadecene, nonadecane, icosane, henicosane, docosane, tricosane, pentacosane, hexacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, squalene unbranched and branched analogs, and their unsaturated analogs, with more preferably being of 1 -octadecene squalane,

pentacosane, hexacosane, octacosane, nonacosane, triacontane. More preferably squalane, pentacosane, hexacosane.

More preferably, the alkane being used as a solvent is a decane, dodecane, tetradecane, hexadecane, octadecane, eicosane. docosane, hexamethyltetracosane. The alkane may be linear or branched with branched alkanes such as squalane being preferred.

In an embodiment of the present invention, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene, preferably an alkene having 6 to 36 carbon atoms, more preferably 8 to 30 carbon atoms, even more preferably 12 to 24 carbon atoms, most preferably 16 to 20 carbon atoms. More preferably, the alkene is a 1 -alkene, such as 1 -decene, 1 -dodecene, 1 - Tetradecene, 1 -hexadecene, 1 -octadecene, 1 -eicosene. 1 -docosene. The alkene may be linear or branched.

Regarding the preparation step of the QD core, alkenes are preferred in view of the other solvents mentioned above. The temperature at which the reaction is performed is not critical. Surprising improvements can be obtained using a high reaction temperature.

Preferably, the preparation of the MSC InP is achieved at a temperature 1 10°C or above, more preferably 1 15°C or above. Preferably, the preparation of the MSC InP is achieved at a temperature in the range of 1 10 to 180°C, more preferably 1 15 to 140°C. In a specific embodiment, the preparation of the MSC InP is preferably achieved in the presence of a carboxylate compound, more preferably carboxylate compound having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms. More preferably, the carboxylate compound is a saturated carboxylate compound. The carboxylate compound could be added to the reaction mixture as a free acid or as a salt. Preferably, the carboxylate compound is added as a precursor, preferably an indium precursor wherein preferred indium precursors are disclosed above and below.

In a preferred embodiment, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are preferably reacted with a ligand in a second reaction step B).

Preferably, the ligand used in the second reaction step B) is a phosphonic acid, preferably an alkyl phosphonic acid having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group. The phosphonic acid can also be added as a salt. In a specific embodiment, the phosphonic acid is added as an indium salt. Preferably, an indium salt of an alkyl phosphonic acid having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group is used for the second reaction step B), such as indium octadecylphosphonate,

tetradecylphosphonate, indium dodecylphosphonate indium and indium hexylphosphonate.

In another embodiment, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are preferably purified before performing the second step B). The purification is preferably performed by adding a solvent to the mixture obtained in the first reaction step A) and preferably precipitating the MSC InP.

In a specific embodiment of the present invention, the magic size clusters (MSC) obtained in a reaction step and/or any product obtained using these MSC can be purified. This purification can be done as intermediate step or to obtain a purified quantum dots according to the present invention.

According to a special embodiment, the purification can be achieved by dispersing 0.1 to 10 equivalents of the crude solution in 1 equivalent of a solvent (by volume), preferably a hydrocarbon solvent, e. g. toluene, hexane, pentane or chloroform. Then, 0.5 to 20 equivalents (by volume) of a cleaning solution such as a ketone, alcohol, preferably acetone, methanol, ethanol or propanol, more preferably an ketone, e. g. acetone is preferably added to the composition. The resultant suspension is preferably centrifuged for a time and at a speed sufficient for a useful precipitation. E.g. good results are achieved with 5 min at a speed of 5000 rpm.

In some embodiments of the present invention, the cleaning solution comprises one compound selected from one or more members of the group consisting of ketones, such as, methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols, such as, methanol, ethanol, propanol, butanol, hexanol, cyclo hexanol, ethylene glycol; hexane; halogenated hydrocarbons, such as chloroform; xylene, and toluene, hexane and pentane.

In a preferred embodiment of the present invention, the cleaning solution comprises three parts the crude solution with the QDs, the solvent and the anti-solvent. The solvent is typically a non-polar compound preferably an alkane or a benzene derivative such as toluene or a halogenated hydrocarbon, more preferably toluene, chloroform, hexane and pentane. The anti-solvent is typically a polar compound such as an alcohol, ester or nitrogen containing compound, preferably methanol, ethanol, isopropanol, butanol, ethyl acetate and acetonitrile. The ratios of the crude, solvent and anti-solvent are in the ranges of 2.5:2.5:1 to 1 :20:80. In a preferred embodiment of the present invention, the cleaning solution comprises one or more of ketones to more effectively remove unreacted core precursors from the composition obtained in step A) and/or the composition obtained in step B) as mentioned above or any other reaction composition and remove e. g. the ligands leftovers.

More preferably, the cleaning solution contains one or more of ketones selected from the group consisting of methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone, and one more solvent selected from halogenated hydrocarbons, preferably chloroform, acetonitrile, ethyl acetate, xylene or toluene to remove unreacted core precursors from the composition obtained in step A) and/or the composition obtained in step B) as mentioned above or any other reaction composition and remove e. g. the ligands leftovers in the solution effectively. More preferably, the cleaning solution contains one or more of ketones selected from methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone, and chloroform.

In some embodiments of the present invention, the mixing ratio of ketones: chloroform can be 1 :2 - 20:1 in a molar ratio. Preferably it is 1 :1 - 5:1 to remove unreacted core precursors from the composition obtained in step A) and/or the ligands contained in the composition obtained in step B) as mentioned above or any other reaction composition and to remove e.g. the ligands leftovers in the solution.

More preferably, the cleaning removes the extra ligands and the unreacted precursor. Preferably, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in the first reaction step A) is preferably reacted with a ligand in a second reaction step B) at a high temperature.

Preferably, the second reaction step B) is performed at a reaction temperature above 100°C, preferably at a reaction temperature above 200°C, more preferably at a reaction temperature above 300°C and even more preferably at a reaction temperature above 350°C.

The upper temperature limit of the second reaction step B) is given by the temperature stability of the product. Preferably, the second reaction step B) is performed at a reaction temperature below 500°C, preferably at a reaction temperature below 450°C, more preferably at a reaction

temperature below 400°C and even more preferably at a reaction temperature above 390°C.

The reaction step B) could be performed in a solvent. Preferably, the solvents mentioned above could be used for performing the reaction step B). More preferably, a non-coordinating solvent is used. Even more preferably, an alkane, especially a squalane having 6 to 46 carbon atoms, more preferably 8 to 40 carbon atoms, even more preferably 12 to 34 carbon atoms, most preferably 16 to 30 carbon atoms is used as a solvent in reaction step B). Regarding the second reaction step B), alkanes are most preferred solvents.

According to a further aspect, the second reaction step B) is preferably stopped by quenching, preferably by lowering the temperature of a reaction mixture for preparing MSC InP by at least 130 °C, preferably at least 150°C within a period of time less than 2 seconds, preferably less than 1 second. Preferably, the second reaction step B) is stopped by adding a solvent to the reaction mixture. Preferably, the solvent exhibits a temperature below 100 °C, more preferably below 50 °C, even more preferably below 30 °C, most preferably below 10 °C.

In a specific embodiment, the volume ratio of the reaction mixture of the second reaction step B) to a solvent being added to the reaction mixture of the second reaction step B) is preferably in the range of 4 to 1 preferably 2 to 1 .

According to a further aspect of the method of the present invention, a shell of a semiconductor is grown onto the magic size cluster comprising indium phosphide (MSC InP) and/or the quantum dots of the present invention as mentioned above and below. In some embodiments of the present invention, said shell comprises group 12 and group 16 elements of the periodic table. Preferably the shell comprises ZnS or ZnSe

A further subject matter of the present invention are quantum dots (QD) being obtainable by a method of the present invention as described above and below.

In another aspect, the present invention also relates to a method for preparing quantum dots comprising a core / shell structure, wherein the method comprises following steps (a), (b) and (c) in this sequence.

(a) synthesis of a core in a solution,

(b) removing the extra ligands from the core

(c) coating the core with at least one shell layer using said solution obtained in step (b), In another aspect, the present invention further relates to a composition comprising or consisting of the QD of the present invention, preferably semiconducting light emitting nanoparticle of the present invention and at least one additional material, preferably the additional material is selected from the group consisting of organic light emitting materials, inorganic light emitting materials, charge transporting materials, scattering particles, host materials, and matrix materials.

A further embodiment of the present invention is a formulation comprising or consisting of the QD of the present invention, preferably semiconducting light emitting nanoparticle of the present invention and at least one solvent. Preferred solvents are mentioned above and below.

In another aspect, the present invention further relates to the use of the QD of the present invention, preferably semiconducting light emitting

nanoparticle of the present invention, the composition of the present invention or the formulation of the present invention in an electronic device, optical device or in a biomedical device. - Optical medium

In another aspect, the present invention further relates to an optical medium comprising the nanosized light emitting material.

In some embodiments of the present invention, the optical medium can be an optical sheet, for example, a color filter, color conversion film, remote phosphor tape, or another film or filter.

According to the present invention, the term ^"sheet^" includes film and / or layer like structured mediums.

- Optical device In another aspect, the invention further relates to an optical device comprising the optical medium.

In some embodiments of the present invention, the optical device can be a liquid crystal display device (LCD), Organic Light Emitting Diode (OLED), backlight unit for an optical display, Light Emitting Diode device (LED), Micro Electro Mechanical Systems (here in after "MEMS"), electro wetting display, or an electrophoretic display, a lighting device, and / or a solar cell.

Further preferred embodiments of the present invention

Embodiment 1 : Quantum Dots (QD) based on Indium Phosphide (InP) characterized in that the QD exhibit a peak maximum in the

photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum (FWHM) of at most 35 nm measured at 25° using a toluene solution, preferably the QD comprise centre area of InP, more preferably the centre area of InP comprises a diameter in the range of 0.8 to 5.0 nm, preferably 0.9 nm to 3.0 nm, more preferably 1 .0 to 1 .5 nm. Embodiment 2: QD according to embodiment 1 , characterized in that the QD are based on magic sized clusters comprising indium phosphide, more preferably the QD are based on magic sized clusters essentially consisting of indium phosphide (MSC InP). Embodiment 3: QD according to embodiment 1 or 2, characterized in that QD are based on a nanocrystal core, which consists solely of fused 6- membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo-tetrahedral arrangement, preferably the nanocrystal core have the formula [ln₂iP₂o]³⁺, [ln₄₂P₄o]⁶⁺, [InesPeop, [ln₈₄P8o] ¹²⁺, [ln₉₅P9o]¹⁵⁺, [|n₃i Pso]³⁺, [lr i P₄o]³⁺, [ln₅i Pso]³⁺, [ln₆i Peo]³⁺, [ln₇i P₇o]³⁺, [ln₈i P₈o]³⁺, and/or [ln₉iP₉o]³⁺. Embodiment 4: QD according to any one of embodiments 1 to 3, characterized in that the QD exhibit a peak maximum in the

photoluminescence spectrum at a wavelength in the range of 402 to 600 nm and a full width half maximum (FWHM) of at most 35 nm, preferably 30 nm, more preferably 25 nm measured at 25° using a toluene solution.

Embodiment 5: QD according to any one of embodiments 1 to 4, characterized in that the QD have a quantum yield of at least 1 .5%, more preferably at least 2.5% and even more preferably at least 3% measured by calculating the ratio of the emission counts of the QD and the dye quinine bisulfate and multiplying by the quantum yield of the dye (55%).

Embodiment 6: QD according to any one of embodiments 1 to 5, characterized in that the QD exhibit a ratio of the peak maximum to the peak minimum in the absorption spectrum of at least 5, more preferably at least 5.5, even more preferably at least 6, even more preferably at least 7 and even more preferably of at least 8.5.

Embodiment 7: Method for preparing QD being based on InP, characterized by preparing Magic Size Cluster MSC of InP (MSC InP).

Embodiment 8: Method for preparing QD according to embodiment 7, characterized in that the preparation method of QD comprises a quenching step, wherein the quenching step preferably includes a lowering of the temperature of a reaction mixture by at least 130 °C, preferably at least 150°C within a period of time less than 2 seconds, preferably less than 1 second.

Embodiment 9: Method for preparing QD according to embodiment 8, characterized in that the quenching step is performed by adding a solvent to the reaction mixture. Embodiment 10: Method for preparing QD according to any one of embodiments 7 to 9, characterized in that the preparation of the MSC InP is achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene, preferably an alkene having 6 to 36 carbon atoms, more preferably 8 to 30 carbon atoms, even more preferably 12 to 24 carbon atoms, most preferably 16 to 20 carbon atoms.

Embodiment 1 1 : Method for preparing QD according to embodiment 10, characterized in that the alkene is a 1 -alkene.

Embodiment 12: Method for preparing QD according to any one of embodiments 7 to 1 1 , characterized in that the preparation of the MSC InP is achieved at a temperature above 1 10 °C, preferably in the range of 1 10 to 180 °C, more preferably above 1 15 °C, even more preferably in the range of 1 15 to 140 °C.

Embodiment 13: Method for preparing QD according to any one of embodiments 7 to 12, characterized in that the MSC InP are prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) and the MSC InP obtained are reacted with a ligand in a second reaction step B).

Embodiment 14: Method for preparing QD according to embodiment 13, characterized in that the ligand is a phosphonic acid, preferably an alkyl phosphonic acid having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more prefer-ably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group, wherein the reaction is preferably performed at a reaction temperature above 100°C, preferably at a reaction temperature above 200°C, more preferably at a reaction temperature above 300°C and even more preferably at a reaction temperature above 350°C. Embodiment 15: Method for preparing QD according to embodiment 13 or 14, characterized in that the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are purified before performing the second reaction step B).

Embodiment 16: QD obtainable by a method according to any one of embodiments 7 to 15.

Embodiment 17: Composition comprising QD according to any one of embodiments 1 to 6 and 16,

and at least one additional material, preferably the additional material is selected from the group consisting of organic light emitting materials, inorganic light emitting materials, charge transporting materials, scattering particles, host materials, and matrix materials.

Embodiment 18: Formulation comprising or consisting of the QD according to any one of embodiments 1 to 6 and 16 or the composition according to embodiment 17, and at least one solvent. Embodiment 19: Use of the QD according to any one of claims according to any one of embodiments 1 to 6 and 16, or the composition according to embodiment 17, or the formulation according to embodiment 18 in an electronic device, optical device or in a biomedical device. Embodiment 20: An optical medium comprising the QD according to any one of embodiments 1 to 6 and 16 or the composition according to embodiment 17.

Embodiment 21 : An optical device comprising the optical medium according to embodiment 20. Definition of Terms

The term "semiconductor" means a material which has electrical

conductivity to a degree between that of a conductor (such as copper) and that of an insulator (such as glass) at room temperature.

The term "organic" means any material containing carbon atoms or any compound that containing carbon atoms ionically bound to other atoms such as carbon monoxide, carbon dioxide, carbonates, cyanides, cyanates, carbides, and thiocyanates.

The term "emission" means the emission of electromagnetic waves by electron transitions in atoms and molecules. Advantages

The quantum dots according to the invention and the optical media and/or the optical devices, obtainable therefrom are distinguished over the prior art by one or more of the following surprising advantages:

1 . The optical media and/or the optical devices obtainable using the

quantum dots according to the invention exhibit very high stability and a very long lifetime compared with optical media and/or optical devices obtained using conventional quantum dots.

2. The quantum dots according to the invention can be processed using conventional methods, so that cost advantages can also be achieved thereby. 3. The quantum dots according to the invention are not subject to any particular restrictions, enabling the workability of the present invention to be employed comprehensively. The quantum dots according to the invention provide a high color purity and a low FWHM.

The quantum dots according to the invention can be produced in a very rapid and easy manner using conventional methods, so that cost advantages can also be achieved thereby.

The quantum dots according to the invention are less toxic than conventional formulations and have a high environmental

acceptability.

The quantum dots according to the invention show a high emission in the visual range of the electromagnetic radiation.

These above-mentioned advantages are not accompanied by an undue impairment of the other essential properties.

it should be pointed out that variations of the embodiments described in the present invention fall within the scope of this invention. Each feature disclosed in the present invention can, unless this is explicitly excluded, be replaced by alternative features which serve the same, an equivalent or a similar purpose. Thus, each feature disclosed in the present invention is, unless stated otherwise, to be regarded as an example of a generic series or as an equivalent or similar feature.

All features of the present invention can be combined with one another in any way, unless certain features and/or steps are mutually exclusive. This applies, in particular, to preferred features of the present invention. Equally, features of non-essential combinations can be used separately (and not in combination). It should furthermore be pointed out that many of the features, and in particular those of the preferred embodiments of the present invention, are themselves inventive and are not to be regarded merely as part of the em- bodiments of the present invention. For these features, independent protection can be sought in addition or as an alternative to each invention presently claimed.

The teaching on technical action disclosed in the present invention can be abstracted and combined with other examples.

The invention is explained in greater detail below with reference to a working example, but without being restricted thereby.

Working Examples

Working Example 1 : Preparation of quantum dots. Preparation of InflylA Solution

In a typical synthesis, 0.93 g (3.20 mmol) of indium acetate and 2.65 g (1 1 .6 mmol) of myristic acid are weighed out into a 100 ml_, 14/20, three- neck round-bottom flask equipped with a thernnowell, reflux condenser, and septum. The apparatus is evacuated with stirring and raised in temperature to 100°C. The solution is allowed to off-gas acetic acid under reduced pressure for approximately 12 h at 100 °C to generate the ln(MA)3 solution. Afterward, the flask is filled with nitrogen, and a 20 ml_ portion of dry 1 - octadecene (being previously pumped down under reduced pressure for several hours at 90C) is added.

Synthesis of InP MA MSCs from InflylA Solution and PfSiMesto In a nitrogen filled glovebox, 600 μΙ_ of P(SiMe3)3 is added to 10 mL of 1 - octadecene (being previously pumped down under reduced pressure for several hours at 90C), drawn into a syringe and sealed with a rubber stopper. The ln(MA)₃ flask is brought up to 130°C and the P(SiMe₃)3 solution is injected and the growth proceeds at 120°C for 80 minutes. The formation of MSCs is monitored via UV-vis of timed aliquots taken from the reaction solution until the MSCs is fully formed as indicated by no further changes in the UV-vis spectra. This procedure can be easily adapted for a wide variety of fatty carboxylic acids in place of myristic acid.

InP MA MSCs Workup Procedure

After UV-vis confirmed formation of MSCs, the flask is cooled and then carefully evacuated until all of the 1 -octadecene is removed. The InP MA MSCs are cleaned by adding 2.5ml of anhydrous chloroform and 10ml of anhydrous acetone to every 1 g of MSCs solution followed by centrifugation. The supernatant is then discarded, and the precipitate dissolved in 2.5ml of chloroform and 4ml of acetone (for each gram of crude material) followed by centrifugation. The supernatant is then discarded. Synthesis of InP ODPA MSCs from InP MA MSCs

In a typical synthesis, 0.234g of indium acetate and 0.484g, of

octadecylphosphonic acid are weighed out into a 50ml 14/20 3-neck round- bottom flask equipped with a stir bar, thermowell, reflux condenser, and septum. Dry squalane (10ml) is quickly injected into the 3-neck flask. The apparatus is evacuated and raised in temperature to 120 °C.

The solution is allowed to off-gas acetic acid under reduced pressure to generate the indium octadecylphosphonate solution for approximately 12 h at 120 °C. After this the flask is filled with nitrogen, the temperature raised to 300 °C for a couple of minutes to form a clear, homogeneous solution, and finally the solution is cooled back to 120 °C and evacuated for another 2 h degassing step. In the glovebox, a solution of 0.5g of purified InP MA MSCs in 5ml of squalane is prepared and drawn up into a plastic syringe and stoppered. The 3-neck flask is then filled with nitrogen and rapidly heated by setting the temperature controller to the maximum setting (450 °C). The InP MA MSCs solution is injected into the indium octadecylphosphonate solution when the temperature controller read 100 °C as the temperature of the solution is rising. Aliquots are taken during the reaction taking note of the time after injection and the temperature of the flask. Once the reaction solution reached a temperature of 350 °C, the temperature controller is set to 370 °C for further growth.

InP ODPA MSC Workup Procedure

After UV-vis confirmed complete conversion to the MSCs, the hot reaction mixture is cooled by injecting 50ml of hexane into the flask using a glass syringe. The hexane composition solution is rapidly injected into the flask under nitrogen. The hexane is briefly evacuated, and backfilled with nitrogen three times prior to the injection.

Thereafter, the hexane is distilled off by heating under reduced pressure and then the temperature is raised to around 200°C to distill off the squalane. Not further cleaning steps are performed. The quantum dots obtained have a very narrow emission as shown in

Figure 1 . The emission peak is about 404 nm and the FWHM is about 16 nm. The emission spectrum of the ODPA MSCs measure with an OD of 0.09 at the excitation wavelength of 350nm measured on a Jasco FP-8300 spectrophotometer

In addition the quantum dots obtained have a relative Quantum Yield (QY) measured at 350 nm in toluene with quinine bisulfate dye in toluene as a reference, having a quantum yield of 55%, using a Jasco FP-8300 spectrophotometer.

The QY is about 3%.

The absorption peak of this material is at 396nm with a max/min ratio of 8.9 as shown in Figure 2. The absorption spectra of the ODPA MSCs measured using a toluene solution in a quartz 1 cm path length cuvette with an optical density (OD) of 0.09 at 350nm on a Shimadzu UV-1800 spectrophotometer at 25°C.

Claims

Patent Claims Quantum Dots (QD) based on Indium Phosphide (InP) characterized in that the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength above 400 nm and a full width half maximum

(FWHM) of at most 35 nm.

QD according to claim 1 , characterized in that the QD are based on magic sized clusters comprising indium phosphide.

QD according to claim 1 or 2, characterized in that QD are based on a nanocrystal core, which consists solely of fused 6-membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo- tetrahedral arrangement.

QD according to any one of claims 1 to 3, characterized in that the QD exhibit a peak maximum in the photoluminescence spectrum at a wavelength in the range of 402 to 600 nm and a full width half maximum (FWHM) of at most 35 nm.

QD according to any one of claims 1 to 4, characterized in that the QD have a quantum yield of at least 1 .5%.

QD according to any one of claims 1 to 5, characterized in that the QD exhibit a ratio of the peak maximum to the peak minimum in the absorption spectrum of at least 5.

Method for preparing QD being based on InP, characterized by preparing Magic Size Cluster MSC of InP (MSC InP).

Method for preparing QD according to claim 7, characterized in that the preparation method of QD comprises a quenching step, wherein the quenching step preferably includes a lowering of the temperature of a reaction mixture by at least 130 °C.

Method for preparing QD according to claim 8, characterized in that the quenching step is performed by adding a solvent to the reaction mixture.

10. Method for preparing QD according to any one of claims 7 to 9,

characterized in that the preparation of the MSC InP is achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene.

1 1 Method for preparing QD according to claim 10, characterized in that the alkene is a 1 -alkene.

12. Method for preparing QD according to any one of claims 7 to 1 1 ,

characterized in that the preparation of the MSC InP is achieved at a temperature above 1 10 °C.

13. Method for preparing QD according to any one of claims 7 to 12,

characterized in that the MSC InP are prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) and the MSC InP obtained are reacted with a ligand in a second reaction step B).

14. Method for preparing QD according to claim 13, characterized in that the ligand is a phosphonic acid, preferably an alkyl phosphonic acid having 1 to 36 carbon atoms. 15. Method for preparing QD according to claim 13 or 14, characterized in that the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are purified before performing the second reaction step B).

16. QD obtainable by a method according to any one of claims 7 to 15.

17. Composition comprising QD according to any one of claims 1 to 6 and 16,

and at least one additional material.

18. Formulation comprising or consisting of the QD according to any one of claims 1 to 6 and 16 or the composition according to claim 17, and at least one solvent.

19. Use of the QD according to any one of claims according to any one of claims 1 to 6 and 16, or the composition according to claim 17, or the formulation according to claim 18 in an electronic device, optical device or in a biomedical device.

20.. An optical medium comprising the QD according to any one of claims 1 to 6 and 16 or the composition according to claim 17.

21 . An optical device comprising the optical medium according to claim 20.