WO2019215060A1

WO2019215060A1 - Core-shell nanoparticles

Info

Publication number: WO2019215060A1
Application number: PCT/EP2019/061492
Authority: WO
Inventors: Shany NEYSHTADT; Miriam KOOLYK; Alex RABKIN; Artyom SEMYONOV
Original assignee: Merck Patent Gmbh
Priority date: 2018-05-09
Filing date: 2019-05-06
Publication date: 2019-11-14
Also published as: TW201947017A

Abstract

The present invention relates to a semiconducting light emitting nanoparticles.

Description

CORE-SHELL NANOPARTICLES

Field of the invention

The present invention relates to new nanoparticles and a process for obtaining them.

Background Art

Semiconducting light emitting nanoparticles are a class of materials possessing excellent properties intermediate between those of small, individual molecules and those of bulk, crystalline semiconductors. These nanocrystals are composed of a quantum dot semiconducting core material and a shell of a distinct semiconducting material. The most important semiconducting materials, which are suitable to produce Quantum Dots, include cadmium compounds, especially CdS and CdSe. However, the disadvantage is that cadmium is highly toxic, which in particular attempts to solve the end products at a later time.

A promising alternative would be InP, but here the quantum yield is not satisfactory. The shell provides protection against environmental changes, photo-oxidative degradation, and provides another route for modularity. Precise control of the size, shape, and composition of both the core and the shell enable the emission wavelength to be tuned over a wider range of wavelengths than with either individual semiconductor. These materials have found applications in biological systems and optics.

In the prior art there are numbers of papers are focused on the core/shell construction of nanoparticles. For example, the article of WORZ ET AL titled“Gap Energies, Exciton Binding Energies and Band Offsets in Ternary ZnMgSe Compounds and ZnSe/ZnMgSe Heterostructures” [Phys. Stat. Sol. (b)202, 805(1997)] is focused on the ZnSe/ZnMgSe Heterostructures grown on GaAs(001 ) by molecular beam epitaxy (MBE) and. Meanwhile, a paper issued by PRETE ET AL titled“MOVPE growth of MgSe and ZnMgSe on (100) GaAs” [Journal of Crystal Growth 214/215 (2000) 1 19}124] describes metalorganic vapor-phase epitaxy (MOVPE) growth of ZnMgSe epilayers on (100) GaAs. In this paper MgSe layers are directly grown on (100) GaAs, while Zm-_xMg_xSe (0.07<x<0.45) epilayers with different Mg compositions are grown on (100) GaAs after deposition of a 4.2nm thin ZnSe butter layer.

Besides, the patent US 9 153 731 B2 discloses a nanocrystal comprising: a) a homogeneous region having a first composition; and b) a smoothly varying region encompassing the homogeneous region, wherein the homogeneous region can consist of any homogeneous single-component Specifically, when the homogeneous region consists of CdSe, the smoothly varying region consisting of CdZnSe, ZnSe, ZnS, ZnSeS, ZnMgSe, ZnMgS, and ZnMgSeS could be used for shelling the Cd-based tight confinement nanocrystal.

Furthermore, the patent application US20170005226A1 also relates to a semiconductor structure comprising CdSe or CdSe_mSm-i as nanocrystalline core, a second semiconductor material different than the first

semiconductor material at least partially surrounding the nanocrystalline core, and an outer nanocrystalline shell comprising a third semiconductor material surrounding the second semiconductor material. In this application the second semiconductor material comprises a magnesium-based semiconductor material such as magnesium chalcogenide, and the third semiconductor material comprises a magnesium-based semiconductor material, such as alloys Cd_nMgi-_nS, Zn_xMgi-_xSe, and Zn_mMgi-_mS.

Another patent application US20120205586A1 reports indium phosphide colloidal nanocrystals, which can have a core shell structure. Additionally, the patent application US20160214862A1 provides Mg_aAbSe semiconductor nanocrystals, wherein A is a Group II metal other than magnesium, such as Zn, Ga, In, S, and Te. It is reported by TAMANG ET AL in the paper“Chemistry of InP

Nanocrystal Syntheses” (Chem. Mater. 2016, 28, 2491 -2506) that the quantum efficiency of the InP/ZnSe nanoparticles is limited by the lattice mismatch of 3.3% between the core and shell materials, which limits the wide application of the nanoparticles.

The issue of the lattice mismatch is more dominant for InP/ZnSeS shell. Specifically, the lattice mismatch is bigger than that of InP/ZnSe

nanoparticles and lies in the range of from 3.3 to 7% depends on the content of S. In view of this it is desired to synthesize an alloyed shell with a band gap larger than ZnSe, and the increased band gap should not lead to the lattice mismatch.

Therefore, it has been the object of the present invention to provide

Semiconducting light emitting nanoparticle with improved quantum yields as well as low self-absorption.

Summary of the invention

A first object of the present invention is directed to semiconducting light emitting nanoparticle comprising at least a core nanoparticle and a Zm- xMg_xSe shell layer covering the core, preferably x is in the range of from 0.1 to 0.9.

A second object of the present invention refers to a method to synthesize semiconducting light emitting nanoparticle comprising Zm-_xMg_xSe as a shell layer, comprising the following steps:

(a) preparing a semiconducting core nanoparticle, (b) reacting said Zn, Mg, Se precursors and the core nanoparticle optionally in an organic solvent and/or in the presence of a ligand compound to form a shell layer onto the core to form nanoparticle, wherein the molar ratio between Mg precursor and Zn precursor is 0.1 or more, preferably in the range from 0.1 to 9.

In another aspect, the present invention further relates to a semiconducting light emitting nanoparticle obtainable or obtained from the method of the invention.

In another aspect, the present invention further relates to a composition comprising at least the semiconducting light emitting nanoparticle, 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, nanosized plasmonic particles, photo initiators, and matrix materials.

In another aspect, the present invention further relates to a formulation comprising at least one semiconducting light emitting nanoparticle, or a composition, and at least one solvent, preferably the solvent is selected from one or more members of the group consisting of aromatic,

halogenated and aliphatic hydrocarbon solvents, more preferably selected from one or more members of the group consisting of toluene, xylene, ethers, tetrahydrofuran, chloroform, dichloromethane and heptane, purified water, ester acetates, alcohols, sulfoxides, formamides, nitrides, ketones. In another aspect, the present invention further relates to an optical medium comprising at least one semiconducting light emitting nanoparticle, or a composition, or the formulation. In another aspect, the present invention further relates to optical device comprising at least said optical medium.

Detailed description of the invention The semiconducting light emitting nanoparticle comprises at least a core nanoparticle and a Zni-_xMg_xSe shell layer covering the core, preferably x is in the range of from 0.1 to 0.9.

Although the term“nanoparticle” is clear for every skilled person working in the technological are to which the present invention belongs, it should be expressed that nanoparticle has the meaning of an average particle diameter in the range of about 2 nm to about 50 nm, preferably about 3 to about 20 and more preferably about 4 to about 15 nm depending on the desired colour of the nanoparticle.

According to the present invention, the term“nanoparticle” includes quantum dots, quantum rods.

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 embodiment of the present invention, said core / shell structure can be core / one shell layer structure, core / double shells structure or core / multishells structure. Furthermore, the term“multishells” stands for the stacked shell layers consisting of three or more shell layers. Each stacked shell layers of double shells and / or multishells can be made from same or different materials. 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.

Suitable semiconducting core of the nanoparticle according to the present invention may represent single compounds or mixtures of two, three or even more of them.

In a preferred embodiment of the present invention, said core comprises one element of the group 13 of the periodic table, and one element of the group 15 of the periodic table.

In a preferred embodiment of the present invention, Cd atom is not included in the core. More preferably, Cd atom is not included in the shell also.

More preferably, the core is represented by the following formula (I), lni-y-2/3zGa_yZn_zP (I) wherein 0£y£1 , 0£z£1 , preferably 0£y<1 , 0£z<1 , more preferably the core is InP, ln_yZn_zP, or lm-_yGa_yP.

In another embodiment of the present invention, the semiconducting light emitting nanoparticle comprise a second shell layer onto said Zm-_xMg_xSe shell layer, preferably the second shell layer comprises or is consisting of an element of group 12 of the periodic table and an element of group 16 of the periodic table, more preferably the element of group 12 is Zn, and the element of group 16 is S, Se, or Te. Even more preferably, the second shell layer is ZnS.

Elemental Analysis According to the present invention, the following elemental analysis is used.

The semiconducting light emitting nanoparticle is dissolved in toluene and the obtained solution is diluted. One droplet of the diluted solution is dripped on a Cu/C TEM grid with ultrathin amorphous carbon layer. The grid is dried in vacuum at 80Ό for 1.5 hours to re move the residues of the solvent as well as possible organic residues.

EDS measurements are carried out in STEM mode using high resolution TEM - Tecnai F20 G2 machine operating at 200kV equipped with EDAX Energy Dispersive X-Ray Spectrometer. TIA software is used for spectra acquisition and calculations and no standards are used.

In some embodiments of the present invention, the semiconducting light emitting nanoparticle can further comprise one or more additional shell layers onto the second shell layer as a multishell.

According to the present invention the said core nanoparticles have a n average diameter in the range of 1 -4 nm, preferably in the range of from 2 to 3.5 nm.

According to the present invention the semiconducting light emitting nanoparticle has an average diameter in the range of 5-15 nm, preferably in the range of from 7 to 13 nm.

The average diameter of the semiconducting nanosized light emitting particles are calculated based on 100 semiconducting light emitting nanoparticles in a TEM image created by a Tecnai G2 Spirit Twin T-12 Transmission Electron Microscope. According to the present invention the volume ratio between the shell and the core is in the range of from 5 to 30, preferably in the range of from 8 to 25, and more preferably in the range of from 10 to 20. According to the present invention the shape of the semiconducting light emitting nanoparticle is dot, sphere, tetrapod, pyramid, elongated shaped or any other shape.

According to the present invention the quantum yields of the

semiconducting light emitting nanoparticle is more than about 40%, preferably more than 50%. Simultaneously the self-absorption is below 0.4, preferably below 0.3.

Surprisingly, the inventors have observed that by introducing Mg into the ZnSe shell the lattice mismatch between the core and the shell materials is reduced and the quantum confinement is improved. Correspondingly the quantum efficiency of the obtained nanoparticles is increased, while the self-absorption is low. A second object of the present invention refers to a method to synthesize semiconducting light emitting nanoparticle comprising Zm-_xMg_xSe as a shell layer, comprising the following steps:

(a) preparing a semiconducting core nanoparticle, (b) reacting said Zn, Mg, Se precursors and the core nanoparticle optionally in an organic solvent and/or in the presence of a ligand compound to form a shell layer onto the core to form nanoparticle, wherein the molar ratio between Mg precursor and Zn precursor is 0.1 or more, preferably in the range from 0.1 to 9. Preferably, the molar ratio between the core nanoparticle and total precursors of step b is from 1/10000 to 1/1000, more preferably from 1/3000 to 1/5000.

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. In a preferred embodiment of the present invention, the molar ratio between the core nanoparticle and total precursors of step b is from 1/10000 to 1/1000, preferably from 1/3000 to 1/5000, and

the molar ratio between Mg precursor and Zn precursor is 0.1 or more, preferably in the range from 0.1 to 9.

According to the present invention, said shell / core ratio (the ratio of shell / the first semiconducting material) is calculated using following formula.

MwCiotal shell elements )

Vshell The element of the group 12 p(Total shell elements )

= ( )

Vcore The element of the group 13 Mw{Total core elements )

p(Total core elements ) wherein the symbols have the following meaning

Vshell = the volume of shell layer(s),

Vcore = the volume of core,

Mw (Total shell elements) = molecular weight of total shell elements, Mw (Total core elements) = molecular weight of total core elements p (Total shell elements) = density of total shell elements

p (Total core elements) = density of total core elements In one embodiment of the present invention said core nanoparticle is obtained by providing at least a first and a second core precursor optionally in a solvent, preferably said first core precursor is a salt of the element of the group 13 and said second core precursor is a source of an element of the group 15 of the periodic table, more preferably the element of the group 13 is In, Ga or a mixture of thereof, and the element of the group 15 is P, or As. Even more preferably the core nanoparticle is InP.

In some embodiments of the present invention, the InP based

semiconducting core nanoparticles such as InP, InZnP, InGaP, InGaZnP, InPZnS, or InPZnSe, can be prepared by reacting at least one indium precursor and at least one phosphor precursor, preferably said indium precursor is a metal halide represented by following chemical formula (II), metal carboxylate represented by following chemical formula (III), or a combination of these, and said phosphor precursor is an amino phosphine represented by following chemical formula (IV), alkyl silyl phosphine such as tris trimethyl silyl phosphine, or a combination of these, lnX¹ ₃ (II)

wherein X¹ is a halogen selected from the group consisting of Cl , B r and I , [ln(0₂CR³)3] - (III) wherein R³ is a linear alkyl group having 1 to 30 carbon atoms, a branched alkyl group having 4 to 30 carbon atoms, a linear alkenyl group having 2 to 30 carbon atoms, or a branched alkenyl group having 4 to 30 carbon atoms, preferably R³ is a linear alkyl group having 1 to 30 carbon atoms, or a linear alkenyl group having 2 to 30 carbon atoms, more preferably, R³ is a linear alkyl group having 5 to 25 carbon atoms, or a linear alkenyl group having 6 to 25 carbon atoms, even more preferably R³ is a linear alkyl group having 10 to 20 carbon atoms, or a linear alkenyl group having 10 to 20 carbon atoms, furthermore preferably R³ is a linear alkenyl group having 10 to 20 carbon atoms,

(R⁴R⁵N)₃P (IV) wherein R⁴ and R⁵ are at each occurrence, independently or dependently, a hydrogen atom or a linear alkyl group having 1 to 25 carbon atoms or a linear alkenyl group having 2 to 25 carbon atoms, preferably a linear alkyl group having 1 to 10 carbon atoms, more preferably a linear alkyl group having 2 to 4 carbon atoms, even more preferably a linear alkyl group having 2 carbon atoms, more preferably said zinc salt is represented by following chemical formula

(V),

ZnX²n (V)

wherein X² is a halogen selected from the group consisting of Cl , B r and I , n is 2. In a specific embodiment, the preparation of the 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 is preferably in the range of 0.8:1 to 4:1 , more preferably 2:1 to 4:1.

The preparation of the InP is preferably achieved using a solvent. The solvent is not specifically restricted. Preferably, the solvent is selected from squalenes, squalanes, heptadecanes, octadecanes, octadecenes, nonadecanes, icosanes, henicosanes, docosanes, tricosanes,

pentacosanes, hexacosanes, octacosanes, nonacosanes, triacontanes, hentriacontanes, dotriacontanes, tritriacontanes, tetratriacontanes, pentatriacontanes, hexatriacontanes, oleylamines, and trioctylamines. In a preferred embodiment of the present invention, the preparation method of InP 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 Ό, preferably at least 150 Ό 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 Ό, more p referably below 50 Ό, even more preferably below 30 Ό, most preferably b elow 10 Ό. 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 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 on 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.

In a specific embodiment, the preparation of the 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 can be added to the reaction mixture as a free acid or as a salt.

Preferably, the carboxylate compound is added as a precursor.

According to the present invention the Zn precursor used at step (b) is a Zn carboxylate, more preferably a zinc carboxylate having 2 to 30 carbon atoms, even more preferably 4 to 26 carbon atoms, furthermore preferably 8 to 24 carbon atoms, most preferably 10 to 20 carbon atoms, the most preferably the Zn precursor is selected from the group consisting of Zn myristate, Zn palmitate, Zn laurate, Zn stearate, or Zn oleate.

According to the present invention, in a preferred embodiment, the Mg precursor is Mg-carboxylates, Mg halides and alkylated Mg. Preferably the Mg precursor is MgCl2 or Mg acetate, Mg stearate, or Bis(cyclopentadienyl) magnesium. More preferably, the Mg precursor is MgCl2, Mg stearate or Mg acetate.

According to the present invention the Se precursor is preferably a Se solution and/or a Se suspension. A Se suspension comprising a

hydrocarbon solvent, e.g. an 1 -alkene, such as 1 -octadecene and/or an organic phosphine compounds, preferably alkyl 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 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 is used as a semiconductor precursor. Preferably, the Se precursor is Se-TOP. According to the present invention the optional ligand compound include phosphines and phosphine oxides such as Trioctylphosphine oxide

(TOPO), Trioctylphosphine (TOP), and Tributylphosphine (TBP); phosphonic acids such as Dodecylphosphonic acid (DDPA), Tetradecyl phosphonic 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.

In view of the ligands mentioned above, carboxylate ligands such as stearate and oleate and phosphine ligands, such as Trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), and Tributylphosphine (TBP) are preferred.

The used solvent at step (b) is not specifically restricted. Preferably, the solvent is selected from amines, aldehydes, alcohols, ketones, ethers, esters, amides, sulfur compounds, nitro compounds, phosphorus

compounds, hydrocarbons, halogenated hydro-carbons (e.g. chlorinated hydrocarbons), aromatic or heteroaromatic hydrocarbons, halogenated aromatic or heteroaromatic hydrocarbons and/or (cyclic) siloxanes, preferably cyclic hydrocarbons, terpenes, epoxides, ketones, ethers and esters. Preferably a non-coordinating solvent is used.

In an embodiment of the present invention, the preparation of the shell 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.

In a further embodiment of the present invention, the preparation of the shell is preferably achieved by a reaction mixture comprising a solvent and the solvent comprises at least one phosphorus compound, such as phosphine compounds, preferably alkyl phosphine compounds having 3 to 108 carbon atoms, phosphine oxide compounds, preferably alkyl phosphine oxide having 3 to 108 carbon atoms and/or phosphonate compounds, more preferably an alkyl phosphonate compounds 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.

Preferably, Trioctylphosphine (TOP) is used as a solvent for the preparation of a shell. Regarding the preparation step of the shell, alkenes are preferred in view of the other solvents mentioned above. In a further preferred embodiment, the solvent for the preparation of the shell comprises a mixture of an alkene and a phosphorus compound. Preferably, the step (b) is conducted at a temperature 150 °C or more, preferably in the range of 150 to 400 °C, more preferably from 200 to 350°C, even more preferably in the range from 250 to 320 °C. furthermore, preferably from 280 to 320 °C. In a preferred embodiment, the method further comprises following step (c): (c) reacting Zn, S precursors and the nanoparticles obtained in step (b) optionally in an organic solvent and/or in the presence of a ligand

compound to form a second shell layer. According to the present invention the Zn precursor is a chemical compound selected from Zn carboxylate, more preferably a zinc carboxylate 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 zinc carboxylate selected from the group consisting of Zn myristate, Zn palmitate, Zn laurate, Zn stearate, Zn oleate. Preferably, the Zn precursor is ZnCl2 or Zn stearate.

According to the present invention the S precursor is a S compound, preferably a sulfur solution and/or a sulfur suspension selected from sulfur, bis(trimethylsilyl)sulfide, tri-n-alkyl phosphine sulfide, hydrogen sulfide, tri-n- alkenyl phosphine sulfide, alkylamino sulfide, alkenyl amino sulfide, tri-n- butyl phosphine sulfide or tri-n-octylphosphine sulfide.

The used ligands and solvents have the same meaning as described above and will not be repeated.

Preferably, the composition comprises a plurality of the semiconducting light emitting nanoparticles.

halogenated and aliphatic hydrocarbon solvents, more preferably selected from one or more members of the group consisting of toluene, xylene, ethers, tetrahydrofuran, chloroform, dichloromethane and heptane, purified water, ester acetates, alcohols, sulfoxides, formamides, nitrides, ketones.

Preferably, the formulation comprises a plurality of the semiconducting light emitting nanoparticles.

In another aspect, the present invention further relates to use of the semiconducting light emitting nanoparticle, or a composition, or the formulation, in an electronic device, optical device or in a biomedical device.

In another aspect, the present invention further relates to an optical medium comprising at least one semiconducting light emitting nanoparticle, or a composition, or the formulation.

Preferably, the optical medium comprises a plurality of the semiconducting light emitting nanoparticles. 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.

In some embodiments of the present invention, the optical medium comprising an anode and a cathode, and at least one organic layer comprising at least one light emitting nanoparticle, or the composition, preferably said one organic layer is a light emission layer, more preferably the medium further comprises one or more layers selected from the group consisting of hole injection layers, hole transporting layers, electron blocking layers, hole blocking layers, electron blocking layers, and electron injection layers.

In some embodiments of the present invention, the organic layer of the optical medium comprises at least one light emitting nanoparticle and a host material, preferably the host material is an organic host material.

In another aspect, the present invention further relates to optical device comprising at least said 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. 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 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 par ticular 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 pro tection 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 InP Cores InP cores are prepared according to the following procedure. A 50 ml 3- necked round-bottom flask is loaded with 0.1 g of InCh, 0.3g of ZnCl2, and 5ml of oleylamine inside a glove box, and sealed with septa and a stopcock. It is vacuumed on a Schlenk line at 120 °C for 1 hour bellow 150mtorr. Then the flask is exposed to the Argon source and heated to 190°C. 0.45ml (DEA)3P is then injected swiftly into the flask and the contents of the flask are reacted for 45 min before cooling by removal of the heat source. InP cores is subjected to purification by dispersion in toluene, precipitation by ethanol, and centrifugation at 5000 rpm for 5 min where crude lnP:toluene:ethanol =1 :1 :8 in volume. This is preformed twice and then InP cores are isolated from the supernatant and stored dry in a glove box.

Comparative Example 1 : Preparation of InP/ZnSe nanoparticles from Pre-synthesized Cores

A ZnSe shell is grown over InP cores synthesized according to Working Example 1 by the following procedure: Dry InP cores corresponding to 2.5ml of crude InP are dispersed in 2.5ml of oleylamine and loaded into a 50ml 3-necked round-bottom flask with ZnCl2 (0.15 g) and TOP: Se (2M, 0.55ml. The flask is sealed with septa and a stopcock, attached to a

Schlenk line set-up, and set to vacuum at room temperature for 30 min below 150 mTorr. It is then exposed to the Argon source and heated to 180°C for 30 min, heated to 200°C for 30 min, and heated to 320°C for 1 h. Zn-stearate in ODE (0.4M, 2.4ml) is then slowly injected over 5 min and the contents of the flask are reacted for 1 h and 15 min. Working Example 2: Preparation of InP/Zm-xMgxSe nanoparticles from Pre- Synthesized Cores using Oxygen-free precursors

A ZnMgSe shell is grown over InP cores synthesized according to Working Example 1 by the following procedure: Dry InP cores corresponding to

2.5ml of crude InP are dispersed in 2.5ml of oleylamine and loaded into a 50ml 3-necked round-bottom flask with ZnCl2 (0.075 g), TOP: Se (2M, 0.55ml) and MgCl2 (0.052 g). The flask is sealed with septa and a stopcock, attached to a Schlenk line set-up, and set to vacuum at room temperature for 30 min below 150 mTorr. It is then exposed to the Argon source and heated to 180°C for 30 min, heated to 200°C for 30 min, and heated to 320°C for 1 h. Zn-oleylamine in ODE (0.4M, 1 2ml, pre-complexed in 1 :2 molar ratio of ZnCl2 to oleylamine by degassing for 1 h at 120°C) and Mg- oleylamine (0.4M, 1 2ml, pre-complexed in 1 :2 molar ratio of MgCl2 to oleylamine by degassing for 1 h at 120°C) are then slowly injected over 5 min and the contents of the flask are reacted for 1 h and 15 min.

Working Example 3: Preparation of InP/Zm-xMgxSe nanoparticles from Resynthesized Cores using Oxygen-containing precursors

A ZnMgSe shell is grown over InP cores synthesized according to Working Example 1 by the following procedure: Dry InP cores corresponding to 2.5ml of crude InP are dispersed in 2.5ml of oleylamine and loaded into a 50ml 3-necked round-bottom flask with ZnCl2 (0.075 g), TOP: Se (2M, 0.55ml) and Mg-acetate (0.078 g). The flask is sealed with septa and a stopcock, attached to a Schlenk line set-up, and set to vacuum at room temperature for 30 min below 150 mTorr. It is then exposed to the Argon source and heated to 180°C for 30 min, heated to 200°C for 30 min, and heated to 320°C for 1 h. Zn-oleylamine in ODE (0.4M, 1 2ml, pre- complexed in 1 :2 molar ratio of ZnCl2 to oleylamine by degassing for 1 h at 120°C) and Mg-oleylamine (0.4M, 1 2ml, pre-complexed in 1 :2 molar ratio of MgCl2 to oleylamine by degassing for 1 h at 120°C) are then slowly injected over 5 min and the contents of the flask are reacted for 1 h and 15 min.

Working Example 4: Preparation of InP/Zm-xMgxSe/ZnS nanoparticles from Pre-synthesized Cores

A ZnSe shell is grown over InP/Zm-xMgxSe nanoparticles synthesized according to Working Example 2 by the following procedure. Steps are taken as in Working Example 2. After reaction for 1 h and 15 min, Zn- oleylamine in ODE (0.4M, 2.4ml, pre-complexed in 1 :2 molar ratio of ZnCl2 to oleylamine by degassing for 1 h at 120°C) and TOP:S (2M, 0.38 ml) are slowly injected over 5 min and the contents of the flask are reacted for 1 h.

The relative quantum yield (QY) and self-absorption (SA) of the obtained various nanoparticles are tested as follows:

-Self-absorption value calculation

According to the present invention, the optical density (hereafter“OD”) of the nanoparticles is measured using Shimadzu UV-1800, double beam spectrophotometer, using toluene baseline, in the range between 350 and 800 nm.

The photoluminescence spectra (hereafter“PL”) of the nanoparticles is measured using Jasco FP fluorimeter, in the range between 460 and 800 nm, using 450 nm excitation.

The OD (l) and PL (l) are the measured optical density and the

photoluminescence at wavelength of l.

OD1 represented by the formula (VI) is the optical density normalized to the optical density at 450 nm, and a1 represented by formula (VII) is the absorption corresponding to the normalized optical density. OD (X)

OD_l

OD (A = 450nm) (VI)

a_x = 1— 10^_oz¾ (VII)

SA = self-absorption.

The self-absorption value of the nanoparticles represented by formula (VIII) is calculated based on the OD and PL measurement raw data.

The relative quantum yield is 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 coumarin 153 dye in ethanol is used as a reference, with a quantum yield of 55%.

wherein the symbols have the following meaning

QY = Quantum Yield of the sample

QY_ref = Quantum Yield of the reference/standard

n = the refractive index of the sample solvent (especially ethanol) nref = the refractive index of the reference/standard

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

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

A = is the percentage absorbance of the sample. The percentage of the sampling light that the sample absorbs. Iret = the integral of the reference emission intensity as measured on the Jasco. Calculated as Jl dv with I intensity, v =wavelength. Aret 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 25Ό.

The results are shown in Table 1.

Table 1

It can be seen that after introducing Mg into the ZnSe shell the quantum efficiency of the obtained nanoparticles is increased from 30 to 50, while the self-absorption is kept at about 0.2.

Claims

Patent Claims

1. A semiconducting light emitting nanoparticle comprising at least a core nanoparticle and a Zm-xMg_xSe shell layer covering the core, preferably x is in the range of from 0.1 to 0.9.

2. The nanoparticle according to claim 1 , wherein the core nanoparticle comprises at least one element of the group 13 of the periodic table, and at least one element of the group 15 of the periodic table.

3. The nanoparticle according to claim 1 or 2, wherein the core is

represented by the following formula (I), lni-y-2/3zGa_yZn_zP (I) wherein 0£y£1 , 0£z£1 , preferably 0£y<1 , 0£z<1 ,

more preferably the core is InP, ln_yZn_zP, or lm-_yGa_yP.

4. The nanoparticle according to any one of claims 1 to 3, wherein the semiconducting light emitting nanoparticle further comprises a second shell layer onto said Zm-_xMg_xSe shell layer, preferably the second shell layer comprises at least an element of group 12 of the periodic table and an element of group 16 of the periodic table, more preferably the element of group 12 is Zn, and the element of group 16 is S, Se, or Te.

5. The nanoparticle according to claim 4, wherein the second shell layer is ZnS.

6. The nanoparticle according to any one of claims 1 to 5, wherein the core nanoparticle has an average diameter in the range of 1 to 4 nm, preferably in the range of from 2 to 3.5 nm.

7. The nanoparticle according to any one of claims 1 to 6, wherein the volume ratio between the shell and the core is in the range of from 5 to 30, preferably in the range of from 8 to 25, and more preferably in the range of from 10 to 20.

8. A method to synthesize semiconducting light emitting nanoparticle comprising Zm-xMg_xSe as a shell layer, comprising the following steps:

9. The method according to claim 8, wherein the Zn precursor used at step

(b) is a Zn carboxylate, more preferably a zinc carboxylate having 2 to 30 carbon atoms, even more preferably 4 to 26 carbon atoms, furthermore preferably 8 to 24 carbon atoms, most preferably 10 to 20 carbon atoms, the most preferably the Zn precursor is selected from the group consisting of Zn myristate, Zn palmitate, Zn laurate, Zn stearate, or Zn oleate.

10. The method according to claim 8 or 9, wherein the Mg precursor in step (b) is selected from the group consisting of Mg-carboxylates, Mg halides and alkylated Mg, preferably the Mg precursor is MgCl2 or Mg acetate, Mg stearate, or Bis(cyclopentadienyl) magnesium, more preferably, the Mg precursor is MgCl2, Mg stearate or Mg acetate.

11. The method according to any one of claims 8 to 10, wherein the step (b) is conducted at a temperature 150 °C or more, preferably in the range of 150 to 400 °C, more preferably from 200 to 350°C, even more preferably in the range from 250 to 320 °C, furthermore preferably from 280 to 320 °C.

12. The method according to any one of claims 8 to 1 1 , wherein the method further comprises following step (c):

(c) reacting Zn, S precursors and the nanoparticles obtained in step (b) optionally in an organic solvent and/or in the presence of a ligand compound to form a second shell layer.

13. A semiconducting light emitting nanoparticle obtainable or obtained from the method according to any one of claims 8 to 12.

14. A composition comprising at least the semiconducting light emitting nanoparticle according to any one of claims 1 to 7, 13, 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, nanosized plasmonic particles, photo initiators, and matrix materials.

15. Formulation comprising at least one semiconducting light emitting nanoparticle according to any one of claims 1 to 7, 13, or a composition according to claim 14, and at least one solvent, preferably the solvent is selected from one or more members of the group consisting of aromatic, halogenated and aliphatic hydrocarbon solvents, more preferably selected from one or more members of the group consisting of toluene, xylene, ethers, tetrahydrofuran, chloroform, dichloromethane and heptane, purified water, ester acetates, alcohols, sulfoxides, formamides, nitrides, ketones.

16. Use of the semiconducting light emitting nanoparticle according to any one of claims 1 to 7, 13, or a composition according to claim 14, or the formulation according to claim 15, in an electronic device, optical device or in a biomedical device.

17. An optical medium comprising at least one semiconducting light emitting nanoparticle according to any one of claims 1 to 7, 13, or a composition according to claim 14, or the formulation according to claim 15.

18. The optical medium of claim 17, comprising an anode and a cathode, and at least one organic layer comprising at least one light emitting nanoparticle according to any one of claims 1 to 7, 13, or the composition of claim 14, preferably said one organic layer is a light emission layer, more preferably the medium further comprises one or more layers selected from the group consisting of hole injection layers, hole transporting layers, electron blocking layers, hole blocking layers, electron blocking layers, and electron injection layers.

19. The optical medium of claim 17 or 18, wherein the organic layer comprises at least one light emitting nanoparticle according to any one of claims 1 to 7, 13, and a host material, preferably the host material is an organic host material.

20. An optical device comprising at least said optical medium according to any one of claims 17 to 19.