Ink composition based on quantum dots with increasing quantum yield over storage time, method of its preparation and use

Abstract

An ink composition with increasing quantum yield over storage time, comprising: from 1 to 8 % by weight of inorganic quantum dots, from 0,1 to 10 % by weight of at least one additive being polymer or copolymer and a mixture at least two organic solvents up to 100 % by weight with respect to the weight of the composition. A method of preparation of the ink composition and its use.

Description

[0001] Ink composition based on quantum dots with increasing quantum yield over storage time, method oF its preparation and use

[0002] The invention relates to an luminescent ink compositions with increasing quantum yield of photoluminescence over storage time comprising inorganic quantum dots, a method of preparation of ink composition and use of the ink composition in anticounterfeiting protections, also in a light emitting device, in particular in a lightemitting diode, also in displays and sensors.

[0003] Document US20080277626A1 discloses the fluorescent ink formulations including quantum dots for various printing processes such as inkjet, flexographic, screen printing, thermal transfer, and pens. The inks include one or more populations of fluorescent quantum dots dispersed in polymeric material, having fluorescence emissions between about 450 nm and about 2500 nm and a liquid or solid vehicle. The vehicle is present in a ratio to achieve an ink viscosity, surface tension effective, drying time and other printing parameters used for printing processes.

[0004] Document TW20203971 1 A describes an inkjet ink for a color filter, containing light-emitting nanocrystal particles, a photopolymerizable compound and / or a thermosetting resin, and light-scattering particles. The light-emitting nanocrystal particles have an organic ligand at the surface thereof. The total content of the light-emitting nanocrystal particles, the organic ligand, the photopolymerizable compound, the thermosetting resin and the light-scattering particles is 41 mass% or more based on the total mass of the inkjet ink. The inkjet ink may further contain an antioxidant, thanks to which the quantum yield can be improved, and the timedependent decrease in the quantum yield can be further suppressed.

[0005] Document US2019021 1259A1 discloses mixture comprising a semiconductor nanocrystal, optical medium, optical device and to fabrication thereof. Moreover the document describes use of the ligands is selected from mercaptocarboxylic acids such as mercapto-octanoic acid, mercaptohexanoic acid, which decreases loss of quantum yield.

[0006] CN1 10041614A discloses the quantum dot light conversion material, prepared from a base material and a quantum dot material, wherein the base material is olefin polymer. The olefin polymer cannot induce a quantum dot ligand to fall off, and the quantum yield is prevented from being reduced. Furthermore, the olefin polymer has good water-oxygen barrier property and can maintain quantum dot stability.

[0007] JP202005591 1A5 describes a production method of a quantum dot dispersion, comprising a solvent replacement step of replacing a nonpolar organic solvent (A) in a liquid containing the nonpolar organic solvent (A) and quantum dots with a polar organic solvent (B) in the presence of a phosphate ester-based dispersant. According to this document, the introduction of the replacement step to the production process can suppress a fall of a quantum yield, expansion of a half value width, and aggregation of a quantum dot.

[0008] Many examples of ink compositions comprising quantum dots have been disclosed in the prior art describing. However, there is no information about compositions that provide the increase of quantum yield after storage. The high quantum yield of quantum dots is a particularly important parameter due to its application in optoelectronics.

[0009] The aim of the invention was to develop an ink composition, containing inorganic quantum dots, which exhibits high stability of quantum yield during storage time. In addition, the aim was to obtain a composition that is resistant for a long time and does not lose its optical properties. The deposited ink comprising quantum dots forms a flexible and non-cracking layer, which can be used in the light emitting devices.

[0010] In the first aspect, the invention relates to an ink composition with increasing quantum yield over storage time, comprising: a. from 1 to 8 % by weight of inorganic quantum dots, b. from 0.1 to 10 % by weight of at least one additive being polymer or copolymer c. and a mixture of at least two organic solvents up to 100 % by weight with respect to the weight of the composition.

[0011] Preferably the increase of quantum yield after 3 months of storage is at least 5% (QY units) of initial value of quantum yield. Preferably quantum dots comprise cadmium.

[0012] Preferably quantum dots comprise a shell comprising sulfur and cadmium or sulfur and zinc.

[0013] Preferably quantum dots have at least one organic ligand on their surfaces, preferably chosen from 2-ethyl-1 -hexanethiol, 1 1 -mercaptoundecanoic acid and 3- mercaptopropionic acid.

[0014] Preferably the composition comprises red-emitting quantum dots having a maximum luminescence peak wavelength in the range from 621 to 652 nm.

[0015] Preferably the composition comprises green-emitting quantum dots having a maximum luminescence peak wavelength in the range from 510 to 540 nm.

[0016] Preferably at least two organic solvents are selected from the group comprising ethylene glycol, ethanol, toluene 1 ,2 - dichlorobenzene, hexane, methanol, isopropanol and propylene glycol.

[0017] Preferably the composition is polar and the main organic solvent is ethylene glycol.

[0018] Preferably the composition is non-polar and the main organic solvent is toluene.

[0019] Preferably the additive being polymer or copolymer is selected from the group comprising Disperbyk 180 - alkylolammonium salt of a copolymer with acidic groups, BYK 4510 - solution of a hydroxy functional copolymer with acidic groups, Antiterra U-100 - salt of unsaturated polyamine amides and lower molecular weight acidic polyesters, BYKJET 9142 - polymer with pigment affinic groups, Tego VariPlus Sk - special polyol resin and polystyrene.

[0020] Preferably the viscosity of the composition is at 20 °C in the range from 1 to 16 cP.

[0021] Preferably the surface tension of the composition is at 20° C in the range from 25 to 40 mN / m.

[0022] Preferably the composition allows printing of high-resolution structures with an inkjet printer.

[0023] The second aspect of the invention is a method of preparation of the ink composition comprising steps: a) modification of the surface of quantum dots by the exchange of organic ligand, b) addition of a mixture at least two organic solvents to the dispersion of quantum dots, c) addition of at least one additive being polymer or copolymer to the mixture from step b) and mixing.

[0024] Preferably step a) comprising: a) placing at least one organic ligand in the reaction vessel and adding at least one non-polar organic solvent, b) adding of a solution of quantum dots in a non-polar organic solvent to the reaction vessel, c) shaking the resulting reaction mixture for 18 hours at 500 rpm and 30°C, d) adding of acetonitrile or ethanol and followed by centrifugation for 10 minutes at 6000 rpm, e) separating the precipitates from the supernatant by decanting, f) redispersing the precipitate in a non-polar organic solvent.

[0025] Preferably step a) comprising: a) placing the organic ligand in the reaction vessel and adding at least one polar organic solvent, b) adding a second organic ligand to the reaction vessel, c) addition a solution of quantum dots in a non-polar organic solvent to the reaction vessel, d) adding an amine to the reaction vessel, e) shaking the resulting reaction mixture for 18 hours at 500 rpm at 30°C, f) centrifugation of the reaction mixture for 10 min at 500 rpm, g) collecting and extracting the non-polar phase with a mixture of hexane: toluene, h) precipitating the quantum dots from the reaction mixture with a precipitating agent, i) redispersing the precipitate in a polar organic solvent and filtration.

[0026] Another aspect of the invention is a use of the ink composition in anticounterfeiting applications, also in a light emitting device, in particular in a lightemitting diode, also in displays and sensors.

[0027] The advantage of the invention is the high stability of the quantum yield (QY) and the maximum peak wavelength of the photoluminescence (PL) over a long time. Surprisingly, it turned out that the developed compositions allow not only to maintain the photoluminescent properties, but also an increase in quantum yield is observed during storage of the compositions.

[0028] Generally the quantum yield of quantum dots decreases over time, because certain physicochemical processes occur on the quantum dot surface caused by external factors (e.g. light, presence of oxygen, etc.). The consequence of these physicochemical processes may be the agglomeration of quantum dots, which results in optical properties degradation (e.g. broadening of the spectrum, decrease in QY), and in extreme cases, complete extinction of photoluminescence.

[0029] It is well known in the literature that certain molecular ligands have a significant effect on maintaining the high QY photoluminescence observed in quantum dots. It is possible that the reason for the increase in QY over time in the described ink compositions is the potential build-up of a new layer of ligands present in selected ink additives or / and the potential replacement of ligands present in the quantum dot with ligands present in selected ink additives.

[0030] Another advantage of the invention is the repeatability of the composition preparation method as well as its universality. The composition, according to the invention can be prepared from various types of quantum dots core-shell structure, not limited to cadmium. The invention also includes quantum dots with different maximum luminescence peak wavelengths: green-emitting QDs and red- emitting QDs. Moreover, each step of the synthesis can be easily scaled-up, which is important from the point of view of industrial application. The observed phenomenon of increasing the quantum yield over time has also direct benefits related to the logistics and transport time of the product - ink based on quantum dots. Due to the fact that QY increases to the certain value over time, the ink does not have to be used in a given application immediately or shortly after production, but it can be stored and used also after a certain period of time, without losing quality parameters.

[0031] Another advantage of the invention is that it can be used in anti-counterfeiting systems. Due to the creation of ink compositions comprising green-emitting and red-emitting quantum dots, a wide range of possibilities appears. Knowing the values of the expected QY increase over time for the selected ink, one possibility is to print the same structure in different time units with the same ink. A properly selected QY measuring instrument will read the differences in QY values between different printed structures.

[0032] Importantly, the described ink formulations can be used for inkjet printing, which enables obtaining high-resolution structures with a line width of less than 50 pm. Structures printed with an ink containing quantum dots, when exposed to UV light, emit light of a certain color, for example green light (when the ink comprises green-emitting quantum dots). The invention is presented on the drawing, in which:

[0033] Fig. 1 QNA logo printed with an inkjet printer in high resolution by using ink composition comprises red-emitting quantum dots

[0034] Fig.2 Example of structures printed with an inkjet printer in high resolution by using ink composition comprises red-emitting quantum dots

[0035] Fig. 3 Quantum Yield stability test over time for Ink 5 and Ink 6.

[0036] The invention is presented in non-limiting examples:

[0037] The synthesis of red-emitting CdSe quantum dots was performed according to the procedure described in X. Peng, DOI 10.1007 / s12274-013-0341 -7. The CdSe cores were coated with an inorganic CdS shell by a reaction carried out according to a modified procedure originally proposed by Bawendi [Bawendi, Nature, DOI: 10.1038 / NMAT3539], The synthesis of green-emitting CdSe@ZnS quantum dots was performed according to the modified (without additional ZnS shell) procedure described in Y. Fu DOI: 10.1039 / C7RA06957J.

[0038] The following additives were used in the preparation of ink compositions (Table 1). Table 1 The additives in ink compositions. Preferably, the polar, green-emitting QDs ink composition comprises from 2 to 6% by weight of QDs, from 60 to 82% by weight of ethylene glycol, from 0.5 to 2.0% by weight of Disperbyk 180, to 0.5% by weight of Byk 4510 and ethanol to 100% by weight with respect to the weight of the composition.

[0039] Preferably, the non-polar, green-emitting QDs ink composition comprises from 2 to 5% by weight of QDs, from 13 to 46% by weight of 1 ,2- dichlorobenzene, to 3.0% by weight of Antiterra U-100, to 3 % by weight of BYKJET 9142, to 6.0% by weight of polystyrene and toluene to 100% by weight with respect to the weight of the composition.

[0040] Preferably, the polar, red-emitting QDs ink composition comprises from 2 to 6% by weight of QDs, from 68 to 86% by weight of ethylene glycol, from 0.5 to 2.0% by weight of Disperbyk 180, to 4% by weight Tego VariPlus SKand ethanol to 100% by weight with respect to the weight of the composition.

[0041] Photoluminescence (PL) spectra were measured to determine the position and broadening (FWHM - Full Width at Half Maximum) of PL peak. Maximum photoluminescence emission peak (PL Amax) and FWHM were measured on PerkinElmer FL 8500 Fluorescence Spectrophotometer (excitation wavelength was set at 405 nm) or Avantes spectrometer AvaSpec-2048XL (excitation wavelength was set at 365 nm). Photoluminescence Quantum Yield was measured on optical system composed of a 365 nm diode (Thorlabs, M365F1), integrating sphere (Giga hertz-Optik, UPB-150-ARTA) and detector (Avantes, AvaSpec- 2048XL). Viscosity was measured on Anton-Paar ViscoQC 300 L Rotational Viscometer at 20°C. Surface tension was measured on goniometer RAME-HART model: 90-U3-PRO at 20°C. Dynamic Light Scattering (DLS) was measured on Anton-Paar Litesizer 500. High-resolution structures were printed on glass substrate by using Dimatix DMP-2831 printer, Fujifilm. Printed structures were observed by using epifluorescence microscope OptaTech MN800FL.

[0042] Samples containing ink compositions were stored at room temperature. In addition, the samples were stored away from light sources and sealed.

[0043] Example 1 a The ligand exchange procedure - green-emitting QDs for polar ink

[0044] The procedure can be divided into two steps. In the First step 1 .6120 mmol oF 1 1 - mercaptoundecanoic acid and 1.4450 mmol of ammonium thiocyanate were added to the reaction vessel (centrifuge tube 50 mL) and then 0.2388 mmol of ethanol and 0.1772 mmol of ethylene glycol were added using automatic pipette. Then 4.1455 mmol of 3-mercaptopropionic acid and 28.75 pL of 0.1 M HCl solution were measured to the reaction mixture. 22 mL of QDs (concentration 20 mg / ml) was then transferred to the reaction vessel. Toluene or hexane may be used as a solvent for QDs. Finally, 17.2956 mmol of te / -butylamine (TBA) was added to the resulting mixture of ligands and QDs. The reaction vessel was capped and placed in a thermal shaker for 18 hours at 500 rpm and 30°C.

[0045] In the second step of the procedure, the centrifuge tube (50 mL) containing the reaction mixture was centrifuged (10 min, 500 rpm). After centrifugation, the upper non-polar phase was collected and extraction was performed with a mixture of hexane:toluene on the remaining volume of QDs in polar solvents (0.5:0.5:1). The centrifuge tube was manually shaken several times and then centrifuged. After centrifugation, the upper non-polar phase was collected from the centrifuge tube. In the next step, quantum dots were precipitated from the mixture and the precipitating agent was acetonitrile. Precipitation takes place in a volume ratio of 1 :2.5 (QDs:acetonitrile). The precipitate was dispersed in the appropriate volume of ethylene glycol so that the final concentration of the QDs concentrate was about 100 mg / ml. Finally, the obtained concentrate was filtered through a nylon filter (0.2 pm).

[0046] Example 1 b

[0047] The ligand exchange procedure - green-emitting QDs for non-polar ink

[0048] In the first step 0.0081 mmol of 2-ethyl-1 -hexanethiol was added to the reaction vessel (centrifuge tube 50 mL) and then 0.1872 mmol of toluene was added using automatic pipette. 30 mL of QDs (concentration 20 mg / ml) was then transferred to the reaction vessel. Toluene or hexane may be used as a solvent for QDs. The reaction vessel was capped and placed in a thermal shaker for 18 hours at 500 rpm and 30°C. In the meantime, the quantum dots from the reaction mixture precipitated. Thus, acetonitrile should be added to the reaction vessel in a volume ratio of 1 :3 (QDs:acetonitrile). Afterwards, the reaction vessel could be placed in a centrifuge for 10 minutes at 6000 rpm. After centrifugation, when complete precipitation occurs, the pellet can be separated from the supernatant by decanting the supernatant. Then the pellet should be carefully dried and dispersed in more [ess 0.2808 mmol of toluene. Then the quantum dots were precipitated once more using acetonitrile and methanol added to QDs in a 1 : 1 : 1 volume ratio.

[0049] In the second step, 0.1872 mmol of toluene was added to the QDs precipitate, followed by 0.0058 mmol of 2-ethyl-1 -hexanethiol. The reaction vessel was capped and placed in a thermal shaker for 18h at 500 rpm and 30 °C. After this time, the QDs were precipitated using acetonitrile and isopropanol added to the reaction mixture in a 1 :1 : 1 volume ratio. The precipitate was then dispersed in 0.1872 mmol of toluene and once more precipitated with acetonitrile and isopropanol in a 1 :1 : 1 volume ratio.

[0050] In the third step, 0.1872 mmol of toluene was added to the QDs precipitate, followed by 0.0003 mmol of 2-ethyl-1 -hexanethiol. The reaction vessel was capped and placed in a thermal shaker for 18 hours at 500 rpm and 30°C. After this time, the QDs were precipitated using acetonitrile and ethanol added in a 1 : 1 : 1 volume ratio. The precipitate was then dispersed in 0.1872 mmol of toluene and once again precipitated with acetonitrile and isopropanol in a 1 :1 :1 volume ratio. The precipitate was dispersed in an appropriate volume of toluene so that the final concentration of the QDs concentrate was about 200 mg / ml.

[0051] Example 1 c

[0052] The procedure can be divided into two steps. In the first step 1 .4014 mmol of 1 1 - mercaptoundecanoic acid was added to the reaction vessel (centrifuge tube 50 mL) and then 0.2605 mmol of ethanol and 0.1933 mmol of ethylene glycol were added using automatic pipette. Then 3.2787 mmol of 3-mercaptopropionic acid should be added. 24 mL of QDs (concentration 20 mg / ml in toluene) was then transferred to the reaction vessel. Finally, 16.6024 mmol of triethylamine (TEA) was added to the resulting mixture of ligands and QDs. The reaction vessel was capped and placed in a thermal shaker for 18 hours at 500 rpm and 30°C.

[0053] In the second step of the procedure, the centrifuge tube together with the reaction mixture was centrifuged (10 min, 500 rpm). After centrifugation, the upper non-polar phase was collected and extraction was performed with a mixture of hexane:toluene on the remaining volume of QDs (0.5:0.5:1). The centrifuge tube was manually shaken several times, then centrifuged. After centrifugation, the upper non-polar phase was collected from the centrifuge tube. In the next step, quantum dots were precipitated from the reaction mixture and the precipitating agent was acetonitrile. Precipitation takes place in a volume ratio of 1 :2.5 (QDs:acetonitrile). The precipitate was dispersed in the appropriate volume of ethylene glycol so that the final concentration of the QDs concentrate was about 100 mg / ml. Finally, the concentrate was filtered through a nylon filter (0.2 pm).

[0054] Example 2

[0055] Preparation of ink composition

[0056] The green-emitting polar blank ink composition - Ink 1

[0057] To prepare green-emitting polar blank (without additional ink additives) ink, 155 pl of QDs dispersion (concentration 129 mg / ml) from the ligand exchange procedure (Example 1 a) was added to the glass vial. Then, 1 1 .59 mmol of ethylene glycol and 3.43 mmol of ethanol were added to QDs dispersion. The ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0058] The green-emitting polar ink composition - Ink 2

[0059] To prepare green-emitting polar ink, 155 pl of QDs dispersion (concentration 129 mg / ml) from the ligand exchange procedure (Example 1 a) was added to the glass vial. Then, 11 .50 mmol of ethylene glycol and 2.65 mmol of ethanol were added to QDs dispersion. The ingredients were mixed using vortex mixer for about 5 minutes at room temperature. In the next step 50 pl of Disperbyk 180 in ethanol solution (concentration 10 % wt.) was added and the ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0060] The red-emitting polar blank ink composition - Ink 3

[0061] To prepare red-emitting polar blank (without additional ink additives) ink, 375 pl of QDs dispersion (concentration 160 mg / ml) from the ligand exchange procedure (Example 1 c) was added to the glass vial. Then, 6.74 mmol of ethylene glycol and 4.28 mmol of ethanol were added to QDs dispersion. The ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0062] The red-emitting polar ink composition - Ink 4

[0063] To prepare red-emitting polar ink, 375 pl of QDs dispersion (concentration 160 mg / ml) from the ligand exchange procedure (Example 1 c) was added to the glass vial. Then, 2.43 mmol of ethylene glycol and 1 .54 mmol of ethanol were added to QDs dispersion. The ingredients were mixed using vortex mixer for about 5 minutes at room temperature. In the next step 200 pl of Disperbyk 180 in ethylene glycol solution (concentration 10 % wt.) was added and the ingredients were mixed using vortex mixer for about 5 minutes at room temperature. Then, 200 pl of Tego VariPlus SK in ethanol solution (concentration 20 % wt.) was added and the ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0064] The green-emitting non-polar blank ink composition - Ink 5

[0065] To prepare green-emitting non-polar blank (without additional ink additives) ink, 148 pl of QDs dispersion (concentration 237 mg / ml) from the ligand exchange procedure (Example 1 b) was added to the glass vial. Then, 5.66 mmol of toluene and 2.22 mmol of 1 ,2-dichlorobenzene were added to QDs dispersion. The ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0066] The green-emitting non-polar ink composition - Ink 6

[0067] To prepare green-emitting polar ink, 148 pl of QDs dispersion (concentration 237 mg / ml) from the ligand exchange procedure (Example 1 b) was added to the glass vial. Then, 3.50 mmol of toluene and 2.22 mmol of 1 ,2-dichlorobenzene were added to QDs dispersion. The ingredientswere mixed using vortex mixer for about 5 minutes at room temperature. In the next step 30 pl of BYKJET 9142 in toluene solution (concentration 50 % wt.) was added and the ingredients were mixed using vortex mixer for about 5 minutes at room temperature. Then, 200 pl of polystyrene in toluene solution (concentration 20 % wt.) was added and the ingredients were mixed using vortex mixer for about 5 minutes at room temperature.

[0068] According to Example 2 have been obtained the following ink compositions:

[0069] Table 2. Ink compositions comprising quantum dots

[0070] Table 3. Parameters of ink compositions comprising quantum dots and additives Example 3

[0071] Stability test For ink compositions.

[0072] In the case of ink compositions, quantum yield, photoluminescent properties (measuring the wavelength at which the maximum emission occurs) and QDs size distributions (DLS) were measured. The tests were performed at room temperature, samples were unprotected from visible light.

[0073] Table 4. Stability test for green-emitting polar Ink 1 and Ink 2

[0074] Table 5. Stability test for red-emitting polar Ink 3 and Ink 4 Table 6. Stability test for green-emitting non-polar Ink 5

[0075] Table 7. Stability test for green-emitting non-polar Ink 6

[0076] Present invention, in addition to the anti-counterfeiting protections mentioned above, could be used in optoelectronics, in particular as a displays, light emitting devices and sensors.

Claims

AMENDED CLAIMS received by the International Bureau on 06 August 2024 (06.08.2024) Patent Claims1 . An ink composition comprising: a. from 1 to 8 % by weight of inorganic quantum dots, having at least one organic ligand on their surfaces, selected from the group: 2-ethyl-1 - hexanethiol, 11-mercaptoundecanoic acid and 3-mercaptopropionic acid, b. from 0.1 to 10 % by weight of at least one additive being polymer or copolymer, selected from the group: alkylol ammonium salt of a copolymer with acidic groups, solution of a hydroxy functional copolymer with acidic groups, salt of unsaturated polyamine amides and lower molecular weight acidic polyesters, polymer with pigment affinic groups, polyol resin and polystyrene. c. and a mixture of at least two organic solvents up to 100 % by weight with respect to the weight of the composition.

2. The ink composition accordingto claim 1 characterized in that quantum dots comprise cadmium.

3. The ink composition accordingto claim 1 or 2 characterized in that quantum dots comprise a shell comprising sulfur and cadmium or sulfur and zinc.

4. The ink composition accordingto claims 1 - 3 characterized in that it comprises red- emitting quantum dots having a maximum luminescence peak wavelength in the range from 621 to 652 nm.

5. The ink composition accordingto claims 1-3 characterized in that it comprises greenemitting quantum dots having a maximum luminescence peak wavelength in the range from 510 to 540 nm.

6. The ink composition accordingto claims 1-5, characterized in that the at least two organic solvents are selected from the group comprising ethylene glycol, ethanol, toluene 1 ,2 - dichlorobenzene, hexane, methanol , isopropanol and propylene glycol.

7. The ink composition accordingto claims 1-6, characterized in that it is polar and the main organic solvent is ethylene glycol.

8. The ink composition accordingto claims 1-6, characterized in that it is non-polar and the main organic solvent is toluene.

9. The ink composition according to claims 1 to 8, characterized in that the viscosity of the composition at 20 °C is in the range from 1 to 16 cP.AMENDED SHEET (ARTICLE 19)10. The ink composition according to claims 1 to 8, characterized in that the surface tension of the composition at 20° C is in the range from 25 to 40 mN / m.11 . The ink composition according to claims 1 to 10, that allows printing of high- resolution structures with an inkjet printer.

12. A method of preparation of the ink composition according to claim 1 , comprising steps: i. modification of the surface of quantum dots by the exchange of organic ligand, ii. addition of a mixture at least two organic solvents to the dispersion of quantum dots, iii. addition of at least one additive being polymer or copolymerto the mixture from step b) and mixing.

13. The method of preparation of the ink composition accordingto claim 12, characterized in that, step a) comprising: iv. placing at least one organic ligand in the reaction vessel and adding at least one non-polar organic solvent, v. adding of a solution of quantum dots in a non-polar organic solvent to the reaction vessel, vi. shaking the resulting reaction mixture for 18 hours at 500 rpm and 30°C, vii. adding of acetonitrile or ethanol and followed by centrifugation for 10 minutes at 6000 rpm, viii. separating the precipitates from the supernatant by decanting, ix. redispersing the precipitate in a non-polar organic solvent.

14. The method of preparation of the ink composition accordingto claim 12, characterized in that, step a) comprising: x. placingthe organic ligand in the reaction vessel and adding at least one polar organic solvent, xi. adding a second organic ligand to the reaction vessel, xii. addition a solution of quantum dots in a non-polar organic solvent to the reaction vessel, xiii. adding an amine to the reaction vessel,AMENDED SHEET (ARTICLE 19)xiv. shaking the resulting reaction mixture for 18 hours at 500 rpm at 30°C, xv. centrifugation of the reaction mixture for 10 min at 500 rpm, xvi. collecting and extracting the non-polar phase with a mixture of hexane: toluene, xvii. precipitating the quantum dots from the reaction mixture with a precipitating agent, xviii. redispersing the precipitate in a polar organic solvent and filtration.

15. A use of the ink composition according to any one of claims 1 to 11 , in anticounterfeiting applications, also in a light emitting device, in particular in a light-emitting diode, also in displays and sensors.AMENDED SHEET (ARTICLE 19)

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