Two-step method for preparation of a colloidal functionalized blue-emitting quantum dots, method of preparation of ink compositions comprising quantum dots and its use

Abstract

A two-step method for preparation of a colloidal functionalized blue-emitting quantum dots, comprising following steps: stabilizing ligand exchange comprising functionalization of the QDs surface with 2-ethyl-1-hexanethiol and ligand exchanging 2-ethyl-1-hexanethiol into mono-2-(methacryloyloxy)ethyl succinate. A preparation method of UV-curable ink, a composition of UV-curable ink, a use of the UV-curable ink and a light-emitting device.

Description

[0001]Two-step method for preparation of a colloidal functionalized blue-emitting quantum dots, method of preparation of ink compositions comprising quantum dots and its use The invention relates to a method for preparation of functionalized blue-emitting quantum dots (QDs), method of preparation UV-curable ink compositions comprising said quantum dots and the use of such ink compositions. Document CN111320981B discloses quantum dots with various types of ligands on their surface. The type of claimed quantum dots is not particularly restricted, provided that the quantum dot are made of semiconducting compounds and may emit light upon stimulation by light. Quantum dots may be homogenous single structures, core- shell structures or mixed structures. The ligands attached to a quantum dot surface via e.g. carboxylic or thiol group may be introduced by ligand exchange reaction. Furthermore, the document discloses ink compositions including the abovementioned quantum dots and photopolymerizable compounds, suitable for inkjet printing. Document CN113248953B describes quantum dots with functionalized surfaces, photo-conversion curable ink compositions with these quantum dots and light emitting devices comprising them. The type of claimed quantum dots is not particularly limited, provided that the quantum dot are made of semiconducting compounds and may emit light upon stimulation by light or by electricity. Quantum dots may be homogenous single structures, core-shell structures, gradient structure or mixed structures. Ligands may be attached to the quantum dot surface using various functional groups, for example: ester, carboxylic, amino, thiol. The ink composition may include photopolymerizable compounds. Application document WO2023054952A1 presents the solvent-free quantum dots composition, method for producing the composition and cured film including the QDs. Homogenous monolayer or multilayer (gradient, core-shell type) structures of quantum dots may be applied. Compounds from II-VI group elements may be freely selected to produce said quantum dots. The surface of quantum dots is functionalized and the ligands covering the surface may be replaced via ligand exchange reactions. The article in ACS Appl. Mater. & Interfaces 2020, 12, 10563 provides description of InP / ZnSexS1-xquantum dots, with surface functionalized by replacing native oleic acid ligands to mono-2-(methacryloyloxy)ethyl succinate (MMES) moieties via ligand exchange process. The MMES ligands improve dispersibility of modified quantum dots in polar solvents like, for example, diethylene glycol monoethyl ether acetate (DGMEA) or similar, which can be utilized for making quantum dots compositions for inkjet printing and for photolithography. The vinyl group present in the MMES moiety can form cross-links with photopolymerizable additives under UV exposure resulting in formation of stable QDs-polymer layer. Blue quantum dots with high optical parameters are desired by the largest technology companies. The demand for this nanomaterial is due to the significant impact of QDs on the quality and energy efficiency of next-generation devices, e.g. displays. Current emitters, usually organic dyes, including blue dyes, are essential in applications such as displays, since the three RGB (Red, Green, Blue) colours are needed to reproduce the colour palette. Interestingly, it has already been possible to obtain green and red emitting quantum dots with the desired physicochemical parameters, but it was not easy to obtain blue- emitting quantum dots with the desired parameters. One of the reasons is the fact that blue-emitting particles emit high-energy photons compared to e.g. green or red, and therefore become much more difficult to control and unstable. An additional difficulty arises from the fact that for environmental protection reasons, the new generation of quantum dots should be cadmium-free, and so far the best optical parameters have been achieved with cadmium-based quantum dots. The aim of the invention was to develop the method for preparation of functionalized blue-emitting quantum dots with enhanced stability of optical parameters over time both in form of dispersion in HDDA and in the UV-curable ink composition. Moreover, the aim was to obtain UV-curable ink compositions comprising the blue-emitting quantum dots, suitable for inkjet printing of flexible and non-cracking layers, and use them as a light emitting device. In the first aspect, the invention relates to a two-step method for preparation of a colloidal functionalized blue-emitting quantum dots comprising following steps: a) stabilizing ligand exchange comprising functionalization of the QDs surface with 2-ethyl-1-hexanethiol, b) ligand exchanging 2-ethyl-1-hexanethiol into mono-2-(methacryloyloxy)ethyl succinate. Preferably the method comprising: placing the QDs dispersion in toluene or hexane of concentration 100 mg / mL with 0.069 mol of 2-ethyl-1-hexanethiol in a thermal shaker for 1.5-3 h at 25-35 °C, adding ethanol in a volume ratio of 1:1.5 (QDs dispersion:ethanol), then decanting and drying an obtained pellet, dispersing the pellet obtained in step ii) in toluene to obtain a QDs dispersion with concentration of 100 mg / mL, adding ethanol in a volume ratio of 1:1 (QDs dispersion:ethanol), then decanting and drying an obtained pellet, dispersing the pellet obtained in a step iv) in toluene to obtain a QDs dispersion with concentration of 100 mg / mL, the obtained QDs dispersion was filtered through a paper filter. Preferably the method comprising: placing QDs dispersion obtained in step a) with 0.160 mol of mono-2- (methacryloyloxy)ethyl succinate, adding PGMEA and toluene in a volume ratio of 1:0.4:0.4 (QDs dispersion:PGMEA:toluene) in a thermal shaker for 3,5-4,5 h at 45-55 °C, adding octane in a volume ratio of 1:2 (QDs dispersion:octane), then decanting and drying an obtained pellet, dispersing a pellet obtained in step viii) in the HDDA to obtain a concentration of about 40-45% by weight, placing a QDs dispersion in a thermal shaker for 3-4 h at 25-35 °C, the obtained QDs dispersion was filtered through a centrifugal filter made of nylon for 10 minutes at 6000 rpm. Preferably the quantum dots are selected from the group comprising ZnS, ZnSe, CdSe, CdS, InP, CuInS, perovskites and preferably the quantum dots are doped with elements such as Te, Cu, Se, S, Li. In the second aspect, the invention relates to a method of preparation of the ink composition comprising functionalized blue-emitting quantum dots obtainable according to any of claims 1 to 4, comprising following steps: dissolving 1-hydroxycyclohexyl phenyl ketone in 1,6-hexanediol diacrylate and tri(propylene glycol) diacrylate wherein their ratio ranges from 1:7:2 to 1:8:3 by weight, respectively, adding QDs dispersion obtained according to any of claims 1 to 4 of concentration 40-45 wt.%, then isobornyl acrylate and then 2-hydroxy-2- methylpropiophenone were added, wherein their ratio ranges from 1:1.4 to 1:1.6 by weight, respectively, placing the mixture in a thermal shaker and stirring for 2-3 h at 20-25°C until complete dissolution of solid compounds. Preferably after the addition of each compound the mixture is mixed on a vortex device for at least 30 seconds. In the second aspect, the invention relates to an UV-curable ink composition. Preferably the UV-curable ink composition comprises: QDs (8-12 wt. %), 1,6-hexanediol diacrylate (57-61 wt. %), tri(propylene glycol) diacrylate (15-19 wt. %), isobornyl acrylate (4.5-5.5 wt. %), 2-hydroxy-2- metylpropiophenone (2.5-4.0 wt. %) and 1-hydroxycyclohexyl phenyl ketone (6-8 wt. %). The invention relates to a use of the UV-curable ink composition in an anti- counterfeiting applications, as a colour (light) converting materials, in a light emitting device, in particular in a light-emitting diode and a displays and a sensors. The invention relates to a light emitting device comprising the UV-curable ink composition wherein UV-LED emission wavelength is 365 nm or 385 nm. In the case of QNA's UV-curable ink compositions, we are dealing with a high degree of conversion (QY > 65%) of UV light into blue light, due to the properties of quantum dots. QNA technology solves the problem of decreasing a certain QY value, which is a key physicochemical parameter of QDs. Due to the use of a two-step ligand exchange procedure and, consequently, by providing better protection of the quantum dot surface, stabilization of quantum dots over time was achieved, which significantly reduces the problem of nanoparticle agglomeration and the related deterioration of the optical parameters of QDs over time. The method of the invention allows to obtain the functionalized quantum dots wherein the quantum dots are selected from the group comprising ZnS, ZnSe, CdSe, CdS, InP, CuInS, perovskites and they can be doped with elements such as Te, Cu, Se, S, Li. Due to selected features and improvements, QNA technology has a number of advantages: 1) Carrying out a stabilizing ligand exchange (the first step) before the second ligand exchange (the second step), which results in an increase of quantum yield value of QDs dispersed in the monomer as compare to initial QDs; 2) The addition of 2-ethylhexanethiol increased the stability of the QDs, which allowed for more thorough purification of the mixture from organic impurities remaining after synthesis without a decrease in quantum yield. These activities contributed to improving the purity of the final product; 3) The presence of a thiol ligand on the surface of the quantum dots also resulted in an extension of the colloidal stability time of the products formed at subsequent stages. Another advantage of the invention is that quantum dots dispersion in HDDA show no deterioration of the optical properties upon long-lasting contact with visible light - quantum yield and stable maximum photoluminescence emission peak wavelength (Table 5 and Table 6). In addition, the performance of said quantum dots in HDDA is equally excellent in the broad range of temperatures, from room temperature up to 90 °C. Ink compositions comprising said quantum dots also show no deterioration of the optical properties over time, however in room temperature and without light access. Optimally selected functionalization conditions and compatibility of ligands on the surface with respect to the monomer enable obtaining high concentrations of QDs in the HDDA monomer (40-45 wt.%). This directly translated into the possibility of obtaining high concentrations of QDs in the ink compositions. Another aspect of the invention is easy use of the UV-curable composition as an ink for precise inkjet printing, which produces flexible and non-cracking layers. The invention is presented on the drawing, in which: Fig. 1 Absorbance and Photoluminescence spectra of UV-curable ink based on blue- emitting QDs Table 1 List of abbreviations The invention is presented in non-limiting examples: Example 1 Blue-emitting ZnSe(Te) / ZnSe / ZnS quantum dots (PureBlue dots) were synthesized according to the following procedure. Synthesis of ZnSe seeds (cores) and tellurium doping of the resulting ZnSe seeds (cores) The system for the flow synthesis consists of a furnace (tubular reactor) and a steel tube 160 cm long and 0.3175 cm (1 / 8 inch) in diameter, through which a flow of reaction solution is conducted, a flow meter with apparatus, a peristaltic pump, an argon source, and also flexible tubes with high chemical and thermal resistance surrounded by heating bands connected to temperature controllers. 1.1 g (0.006 moles) of anhydrous zinc acetate (Zn(Ac)2), 5.37 g (0.019 moles) of oleic acid (OA) and 35.51 g (0.14 moles) of 1-octadecene (ODE) were weighed and all the ingredients were placed in a glass flask. The entire stage of the process on the Schlenk line was conducted under argon. Under the fume cupboard, the system was connected to a Schlenk line and the flask with the reagents was placed in a heating basket and connected to a temperature controller set on a magnetic stirrer (500 rpm). The solution was pre-gassed at room temperature for 5 minutes and with the pressure in the flask gradually reduced until it reached 1 mbar. Later, the solution was heated to 120 °C in about 12 minutes. At this temperature the solution was degassed again for a further hour. Argon was then connected to the system and a 1.5 M solution of selenium precursor (0.237 g selenium) in diphenylphosphine (1.56 g diphenylphosphine) (Se-DPP) was rapidly injected and the solution incubated at 120 °C for 30 min. After this time, a peristaltic pump set to a flow rate of 1.3 mL / min was started and the reaction solution was passed through a tubular reactor, heated to 250 °C, which is part of the flow synthesis system. For the first 10 minutes, the reaction solution was collected in a separate beaker. Subsequently, the reaction solution containing the resulting ZnSe seeds (cores) was collected into a flask for about 42 minutes, until a volume of 54 mL was collected. The collected solution was degassed again for 10 minutes at 100 °C. The Ar supply was turned off, the solution was heated to 210 °C and then 0.056 M tellurium solution (0.016 g tellurium) in trioctylphosphine (1.86 g trioctylphosphine) (Te-TOP) was injected into the reaction mixture. The solution was then heated to 300 °C and incubated for 60 minutes at 300 °C. The resulting ZnSe(Te) cores were used further in the synthesis, i.e. during the growth of the ZnSe shell. Synthesis of ZnSe shell In an anaerobic atmosphere, 60 mL of a 0.75 M solution of zinc precursor (8.25 g zinc) in oleic acid (26.73 g OA), 12.46 g TOP and 12.13 g trioctylamine (TOA) were melted on a hotplate at 180 °C and then transferred to a glass bottle. 15.12 mL of a 1.2 M solution of selenium (1.48 g Se) in trioctylphosphine (12.47 g TOP) (Se-TOP) was drawn into a syringe. Under the fume hood, a tube and needle were connected to the syringe with Se-TOP. The syringe was placed in a syringe pump set to a flow rate of 126 µl / min. The zinc precursor bottle was placed on a heating plate set at 180 °C and with 200 rpm stirring. The bottle was capped with a ferrule cap, and a hose fitted to the peristaltic pump was drawn through one of the ferrules (feed rate 501 µl / min), an argon feed hose was connected to the other and the argon was unscrewed. To the solution of the ZnSe(Te) cores obtained in the earlier step, after their incubation at 300 °C, precursor solutions were supplied by connecting hoses with needles and septum to the flask, and the injection of Se-TOP (126 µl / min) and Zn(OA)2(501 µl / min) was started. Both injections should last 120 min. After the injections were completed, the heating basket was turned off and the flask was left in the heating basket to cool the reaction solution. The reaction solution was poured into a vessel and weighed. A mass of ethanol corresponding to the mass of the reaction solution and a mass of 2-propanol corresponding to twice the mass of the reaction solution were added to the vessel. The solution was centrifuged for 10 min at 4500 rpm. After completion, the precipitate was dried and dispersed in 17.5 g (0.2 moles) of hexane. The resulting ZnSeTe / ZnSe product was used in the further part of the synthesis, namely during the growth of the ZnS shell. Synthesis of ZnS shell 8.69 g (0.036 moles) of hexadecylamine (HDA), 16.11 g (0.057 moles) of oleic acid (OA), 145.65 g (0.412 moles) of trioctylamine (TOA) and 3.3 g (0.018 moles) of anhydrous zinc acetate were weighed and all ingredients were placed together in a glass flask. In an anaerobic atmosphere, 54 mL of a 0.75 M solution of the zinc precursor (7.43 g Zn) in oleic acid (24.06 g OA) was melted on a hotplate at 180 °C and was transferred to a glass bottle. A 13.5 mL 1.2 M solution of the sulphur precursor (0.53 g sulphur) in trioctylphosphine (11.22 g TOP) was drawn into a syringe. Under the fume hood, a tube and needle were connected to the syringe containing the sulphur precursor. The syringe was placed in a syringe pump set to a flow rate of 225 µl / min. The bottle containing the zinc precursor was placed on a heating plate set at 180 °C and with stirring at 200 rpm. The bottle was capped with a ferrule cap, and a hose fitted to the peristaltic pump (feed rate 900 µl / min) was threaded through one ferrule, an argon feed hose was connected to the other and the argon was unscrewed. The sulphur precursor was added using a syringe pump, and the zinc precursor was added by a peristaltic pump. The sulphur precursor and zinc precursor are ready to be added at a further stage of the synthesis. A system was connected to the Schlenk line under the fume cupboard and the flask with the reagents weighed in the first step (HDA, OA, TOA and anhydrous zinc acetate) was placed in a heating basket and connected to a temperature controller set on a magnetic stirrer (500 rpm). Initially, the solution was degassed at room temperature for 5 minutes and with the pressure in the flask gradually reduced until a range of 1- 10 mbar was reached. Later, the solution was heated to 120 °C in about 12 minutes. At this temperature, the solution was degassed again for 10 minutes. Argon was then connected to the system and the solution was heated to 180 °C. The ZnSeTe / ZnSe product obtained at the earlier stage (dissolved in hexane) was then taken into syringes and injected vigorously into the solution over about 1 minute. The solution was heated to 185 °C and simultaneous administration of the prepared zinc and sulphur precursors was initiated over approximately 60 min. Simultaneously, the solution was heated to 330 °C during the administration of the precursors. Once 330 °C was reached and the feed of both precursors was completed, the heating basket was turned off and the flask was left to cool in the heating basket. The reaction solution was poured into a vessel and weighed. A mass of ethanol corresponding to the mass of the reaction solution and a mass of 2-propanol corresponding to twice the mass of the reaction solution were added to the vessel. The solution was centrifuged for 10 minutes at 4500 rpm. After completion, the precipitate was dried and dispersed in toluene so that the final concentration of the blue-emitting ZnSe(Te) / ZnSe / ZnS quantum dots was about 100 mg / mL. The two-step ligand exchange procedure The ligand exchange procedure was performed in two steps – in the first step stabilizing ligand exchange was made and in the second step the ligand exchange to the monomer was made. Stabilizing ligand exchange procedure: During stabilizing ligand exchange 0.069 mol of 2-ethyl-1-hexanethiol (EHT) was added to the reaction vessel (glass bottle 500 mL), 200 mL of colloidal solution of quantum dots in toluene (concentration about 100 mg / mL) and then 0.941 mol of toluene were added using automatic pipette. The mixture 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 2 hours at 150 rpm and 30 °C and then the quantum dots from the reaction mixture precipitated. Thus, ethanol was added to the reaction vessel in a volume ratio of 1:1.5 (QDs:ethanol). Afterwards, the reaction vessel was placed in a centrifuge for 10 minutes at 4400 rpm. After centrifugation, when complete precipitation occurs, the pellet was separated from the supernatant by decanting the supernatant. Then the pellet was dried and dispersed in 0.753 mol of toluene. In the next step, ethanol was added to the reaction vessel in a volume ratio of 1:1 (QDs:ethanol). Afterwards, the reaction vessel was placed in a centrifuge for 10 minutes at 4400 rpm and when complete precipitation occurs, the pellet was separated from the supernatant by decanting the supernatant. The precipitate was centrifuged and dispersed in the appropriate volume of toluene, so that the final concentration of the QDs dispersion was about 100 mg / mL. Finally, the obtained QDs dispersion was filtered through a paper filter with pore size 20-45 μm. Ligand exchange to the monomer procedure: 0,160 mol of mono-2-(methacryloyloxy)ethyl succinate (MMES) and 125 mL of QDs dispersion (concentration about 100 mg / mL) were added to the reaction vessel (glass bottle 500 mL). PGMEA and toluene were added to the reaction vessel using an automatic pipette: PGMEA and toluene in a volume ratio of 0.4:0.4:1 (PGMEA / toluene / QDs). The mixture was then transferred to the reaction vessel. The reaction vessel was capped and placed a in a thermal shaker for 4 hours at 150 rpm and 50 °C and then the quantum dots from the reaction mixture precipitated. Thus, octane was added in a volume ratio of 1:2 (QDs:octane). Afterwards, the reaction vessel was placed in a centrifuge for 10 minutes at 4400 rpm. After centrifugation, when complete precipitation occurs, the pellet was separated from the supernatant by decanting the supernatant. Then the pellet was dried and dispersed in the HDDA, so that the final concentration of the QDs dispersion was about 40-45 wt.%. The reaction vessel was once again capped and placed a in a thermal shaker for 3 hours at 100 rpm and 30 °C. Finally, the obtained QDs dispersion was filtered through a centrifugal filter made of nylon with a pore size of 0.22 μm for 10 minutes at 6000 rpm. QDs dispersion was transferred into a previously prepared vessel. The UV-curable ink formulation All activities were carried out in daylight, but without access to additional light. To prepare UV-curable ink 0.32 mmol of 1-hydroxycyclohexyl phenyl ketone was dissolved in 1.85 mmol of 1,6-hexanediol diacrylate and 0.47 mmol of tri(propylene glycol) diacrylate in a glass vial. All ingredients were mixed on a vortex device for about 30 seconds. Then 224.2 mg (concentration about 44.6 wt.%) of QDs dispersion in HDDA from the previous ligand exchange procedure was added to the mixture. All ingredients were mixed on a vortex device for about 30 seconds. In the next step 0,18 mmol of isobornyl acrylate was added to the mixture and mixed on a vortex device for about 30 seconds. Then 0.18 mmol of 2-hydroxy-2- methylpropiophenone was added to the mixture. All ingredients were mixed on a vortex device for about 30 seconds. Then the mixture was placed in a shaker and stirred for 2 h at 23 °C and 500 rpm until complete dissolution of solid compounds. The UV-curable ink is ready to use. Example 2 Blue-emitting ZnSe / ZnSe / ZnS quantum dots (DeepBlue dots) were synthesized according to the following procedure. Blue-emitting ZnSe / ZnSe / ZnS quantum dots (DeepBlue dots) were synthesized according to the same procedure as before, however, in the “Synthesis of ZnSe seeds (cores)” section, tellurium doping was omitted. As a result, the resulting quantum dots exhibit emission towards shorter wavelengths (below 450 nm) compared to PureBlue dots. All next steps (synthesis of ZnS shell, ligand exchange, ink formulation, etc.) of the previous procedure were the same. Nanomaterials characterization 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 λmax), FWHM and Photoluminescence Quantum Yield (QY) were measured on spectrometer Hamamatsu Quantaurus-QY Absolute PL quantum yield, C11347-11. The average particle size was measured by Dynamic Light Scattering (DLS) in an Anton-Paar Litesizer 500. Viscosity was measured on Anton-Paar ViscoQC 300 L Rotational Viscometer at 20°C. Surface tension was measured on goniometer RAMÈ-HART model: 90-U3-PRO at 20°C. Samples containing ink compositions were stored at room temperature. In addition, the samples were stored away from light sources and sealed. Table 2 UV-curable ink composition based on blue-emitting quantum dots Table 3 Parameters of the UV-curable ink based on PureBlue dots - Ink 1 Table 4 Parameters of the UV-curable ink based on DeepBlue dots – Ink 2 Table 5 Stability over time of PureBlue dots dispersion in HDDA after two-step ligand exchange Table 6 Stability over time of UV-curable ink based on PureBlue dots – Ink 3

Claims

AMENDED CLAIMS received by the International Bureau on 18 August 2025 (18.08.2025)Claims1. A two-step method for preparation of a colloidal functionalized blue-emitting quantum dots comprising following steps: a) stabilizing ligand exchange comprising functionalization of the QDs surface with 2-ethyl-1 -hexanethiol, comprising: placing the QDs dispersion in toluene or hexane of concentration 100 mg / mL with 0.069 mol of 2-ethyl-1 -hexanethiol in a thermal shaker for 1.5-3 h at 25-35 °C, ii) adding ethanol in a volume ratio of 1 : 1.5 (QDs dispersion:ethanol), then decanting and drying an obtained pellet, iii) dispersing the pellet obtained in step ii) in toluene to obtain a QDs dispersion with concentration of 100 mg / mL, iv) adding ethanol in a volume ratio of 1:1 (QDs dispersion:ethanol), then decanting and drying an obtained pellet, v) dispersing the pellet obtained in a step iv) in toluene to obtain a QDs dispersion with concentration of 100 mg / mL, vi) the obtained QDs dispersion was filtered through a paper filter. b) exchanging 2-ethyl-1-hexanethiol into mono-2-(methacryloyloxy)ethyl succinate, comprising: vii) placing QDs dispersion obtained in step a) with 0.160 mol of mono-2- (methacryloyloxy)ethyl succinate, adding PGMEA and toluene in a volume ratio of 1:0.4:0.4 (QDs dispersion:PGMEA:toluene) in a thermal shaker for 3, 5-4, 5 h at 45-55 °C, viii) adding octane in a volume ratio of 1:2 (QDs dispersion:octane), then decanting and drying an obtained pellet, ix) dispersing a pellet obtained in step viii) in the HDDA to obtain a concentration of about 40-45% by weight, x) placing a QDs dispersion in a thermal shaker for 3-4 h at 25-35 °C,xi) the obtained QDs dispersion was filtered through a centrifugal filter made of nylon for 10 minutes at 6000 rpm.

2. The method according to claim 1 , wherein the quantum dots are selected from the group comprising ZnS, ZnSe, CdSe, CdS, InP, CulnS, perovskites and preferably the quantum dots are doped with elements such as Te, Cu, Se, S, Li.

3. A method of preparation of the ink composition comprising functionalized quantum dots obtained according to any of claims 1 to 2, comprising following steps: a) dissolving 1 -hydroxycyclohexyl phenyl ketone in 1 ,6-hexanediol diacrylate and tri(propylene glycol) diacrylate wherein their ratio ranges from 1 :7:2 to 1 :8:3 by weight, respectively, b) adding QDs dispersion obtained according to any of claims 1 to 4 of concentration 40-45 wt.%, then isobornyl acrylate and then 2-hydroxy-2- methylpropiophenone were added, wherein their ratio ranges from 1 :1.4 to 1 :1.6 by weight, respectively, c) placing the mixture in a thermal shaker and stirring for 2-3 h at 20-25°C until complete dissolution of solid compounds.

4. The method according to claim 3 wherein in step b), after the addition of each compound the mixture is mixed on a vortex device for at least 30 seconds.

5. An UV-curable ink composition obtained by the method according to any of claims 3 to 4.

6. The UV-curable ink composition, according to claim 5, wherein the composition comprises:QDs (8-12 wt. %), 1 ,6-hexanediol diacrylate (57-61 wt. %), tri(propylene glycol) diacrylate (15-19 wt. %), isobornyl acrylate (4.5-5.5 wt. %), 2-hydroxy-2- metylpropiophenone (2.5-4.0 wt. %) and 1 -hydroxycyclohexyl phenyl ketone (6-8 wt. %).

7. A use of the UV-curable ink composition according to any of claims 5 to 6 in an anti- counterfeiting applications, as a colour (light) converting materials, in a light emitting device, in particular in a light-emitting diode and a displays and a sensors.

8. A light emitting device comprising the UV-curable ink composition according to any of claims 5 to 6, characterized in that UV-LED emission wavelength is 365 nm or 385 nm.

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