UPCONVERSION MULTICOLOR LIGHT-EMITTING POLYMER COMPOSITE, TRANSPARENT DISPLAY INCLUDING THE SAME AND METHOD FOR MANUFACTURING THE SAME

Abstract

An upconversion multicolor light-emitting polymer composite implements red, green, and blue colors at wavelengths in each specific region by mixing: an upconversion nanophosphor emitting light in red and blue colors at wavelengths in each specific region by absorbing the infrared light; an upconversion nanophosphor emitting light in green and blue colors at wavelengths in each specific region by absorbing the infrared light; and a polydimethylsiloxane (PDMS) polymer. Accordingly, a volumetric display with excellent color reproducibility may be realized with a simple manufacturing process.

Claims

1. An upconversion multicolor light-emitting polymer composite that implements red, green, and blue colors at wavelengths in each specific region of infrared light spectrum by mixing: an upconversion nanophosphor emitting light in red and blue colors at wavelengths in each specific region by absorbing the infrared light; an upconversion nanophosphor emitting light in green and blue colors at wavelengths in each specific region by absorbing the infrared light; and a polydimethylsiloxane (PDMS) polymer.

2. The upconversion multicolor light-emitting polymer composite of claim 1, wherein the upconversion nanophosphor emitting light in red and blue colors comprises a nanoparticle having a core-shell-shell-shell structure sequentially from a center.

3. The upconversion multicolor light-emitting polymer composite of claim 2, wherein the nanoparticle comprises: core exhibiting light emission in red color; a first shell being an optically inactive layer to surround the core; a second shell being a light emitting layer to surround the first shell and exhibit light emission in blue color; and a third shell being a crystalline layer to protect the second shell.

4. The upconversion multicolor light-emitting polymer composite of claim 1, wherein the upconversion nanophosphor emitting light in green and blue colors comprises nanoparticles having a core-shell-shell-shell-shell structure sequentially from a center.

5. The upconversion multicolor light-emitting polymer composite of claim 4, wherein the nanoparticle comprises: a core exhibiting light emission in green color; a first shell being an absorbing layer to absorb light in each specific wavelength region; a second shell being an optically inactive layer to surround the first shell; a third shell being a light emitting layer to surround the second shell and exhibit light emission in blue color; and a fourth shell being a crystalline layer to protect the third shell.

6. The upconversion multicolor light-emitting polymer composite of claim 1, wherein the upconversion multicolor light-emitting polymer composite exhibits light emission in red, green, and blue colors, respectively, when irradiated with infrared light having a peak of 1532 nm, 800 nm, and 980 nm.

7. The upconversion multicolor light-emitting polymer composite of claim 1, comprising: an upconversion nanophosphor emitting light in red and blue colors represented by Chemical Formula 1 below; and an upconversion nanophosphor emitting light in green and blue colors represented by Chemical Formula 2 below,
NaEr.sub.1-xF.sub.4:Tm.sub.x/NaYF.sub.4/NaYb.sub.1-yF.sub.4:Tm.sub.y/NaYF.sub.4[Chemical Formula 1] Here, x is a real number selected from the range satisfying 0?x?0.3 and y is 0<y?0.3,
NaY.sub.1-a-bF.sub.4:Yb.sub.a,Er.sub.b/NaY.sub.1-c-dF.sub.4:Nd.sub.c,Yb.sub.d/NaYF.sub.4/NaYb.sub.1-eF.sub.4:Tm.sub.e/NaYF.sub.4[Chemical Formula 2] Here, a is a real number selected from the range satisfying 0<a?0.5, b is a real number selected from the range satisfying 0<b?0.4, c is a real number selected from the range satisfying 0<c?1.0, d is a real number selected from the range satisfying 0?d?0.2, where c and d are real numbers selected from the range satisfying 0<c+d?1, and e is a real number selected from the range satisfying 0<e?0.3.

8. A transparent display comprising the upconversion multicolor light-emitting polymer composite according to claim 1.

9. A method of preparing an upconversion multicolor light-emitting polymer composite, comprising: preparing an upconversion nanophosphor solution that absorbs infrared light to emit light in red and blue colors at wavelengths in each specific region; preparing an upconversion nanophosphor solution that absorbs the infrared light to emit light in green and blue colors at wavelengths in each specific region; preparing a mixed solution by mixing the prepared upconversion nanophosphor solution emitting light in red and blue colors with the upconversion nanophosphor solution emitting light in green and blue colors; and mixing the prepared mixed solution with a polydimethylsiloxane (PDMS) polymer.

10. A method of claim 9, wherein the preparing of the upconversion nanophosphor solution emitting light in red and blue colors comprises: creating a core exhibiting light emission in red color; creating a first shell being an optically inert layer to surround the core; creating a second shell being a light emitting layer to surround the first shell and exhibit light emission in blue color; and creating a third shell being a crystalline layer to protect the second shell.

11. The method of claim 9, wherein the preparing of the upconversion nanophosphor solution emitting light in green and blue colors comprises: creating a core exhibiting light emission in green color; creating a first shell being an absorbing layer to absorb wavelengths in each specific region; creating a second shell being an optically inactive layer to surround the first shell; creating a third shell being a light-emitting layer to surround the second shell and exhibit light emission in a blue color; and creating a fourth shell being a crystalline layer to protect the third shell.

12. The method of claim 9, wherein the preparing of the upconversion nanophosphor solution emitting light in red and blue colors further comprises: diluting the prepared nanophosphor solution by 1/2.

13. The method of claim 9, wherein the preparing of the upconversion nanophosphor solution emitting light in green and blue colors further comprises: diluting the prepared nanophosphor solution by 1/2.

14. The method of claim 9, wherein the preparing of the mixed solution further comprises: mixing the upconversion nanophosphor solution emitting light in red and blue colors with the upconversion nanophosphor solution emitting light in green and blue colors in a 1:2 ratio.

15. The method of claim 9, wherein in the preparing of the mixed solution, an upconversion nanophosphor emitting light in red and blue colors represented by Chemical Formula 1 below is mixed with an upconversion nanophosphor emitting light in green and blue colors represented by Chemical Formula 2 below,
NaEr.sub.1-xF.sub.4:Tm.sub.x/NaYF.sub.4/NaYb.sub.1-yF.sub.4:Tm.sub.y/NaYF.sub.4[Chemical Formula 1] Here, x is a real number selected from the range satisfying 0?x?0.3 and y is 0<y?0.3,
NaY.sub.1-a-bF.sub.4:Yb.sub.a,Er.sub.b/NaY.sub.1-c-dF.sub.4:Nd.sub.c,Yb.sub.d/NaYF.sub.4/NaYb.sub.1-eF.sub.4:Tm.sub.e/NaYF.sub.4[Chemical Formula 2] Here, a is a real number selected from the range satisfying 0<a?0.5, b is a real number selected from the range satisfying 0<b?0.4, c is a real number selected from the range satisfying 0<c?1.0, d is a real number selected from the range satisfying 0?d?0.2, where c and d are real numbers selected from the range satisfying 0<c+d?1, and e is a real number selected from the range satisfying 0<e?0.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIGS. 1A to 1D are transmission electron microscope images of nanoparticles of a core or a core-shell-shell-shell structure, according to an embodiment of the present disclosure.

[0034] FIG. 2A is a PL spectrum of a nanoparticle with a core-shell-shell-shell structure under 980 nm near-infrared excitation according to an embodiment of the present disclosure.

[0035] FIG. 2B is a PL spectrum of a nanoparticle with a core-shell-shell-shell structure under 1532 nm near-infrared excitation according to an embodiment of the present disclosure.

[0036] FIGS. 3A to 3E are transmission electron microscope images of nanoparticles of a core or a core-shell-shell-shell-shell structure, according to an embodiment of the present disclosure.

[0037] FIG. 4A is a PL spectrum of a nanoparticle with a core-shell-shell-shell-shell structure under 800 nm near-infrared excitation according to an embodiment of the present disclosure.

[0038] FIG. 4B is a PL spectrum of a nanoparticle with a core-shell-shell-shell-shell structure under 980 nm near-infrared excitation according to an embodiment of the present disclosure.

[0039] FIG. 5A is a PL spectrum of a mixed solution of nanoparticles under 1532 nm near-infrared excitation according to an embodiment of the present disclosure.

[0040] FIG. 5B is a PL spectrum of a mixed solution of nanoparticles under 800 nm near-infrared excitation according to an embodiment of the present disclosure.

[0041] FIG. 5C is a PL spectrum of a mixed solution of nanoparticles under 980 nm near-infrared excitation according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The following detailed description of the present disclosure will be made with reference to the accompanying drawings illustrating specific exemplary embodiments for carrying out the present disclosure. These exemplary embodiments will be described in detail enough to carry out the present disclosure by those skilled in the art. It should be understood that various exemplary embodiments of the present disclosure are different from one another but need not be mutually exclusive. For example, particular shapes, structures, and characteristics described herein in respect to one exemplary embodiment may be implemented in other exemplary embodiments without departing from the spirit and scope of the present disclosure. In addition, it should be understood that the position or arrangement of each constituent element in the respective disclosed exemplary embodiments may be changed without departing from the spirit and scope of the present disclosure. Therefore, the following detailed description is not considered as having limited meanings, and the scope of the present disclosure, if adequately explained, is limited only by the appended claims as well as all the scopes equivalent to the appended claims. Like reference numerals in the drawings refer to the same or similar functions throughout several aspects.

[0043] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings.

[0044] Synthesizing nanoparticles that implement light emission in red (R), green (G), and blue (B) colors from a single nanoparticle requires designing nanoparticles with very complex structures, and it is very challenging to achieve strong emission of all three colors.

[0045] Accordingly, the present disclosure provides a transparent polymer composite that is capable of emitting light in red, green, and blue colors by mixing two types of nanoparticles that are capable of emitting two strong colors.

[0046] An upconversion multicolor light-emitting polymer composite according to the present disclosure is manufactured by mixing nanophosphors that absorb infrared light and emit light in red and blue colors at wavelengths in each specific region with nanophosphors that absorb infrared light and emit light in green and blue colors at wavelengths in each specific region.

[0047] In addition, the upconversion multicolor light-emitting polymer composite is a transparent composite manufactured by mixing polydimethylsiloxane (PDMS) polymers and others to implement red, green, and blue colors at wavelengths in each specific region of the Infrared.

[0048] In an embodiment, the upconversion multicolor light-emitting polymer composite according to the present disclosure is produced by mixing upconversion nanoparticles that emit light in red color when absorbing about 1532 nm infrared light and emit light in blue color when absorbing about 980 nm infrared light with upconversion nanoparticles that emit light in green color when absorbing about 800 nm infrared light and emit light in blue color when absorbing about 980 nm infrared light.

[0049] The upconversion multicolor light-emitting polymer composite according to the present disclosure is capable of absorbing about 1532 nm, about 800 nm, and about 980 nm infrared light to emit light in red, green, and blue colors, respectively. In addition, the upconversion multicolor light-emitting polymer composite is a transparent polymer composite, which may be applied to color displays or transparent displays. In addition, the upconversion multicolor light-emitting polymer composite may also be applied to volumetric displays or head-up displays (HUDs) in vehicles.

[0050] An upconversion nanophosphor that emits light in red and blue colors may have a nanoparticle with a core-shell-shell-shell structure, sequentially from a center.

[0051] For example, a nanoparticle constituting an upconversion nanophosphor that emits light in red and blue colors may have a structure that has a core that exhibits light emission in red color, a first shell that is an optically inactive layer that surrounds the core, a second shell that is a light emitting layer that surrounds the first shell and exhibits light emission in blue color, and a third shell that is a crystalline layer that protects the second shell.

[0052] An upconversion nanophosphor that emits light in green and blue colors may have a nanoparticle with a core-shell-shell-shell-shell structure, sequentially from a center.

[0053] For example, a nanoparticle constituting an upconversion nanophosphor that emits light in green and blue colors may have the structure that have a core that exhibits light emission in green color, a first shell that is an absorbing layer that absorbs wavelengths in each specific region, a second shell that is an optically inactive layer that surrounds the first shell, a third shell that is a light emitting layer that surrounds the second shell and exhibits light emission in blue color, and a fourth shell that is a crystalline layer that protects the third shell.

[0054] FIGS. 1A to 1D are transmission electron microscope images of nanoparticles of a core or a core-shell-shell-shell structure, according to an embodiment of the present disclosure.

[0055] Hereinafter, with reference to FIGS. 1A to 1D, a method of manufacturing a nanophosphor that emits light in red and blue colors is described according to an embodiment of the present disclosure.

[0056] First, according to an embodiment, an upconversion core nanophosphor doped with a Tm.sup.3+ and emitting light in red color is prepared (see FIG. 1A). For example, NaErF.sub.4:Tm.sup.3+ nanoparticle doped with about 0.005 mmol of Tm.sup.3+ may be prepared.

[0057] About 0.995 mmol of erbium chloride hexahydrate (ErCl.sub.3.Math.6H.sub.2O) and about 0.005 mmol of thulium chloride hexahydrate (TmCl.sub.3.Math.6H.sub.2O) were mixed with a solution including oleic acid and 1-octadecene, and a mixed solution including a lanthanide complex was prepared by heat treatment at about 150? C. for about 30 minutes (first mixed solution preparation step).

[0058] About 10 ml of a methanol solution including about 2.5 mmol of sodium hydroxide and about 4 mmol of ammonium fluoride was prepared (second mixed solution preparation step), and then mixed into the first mixed solution (reaction solution preparation step).

[0059] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0060] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0061] FIG. 1A is a transmission electron microscope image of the upconversion nanophosphors prepared through the process described above, and it was confirmed that core nanophosphors with uniform size and shape were synthesized.

[0062] Then, according to an embodiment, upconversion nanophosphors with a core-shell structure through fluoride shell formation are prepared (see FIG. 1B).

[0063] Using the NaErF.sub.4:Tm.sup.3+ nanoparticle prepared according to the embodiment in FIG. 1A as a core, a nanophosphor with a core-shell (NaErF.sub.4:Tm.sup.3+/NaYF.sub.4) structure including a fluoride-based compound was prepared.

[0064] Accordingly, the shell prepared may be a crystalline shell represented by chemical formula NaYF.sub.4. First, about 2.5 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O) was mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for about 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0065] The first mixed solution was mixed with a solution including NaErF.sub.4:Tm.sup.3+ nanoparticles prepared according to the embodiment in FIG. 1A to prepare a second mixed solution (second mixed solution preparation step).

[0066] About 25 ml of a methanol solution including about 6.25 mmol of sodium hydroxide and about 10 mmol of ammonium fluoride was prepared in the second mixing solution (third mixing solution preparation step), and then mixed into the mixed solution including the lanthanide complex (reaction solution preparation step).

[0067] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0068] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0069] FIG. 1B is a transmission electron microscope image of the core-shell upconversion nanophosphors prepared through the process described above, and it was confirmed that core-shell upconversion nanophosphors with uniform size and shape were synthesized.

[0070] Then, according to an embodiment, upconversion nanophosphors with a core-shell-shell structure are prepared (see FIG. 1C).

[0071] Using the NaErF.sub.4:Tm.sup.3+/NaYF.sub.4 nanoparticle prepared according to the embodiment in FIG. 1B as a core, a nanophosphor with a core-shell-shell structure including NaYbF.sub.4:Tm.sup.3+ compound was prepared. The prepared NaYbF.sub.4:Tm.sup.3+ compound may be understood as, for example, a NaYb.sub.0.99F.sub.4:Tm.sup.3+.sub.0.01 compound. In addition, the shell including the NaYbF.sub.4:Tm.sup.3+ compound may be a shell emitting light in blue color.

[0072] About 2.97 mmol of ytterbium chloride hexahydrate (YbCl.sub.3.Math.6H.sub.2O) and about 0.03 mmol of thulium chloride hexahydrate (TmCl.sub.3.Math.6H.sub.2O) were mixed with a solution including oleic acid and 1-octadecene, and a mixed solution including a lanthanide complex was prepared by heat treatment at about 150? C. for about 30 minutes (first mixed solution preparation step).

[0073] The first mixed solution was mixed with a solution including NaErF.sub.4:Tm.sup.3+/NaYF.sub.4 nanoparticles prepared according to the embodiment in FIG. 1B to prepare a second mixed solution (second mixed solution preparation step).

[0074] About 30 ml of a methanol solution including about 7.5 mmol of sodium hydroxide and about 12 mmol of ammonium fluoride was prepared (third mixing solution preparation step), and then mixed into the second mixed solution including the lanthanide complex (reaction solution preparation step).

[0075] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0076] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0077] FIG. 1C illustrated a transmission electron microscope image of the upconversion nanophosphors with the core-shell-shell structure synthesized through the process described above. It could be confirmed from the transmission electron microscope image that the particles further increased in size due to the formation of a second shell around the core-shell.

[0078] Then, according to an embodiment, upconversion nanophosphors with a core-shell-shell-shell structure are prepared (see FIG. 1D).

[0079] Using the NaErF.sub.4:Tm.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+ nanoparticle prepared according to the embodiment in FIG. 1C as a core, a nanophosphor with a core-shell-shell-shell (NaErF.sub.4:Tm.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+/NaYF.sub.4) structure including NaYF.sub.4 compound was prepared.

[0080] Here, the shell prepared may be a crystalline shell represented by a chemical formula NaYF.sub.4. First, about 1 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O) was mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for about 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0081] The first mixed solution was mixed with a solution including NaErF.sub.4:Tm.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+ nanoparticles prepared according to the embodiment in FIG. 1C to prepare a second mixed solution (second mixed solution preparation step).

[0082] About 10 ml of a methanol solution including about 2.5 mmol of sodium hydroxide and about 4 mmol of ammonium fluoride was prepared (third mixing solution preparation step), and then mixed into the second mixed solution including the lanthanide complex (reaction solution preparation step).

[0083] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0084] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0085] FIG. 1D illustrated a transmission electron microscope image of the upconversion nanophosphors with the core-shell-shell-shell structure synthesized through the process described above. It could be confirmed from the transmission electron microscope image that the particles further increased in size due to the formation of a shell around the core-shell-shell.

[0086] FIG. 2 illustrates PL spectra conditions of each wavelength for the upconversion nanoparticle with the core-shell-shell-shell structure prepared according to the embodiment in FIG. 1.

[0087] With reference to FIG. 2A, it can be seen that under near-infrared light excitation with 980 nm, the upconversion nanophosphor with the core-shell-shell-shell structure exhibits a strong light emission peak of blue color. In contrast, with reference to FIG. 2B, PL spectrum under near-infrared light excitation with 1532 nm is illustrated, and it can be seen that the upconversion nanophosphor with the core-shell-shell-shell structure exhibits a strong light emission peak of red color. It can be seen that the upconversion nanophosphor with the core-shell-shell-shell structure exhibit light emission of blue and red colors, respectively, when irradiated with 980 nm and 1532 nm near-infrared light-emitting lasers.

[0088] FIGS. 3A to 3E are transmission electron microscope images of nanoparticles of a core or a core-shell-shell-shell-shell structure, according to an embodiment of the present disclosure.

[0089] Hereinafter, with reference to FIGS. 3A to 3E, a method of manufacturing a nanophosphor that emits light in green and blue colors is described according to an embodiment of the present disclosure.

[0090] First, according to an embodiment, an upconversion core nanophosphor doped with a Yb.sup.3+ and Er.sup.3+ and emitting light in green color is prepared (see FIG. 3A). For example, about 0.18 mmol of Yb.sup.3+ and about 0.02 mmol of Er.sup.3+ doped NaYF.sub.4:Yb.sup.3+,Er.sup.3+ nanoparticle may be prepared.

[0091] About 0.8 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O), about 0.18 mmol of ytterbium chloride hexahydrate (YbCl.sub.3.Math.6H.sub.2O), and about 0.02 mmol of erbium chloride hexahydrate (ErCl.sub.3.Math.6H.sub.2O) were mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0092] About 10 ml of a methanol solution including about 2.5 mmol of sodium hydroxide and about 4 mmol of ammonium fluoride was prepared (second mixed solution preparation step), and then mixed into the first mixed solution (reaction solution preparation step).

[0093] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0094] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0095] FIG. 3A is a transmission electron microscope image of the upconversion nanophosphors prepared through the process described above, and it was confirmed that core nanophosphors with uniform size and shape were synthesized.

[0096] Then, according to an embodiment, upconversion nanophosphors with a core-shell structure are prepared (see FIG. 3B).

[0097] Using the NaYF.sub.4:Yb.sup.3+,Er.sup.3+ nanoparticle prepared according to the embodiment of FIG. 3A as a core, a nanophosphor with a core-shell (NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+) structure including a fluoride-based compound was prepared. Here, the shell prepared may be a crystalline shell represented by a chemical formula NaYF.sub.4:Nd.sup.3+,Yb.sup.3+.

[0098] First, about 0.36 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O), about 0.18 mmol of neodymium chloride hexahydrate (NdCl.sub.3.Math.6H.sub.2O), and about 0.06 mmol of ytterbium chloride hexahydrate (YbCl.sub.3.Math.6H.sub.2O) were mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0099] The first mixed solution was mixed with a solution including NaYF.sub.4:Yb.sup.3+,Er.sup.3+ nanoparticles prepared according to the embodiment in FIG. 3A to prepare a second mixed solution (second mixed solution preparation step).

[0100] About 6 ml of a methanol solution including about 1.5 mmol of sodium hydroxide and about 2.4 mmol of ammonium fluoride was prepared in the second mixing solution (third mixing solution preparation step), and then mixed into the mixed solution including the lanthanide complex (reaction solution preparation step).

[0101] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0102] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0103] FIG. 3B is a transmission electron microscope image of the core-shell upconversion nanophosphors prepared through the process described above, and it was confirmed that core-shell upconversion nanophosphors with uniform size and shape were synthesized.

[0104] Then, according to an embodiment, upconversion nanophosphors with a core-shell-shell structure are prepared (see FIG. 3C).

[0105] Using the NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+ core-shell nanoparticle illustrated in FIG. 3B as a core, a nanophosphor with a core-shell-shell structure including NaYF.sub.4 compound was prepared.

[0106] About 2.5 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O) was mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for about 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0107] The first mixed solution was mixed with a solution including NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+ nanoparticles prepared according to the embodiment in FIG. 3B to prepare a second mixed solution (second mixed solution preparation step).

[0108] About 25 ml of a methanol solution including about 6.25 mmol of sodium hydroxide and about 10 mmol of ammonium fluoride was prepared (third mixing solution preparation step), and then mixed into the second mixed solution including the lanthanide complex (reaction solution preparation step).

[0109] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0110] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0111] FIG. 3C illustrated a transmission electron microscope image of the upconversion nanophosphors with the core-shell-shell structure synthesized through the process described above. It could be confirmed from the transmission electron microscope image that the particles further increased in size due to the formation of a second shell around the core-shell.

[0112] Then, according to an embodiment, upconversion nanophosphors with a core-shell-shell-shell structure are prepared (see FIG. 3D).

[0113] Using the NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4 nanoparticle prepared according to the embodiment in FIG. 3C as a core, a nanophosphor with a core-shell-shell-shell (NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+) structure including a NaYbF.sub.4:Tm.sup.3+ compound was prepared.

[0114] The NaYbF.sub.4:Tm.sup.3+ compound prepared according to the embodiment in FIG. 3D may be understood as a compound of a chemical formula NaYb.sub.0.995F.sub.4:Tm.sup.3+.sub.0.005. First, about 2.985 mmol of ytterbium chloride hexahydrate (YbCl.sub.3.Math.6H.sub.2O) and about 0.015 mmol of thulium chloride hexahydrate (TmCl.sub.3.Math.6H.sub.2O) were mixed with a solution including oleic acid and 1-octadecene, and a mixed solution including a lanthanide complex was prepared by heat treatment at about 150? C. for about 30 minutes (first mixed solution preparation step).

[0115] The first mixed solution was mixed with a solution including NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4 nanoparticles prepared according to the embodiment in FIG. 3C to prepare a second mixed solution (second mixed solution preparation step).

[0116] About 30 ml of a methanol solution including about 7.5 mmol of sodium hydroxide and about 12 mmol of ammonium fluoride was prepared (third mixing solution preparation step), and then mixed into the second mixed solution including the lanthanide complex (reaction solution preparation step).

[0117] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0118] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0119] FIG. 3D illustrated a transmission electron microscope image of the upconversion nanophosphors with the core-shell-shell-shell structure synthesized through the process described above. It could be confirmed from the transmission electron microscope image that the particles further increased in size due to the formation of a shell around the core-shell-shell.

[0120] Then, according to an embodiment, upconversion nanophosphors with a core-shell-shell-shell-shell structure are prepared (see FIG. 3E).

[0121] Using the NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+ nanoparticle prepared according to the embodiment in FIG. 3D as a core, a nanophosphor with a core-shell-shell-shell-shell (NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+/NaYF.sub.4) structure including NaYF.sub.4 compound was prepared.

[0122] The compound prepared according to the embodiment in FIG. 3E may be understood as a compound of a chemical formula NaYF.sub.4. First, about 1 mmol of yttrium chloride hexahydrate (YCl.sub.3.Math.6H.sub.2O) was mixed with a solution including oleic acid and 1-octadecene and heat treated at about 150? C. for about 30 minutes to prepare a mixed solution including a lanthanide complex (first mixed solution preparation step).

[0123] The first mixed solution was mixed with a solution including NaYF.sub.4:Yb.sup.3+,Er.sup.3+/NaYF.sub.4:Nd.sup.3+,Yb.sup.3+/NaYF.sub.4/NaYbF.sub.4:Tm.sup.3+ nanoparticles prepared according to the embodiment in FIG. 3D to prepare a second mixed solution (second mixed solution preparation step).

[0124] About 10 ml of a methanol solution including about 2.5 mmol of sodium hydroxide and about 4 mmol of ammonium fluoride was prepared (third mixing solution preparation step), and then mixed into the second mixed solution including the lanthanide complex (reaction solution preparation step).

[0125] After being thoroughly mixed, methanol was removed and heat treated under an inert gas atmosphere. Preferably, the heat treatment temperature is about 200 to 370? C. and the heat treatment time is about 10 minutes to 4 hours (nanoparticle formation step).

[0126] After the heat treatment process and cooling to room temperature, nanophosphors in a colloidal state is obtained. The prepared nanophosphors were washed with acetone or ethanol and distributed in non-polar solvents such as hexane, toluene, and chloroform for storage.

[0127] FIG. 3E illustrated a transmission electron microscope image of the upconversion nanophosphors with the core-shell-shell-shell-shell structure synthesized through the process described above. It could be confirmed from the transmission electron microscope image that the particles further increased in size due to the formation of a shell around the core-shell-shell-shell.

[0128] FIG. 4 illustrates PL spectra under near-infrared excitation conditions of each wavelength for the upconversion nanoparticle with the core-shell-shell-shell-shell structure prepared according to the embodiment in FIG. 3.

[0129] In FIG. 4A, it can be seen that the upconversion nanoparticle with core-shell-shell-shell-shell structure exhibit a strong light emission peak of green color under the near-infrared excitation condition of about 800 nm. The light emission intensity in the red spectrum is also strong, but taking into account the human eye sensitivity, it is observed as the light emission in green color.

[0130] In contrast, in FIG. 4B, it can be seen that the upconversion nanoparticle with core-shell-shell-shell-shell structure exhibit the PL spectrum under the near-infrared excitation condition of about 980 nm, with a strong light emission peak of blue color. It can be seen that irradiation with lasers at about 800 nm and about 980 nm resulted in the light emission of green and blue colors, respectively.

[0131] Next, a mixed solution of an upconversion nanophosphor with light emission in red-green-blue colors is prepared.

[0132] A mixed solution of mixing the nanophosphor solutions prepared in FIGS. 1 and 3, respectively, was prepared. At this time, the nanophosphor solution prepared in FIG. 1 was diluted by about 1/2 and 0.5 mL thereof was taken, and the nanophosphor solution prepared in FIG. 3 was diluted by about 1/2 and about 1 mL thereof was taken and then mixed.

[0133] FIG. 5 illustrates light emission spectra under near-infrared excitation for the prepared nanophosphor solution, and it was confirmed that the nanophosphor mixed solution prepared with reference to the embodiment in FIG. 5 can exhibit light emission in red, green, and blue colors, respectively, depending on the excitation wavelength of the applied laser.

[0134] Finally, an upconversion nanophosphor-polymer composite with light emission in red-green-blue colors is prepared.

[0135] The prepared mixed solution of the upconversion nanophosphors with light emission in red-green-blue colors was mixed with polydimethyl siloxane (PDMS) polymer to prepare a polymer composite.

[0136] Therefore, about 0.4 mL of the prepared nanophosphor mixed solution was mixed with about 10 mL of Sylgard 184 PDMS polymer and about 1 mL of a curing agent, and then heat treated at about 80? C. for about 1 hour to prepare a polymer composite.

[0137] The polymer composite according to an embodiment of the present disclosure may include an upconversion nanophosphor emitting light in red and blue colors represented by Chemical Formula 1 below and an upconversion nanophosphor emitting light in green and blue colors represented by Chemical Formula 2 below.

NaEr.sub.1-xF.sub.4:Tm.sub.x/NaYF.sub.4/NaYb.sub.1-yF.sub.4:Tm.sub.y/NaYF.sub.4[Chemical Formula 1]

[0138] Here, x is a real number selected from the range satisfying 0?x?0.3 and y is 0<y?0.3.

NaY.sub.1-a-bF.sub.4:Yb.sub.a,Er.sub.b/NaY.sub.1-c-dF.sub.4:Nd.sub.c,Yb.sub.d/NaYF.sub.4/NaYb.sub.1-eF.sub.4:Tm.sub.e/NaYF.sub.4[Chemical Formula 2]

[0139] Here, a is a real number selected from the range satisfying 0<a?0.5, b is a real number selected from the range satisfying 0<b?0.4, c is a real number selected from the range satisfying 0<c?1.0, d is a real number selected from the range satisfying 0?d?0.2, where c and d are real numbers selected from the range satisfying 0<c+d?1, and e is a real number selected from the range satisfying 0<e?0.3.

[0140] Experimental results showed that, like the prepared nanophosphor solution, the upconversion nanophosphor-polymer composite exhibited light emission in green, blue, and red colors, respectively, when excited by near-infrared with peaks near 800 nm, 980 nm, and 1532 nm.

[0141] In addition, it can be seen that the nanophosphor-polymer composite emits light in green, blue, and red colors when three wavelengths of near-infrared are applied simultaneously, and the alphabet of different colors could be displayed by controlling positions of the applied lasers.

[0142] While the present disclosure has been described above with reference to the exemplary embodiments, it may be understood by those skilled in the art that the present disclosure may be variously modified and changed without departing from the spirit and scope of the present disclosure disclosed in the claims.

[0143] According to the present disclosure, a transparent polymer composite capable of exhibiting R/G/B light emission may be prepared by mixing upconversion nanoparticles exhibiting strong R/B light emission and G/B light emission into a polymer, from which a three-dimensional image may be realized.

[0144] In addition, a polymer film that includes nanoparticles exhibiting strong R/G light emission and G/B light emission is manufactured, which is applicable to the windshield of an automobile as a head up display (HUD). In this case, the polymer film uses a self-light emitting display method, which provides a wider viewing angle than the HUD with the current reflective display, thereby overcoming the disadvantage of needing to adjust the display position according to the driver's eye level.