Color tunable multifunctional nanophosphor, synthesis method thereof, and polymer composite including the nanophosphor

Abstract

A nanophosphor in accordance with one exemplary embodiment of the present disclosure includes a fluoride-based nanoparticle co-doped with Ce.sup.3+ and one selected from a group consisting of Tb.sup.3+, Eu.sup.3+ and a combination thereof. The nanophosphor may be excited by a single wavelength of ultraviolet rays to emit various colors of green, yellow, orange, red and the like, and exhibit high photostability without photoblinking. The nanophosphor may be utilized as a bio imaging contrast agent, a transparent display device, an anti-counterfeit code and the like.

Claims

1. A nanophosphor comprising a fluoride-based nanoparticle expressed by the following chemical formula 1 and co-doped with Ce.sup.3+ and one selected from a group consisting of Tb.sup.3+, Eu.sup.3+ and a combination thereof,
NaY.sub.1-w-x-y-zGd.sub.wF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y,Eu.sup.3+.sub.z  [Chemical formula 1] where x denotes a real number in the range of 0.1≦x≦0.5, y denotes a real number in the range of 0≦y≦0.4, z denotes a real number in the range of 0≦z≦0.3, w denotes a real number in the range of 0≦w≦0.9, and 0<y+z and 0≦w+x+y+z≦1 are satisfied.

2. A nanophosphor having a core-shell structure comprising: a core comprising a fluoride-based nanoparticle expressed by chemical formula 1 and co-doped with Ce.sup.3+ and one selected from a group consisting of Tb.sup.3+, Eu.sup.3+ and a combination thereof; and a shell covering a surface of the core, wherein the shell consists of a compound expressed by the following chemical formula 2,
NaY.sub.1-w-x-y-zGd.sub.wF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y,Eu.sup.3+.sub.z  [Chemical formula 1]
NaGd.sub.1-rM.sub.rF.sub.4  [Chemical formula 2] wherein in the chemical formula 1, x denotes a real number in the range of 0.1≦x≦0.5, y denotes a real number in the range of 0≦y≦0.4, z denotes a real number in the range of 0≦z≦0.3, w denotes a real number in the range of 0≦w≦0.9, and 0<y+z and 0≦w+x+y+z≦1 are satisfied, and wherein in the chemical formula 2, r denotes a real number in the range of 0≦r<1, and M denotes one selected from a group consisting of yttrium (Y), lanthanide element and a combination thereof.

3. The nanophosphor of claim 1, wherein a size of the fluoride-based nanoparticle is in the range of 1 to 50 nm.

4. The nanophosphor of claim 1, wherein the fluoride-based nanoparticle has a hexagonal structure.

5. The nanophosphor of claim 2, wherein the nanophosphor having the core-shell structure is greater than 1 nm and 60 nm or less.

6. The nanophosphor of claim 1, wherein the nanophosphor has a down-conversion photoluminescence property of emitting a green, yellowish green, yellow, orange or red color under a single wavelength excitation according to the content of lanthanide elements.

7. The nanophosphor of claim 1, wherein the nanophosphor comprises a fluoride-based nanoparticle containing Tb.sup.3+ and Eu.sup.3+ in a molar ratio of 30 to 15:1, and has a yellowish green-emitting photoluminescence property.

8. The nanophosphor of claim 1, wherein the nanophosphor comprises a fluoride-based nanoparticle containing Tb.sup.3+ and Eu.sup.3+ in a molar ratio of 7 to 8:1, and has a yellow-emitting photoluminescence property.

9. The nanophosphor of claim 1, wherein the nanophosphor comprises a fluoride-based nanoparticle containing Tb.sup.3+ and Eu.sup.3+ in a molar ratio of 3 to 4:1, and has an orange-emitting photoluminescence property.

10. The nanophosphor of claim 1, wherein the nanophosphor comprises a fluoride-based nanoparticle containing Tb.sup.3+ and Eu.sup.3+ in a molar ratio of 1 to 2:1, and has a scarlet-emitting photoluminescence property.

11. A method of synthesizing a nanophosphor comprising: a complex compound preparing step of heat treating a mixture including at least one selected from a group consisting of terbium precursor and europium precursor, yttrium precursor, gadolinium precursor, cerium precursor, oleic acid, and a mixture solvent to prepare a lanthanide complex compound; a first mixed-solution preparing step of mixing the lanthanide complex compound with a solution including oleic acid and 1-octadecene to prepare a first mixed-solution containing the lanthanide complex compound; a reaction-solution preparing step of mixing the first mixed-solution with a second mixed-solution including sodium precursor, fluorine precursor and alcohol to prepare a reaction-solution; and a nanoparticle preparing step of forming a fluoride-based nanoparticle by removing the alcohol from the reaction-solution, followed by heat treatment, wherein the nanoparticle is a fluoride-based nanoparticle expressed by chemical formula 1, and co-doped with Ce.sup.3+ and one selected from a group consisting of Tb.sup.3+, Eu.sup.3+ and a combination thereof,
NaY.sub.1-w-x-y-zGd.sub.wF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y,Eu.sup.3+.sub.z  [Chemical formula 1] where x denotes a real number in the range of 0.1≦x≦0.5, y denotes a real number in the range of 0≦y≦0.4, z denotes a real number in the range of 0≦z≦0.3, w denotes a real number in the range of 0≦w≦0.9, and 0<y+z and 0≦w+x+y+z≦1 are satisfied.

12. The method of claim 11, wherein the yttrium precursor is one selected from a group consisting of yttrium acetate (Y(CH.sub.3COO).sub.3), yttrium chloride (YCl.sub.3), yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), and any combination thereof, wherein the gadolinium precursor is one selected from a group consisting of gadolinium acetate (Gd(CH.sub.3COO).sub.3), gadolinium chloride (GdCl.sub.3), gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), and any combination thereof, wherein the cerium precursor is one selected from a group consisting of cerium acetate (Ce(CH.sub.3COO).sub.3), cerium chloride (CeCl.sub.3), cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), and any combination thereof, wherein the terbium precursor is one selected from a group consisting of terbium acetate (Tb(CH.sub.3COO).sub.3), terbium chloride (TbCl.sub.3), terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), and any combination thereof, and wherein the europium precursor is one selected from a group consisting of europium acetate (Eu(CH.sub.3COO).sub.3), europium chloride (EuCl.sub.3), europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and any combination thereof.

13. The method of claim 11, wherein the heat treatment in the nanoparticle preparing step is carried out at temperature of 200 to 370° C. for 10 minutes to four hours.

14. The method of claim 11, further comprising a shell preparing step after the nanoparticle preparing step, wherein the shell preparing step comprises: a shell solution preparing step of preparing a third mixed-solution containing lanthanide precursor comprising gadolinium precursor, oleic acid, and 1-octadecene; a nanoparticle mixing step of heat treating the third mixed-solution to form gadolinium oleate therein and mixing the heat treated third mixed-solution with fluoride-based nanoparticles to prepare a fourth mixed-solution; a shell reaction-solution preparing step of to mix the fourth mixed-solution with a solution containing sodium precursor, fluorine precursor and alcohol to prepare a shell reaction-solution; and a shell forming step of growing a shell on a surface of a core, which comprises the fluoride-based nanoparticles, by removing the alcohol from the shell reaction-solution, followed by heat treatment, and wherein the shell consists of a compound expressed by the following chemical formula 2,
NaGd.sub.1-rM.sub.rF.sub.4  [Chemical formula 2] where r denotes a real number in the range of 0≦r<1, and M denotes one selected from a group consisting of yttrium (Y), lanthanide element and a combination thereof.

15. The method of claim 14, wherein the gadolinium precursor is one selected from a group consisting of gadolinium acetate (Gd(CH.sub.3COO).sub.3), gadolinium chloride (GdCl.sub.3), gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), and any combination thereof.

16. A nanophosphor-polymer composite comprising the nanophosphor according to claim 1 and a polymer.

17. A nanophosphor-polymer composite comprising the nanophosphor according to claim 2 and a polymer.

18. A fluorescent or magnetic resonance imaging contrast agent comprising the nanophosphor according to claim 1.

19. An anti-counterfeit code comprising the nanophosphor according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the disclosure.

(3) In the drawings:

(4) FIG. 1 illustrates photoluminescence (PL) spectra of respective Examples with varied contents of Tb and Eu of Na(Y,Gd)F.sub.4:Ce,Tb,Eu nanophosphor in accordance with an exemplary embodiment of the present disclosure;

(5) FIG. 2 illustrates TEM images of respective Examples with varied contents of Tb and Eu of Na(Y,Gd)F.sub.4:Ce,Tb,Eu nanophosphor in accordance with an exemplary embodiment of the present disclosure;

(6) FIG. 3 illustrates X-ray diffraction patterns of respective Examples with varied contents of Tb and Eu of Na(Y,Gd)F.sub.4:Ce,Tb,Eu nanophosphor in accordance with an exemplary embodiments of the present disclosure;

(7) FIG. 4 illustrates color coordinates of luminescent colors of each Example with varied contents of Tb and Eu of Na(Y,Gd)F.sub.4:Ce,Tb,Eu nanophosphor in accordance with an exemplary embodiment of the present disclosure;

(8) FIG. 5 illustrates luminescence images of nanophosphor solutions of each Example with varied contents of Tb and Eu of Na(Y,Gd)F.sub.4:Ce,Tb,Eu nanophosphor in accordance with an exemplary embodiment of the present disclosure;

(9) FIG. 6 is a TEM image of Na(Y,Gd)F.sub.4:Ce,Tb,Eu core nanophosphor having a size less than 10 nm in accordance with an exemplary embodiments of the present disclosure;

(10) FIG. 7 is a TEM image of Na(Y,Gd)F.sub.4:Ce,Tb,Eu/NaGdF.sub.4 core-shell nanophosphor in accordance with an exemplary embodiment of the present disclosure;

(11) FIG. 8 illustrates a PL spectrum of Na(Y,Gd)F.sub.4:Ce,Tb,Eu/NaGdF.sub.4 core-shell nanophosphor in accordance with an exemplary embodiment of the present disclosure; and

(12) FIG. 9 is an image of a polymer composite that Na(Y,Gd)F.sub.4:Ce,Tb,Eu/NaGdF.sub.4 core-shell nanophosphor is dispersed in polydimethylsiloxane (PDMS) polymer in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

(13) Description will now be given in detail of the exemplary embodiments, with reference to the accompanying drawings, to be easily practiced by a person skilled in the art to which the present disclosure belongs. However, the present disclosure may be implemented in various forms, without being limited to the exemplary embodiments disclosed herein.

Example 1: Synthesis of Green-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(14) 0.15 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2) were weighed, respectively, to be added into a mixture solvent (with a mixture of water, ethanol, and hexane), thereby preparing a mixture. The mixture was heat treated at 70° C. to prepare a lanthanide complex compound (Complex compound preparing step).

(15) The lanthanide complex compound was mixed with a solution containing oleic acid and 1-octadicene, and heat-treated at 150° C. for 30 minutes, preparing a first mixed-solution containing the lanthanide complex compound (First mixed-solution preparing step).

(16) 2.5 mmol of sodium hydroxide was mixed with 10 ml of methanol solution containing 4 mmol of ammonium fluoride, to prepare a second mixed-solution. The second mixed-solution was then mixed with the first mixed-solution, to prepare a reaction-solution (Reaction-solution preparing step).

(17) After fully mixing the reaction-solution, the methanol was removed, followed by heat treatment under an inert gas atmosphere. The heat treatment was carried out at 320° C. for 1.5 hours (Nanoparticle preparing step).

(18) After completion of the heat treatment of the nanoparticle preparing step, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 1 which was in a colloid state having a diameter of about 18.5 nm. The thusly obtained nanophosphor of Example 1 was washed with acetone or ethanol, and stored by being dispersed in a non-polar solvent, such as hexane, toluene, chloroform and the like.

Example 2: Fabrication of Yellowish Green-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0.005 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(19) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.145 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.005 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(20) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 2 which was in a colloid state having a diameter of about 16.5 nm. The thusly obtained nanophosphor of Example 2 was stored as equal to Example 1.

Example 3: Fabrication of Greenish Yellow-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0.01 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(21) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.14 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.01 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(22) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 3 which was in a colloid state having a diameter of about 15.7 nm. The thusly obtained nanophosphor of Example 3 was stored as equal to Example 1.

Example 4: Fabrication of Yellow-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0.02 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(23) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.13 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.02 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(24) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 4 which was in a colloid state having a diameter of about 15.5 nm. The thusly obtained nanophosphor of Example 4 was stored as equal to Example 1.

Example 5: Fabrication of Orange-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0.05 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(25) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.1 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.05 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(26) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 5 which was in a colloid state having a diameter of about 14.6 nm. The thusly obtained nanophosphor of Example 5 was stored as equal to Example 1.

Example 6: Fabrication of Scarlet-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, and 0.1 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(27) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.05 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.1 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(28) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 6 which was in a colloid state having a diameter of about 13.7 nm. The thusly obtained nanophosphor of Example 6 was stored as equal to Example 1.

Example 7: Fabrication of Red-Emitting Nanophosphor as 0.1 mmol Ce3+, 0 mmol Tb3+, and 0.05 mmol Eu3+-Doped Fluoride-Based Nanoparticle

(29) A reaction-solution was prepared by carrying out the complex compound preparing step, the first mixed-solution preparing step and the reaction-solution preparing step, as equal to Example 1, except for a mixture, applied in the complex compound preparing step, which was prepared by adding in a mixture solvent 0.25 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.05 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2).

(30) Afterwards, the heat treatment of the nanoparticle preparing step was carried out at 320° C. for 1.5 hours. After completion of the heat treatment, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor of Example 7 which was in a colloid state having a diameter of about 16.4 nm. The thusly obtained nanophosphor of Example 7 was stored as equal to Example 1.

Experimental Example: Evaluation of Characteristics of Nanophosphors of Examples 1 to 7

(31) 1. Measurement of PL Spectrum

(32) Photoluminescence spectra of the nanophosphors of Examples 1 to 7 have been measured using F-7000 model of Hitachi, and the measurement results are shown in FIG. 1. Referring to FIG. 1, it can be understood that relative intensities of PL peaks from green to red regions are changed in response to variation of the content of europium when the nanophosphor is excited by 254-nm ultraviolet rays. That is, it can be noticed that the green-emitting peak is reduced and the red-emitting peak is increasing as the content of europium increases within the nanoparticle host. It may thusly be observed from such results that the nanophosphors with the tuned PL peaks from green to red regions by adjustment of the content of europium can be fabricated.

(33) 2. Observation of TEM Images

(34) TEM images of the nanophosphors synthesized in Examples 1 to 7 have been measured, respectively, by using FEI TECNAI F20 G2, and the measurement results are shown in FIG. 2. Referring to FIG. 2, it can be observed that the nanophosphors synthesized according to the present disclosure all exhibit nano-scaled sizes less than 50 nm, and have sizes in the range of 13.7 nm to 18.5 nm irrespective of the contents of the doped terbium and europium.

(35) 3. Observation of X-ray Diffraction Pattern

(36) X-ray diffraction patterns of the nanophosphors synthesized in Examples 1 to 7 are shown in FIG. 3. Referring to FIG. 3, it can be observed that a single β-phase without impurities has been formed irrespective of the content of terbium or europium doped. It can also be checked that a full width at half maximum (FWHM) of a diffraction peak has increased upon comparing with a reference x-ray diffraction pattern. Accordingly, it may be sure that the nanophosphors of Examples 1 to 7 have been well formed in the range of extremely small particle size.

(37) 4. Observation of Chromaticity Diagram

(38) A CIE chromaticity diagram of the nanophosphors of Examples 1 to 7 are shown in FIG. 4. Referring to FIG. 4, as the same as being observed in FIG. 1, it can be noticed that the relative intensities of PL spectra of the green and red regions are changed in response to the variation of the contents of terbium and europium within the nanophosphor host, and accordingly the color emitted from each nanophosphor is tunable.

(39) 5. Observation by the Naked Eye under Ultraviolet Excitation Condition

(40) Photoluminescence images of the nanophosphors synthesized in Examples 1 to 7 are shown in FIG. 5. Referring to FIG. 5, it can be observed that the nanophosphors fabricated according to the present disclosure can emit various luminescent colors of green, yellowish green, yellow, orange and red under an excitation condition of the same wavelength of ultraviolet rays.

Example 8: Fabrication of Orange-Emitting Nanophosphor as 0.1 mmol Ce3+, 0.15 mmol Tb3+, 0.05 mmol Eu3+-Doped Fluoride-Based Nanoparticle with Size Below 10 nm

(41) 0.05 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.6 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O), 0.1 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.15 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.05 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33NaO.sub.2) were weighed, respectively, to be added into a mixture solvent (a mixture of water, ethanol, and hexane), thereby preparing a mixture. The mixture was heat treated at 70° C. to prepare a lanthanide complex compound (Complex compound preparing step).

(42) The lanthanide complex compound was mixed with a solution containing oleic acid and 1-octadicene, and heat treated at 150° C. for 30 minutes, preparing a first mixed-solution containing the lanthanide complex compound (First mixed-solution preparing step).

(43) 2.5 mmol of sodium hydroxide was mixed with 10 ml of methanol solution containing 4 mmol of ammonium fluoride, to prepare a second mixed-solution. The second mixed-solution was then mixed with the first mixed-solution, to prepare a reaction-solution (Reaction-solution preparing step).

(44) After fully mixing the reaction-solution, the methanol was removed, followed by heat treatment under an inert gas atmosphere. The heat treatment was carried out at 300° C. for 1.5 hours (Nanoparticle preparing step).

(45) After completion of the heat treatment of the nanoparticle preparing step, the reaction-solution was cooled down to room temperature, thereby obtaining a nanophosphor in a colloid state having a diameter of about 4.9 nm. The thusly obtained nanophosphor was washed with acetone or ethanol, and stored by being dispersed in a non-polar solvent, such as hexane, toluene, chloroform and the like.

Example 9: Fabrication of Core-Shell Nanophosphor Having Fluoride-Based Nanoparticle

(46) β-NaY.sub.0.1Gd.sub.0.6F.sub.4:Ce.sup.3+.sub.0.1,Tb.sup.3+.sub.0.15Eu.sub.0.05 nanoparticle having a size below 10 nm, obtained through Example 8, was used as a core, and a shell, which exhibited a magnetic characteristic, was formed around the core according to a method to be explained hereinafter.

(47) A third mixed-solution was prepared by dissolving 1.0 mmol of gadolinium chloride hydrate (GdCl.sub.3.6H.sub.2O) in 6 ml of oleic acid and 15 ml of 1-octadicene. Afterwards, β-NaY.sub.0.1Gd.sub.0.6F.sub.4:Ce.sup.3+.sub.0.1,Tb.sup.3+.sub.0.15Eu.sub.0.05 dispersed in 10 ml of hexane was added into the third mixed-solution, thereby preparing a fourth mixed-solution (Shell solution preparing step and nanoparticle mixing step).

(48) After evenly mixing the fourth mixed-solution using a magnetic stirrer, 10 ml of methanol solution containing 2.5 mmol of sodium chloride and 4 mmol of ammonium chloride was injected into the fourth mixed-solution (Shell reaction-solution preparing step), followed by heat treatment as disclosed in Example 1 (Shell preparing step). After the heat treatment, the mixture was washed with ethanol, obtaining a nanophosphor having the core and the shell, with a size of about 8.8 nm. The nanophosphor of Example 9 was stored by being dispersed in chloroform.

Experimental Example: Evaluation of Characteristics of Nanophosphors of Examples 8 and 9

(49) 1. Observation of TEM Image

(50) The nanophosphors of Examples 8 and 9 have been observed, respectively, using FEI TECNAI F20 G2, and the observed results are shown in FIGS. 6 and 7.

(51) FIG. 6 is a TEM image and a high resolution TEM image of the nanophosphor synthesized in Example 8. Referring to FIG. 6, the nanophosphor synthesized in Example 8 has a size of 4.9 nm. Referring to the high resolution TEM image inserted in a right upper end of FIG. 6, a lattice pattern is clearly observed on one nanophosphor particle. This may indicate that the synthesized nanophosphor has an extremely high crystallinity. The nanophosphor of Example 8 may exhibit a strong PL characteristic by virtue of the high crystallinity in spite of the ultra small size below 10 nm.

(52) FIG. 7 is a TEM image of a β-NaY.sub.0.1Gd.sub.0.6F.sub.4:Ce.sup.3+.sub.0.1,Tb.sup.3+.sub.0.15Eu.sub.0.05/β-NaGdF.sub.4 core-shell nanophosphor, synthesized in Example 9. It can be observed that the core-shell nanophosphor synthesized in Example 9 has a size of 8.8 nm, which is greater than the nanophosphor of Example 8 used as the core, by virtue of the growth of the shell around the core. Referring to the high resolution TEM image shown on a right upper end of FIG. 7, it can be noticed that a lattice pattern of the core-shell nanoparticle is clearly observed and the shell has been epitaxially grown based on the continuous lattice pattern around the core nanoparticle.

(53) 2. Measurement of PL Spectrum

(54) Photoluminescence spectra of the nanophosphor consisting of the nanoparticle synthesized in Example 8, and the core-shell nanophosphor synthesized in Example 9 have been measured using Hitachi F-7000, and the measurement results are shown in FIG. 8. Referring to FIG. 8, it can be observed that the photoluminescence of the nanophosphor of Example 9 has greatly increased as compared to Example 8. Also, compared to Example 8, the nanophosphor of Example 9 exhibits the increase in photoluminescence intensity by about 2.3 times than the nanophosphor of Example 8. This may result from the growth (formation) of the epitaxial shell around the core.

Example 10: Synthesis of Composite of Core-Shell Fluoride Nanophosphor and PDMS

(55) 0.4 ml of the core-shell nanophosphor obtained in Example 9 was mixed with 4 ml of polydimethylsiloxane (PDMS) and 0.4 ml of curing agent, preparing a core-shell nanophosphor polymer mixture. The mixture was cooled down to room temperature after being maintained at 80° C. for one hour, thereby obtaining nanophosphor-polymer composite of Example 10.

Experimental Example: Evaluation of Transparency and Photoluminescence Property

(56) The image of the nanophosphor-polymer composite of Example 10 is shown in FIG. 9.

(57) Referring to a left image of FIG. 9, it can be noticed that the composite is very transparent and characters of a document laid under it are clearly visible. Also, referring to a right image of FIG. 9, which is a photoluminescence image obtained when the nanophosphor was excited by 254-nm ultraviolet lamp, a red luminescent color is observed. The synthesis of the nanophosphor-polymer composite having high transparency and superior photoluminescence property was confirmed from the images of FIG. 9.

(58) The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments.

(59) As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.