Multicolor tunable nanophosphor and its synthesis method and transparent polymer composite including the nanophosphor

Abstract

The present invention relates to a nanophosphor which may be used as a wavelength conversion part of a solar cell, a fluorescent contrast agent, and a light emitting part of a display device, and a synthesis method thereof. The nanophosphor of the present invention is excited by ultraviolet light to exhibit strong green light emission, and has multicolor light emission characteristics capable of controlling a color such as green, yellowish green, yellow, and orange color by only adjusting the amount of a doping agent.

Claims

1. A fluoride-based LiYF.sub.4 nanophosphor co-doped with Ce.sup.3+ and Tb.sup.3+, which is represented by the following Formula 1:
LiY.sub.1xyF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y [Formula 1] (x is a real number in the range of 0.01x0.2, and y is a real number in the range of 0.01y0.3).

2. A fluoride-based multicolor light emission LiYF.sub.4 nanophosphor co-doped with Ce.sup.3+, Tb.sup.3+ and Eu.sup.3+ which is represented by the following Formula 2:
LiY.sub.1xyzF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y, Eu .sup.3+.sub.z [Formula 2] (x is a real number in the range of 0.1x0.15, y is a real number in the range of 0<y0.2, and z is a real number in the range 0<z0.1).

3. A fluoride-based nanophosphor having a core/shell structure, wherein the core is represented by the following Formula 1 or 2, and the shell is represented by the following Formula 3:
LiY.sub.1xyF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y [Formula 1] (x is a real number in the range of 0.01x0.2, and y is a real number in the range of 0.01y0.3)
LiY.sub.1xyzF.sub.4:Ce.sup.3+.sub.x,Tb.sup.3+.sub.y, Eu.sup.3+.sub.z [Formula 2] (x is a real number in the range of 0.1x0.15, y is a real number in the range of 0y0.2, and z is a real number in the range of 0z0.1).
LiY.sub.1rM.sub.rF.sub.4 [Formula 3] (r is a real number in the range of 0r<1, and M is a lanthanide element selected from the group consisting of La, Pr, Nd, Pm, Sm, Er, Gd, Dy, Ho, Tm, Lu and a combination thereof).

4. The nanophosphor of claim 1 wherein the nanophosphor represented by Formula 1 has a diameter of 2 to 60 nm.

5. The nanophosphor of claim 1 wherein the nanophosphor has a tetragonal structure.

6. The nanophosphor of claim 3, wherein the nanophosphor having a core/shell structure has a diameter of 2 nm to 70 nm.

7. The nanophosphor of claim 2, wherein the nanophosphor shows multicolor light emission characteristic of green, yellowish green, yellow and orange colors.

8. The nanophosphor of claim 1, wherein the nanophosphor absorbs ultraviolet light of a single wavelength to show light emission characteristic.

9. A polymer composite comprising the nanophosphor of claim 1.

10. A solar cell comprising the nanophosphor of claim 1 as a wavelength conversion layer.

11. A forgery prevention code comprising the nanophosphor of claim 1 as a wavelength conversion layer.

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 invention 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 invention.

(3) In the drawings:

(4) FIG. 1 is PL light emission spectra of LiYF.sub.4:Ce,Tb and NaYF.sub.4:Ce,Tb nanophosphors according to preferred exemplary embodiments of the present invention.

(5) FIG. 2 is a transmission electron microscopy image of a LiYF.sub.4:Ce,Tb nanophosphor according to a preferred exemplary embodiment of the present invention.

(6) FIG. 3 is an X-ray diffraction pattern of the LiYF.sub.4:Ce,Tb nanophosphor according to a preferred exemplary embodiment of the present invention.

(7) FIG. 4 is an X-ray diffraction patterns according to a variation in amount of Tb and Eu of LiYF.sub.4:Ce,Tb,Eu nanophosphors according to a preferred exemplary embodiment of the present invention.

(8) FIG. 5 is PL light emission spectra according to a change in amount of Tb and Eu of LiYF.sub.4:Ce,Tb,Eu nanophosphors according to a preferred exemplary embodiment of the present invention.

(9) FIG. 6 is color coordinates of a light emission color according to a change in amount of Tb and Eu of LiYF.sub.4:Ce,Tb,Eu nanophosphors according to a preferred exemplary embodiment of the present invention.

(10) FIG. 7 is a light emission photograph according to a change in amount of Tb and Eu of LiYF.sub.4:Ce,Tb,Eu nanophosphor solutions according to a preferred exemplary embodiment of the present invention.

(11) FIG. 8 is a transmission electron microscopy image of a LiYF.sub.4:Ce,Tb/LiYF.sub.4 core/shell nanophosphor according to a preferred exemplary embodiment of the present invention.

(12) FIG. 9 is PL light emission spectra of a LiYF.sub.4:Ce,Tb core and a LiYF.sub.4:Ce,Tb/LiYF.sub.4 core/shell nanophosphor according to a preferred exemplary embodiment of the present invention.

(13) FIG. 10 is a photograph of a polymer composite in which a LiYF.sub.4:Ce,Tb,Eu nanophosphor according to an exemplary embodiment of the present invention is dispersed in a PDMS polymer.

(14) FIG. 11 is a photograph of a nanophosphor-polymer composite prepared in Example 10 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(15) Description will now be given in detail of the exemplary embodiments, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated.

(16) Hereinafter, the present invention will be described in more detail through the Examples. These Examples are provided only for more specifically describing the present invention, and it will be obvious to a person with ordinary skill in the art to which the present invention pertains that the scope of the present invention is not limited by these Examples.

EXAMPLE

Example 1

Preparation of Fluoride Nanophosphor Doped with 0.15 mmol of Ce3+ and 0.15 mmol of Tb3+

(17) 0.15 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.15 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.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(18) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(19) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a size of 1 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Comparative Example 1

Fluoride Nanophosphor Doped with 0.1 mmol of Ce3+ and 0.15 mmol of Tb3+

(20) 0.1 mmol of yttrium chloride hydrate (YCl.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.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(21) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(22) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single n-phase nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

(23) FIG. 1 illustrates light emission spectra of nanophosphors synthesized by the methods suggested in Example 1 and Comparative Example 1 according to the present invention. The light emission spectra were measured by using F-7000 model manufactured by Hitachi Ltd. In the case of comparing the maximum light emission intensity of the nanophosphor prepared according to Example 1 with that of the nanophosphor prepared according to Comparative Example 1, 25 times stronger green light emission was exhibited in the case where the nanophosphor of the present invention prepared according to Example 1 when excited by ultraviolet light was compared to the existing nanophosphor prepared according to Comparative Example 1.

(24) FIG. 2 is a transmission electron microscopy image of the nanophosphor synthesized in Example 1 according to the present invention. The transmission electron microscopy image illustrated in FIG. 2 was taken by using a TECNAI F20 G.sup.2 model manufacture by FEI Co., Ltd. Nanophosphors synthesized through the present invention showed a size in a nano range of 60 nm or less. Referring to the high-resolution transmission electron microscopy image illustrated in FIG. 2, it can be confirmed that one nanophosphor particle has a clear lattice pattern, meaning that the synthesized nanophospohor had very high crystallinity. Since the crystallinity of the phosphor host material needs to be high in order to obtain strong light emission from the phosphor, it can be seen that it is possible to obtain a nanophosphor showing excellent light emission characteristics from high crystallinity of the nanophosphor according to the present invention.

(25) FIG. 3 illustrates an X-ray diffraction pattern of the nanophosphor synthesized in Example 1 according to the present invention. It can be confirmed that a single tetragonal phase was formed well from the measured diffraction pattern.

Example 2

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+ and 0.14 mmol of Tb3+

(26) 0.73 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(27) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(28) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Example 3

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+, 0.14 mmol of Tb3+, and 0.01 mmol of Eu3+

(29) 0.72 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 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 (Cl.sub.18H.sub.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(30) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(31) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Example 4

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+, 0.14 mmol of Tb3+, and 0.02 mmol of Eu3+

(32) 0.71 mmol of yttrium chloride hydrate (YCl.sub.3.7H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 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 (Cl.sub.18H.sub.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(33) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(34) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Example 5

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+, 0.14 mmol of Tb3+, and 0.03 mmol of Eu3+

(35) 0.70 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.03 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(36) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(37) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Example 6

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+, 0.14 mmol of Tb3+, and 0.04 mmol of Eu3+

(38) 0.69 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 mmol of terbium chloride hydrate (TbCl.sub.3.6H.sub.2O), 0.04 mmol of europium chloride hydrate (EuCl.sub.3.6H.sub.2O), and 3.1 mmol of sodium oleate (C.sub.18H.sub.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(39) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(40) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

Example 7

LiYF4 Nanophosphor Doped with 0.13 mmol of Ce3+, 0.14 mmol of Tb3+, and 0.05 mmol of Eu3+

(41) 0.68 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O), 0.13 mmol of cerium chloride hydrate (CeCl.sub.3.7H.sub.2O), 0.14 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.33O.sub.2Na) were weighed, a mixed solvent of a predetermined amount of water, ethanol, and hexane was added thereto, and heat treatment was performed at 70 C., thereby forming a lanthanide complex compound (a complex compound forming step). A mixed solution including a lanthanide complex compound was prepared by mixing the complex compound with a solution including oleic acid and 1-octadecene, and subjecting the resulting mixture to heat treatment at 140 C. for 30 minutes (a first mixed solution preparing step).

(42) 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was prepared (a second mixed solution preparing step), and then was mixed with a mixed solution including a lanthanide complex compound (a reaction solution preparing step).

(43) The mixture was sufficiently mixed, methanol was removed from the mixture, and then heat treatment was performed under an inert gas atmosphere. At this time, when the heat treatment temperature is less than 200 C., a single tetragonal nano crystal is not completely produced, and accordingly, the phosphor fails to exhibit strong light emission. When the temperature is higher than 370 C., there occurs a disadvantage in that aggregation of particles and the like occur due to an overreaction, the size of particles is very large, the size distribution is not uniform, and accordingly, brightness deteriorates. Therefore, it is preferred that the heat treatment temperature is 200 to 370 C. and the heat treatment time is 10 minutes to 4 hours (a nanoparticle forming step). After the heat treatment process was completed, the temperature was cooled to room temperature, and then a nanophosphor having a diameter of 2 to 60 nm in a colloidal state was obtained. The nanophosphor thus prepared was washed with acetone or ethanol, and then was stored while being dispersed in a non-polar solvent such as hexane, toluene, and chloroform.

(44) FIG. 4 illustrates an X-ray diffraction pattern of each of the nanophosphors synthesized in Examples 2 to 7 according to the present invention. It can be seen that a single tetragonal phase without impurities was formed regardless of a doping amount of terbium or europium. Further, it can be seen that when compared to a reference X-ray diffraction pattern, the full width at half maximum of the diffraction peak was widened, and it can be additionally confirmed through this that a very small nanoparticle was formed.

(45) FIG. 5 illustrates PL light emission spectrum of each of the nanophosphors synthesized in Examples 2 to 7 according to the present invention. As the amount of terbium and europium in the host material varies, the relative intensities of light emission spectra in a green spectral region and a red spectral region are changed, and as a result, the luminescence color-emitted from the nanophosphor may be tuned.

(46) FIG. 6 illustrates a CIE color coordinates of the nanophosphors synthesized in Examples 2 to 7 according to the present invention. As illustrated in FIG. 5, as the amount of terbium and europium in the host material varies, the relative intensities of light emission spectra in the green region and the red region are changed, and as a result, referring to FIG. 6, it can be confirmed that the luminescence color-emitted from the nanophosphor may be tuned.

(47) FIG. 7 is a light emission photograph of the nanophosphors synthesized in Examples 2 to 7 according to the present invention. Referring to FIGS. 6 and 7, it can be confirmed that the nanophosphor according to the present invention may emit light with various colors such as green, yellowish green, yellow, and orange color under the ultraviolet light excitation conditions at the same wavelength.

Example 8

Preparation of Fluoride Nanophosphor having Core/Shell Structure

(48) The LiY.sub.0.7F.sub.4:Ce.sup.3+.sub.0.15, Tb.sup.3+.sub.0.15 nanophosphor obtained through Example 1 was used as a core. In order to form a shell around the core, 1.0 mmol of yttrium chloride hydrate (YCl.sub.3.6H.sub.2O) was dissolved in 6 ml of oleic acid and 15 ml of 1-octadecene and then LiY.sub.0.7F.sub.4:Ce.sup.3+.sub.0.15, Tb.sup.3+.sub.0.15 dispersed in 10 ml of chloroform was added thereto. After the mixture was uniformly stirred by using a magnetic stirrer, 10 ml of a methanol solution including 2.5 mmol of lithium hydroxide and 4 mmol of ammonium fluoride was injected into the mixture, and heat treatment was performed as described above in Example 1. After the heat treatment process, the mixture was washed with ethanol, and then was stored while being dispersed in chloroform.

(49) FIG. 8 is a transmission electron microscopy image of a LiY.sub.0.7F.sub.4:Ce.sup.3+.sub.0.15, Tb.sup.3+.sub.0.15/LiYF.sub.4 core/shell nanophosphor synthesized in Example 8 of the present invention. The size of the nanophosphor having a core/shell structure synthesized in Example 8 was 40.0 nm, and it can be confirmed that as the shell was formed around the core, the size was increased. From the high-resolution transmission electron microscopy image of the core/shell nanoparticle, it can be confirmed that a clear lattice pattern was formed, and that the shell was epitaxially formed around the core nanoparticle from the continuous lattice pattern.

(50) FIG. 9 illustrates light emission spectra of a core nanophosphor and a core/shell nanophosphor, which were synthesized in Example 8 of the present invention. It can be confirmed that as an epitaxial shell was formed around the core, light emission of the nanophosphor was significantly increased, and the light emission intensity was increased by about 33%.

Example 9

Preparation of LiY4:Ce0.13, Tb0.14 Nanophosphor and PDMS Polymer Composite

(51) 0.4 ml of the LiYF.sub.4:Ce.sub.0.13, Tb.sub.0.14 nanophosphor obtained through Example 2 was mixed with 10 ml of a polydimethylsiloxane (PDMS) polymer and 1 ml of a curing agent. A nanophosphor-polymer composite could be obtained by maintaining a nanophosphor polymer mixture having a core/shell structure at 80 C. for 1 hour, and then cooling the mixture to room temperature.

(52) FIG. 10 is a photograph of a nanophosphor-polymer composite prepared in Example 9 of the present invention. As illustrated in FIG. 10, the polymer composite in which the nanophosphor was dispersed was so transparent that letters on a document placed under the polymer composite could be clearly confirmed. Furthermore, when the nanophosphor was excited by an ultraviolet light lamp at 306 nm, it could be confirmed that light with green color was emitted, and through this, it could be confirmed that a nanophosphor-polymer composite having high transparency and excellent light emission characteristics was prepared.

Example 10

Preparation of LiYF4:Ce0.13, Tb0.14Eu0.02 Nanophosphor and PDMS Polymer Composite

(53) 0.4 ml of the LiYF.sub.4:Ce.sub.0.13, Tb.sub.0.14Eu.sub.0.02 nanophosphor obtained through Example 4 was mixed with 10 ml of a polydimethylsiloxane (PDMS) polymer and 1 ml of a curing agent. A nanophosphor-polymer composite could be obtained by maintaining a nanophosphor polymer mixture having a core/shell structure at 80 C. for 1 hour, and then cooling the mixture to room temperature.

(54) FIG. 11 is a photograph of a nanophosphor-polymer composite prepared in Example 10 of the present invention. As illustrated in FIG. 11, the polymer composite in which the nanophosphor was dispersed was so transparent that letters on a document placed under the polymer composite could be clearly confirmed. Furthermore, when the nanophosphor was excited by an ultraviolet light lamp at 306 nm, it could be confirmed that light with yellowish green color was emitted, and through this, it could be confirmed that a nanophosphor-polymer composite having high transparency and excellent light emission characteristics was prepared.

(55) As described above, although the present invention has been described with reference to preferred exemplary embodiments of the present invention, it can be understood by a person with ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention as described in the following claims.

(56) The person with ordinary skill in the art may improve and modify the technical spirit of the present invention in various forms. Accordingly, the improvements and modifications will fall within the scope of the present invention as long as they are obvious to the person with ordinary skill in the art. The foregoing embodiments and advantages are merely exemplary and are not to be considered as limiting the present invention. 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.

(57) 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 considered 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.