Color-tunable up-conversion nanophosphor

Abstract

Provided are a nanophosphor and a silica composite including the nanophosphor. The nanophosphor has a core/first shell/second shell structure or a core/first shell/second shell/third shell structure, wherein the core includes a Yb.sup.3+-doped fluoride-based nanoparticle, the first shell is an up-conversion shell including a Yb.sup.3+ and Tm.sup.3+-codoped fluoride-based crystalline composition, the second shell is a fluoride-based emission shell, and the third shell is an outermost crystalline shell.

Claims

1. An up-conversion nanophosphor comprising: a core comprising a Yb.sup.3+-doped fluoride-based nanoparticle represented by LiY.sub.1-x-yL.sub.yF.sub.4:Yb.sup.3+.sub.x, where, x and y are real numbers, and 0x1, 0y1, and 0x+y1, and L is any one selected from Y, Dy, Ho, Er, Tm, Lu, and a combination thereof; a first shell comprising a fluoride-based crystalline compound that is co-doped with at least one selected from Yb.sup.3+ and Tm.sup.3+, the fluoride-based crystalline compound surrounding at least a portion of the core, and represented by LiGd.sub.1-p-q-rM.sub.rF.sub.4:Yb.sup.3+.sub.p,Tm.sup.3+.sub.q, where, p, q and r are real numbers, and 0<p0.5, 0<q0.2, 0r1, and 0<p+q+r<1, and M is any one selected from a first rare-earth element and a combination thereof, wherein the first rare-earth element comprises any one selected from Gd, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Lu; and a second shell that is a fluoride-based emission shell comprising a compound surrounding at least a portion of the first shell, and represented by LiGd.sub.1-s-t-uN.sub.uF.sub.4:Tb.sup.3+, Eu.sup.3+.sub.t where, s, t and u are real numbers, and 0s0.5, 0<t0.5, 0u1, and 0<s+t+u<1, and N is any one selected from a second rare-earth element and a combination thereof, wherein the second rare-earth element comprises any one selected from Gd, Y, La, Ce, Pr, Nd, Pm, Sm, Dy, Ho, Er, Tm, Yb, and Lu.

2. The up-conversion nanophosphor of claim 1, further comprising: a second shell that is a fluoride-based emission shell including a compound represented by Formula 3, and surrounds at least a portion of the first shell; and a third shell that is a crystalline shell including a compound represented by Formula 4, and surrounds at least a portion of the second shell:
LiGd.sub.1-s-t-uN.sub.uF.sub.4:Tb.sup.3+.sub.s,Eu.sup.3+.sub.t.[Formula 3] wherein, in Formula 3, s satisfies the condition of 0<s0.5 and is a real number, t satisfies the condition of 0<t0.5 and is a real number, u satisfies the condition of 0u1 and is a real number, u is any real number that satisfies the condition of 0<s+t+u<1, and N is any one selected from a second rare-earth element and a combination thereof, wherein the second rare-earth element comprises any one selected from Gd, Y, La, Ce, Pr, Nd, Pm, Sm, Dy, Ho, Er, Tm, Yb, and Lu, and
LiY.sub.1-vO.sub.vF.sub.4,[Formula 4] wherein, in Formula 4, v satisfies the condition of 0v1 and is a real number, and O is any one selected from a third rare-earth element and a combination thereof, wherein the third rare-earth element comprises any one selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

3. The up-conversion nanophosphor of claim 1, wherein a third shell that is a crystalline shell including a compound represented by Formula 4, and surrounds at least a portion of the first shell:
LiY.sub.1-vO.sub.vF.sub.4[Formula 4] wherein, in Formula 4, v satisfies the condition of 0v1 and is a real number, and O is any one selected from a third rare-earth element and a combination thereof, wherein the third rare-earth element comprises any one selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

4. The up-conversion nanophosphor of claim 1, wherein the Yb.sup.3+-doped fluoride-based nanoparticle has a tetragonal structure, and the core has a size of about 1 nm to about 40 nm.

5. The up-conversion nanophosphor of claim 1, wherein the up-conversion nanophosphor has a size of about 2 nm to about 50 nm.

6. The up-conversion nanophosphor of claim 2, wherein the up-conversion nanophosphor has a size of about 2 nm to about 70 nm.

7. A silica composite comprising: a core comprising a Yb.sup.3+-doped fluoride-based nanoparticle represented by LiY.sub.1-x-yL.sub.yF.sub.4:Yb.sup.3+.sub.x, where, x and y are real numbers, and 0x1, 0y1, and 0x+y1, and L is any one selected from Y, Dy, Ho, Er, Tm, Lu, and a combination thereof; a first shell comprising a fluoride-based crystalline compound that is co-doped with at least one selected from Yb.sup.3+ and Tm.sup.3+, the fluoride-based crystalline compound surrounding at least a portion of the core, and represented by LiGd.sub.1-p-q-rM.sub.rF.sub.4:Yb.sup.3+.sub.p, Tm.sup.3+.sub.q, where, p, q and r are real numbers, and 0<p0.5, 0<q0.2, 0r1, and 0<p+q+r<1, and M is any one selected from a first rare-earth element and a combination thereof, wherein the first rare-earth element comprises any one selected from Gd, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Lu; and a second shell that is a fluoride-based emission shell comprising a compound surrounding at least a portion of the first shell, and represented by LiGd.sub.1-s-t-uN.sub.uF.sub.4:Tb.sup.3+.sub.s, Eu.sup.3+.sub.t where, s, t and u are real numbers, and 0<s0.5, 0<t0.5, 0u1, and 0<s+t+u<1, and N is any one selected from a second rare-earth element and a combination thereof, wherein the second rare-earth element comprises any one selected from Gd, Y, La, Ce, Pr, Nd, Pm, Sm, Dy, Ho, Er, Tm, Yb, and Lu.

8. A display device comprising the up-conversion nanophosphor of claim 1.

9. A fluorescent contrast media comprising the up-conversion nanophosphor of claim 1.

10. A solar cell comprising the up-conversion nanophosphor of claim 1.

11. An anti-falsification code comprising the up-conversion nanophosphor of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 shows a conceptual view of a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment of the present disclosure;

(3) FIG. 2 shows an X-ray diffraction pattern showing a core up-conversion nanophosphor prepared according to Comparative Example;

(4) FIG. 3 shows X-ray diffraction patterns of a nanophosphor including a core prepared according to Example 1 and a nanophosphor including a core/first shell structure prepared according to Example 2;

(5) FIG. 4 shows a transmission electron microscopic image of a core nanoparticle according to an embodiment;

(6) FIG. 5 shows a transmission electron microscopic image of a nanophosphor having a core/first shell structure according to an embodiment;

(7) FIG. 6 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell structure according to an embodiment;

(8) FIG. 7 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment;

(9) FIG. 8 shows an up-conversion emission spectrum of a nanophosphor having a core/first shell structure according to an embodiment;

(10) FIG. 9 shows an up-conversion emission spectra of a nanophosphor having a core/first shell/second shell structure prepared according to Example 3 and a nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 4;

(11) FIG. 10 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell structure according to an embodiment;

(12) FIG. 11 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment;

(13) FIG. 12 shows up-conversion emission spectra of a nanophosphor having a core/first shell/second shell structure prepared according to Example 5 and a nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 6;

(14) FIG. 13 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell structure according to an embodiment;

(15) FIG. 14 shows a transmission electron microscopic image of a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment;

(16) FIG. 15 shows up-conversion emission spectra of a nanophosphor having a core/first shell/second shell structure prepared according to Example 7 and a nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 8; and

(17) FIG. 16 shows up-conversion emission images of solutions of a nanophosphor having a core/first shell/second shell structure and nanophosphors having a core/first shell/second shell/third shell structure.

DETAILED DESCRIPTION

(18) Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. For ease of description, in the drawings, the sizes of at least some elements are exaggerated for clarity. Like reference numbers in the drawings denote like elements.

(19) Hereinafter, with reference to the attached drawings, a color-tunable core/first shell/second shell/third shell structure according to embodiments of the present disclosure will be described. The core/first shell/second shell/third shell structure may include a LiY.sub.1-x-yL.sub.yF.sub.4:Yb.sup.3+.sub.x/LiGd.sub.1-p-q-rM.sub.rF.sub.4:Yb.sup.3+.sub.p,Tm.sup.3+.sub.q/LiGd.sub.1-s-t-uN.sub.uF.sub.4:Tb.sup.3+.sub.s,Eu.sup.3+.sub.t/LiY.sub.1-vO.sub.vF.sub.4 structure. Regarding this structure, x satisfies the condition of 0x1 and is a real number; y satisfies the condition of 0y1, is a real number, satisfies the condition of 0x+y1, and may be any real number that satisfies the condition of x+y1; and L may be any one selected from Y, Dy, Ho, Er, Tm, Lu, and a combination thereof; p satisfies the condition of 0<p0.5 and is a real number, q satisfies the condition of 0<q0.2 and is a real number, r satisfies the condition of 0r1 and is a real number, r may be any real number that satisfies the condition of 0<p+q+r<1, and M may be any one selected from a rare-earth element and a combination thereof; s satisfies the condition of 0<s0.5 and is a real number, t satisfies the condition of 0<t0.5 and is a real number, u satisfies the condition of 0u1 and is a real number, u may be any real number that satisfies the condition of 0<s+t+u<1, and N may be any one selected from a rare-earth element and a combination thereof; and v satisfies the condition of 0v1 and is a real number, and O may be any one selected from a rare-earth element and a combination thereof. Hereinafter, up-conversion nanophosphors will be described. However, the concept of the present disclosure is not limited to embodiments to be presented below, and other embodiments may also be provided by, for example, the addition or substitution of constituting elements.

(20) Embodiments explained in connection with the drawings are not interpreted as limiting the concept of the present disclosure, and shall be considered as to fully explain the present disclosure.

(21) Hereinafter, examples of a method of preparing an up-conversion/down-conversion double emission fluoride-based nanophosphor having a core/first shell/second shell/third shell structure will be described.

Preparation of 0.25 mmol Yb3+ and 0.01 mmol Tm3+-Doped Up-Conversion Core Nanophosphor

(22) 0.74 mmol gadolinium chloride hexahydrate (GdCl.sub.3.6H.sub.2O), 0.25 mmol ytterbium chloride hexahydrate (YbCl.sub.3.6H.sub.2O), 0.01 mmol thulium chloride hexahydrate (TmCl.sub.3.6H.sub.2O), and 3.1 mmol oleic acid sodium (C.sub.18H.sub.33O.sub.2Na) were estimated, and a mixed solvent including water, ethanol, and hexane was added thereto in a predetermined amount. The mixture was heat-treated at a temperature of 70 C. to form a lanthanide complex compound (step of preparing a complex compound). The complex compound was mixed with a solution including an oleic acid and 1-octadecene, and then, heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including the lanthanide complex compound (step of preparing a first mixed solution).

(23) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a second mixed solution) and then mixed with the mixed solution including the lanthanide complex compound (step of preparing a reaction solution).

(24) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 40 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

Preparation of 0.8 mmol Yb3+-Doped Up-Conversion Core Nanophosphor

(25) 0.2 mmol yttrium chloride hexahydrate (YCl.sub.3.6H.sub.2O), 0.8 mmol ytterbium chloride hexahydrate (YbCl.sub.3.6H.sub.2O), and 3.1 mmol oleic acid sodium (Cl.sub.18H.sub.33O.sub.2Na) were estimated, and a mixed solvent including water, ethanol, and hexane was added thereto in a predetermined amount. The mixture was heat-treated at a temperature of 70 C. to form a lanthanide complex compound (step of preparing a complex compound). The complex compound was mixed with a solution including an oleic acid and 1-octadecene, and then, heat-treated at a temperature of 150 C. for 30 minutes to prepare a first mixed solution including the lanthanide complex compound (step of preparing a first mixed solution).

(26) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a second mixed solution), and then mixed with the first mixed solution including the lanthanide complex compound (step of preparing a reaction solution).

(27) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 40 nm. The nanophosphor prepared according to Example 1 included LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8 nanoparticle. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

Preparation of Up-Conversion Nanophosphor Having Core/First Shell Structure by Using Yb3+ and Tm3+-Codoped Fluoride Shell

(28) A nanophosphor having a core/first shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8 nanoparticle prepared according to Example 1, which is a core, and a Yb.sup.3+ and Tm.sup.3+-codoped fluoride-based compound.

(29) 0.74 mmol gadolinium chloride hexahydrate (GdCl.sub.3.6H.sub.2O), 0.25 mmol ytterbium chloride hexahydrate (YbCl.sub.3.6H.sub.2O), and 0.01 mmol thulium chloride hexahydrate (TmCl.sub.3.6H.sub.2O) were mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a lanthanide complex compound (step of preparing a first mixed solution).

(30) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8 nanoparticle prepared according to Example 1 to prepare a second mixed solution.

(31) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the lanthanide complex compound (step of preparing a reaction solution).

(32) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 30 nm. The nanophosphor prepared according to Example 2 included the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8 core prepared according to Example 1 and a LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 shell. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(33) FIG. 1 shows a conceptual view of a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment of the present disclosure. FIG. 2 shows an X-ray diffraction pattern showing a core up-conversion nanophosphor prepared according to Comparative Example 1. FIG. 3 shows X-ray diffraction patterns of an up-conversion nanophosphor including a core synthesized according to Example 1 and an up-conversion nanophosphor including a core/first shell structure synthesized according to Example 2.

(34) In a nanophosphor having a core/first shell/second shell/third shell structure according to an embodiment, the core corresponds to the sensitizer-doped core illustrated in FIG. 1, the first shell corresponds to the emission layer doped with activators illustrated in FIG. 1, the second shell corresponds to the emission conversion layer illustrated in FIG. 1, and the third shell corresponds to the emission enhancement layer illustrated in FIG. 1.

(35) Referring to the X-ray diffraction pattern of FIG. 2, it was confirmed that the synthesized nanophosphor according to Comparative Example 1 did not have a tetragonal structure, but have an orthorhombic-based GdF.sub.3 structure. This result shows that the nanophosphor having a LiGdF.sub.4 structure, which was the target product, was not synthesized. However, referring to the X-ray diffraction pattern of FIG. 3, it was confirmed that the synthesized nanophosphor having the core and the synthesized nanophosphor having the core/first shell structure each have a tetragonal structure. This result shows that LiGdF.sub.4 crystal has been formed well. Referring to FIG. 4, which shows the transmission electron microscopic image of the core nanoparticle synthesized according to Example 1, it was confirmed that the formed core nanoparticle was uniform and had a small particle size of 20 nm or less. Referring to FIG. 5, which shows the transmission electron microscopic image of the nanophosphor having a core/first shell structure, it was confirmed that the formed core nanoparticle had a uniform particle size and shape. Referring to the high-resolution transmission electron microscopic image on the bottom right side of FIG. 5, it was confirmed that a shell was epitaxially grown on the core.

Preparation of Green Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell Structure

(36) A nanophosphor having a core/first shell/second shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2, as a core, and a LiGdF.sub.4:Tb.sup.3+ compound.

(37) 0.85 mmol gadolinium chloride hexahydrate (GdCl.sub.3.6H.sub.2O) and 0.15 mmol terbium chloride hexahydrate (TbCl.sub.3.6H.sub.2O) were mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a lanthanide complex compound (step of preparing a first mixed solution).

(38) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2 to prepare a second mixed solution.

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

(40) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 50 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(41) FIG. 6 shows a transmission electron microscopic image of an up-conversion nanophosphor having the core/first shell/second shell structure prepared according to Example 3. Referring to the transmission electron microscopic image, it was confirmed that a second shell was formed around the core/first shell, thereby resulting in a greater particle size.

Preparation of Green Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell/Third Shell Structure

(42) A nanophosphor having a core/first shell/second shell/third shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01/LiGdF.sub.4:Tb.sup.3+.sub.0.15 nanoparticle prepared according to Example 3, as a core, and a LiYF.sub.4 compound.

(43) 1 mmol yttrium chloride hexahydrate (YCl.sub.3.6H.sub.2O) was mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a yttrium complex compound (step of preparing a first mixed solution).

(44) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01/LiGdF.sub.4:Tb.sup.3+.sub.0.15 nanoparticle prepared according to Example 3 to prepare a second mixed solution.

(45) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the yttrium complex compound (step of preparing a reaction solution).

(46) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 70 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(47) FIG. 7 shows a transmission electron microscopic image of an up-conversion nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 4. Referring to FIG. 7, it was confirmed that a third shell was formed around the core/first shell/second shell, thereby resulting in a greater particle size. Referring to the emission spectrum of FIG. 8, the nanophosphor having the core/first shell structure synthesized according to Example 2 had its emission peak in the blue spectrum region. Referring to the emission spectrum of FIG. 9, the nanophosphor having the core/first shell/second shell structure synthesized according to Example 3 had its emission peak in the green spectrum region. Also, it was confirmed that, due to the formation of the additional shell around the core/first shell/second shell, the nanophosphor having the core/first shell/second shell/third shell structure prepared according to Example 4 had much stronger emission intensity in the green spectrum region than the core/first shell/second shell structure synthesized according to Example 3.

Preparation of Red Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell Structure

(48) A nanophosphor having a core/first shell/second shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2, as a core, and a LiGdF.sub.4:Eu.sup.3+ compound. 0.85 mmol gadolinium chloride hexahydrate (GdCl.sub.3.6H.sub.2O) and 0.15 mmol europium chloride hexahydrate (EuCl.sub.3.6H.sub.2O) were mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a lanthanide complex compound (step of preparing a first mixed solution).

(49) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2 to prepare a second mixed solution.

(50) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the lanthanide complex compound (step of preparing a reaction solution).

(51) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 50 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(52) FIG. 10 shows a transmission electron microscopic image of an up-conversion nanophosphor having a core/first shell/second shell structure prepared according to Example 5. Referring to FIG. 10, it was confirmed that a second shell was formed around the core/first shell, thereby resulting in a greater particle size.

Preparation of Red Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell/Third Shell Structure

(53) A nanophosphor having a core/first shell/second shell/third shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01/LiGdF.sub.4:Eu.sup.3+.sub.0.15 nanoparticle prepared according to Example 5, as a core, and a LiYF.sub.4 compound.

(54) 1 mmol yttrium chloride hexahydrate (YCl.sub.3.6H.sub.2O) was mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a yttrium complex compound (step of preparing a first mixed solution).

(55) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01/LiGdF.sub.4:Eu.sup.3+.sub.0.15 nanoparticle prepared according to Example 3 to prepare a second mixed solution.

(56) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the yttrium complex compound (step of preparing a reaction solution).

(57) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 70 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(58) FIG. 11 shows a transmission electron microscopic image of an up-conversion nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 6. Referring to FIG. 11, it was confirmed that a third shell was formed around the core/first shell/second shell, thereby resulting in a greater particle size. Referring to the emission spectrum of FIG. 12, the core/first shell/second shell structure synthesized according to Example 5 had its emission peak in the red spectrum region. Also, it was confirmed that, due to the formation of the additional shell around the core/first shell/second shell, the nanophosphor having the core/first shell/second shell/third shell structure prepared according to Example 6 had much stronger emission intensity in the red spectrum region than the core/first shell/second shell structure synthesized according to Example 5.

Preparation of White Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell Structure

(59) A nanophosphor having a core/first shell/second shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2, as a core, and a LiGdF.sub.4:Tb.sup.3+,Eu.sup.3+ compound.

(60) 0.83 mmol gadolinium chloride hexahydrate (GdCl.sub.3.6H.sub.2O), 0.15 mmol terbium chloride hexahydrate (TbCl.sub.3.6H.sub.2O), and 0.02 mmol europium chloride hexahydrate (EuCl.sub.3.6H.sub.2O) were mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a lanthanide complex compound (step of preparing a first mixed solution).

(61) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2 to prepare a second mixed solution.

(62) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the lanthanide complex compound (step of preparing a reaction solution).

(63) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 50 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(64) FIG. 13 shows a transmission electron microscopic image of an up-conversion nanophosphor having a core/first shell/second shell structure prepared according to Example 7. Referring to FIG. 7, it was confirmed that a second shell was formed around the core/first shell, thereby resulting in a greater particle size.

Preparation of White Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell/Third Shell Structure

(65) A nanophosphor having a core/first shell/second shell/third shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25, Tm.sup.3+.sub.0.01/LiGdF.sub.4:Tb.sup.3+.sub.0.15,Eu.sup.3+.sub.0.02 nanoparticle prepared according to Example 7, as a core, and a LiYF.sub.4 compound.

(66) 1 mmol yttrium chloride hexahydrate (YCl.sub.3.6H.sub.2O) was mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a yttrium complex compound (step of preparing a first mixed solution).

(67) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25, Tm.sup.3+.sub.0.01/LiGdF.sub.4:Tb.sup.3+.sub.0.15,Eu.sup.3+.sub.0.02 nanoparticle prepared according to Example 7 to prepare a second mixed solution.

(68) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the yttrium complex compound (step of preparing a reaction solution).

(69) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., single tetragonal nanocrystals are not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 70 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(70) FIG. 14 shows a transmission electron microscopic image of an up-conversion nanophosphor having a core/first shell/second shell/third shell structure prepared according to Example 8. Referring to FIG. 14, it was confirmed that a third shell was formed around the core/first shell/second shell, thereby resulting in a greater particle size. Referring to the emission spectrum of FIG. 15, the core/first shell/second shell structure synthesized according to Example 7 had its emission peaks in blue, green, and red spectrum regions. Also, it was confirmed that, due to the formation of the additional shell around the core/first shell/second shell, the nanophosphor having the core/first shell/second shell/third shell structure prepared according to Example 8 had much stronger emission intensity in the blue, green, and red spectrum regions than the core/first shell/second shell structure synthesized according to Example 7. As a result, as shown in the emission image of FIG. 16, it was confirmed that white light was emitted by the solution of the up-conversion nanophosphor having the core/first shell/second shell/third shell structure prepared according to Example 8.

Preparation of Blue Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell Structure

(71) A nanophosphor having a core/first shell/second shell structure was prepared by using the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2, as a core, and a LiYF.sub.4 compound.

(72) 1 mmol yttrium chloride hexahydrate (YCl.sub.3.6H.sub.2O) was mixed with a solution including an oleic acid and 1-octadecene, and the resultant mixture was heat-treated at a temperature of 150 C. for 30 minutes to prepare a mixed solution including a yttrium complex compound (step of preparing a first mixed solution).

(73) The first mixed solution was mixed with a solution including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01 nanoparticle prepared according to Example 2 to prepare a second mixed solution.

(74) 10 ml of a methanol solution including 2.5 mmol lithium hydroxide and 4 mmol ammonium fluoride was prepared (step of preparing a third mixed solution), and then mixed with the second mixed solution including the yttrium complex compound (step of preparing a reaction solution).

(75) The resultant mixed solution was sufficiently mixed, and then, methanol was removed therefrom, followed by heat-treatment in inert gas atmosphere. In this regard, when the heat-treatment temperature is less than 200 C., a single tetragonal nanocrystal is not completely formed, and thus, the formed phosphor may not have strong emission characteristics; and when the heat-treatment temperature exceeds 370 C., over-reaction may occur, and thus, particles may agglomerate together to form larger particles, and the size distribution of formed particles is not uniform, leading to low luminance. Accordingly, the heat-treatment temperature was controlled to be in a range of 200 to 370 C., and the heat-treatment time was controlled to be in a range of 10 minutes to 4 hours (step of forming a nanoparticle). After the heat-treatment, the result was cooled to room temperature, thereby producing nanophosphor in the colloid state, having a particle diameter of 1 nm to 50 nm. The nanophosphor was washed with acetone or ethanol, and then, for storage purpose, dispersed in a non-polar solvent, for example, hexane, toluene, chloroform, or like.

(76) As shown in the emission image of FIG. 16, it was confirmed that blue light was emitted by the solution of the up-conversion nanophosphor having the core/first shell/second shell structure prepared according to Example 9. It was also confirmed that bright green and red light was emitted by the solutions of the up-conversion nanophosphors of the core/first shell/second shell/third shell structures synthesized according to Example 4 and Example 6. This result shows that various emission colors including red, green, blue, and white can be embodied by adjusting the shell composition of an up-conversion nanophosphor having a core/first shell/second shell/third shell structure.

Preparation of Silica Composite Including Red Emitting Up-Conversion Nanophosphor Having Core/First Shell/Second Shell/Third Shell Structure

(77) A silica composite including the LiY.sub.0.2F.sub.4:Yb.sup.3+.sub.0.8/LiGdF.sub.4:Yb.sup.3+.sub.0.25,Tm.sup.3+.sub.0.01/LiGdF.sub.4:Eu.sup.3+.sub.0.15/LiYF.sub.4 nanoparticle prepared according to Example 6 was prepared

(78) 1.00 ml of a solution of the red emission up-conversion nanophosphor having the core/first shell/second shell/third shell structure prepared according to Example 6 was added to 2.00 ml of a perhydropolysilazane solution (Samsung SDI model number: CISD-15001, 18.6 wt % dibutyl ether solution), and then, annealed at room temperature in the atmosphere condition for 24 hours. The obtained product was milled by using a mortar and a pestle, and then, dried at a temperature of 60 C. for 7 hours and 30 minutes to prepare an up-conversion nanophosphor-silica composite.

(79) This experiment has been explained in connection with the nanophosphor having the core/first shell/second shell/third shell structure. However, the nanophosphor according to the inventive concept is not limited thereto, and various other examples of the nanophosphor are also applicable herein. For example, the nanophosphor according to the inventive concept may have the core/first shell structure alone, the core/first shell/second shell structure alone, or the core/first shell/third shell structure alone.

(80) An inorganic nanophosphor having the core/first shell/second shell/third shell structure according to embodiments of the present disclosure shows up-conversion emission having emission peaks in blue, green, and red wavelength regions corresponding to Tm, Tb, and Eu, has increased up-conversion emission intensity due to the formation of a shell on the outermost shell, enabling color-tunable high luminance up-conversion emission, and has white light emission characteristics in addition to mono-color light emission characteristics.

(81) An inorganic nanophosphor according to embodiments of the present disclosure uses up-conversion emission. Accordingly, the inorganic nanophosphor can be used as contrast media for bio imaging, and also used in disease diagnosis fields. Various wavelength regions of emission may contribute to accuracy of fluorescent imaging. Also, due to the strong up-conversion emission from the core/first shell/second shell/third shell structure, the inorganic nanophosphor can be used as a sensor that detects infrared light that is not detectable by the human eye.

(82) The increased efficiency of light emission characteristics may lead to a greater level of sensitivity of an infrared-ray sensor. The conversion of the infrared light, which is not used in a solar cell, into visible light may result in a greater efficiency of the solar cell.

(83) The up-conversion nanophosphor having the core and core/first shell/second shell/third shell structure according to embodiments of the present disclosure uses infrared light that is not detectable by the human eye. Accordingly, the up-conversion nanophosphor can be used in security-related fields, for example, in a counterfeit prevention code. Since particles of the up-conversion nanophosphor have a size of 50 nm or less, it is difficult to detect the up-conversion nanophosphor. Also, since the up-conversion nanophosphor can show an emission characteristic that is not obtainable from bulk powder phosphor, it can be used in high-grade security code. Due to the uniform and small size thereof, a transparent polymer composite can be manufactured, and since the manufactured polymer composite can emit various wavelengths of color, it can be applied in a transparent display device.

(84) The up-conversion nanophosphor can emit white light. In this case, the up-conversion nanophosphor can be used in, for example, an illuminating device using infrared light. However, these effects thereof are an example only, and do not limit the scope of the inventive concept.

(85) As described above, the inventive concept has been described in connection with example embodiments. However, it is obvious to one of ordinary skill in the art that the embodiments described above may be modified or changed in various manners as long as within the inventive concept or region recited in the following claims.

(86) One of ordinary skill in the art may improve or change the inventive concept in various manners, and as long as being obvious to one of ordinary skill in the art, the improvement and change may be within the claimed scope of the inventive concept.