SURFACE MODIFICATION METHOD FOR FLUORIDE LUMINESCENT MATERIAL AND FLUORIDE LUMINESCENT MATERIAL PREPARED THEREFROM

Abstract

In a surface modification method for fluoride luminescent materials, an inorganic coating layer A.sub.xMF.sub.y coated substrate A.sub.xMF.sub.y:Mn.sup.4+ is mixed with an organic solution containing a metal phosphate, an alkoxysilane, an organic carboxylic acid or an organic amine. The solution is evaporated to give the organic-inorganic coating layer coated surface-modified fluoride luminescent material. The phosphor photoluminescence intensity and quantum efficiency of the modified phosphors can be maintained at 85%-95% under high temperature and high humidity conditions. After being coated with the inorganic coating layer, the surface defects of the phosphor are reduced, and the photoluminescence intensity and quantum yield of the phosphor are increased by 5%-15%. After being coated with the organic coating layer, the photoluminescence intensity of the phosphor is reduced <3%.

Claims

1. A surface-modified fluoride luminescent material, wherein the luminescent material comprises a substrate, an inorganic coating layer and an organic coating layer, the inorganic coating layer being coated on the outer surface of the substrate, and the organic coating layer being coated on the outer surface of the inorganic coating layer; wherein the substrate is A.sub.xMF.sub.y:Mn.sup.4+, and the inorganic coating layer is A.sub.xMF.sub.y; wherein A is selected from one of alkali metals Li, Na, K, Rb and Cs and a combination thereof; M is selected from one of Ti, Si, Ge, Sn, Zr, Al, Bi, Ga and In, and a combination thereof; x is an absolute value of the charge of [MF.sub.y] ion; y is 4, 5, 6 or 7; and Mn.sup.4+ is a luminescence center ion.

2. The surface-modified fluoride luminescent material according to claim 1, wherein x is an absolute value of the charge of [MF.sub.6] ion, and y is 6.

3. The surface-modified fluoride luminescent material according to claim 1, wherein the inorganic coating layer can be a single layer or multiple layers, and the organic coating layer coated on the outer surface of the inorganic coating layer can also be a single layer or multiple layers.

4. The surface-modified fluoride luminescent material according to claim 1, wherein the organic coating layer is at least one of metal phosphate, alkoxysilane, organic carboxylic acid and organic amine.

5. The surface-modified fluoride luminescent material according to claim 1, wherein the phosphate in the metal phosphate is phosphomonoester or phosphodiester, such as P(O)(OH).sub.2(OR) or P(O)(OH)(OR).sub.2, wherein R is hydrocarbyl; preferably, the phosphate is obtained by esterifying a phosphorus source with an alcohol, wherein the phosphorus source is selected from one of P.sub.2O.sub.5 and POCl.sub.3, or a combination thereof; and the alcohol is at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; preferably, the metal in the metal phosphate is selected from one of Al, Ti, Si, Ga and Zn ions, and a combination thereof; preferably, the alkoxysilane is Si(OR.sup.1).sub.3(R.sup.2), wherein R.sup.1 is C.sub.1-6 alkyl, and R.sup.2 is C.sub.1-20 alkyl or C.sub.1-20 alkenyl; for example, the alkoxysilane is selected from methyl trimethoxysilane, ethyl trimethoxysilane, n-propyl trimethoxysilane, n-octyl trimethoxysilane, ethenyl trimethoxysilane, dodecyl trimethoxysilane, hexadecyl trimethoxysilane, and octadecyl trimethoxysilane; preferably, the organic carboxylic acid is R.sup.3COOH, wherein R.sup.3 is C.sub.1-30 alkyl; for example, the organic carboxylic acid is selected from oleic acid, stearic acid, docosanoic acid, octacosanoic acid, and lauric acid; preferably, the organic amine is NR.sup.4(R.sup.5).sub.2, wherein R.sup.4 is C.sub.1-10 alkyl, and R.sup.5, which may be the same or different, is H or C.sub.1-10 alkyl; for example, the organic amine is selected from methylamine, ethylamine, propylamine, butylamine, octylamine, and hexylamine, and the corresponding secondary amine or tertiary amine.

6. A preparation method for the surface-modified fluoride luminescent material according to claim 1, comprising the following steps: (1) dissolving the compound A.sub.xMF.sub.y in hydrofluoric acid solution to form a saturated solution; (2) adding the substrate A.sub.xMF.sub.y:Mn.sup.4+ into the saturated solution in step (1), and obtaining an substrate A.sub.xMF.sub.y:Mn.sup.4+ coated with inorganic coating layer A.sub.xMF.sub.y by ion exchange reaction, which is denoted as A.sub.xMF.sub.y:Mn.sup.4+@A.sub.xMF.sub.y; (3) preparing an organic solution; (4) mixing the substrate A.sub.xMF.sub.y:Mn.sup.4+ coated with inorganic coating layer A.sub.xMF.sub.y obtained in step (2) with the organic solution in step (3), and heating and stirring the mixture until the organic solvent is removed, to give the surface-modified fluoride luminescent material, which is denoted as A.sub.xMF.sub.y:Mn.sup.4+@A.sub.xMF.sub.y organic layer; wherein A is selected from one of alkali metals Li, Na, K, Rb and Cs, or a combination thereof; M is selected from one of Ti, Si, Ge, Sn, Zr, Al, Bi, Ga and In, or a combination thereof; x is an absolute value of the charge of [MF.sub.y] ion; y is 4, 5, 6 or 7; and Mn.sup.4+ is a luminescence center ion.

7. The preparation method according to claim 6, wherein in step (2), the mass ratio of the substrate A.sub.xMF.sub.y:Mn.sup.4+ to the compound A.sub.xMF.sub.y in the saturated solution in step (1) is 10:1-1:5, and preferably, 1:1; preferably, in step (2), the ion exchange process is performed at 0-100° C., and preferably, at 25-80° C.

8. The preparation method according to claim 6, wherein in step (3), the organic solution is at least one of a metal phosphate solution, an alkoxysilane solution, an organic carboxylic acid solution and an organic amine solution, and the preparation process for the solution is, for example: dissolving an alkoxysilane, an organic carboxylic acid or an organic amine in an organic solvent, wherein the organic solvent is at least one selected from methanol, ethanol, propanol, n-hexane, and cyclohexane; mixing a metal source and a phosphorus source with an alcohol for esterification to give a metal phosphate solution, wherein the phosphorus source is selected from one of P.sub.2O.sub.5 and POCl.sub.3, or a combination thereof; the alcohol is at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; and the metal source is metal nitrate, metal sulfate or metal oxalate, or one or more of metal organic salts such as isopropoxide, ethoxide, propoxide or butoxide, and preferably, the metal source is Al(NO.sub.3).sub.3.9H.sub.2O, Zn(NO.sub.3).sub.2.6H.sub.2O, titanium butoxide, or aluminum isopropoxide.

9. The preparation method according to claim 6, wherein in step (4), the temperature of the heating and stirring is at least 30° C., and preferably, at least 50° C.; preferably, in step (4), the mass ratio of the substrate A.sub.xMF.sub.y:Mn.sup.4+ coated with inorganic coating layer A.sub.xMF.sub.y to the organic solution is 5:1-1:20, and preferably, 1:1-1:5.

10. The method according to claim 6, wherein in step (2), the A.sub.xMF.sub.y:Mn.sup.4+ is selected from A.sub.2MF.sub.6:Mn.sup.4+ and A.sub.3MF.sub.6:Mn.sup.4+, wherein the A.sub.2MF.sub.6:Mn.sup.4+ is selected from K.sub.2TiF.sub.6:Mn.sup.4+, K.sub.2SiF.sub.6:Mn.sup.4+, Na.sub.2SiF.sub.6:Mn.sup.4+, Na.sub.2TiF.sub.6:Mn.sup.4+, K.sub.2GeF.sub.6:Mn.sup.4+, Na.sub.2SnF.sub.6:Mn.sup.4+, Cs.sub.2TiF.sub.6:Mn.sup.4+ and Cs.sub.2SiF.sub.6:Mn.sup.4+; and the A.sub.3MF.sub.6:Mn.sup.4+ is selected from Na.sub.3AlF.sub.6:Me, K.sub.3AlF.sub.6:Mn.sup.4+, Li.sub.3AlF.sub.6:Mn.sup.4+, Rb.sub.3AlF.sub.6:Mn.sup.4+, Cs.sub.3AlF.sub.6:Mn.sup.4+, K.sub.2NaAlF.sub.6:Mn.sup.4+ and K.sub.2LiAlF.sub.6:Mn.sup.4+; and preferably, in step (1), the A.sub.xMF.sub.y is selected from A.sub.2MF 6 and A.sub.3MF.sub.6, wherein the A.sub.2MF.sub.6 is selected from K.sub.2TiF.sub.6, K.sub.2SiF.sub.6, Na.sub.2SiF.sub.6, Na.sub.2TiF.sub.6, K.sub.2GeF.sub.6, Na.sub.2SnF.sub.6, Cs.sub.2TiF.sub.6 and Cs.sub.2SiF.sub.6; and the A.sub.3MF.sub.6 is selected from Na.sub.3AlF.sub.6, K.sub.3AlF.sub.6, Li.sub.3AlF.sub.6, Rb.sub.3AlF.sub.6, Cs.sub.3AlF.sub.6, K.sub.2NaAlF.sub.6 and K.sub.2LiAlF.sub.6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 shows the XRD diffraction pattern of the K.sub.2TiF.sub.6:Mn.sup.4+@K.sub.2TiF.sub.6@metal phosphate phosphor in (C) of Example 1 of the present invention.

[0048] FIG. 2 shows the XRD diffraction pattern of the K.sub.2SiF.sub.6:Mn.sup.4+@K.sub.2SiF.sub.6@metal phosphate phosphor in (C) of Example 2 of the present invention.

[0049] FIG. 3 shows the XRD diffraction pattern of the K.sub.2GeF.sub.6:Mn.sup.4+@K.sub.2GeF.sub.6@metal phosphate phosphor in (C) of Example 3 of the present invention.

[0050] FIG. 4 shows the scanning electron micrograph of the K.sub.2TiF.sub.6:Mn.sup.4+ phosphor in (A) of Example 1 of the present invention.

[0051] FIG. 5 shows the scanning electron micrograph of the K.sub.2TiF.sub.6:Mn.sup.4+@K.sub.2TiF.sub.6 phosphor in (B) of Example 1 of the present invention.

[0052] FIG. 6 shows the scanning electron micrograph of the K.sub.2TiF.sub.6:Mn.sup.4+@K.sub.2TiF.sub.6@metal phosphate phosphor in (C) of Example 1 of the present invention.

[0053] FIG. 7 shows the changes in photoluminescence intensity of the sample encapsulated with the phosphors in Example 1 and Preparation Example 1 of the present invention and with silica gel after aging at 85° C. and 85% humidity.

[0054] FIG. 8 shows the changes in photoluminescence intensity of the sample encapsulated with the phosphors in Example 2 and Preparation Example 2 of the present invention and with silica gel after aging at 85° C. and 85% humidity.

[0055] FIG. 9 shows the changes in photoluminescence intensity of the sample encapsulated with the phosphors in Example 3 and Preparation Example 3 of the present invention and with silica gel after aging at 85° C. and 85% humidity.

[0056] FIG. 10 is a schematic diagram of the structure of the surface-modified phosphor according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION

[0057] The preparation method of the present invention will be further illustrated in detail with reference to the following specific examples. It should be understood that the following examples are merely exemplary illustration and explanation of the present invention, and should not be construed as limiting the scope of protection of the present invention. All techniques implemented based on the aforementioned contents of the present invention are encompassed within the scope of protection of the present invention.

[0058] Unless otherwise stated, the experimental methods used in the following examples are conventional methods. Unless otherwise stated, the reagents, materials, and the like used in the following examples are commercially available.

Instruments and Equipment

[0059] An X-ray powder diffractometer (DMAX 2500PC, Rigaku) was used for phase analysis; a field emission scanning electron microscopy (FE-SEM, Hitachi SU1510) was used to observe the sample morphology; and an FLS980 (Edinburgh Instrument) fluorescence spectrometer was used to characterize the fluorescence spectra of the samples.

[0060] The fluoride phosphor in the specific example of the present invention had a chemical general formula of A.sub.2MF.sub.6:Mn.sup.4+, wherein A was selected from one of alkali metals Li, Na, K, Rb and Cs, and a combination thereof; M was selected from one of Ti, Si, Ge, Sn, Zr, Al, Bi, Ga and In, and a combination thereof; and Mn.sup.4+ was a luminescence center ion. The preparation process is as follows: an oxide, a salt or an acid containing M was dissolved in a 20%-50% HF solution according to the formula stoichiometric ratio of the Mn.sup.4+-doped fluoride phosphor material, and then the fluoride of A was added; after being stirred for 1-10 min, the mixture was added with A.sub.2MnF.sub.6, stirred for 30-90 min, then left to stand, and filtered; and the resulting precipitate was washed, and dried to give the fluoride red phosphor A.sub.2MF.sub.6.

Preparation Examples 1-3: Preparation of A.SUB.2.MF.SUB.6.:Mn.SUP.4+ Phosphor

[0061] The synthesis methods of Preparation Examples 1-3 were the same, except for differences in the type and amount of starting materials. The specific parameters are shown in Table 1 below. The specific process was illustrated by taking the K.sub.2MF.sub.6:Mn.sup.4+ phosphor of Preparation Example 1 as an example: K.sub.2MnF.sub.6 was dissolved in a hydrofluoric acid solution; after being stirred for 1-10 min, the solution was added with the A.sub.2MF.sub.6 powder, stirred at room temperature for 30-90 min, and filtered; and the resulting precipitate was washed with acetone to remove the residual HF completely, dried in an oven at 70° C. for 4 h to give the final phosphor. The excitation and emission spectra, fluorescence quantum yield and absorption efficiency of the product were measured by an FLS980 (Edinburgh Instrument) fluorescence spectrometer. The results are shown in Table 2.

TABLE-US-00001 TABLE 1 Synthesis technical parameters of Preparation Examples 1-3 HF Preparation concen- Example Starting material Reaction time tration Preparation K.sub.2TiF.sub.6 2.5 g K.sub.2MnF.sub.6 0.18 g 30 min 49% Example 1 Preparation K.sub.2SiF.sub.6 2.5 g K.sub.2MnF.sub.6 0.10 g 90 min 49% Example 2 Preparation K.sub.2GeF.sub.6 2.5 g K.sub.2MnF.sub.6 0.12 g 60 min 49% Example 3

Example 1

[0062] (A) Preparation of Modified K.sub.2TiF.sub.6:Mn.sup.4+@K.sub.2TiF.sub.6 Phosphor

[0063] Compound K.sub.2TiF.sub.6 was added to a 49% HF solution (10 mL) until it was no longer dissolved. The solution was filtered to remove the undissolved K.sub.2TiF.sub.6 to give a saturated solution of K.sub.2TiF.sub.6 in the 49% HF solution. Then the saturated solution was added to a container containing the K.sub.2TiF.sub.6:Mn.sup.4+ phosphor (1 g) obtained in Preparation Example 1. The solution was stirred at room temperature for 30 min, filtered under vacuum, washed with acetone 3 times to remove the residual HF, and dried in an oven at 70° C. for 4 h to give the inorganic coating layer K.sub.2TiF.sub.6 coated substrate K.sub.2TiF.sub.6:Mn.sup.4+, which was denoted as K.sub.2TiF.sub.6:Mn.sup.4+@K.sub.2TiF.sub.6 phosphor. The excitation and emission spectra and internal fluorescence quantum yield of the product were measured by an FLS980 fluorescence spectrometer. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(B) Preparation of Modified K.sub.2TiF.sub.6:Mn.sup.4+@Metal Phosphate Phosphor

[0064] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2TiF.sub.6:Mn.sup.4+ phosphor (1 g) in Preparation Example 1, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor, which was denoted as K.sub.2TiF.sub.6:Mn.sup.4+@metal phosphate phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6@Metal Phosphate Phosphor

[0065] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6 phosphor (1 g) prepared in (A) of Example 1, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor, which was denoted as K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6@metal phosphate phosphor. The X-ray powder diffraction shows that the product is still pure-phase K.sub.2TiF.sub.6 (FIG. 1), and no other impurity phases are introduced. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6@Octadecyl Trimethoxysilane Phosphor

[0066] Octadecyl trimethoxysilane (2.5 mL) was added to n-hexane (50 mL). The solution was stirred for 30 min, and added with the K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6 phosphor (1 g) prepared in (A) of Example 1. Then the solution was heated to 70° C. and stirred until the solution was evaporated to dryness. The residue was washed with n-hexane several times, dried in an oven at 150° C. for 4 h to give a phosphor, which was denoted as K.sub.2TiF.sub.6:Me@K.sub.2TiF.sub.6@octadecyl trimethoxysilane phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

[0067] FIGS. 4-6 are the scanning electron micrographs of the phosphors prepared in (A), (B) and (C) of Example 1. It can be seen from those figures that the inorganic coating layer coated sample has a smooth surface and an unchanged particle size, and the organic coating layer coated sample has a small amount of fine substances on the surface.

Example 2

[0068] (A) Preparation of Modified K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6 Phosphor

[0069] Compound K.sub.2SiF.sub.6 was added to a 49% HF solution (10 mL) until it was no longer dissolved. The solution was filtered to remove the undissolved K.sub.2SiF.sub.6 to give a saturated solution of K.sub.2SiF.sub.6 in the 49% HF solution. Then the saturated solution was added to a container containing the K.sub.2SiF.sub.6:Mn.sup.4+ phosphor (1 g) obtained in Preparation Example 2. The solution was stirred at room temperature for 30 min with an ethanol being added dropwise at 0.5 mL/min. Then the solution was filtered under vacuum, washed with acetone 3 times to remove the residual HF, and dried in an oven at 70° C. for 4 h to give the K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6 phosphor. The excitation and emission spectra and internal fluorescence quantum yield of the product were measured by an FLS980 fluorescence spectrometer. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(B) Preparation of Modified K.sub.2SiF.sub.6:Me@Metal Phosphate Phosphor

[0070] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2SiF.sub.6:Mn.sup.4+ phosphor (1 g) in Preparation Example 2, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6@Metal Phosphate Phosphor

[0071] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6 phosphor (1 g) prepared in (A) of Example 2, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor. The X-ray powder diffraction shows that the product is still pure-phase K.sub.2SiF.sub.6 (FIG. 2), and no other impurity phases are introduced. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6@Hexadecyl Trimethoxysilane Phosphor

[0072] Hexadecyl trimethoxysilane (5 mL) was added to n-hexane (50 mL). The solution was stirred for 30 min, and added with the K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6 phosphor (1 g) prepared in (A) of Example 2. Then the solution was heated to 70° C. and stirred until the solution was evaporated to dryness. The residue was washed with n-hexane several times, dried in an oven at 150° C. for 4 h to give a phosphor, which was denoted as K.sub.2SiF.sub.6:Me@K.sub.2SiF.sub.6@hexadecyl trimethoxysilane phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

Example 3

[0073] (A) Preparation of Modified K.sub.2GeF.sub.6:Me@K.sub.2GeF.sub.6 Phosphor

[0074] Compound K.sub.2GeF.sub.6 was added to a 49% HF solution (10 mL) until it was no longer dissolved. The solution was filtered to remove the undissolved K.sub.2GeF.sub.6 to give a saturated solution of K.sub.2GeF.sub.6 in the 49% HF solution. Then the saturated solution was added to a container containing the K.sub.2GeF.sub.6:Mn.sup.4+ phosphor obtained in Preparation Example 3. The solution was stirred at room temperature for 30 min with an ethanol being added dropwise at 0.5 mL/min. Then the solution was filtered under vacuum, washed with acetone 3 times to remove the residual HF, and dried in an oven at 70° C. for 4 h to give the K.sub.2GeF.sub.6:Me@K.sub.2GeF.sub.6 phosphor. The excitation and emission spectra and internal fluorescence quantum yield of the product were measured by an FLS980 fluorescence spectrometer. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(B) Preparation of Modified K.sub.2GeF.sub.6:Me@Metal Phosphate Phosphor

[0075] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2GeF.sub.6:Mn.sup.4+ phosphor (1 g) in Preparation Example 3, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K.sub.2GeF.sub.6:Me@K.sub.2GeF.sub.6@Metal Phosphate Phosphor

[0076] P.sub.2O.sub.5 (0.0350 g) was added to an ethanol solution (10 mL). The solution was stirred continuously, and added with Al(NO.sub.3).sub.3.9H.sub.2O (0.1468 g) with a molar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. while stirring, added with the K.sub.2GeF.sub.6:Mn.sup.4+@K.sub.2GeF.sub.6 phosphor (1 g) prepared in (A) of Example 3, heated and stirred until the solution was evaporated to dryness. The residue was washed with acetone several times, dried in an oven at 140° C. for 4 h to give a phosphor. The X-ray powder diffraction shows that the product is still pure-phase K.sub.2GeF.sub.6 (FIG. 3), and no other impurity phases are introduced. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K.sub.2GeF.sub.6:Mn.sup.4+@K.sub.2GeF.sub.6@Dodecyl Trimethoxysilane Phosphor

[0077] Dodecyl trimethoxysilane (5 mL) was added to n-hexane (50 mL). The solution was stirred for 30 min, and added with the K.sub.2GeF.sub.6:Mn.sup.4+@K.sub.2GeF.sub.6 phosphor (1 g) prepared in (A) of Example 3. Then the solution was heated to 70° C. and stirred until the solution was evaporated to dryness. The residue was washed with n-hexane several times, dried in an oven at 150° C. for 4 h to give a phosphor, which was denoted as K.sub.2GeF.sub.6:Mn.sup.4+@K.sub.2GeF.sub.6@dodecyl trimethoxysilane phosphor. The important luminescence performance parameters of the prepared phosphor are shown in Table 2.

TABLE-US-00002 TABLE 2 Luminescence performance parameters of aged samples Quantum Relative System Example yield AbsorptanceAbsorptance luminance K.sub.2TiF.sub.6:Mn.sup.4+ Preparation 93% 71% 94% Example 1 Example 1 (A) 98% 68% 100%  Example 1 (B) 85% 60% 88% Example 1 (C) 94% 67% 95% Example 1 (D) 93% 65% 94% K.sub.2SiF.sub.6:Mn.sup.4+ Preparation 91% 64% 91% Example 2 Example 2 (A) 96% 62% 100%  Example 2 (B) 84% 56% 85% Example 2 (C) 93% 61% 93% Example 2 (D) 92% 60% 92% K.sub.2GeF.sub.6:Mn.sup.4+ Preparation 89% 58% 92% Example 3 Example 3 (A) 94% 56% 100%  Example 3 (B) 81% 52% 86% Example 3 (C) 91% 55% 94% Example 3 (D) 90% 54% 91%

[0078] It can be seen from Table 2 that an inorganic coating layer coated phosphor has increased quantum yield and luminance but a slightly decreased absorptance; an organic coating layer coated phosphor has significantly decreased luminance and quantum yield; and an inorganic-organic coating layer coated phosphor has a basically unchanged or slightly increased quantum yield as compared to an uncoated phosphor.

Example 4. Stability Test

[0079] Each of the phosphor samples (0.1 g) prepared in Preparation Examples 1-3 and Examples 1-3 was mixed well with silica gel (A and B), encapsulated in a customized polytetrafluoroethylene mold, defoamed and hardened to give phosphor films. The films were aged in a programmable temperature & humidity chamber at 85° C. and 85% relative humidity. The spectrum and quantum efficiency of the samples were measured every 24 h to evaluate the high temperature and high humidity stability of the phosphors.

[0080] FIGS. 7, 8 and 9 show the changes in photoluminescence intensity of the above phosphors after aging at 85° C. and 85% relative humidity. It can be seen from FIG. 7 that the humidity resistance of the inorganic-organic coating layer coated phosphor disclosed herein has been greatly improved. After 240 h, the photoluminescence intensity of the phosphor prepared in (C) of Example 1 still maintains 92%. The photoluminescence intensity of the inorganic coating layer coated fluoride phosphor ((A) of Example 1) is only 83%, and the photoluminescence intensity of the fluoride phosphor without surface modification (prepared in Preparation Example 1) is only 59%. It can be seen that the inorganic-organic layer coating achieves a more excellent effect compared with the organic layer coating or the inorganic layer coating. The aging test results of other examples and preparation examples are similar (see FIG. 8 and FIG. 9).

[0081] The examples of the present invention have been described above. However, the present invention is not limited to the above examples. Any modification, equivalent, improvement and the like made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.