RED PHOSPHOR AND METHOD FOR PRODUCING SAME

Abstract

A red phosphor that has optical characteristics and durability under high-temperature and high-humidity environments, and a method for producing the same. The red phosphor includes a Mn-activated complex fluoride represented by the following general formula (1) and bismuth:

A2MF6:Mn4+  (1)

wherein A represents at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and M represents at least one tetravalent element selected from the group consisting of silicon, germanium, tin, titanium, zirconium and hafnium.

Claims

1. A red phosphor comprising a Mn-activated complex fluoride represented by the following general formula (1) and bismuth:
A.sub.2MF.sub.6:Mn.sup.4+  (1) wherein A represents at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and M represents at least one tetravalent element selected from the group consisting of silicon, germanium, tin, titanium, zirconium and hafnium.

2. The red phosphor according to claim 1, wherein the Mn-activated complex fluoride is particulate, and the bismuth is present on at least a part of the surface of the particulate Mn-activated complex fluoride.

3. The red phosphor according to claim 2, wherein a coating layer is provided on the surface of the particulate Mn-activated complex fluoride, and the coating layer contains the bismuth.

4. The red phosphor according to claim 3, wherein the coating layer is composed of a bismuth elemental substance and/or a bismuth compound.

5. The red phosphor according to claim 4, wherein the bismuth compound is at least one selected from the group consisting of BiF.sub.3, BiCl.sub.3, BiBr.sub.3, BiI.sub.3, Bi.sub.2O.sub.3, Bi.sub.2S.sub.3, Bi.sub.2Se.sub.3, BiSb, Bi.sub.2Te.sub.3, Bi(OH).sub.3, (BiO).sub.2CO.sub.3, BiOCl, BiPO.sub.4, Bi.sub.2Ti.sub.2O.sub.7, Bi(WO.sub.4).sub.3, Bi.sub.2(SO.sub.4).sub.3, BiOCH.sub.3COO, 4BiNO.sub.3(OH).sub.2.Math.BiO(OH), C.sub.3F.sub.9O.sub.9S.sub.3Bi, C.sub.7H.sub.7BiO.sub.7, C.sub.9H.sub.2BiO.sub.3, C.sub.15H.sub.33BiO.sub.3, C.sub.30H.sub.57BiO.sub.6, C.sub.12H.sub.10BiK.sub.3O.sub.14, C.sub.3F.sub.9O.sub.9S.sub.3Bi and C.sub.6H.sub.4(OH)CO.sub.2BiO.Math.H.sub.2O.

6. The red phosphor according to claim 1, wherein the content of bismuth is in a range of 0.01% by mass to 15% by mass with respect to the total mass of the red phosphor.

7. The red phosphor according to claim 1, wherein a molar ratio of Mn in the Mn-activated complex fluoride is in a range of 0.005 to 0.15 relative to the total number of mols of M and Mn.

8. A method for producing red phosphor, which comprises a step of bringing a treatment liquid containing bismuth into contact with the Mn-activated complex fluoride represented by the following general formula (1):
A.sub.2MF.sub.6:Mn.sup.4+  (1) wherein A represents at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and M represents at least one tetravalent element selected from the group consisting of silicon, germanium, tin, titanium, zirconium and hafnium.

9. The method for producing red phosphor according to claim 8, wherein the content of bismuth in the treatment liquid is in a range of 0.01% by mass to 15% by mass relative to the total mass of the treatment liquid.

10. The method for producing red phosphor according to claim 8, wherein a solvent of the treatment liquid is water, an organic solvent, a mixed solvent thereof, or an acidic solvent thereof.

11. The method for producing red phosphor according to claim 10, wherein the acidic solvent is an acidic solvent containing hydrogen fluoride, and a mixing ratio of the acidic solvent containing hydrogen fluoride to the bismuth is in a range of 30:1 to 3,500:1 on a mass basis.

12. The method for producing red phosphor according to claim 11, wherein the concentration of the hydrogen fluoride in the acidic solvent containing hydrogen fluoride is in a range of 1% by mass to 70% by mass relative to the total mass of the acidic solvent.

13. The method for producing red phosphor according to claim 8, wherein bismuth is contained in the treatment liquid as at least one selected from the group consisting of Bi elemental substance, BiF.sub.3, BiCl.sub.3, BiBr.sub.3, BiI.sub.3, Bi.sub.2O.sub.3, Bi.sub.2S.sub.3, Bi.sub.2Se.sub.3, BiSb, Bi.sub.2Te.sub.3, Bi(OH).sub.3, (BiO).sub.2CO.sub.3, BiOCl, BiPO.sub.4, Bi.sub.2Ti.sub.2O.sub.7, Bi(WO.sub.4).sub.3, Bi.sub.2(SO.sub.4).sub.3, BiOCH.sub.3COO, 4BiNO.sub.3(OH).sub.2.Math.BiO(OH), C.sub.3F.sub.9O.sub.9S.sub.3Bi, C.sub.7H.sub.7BiO.sub.7, C.sub.9H.sub.21BiO.sub.3, C.sub.15H.sub.33BiO.sub.3, C.sub.30H.sub.57BiO.sub.6, C.sub.12H.sub.10BiK.sub.3O.sub.14, C.sub.3F.sub.9O.sub.9S.sub.3Bi and C.sub.6H.sub.4(OH)CO.sub.2BiO.Math.H.sub.2O.

Description

EXAMPLES

[0071] The present invention will be described in detail by way of Examples, but the present invention is not limited to the following Examples without departing from the scope of the present invention.

(Formation of Mn-Activated Complex Fluoride)

[0072] A Mn-activated complex fluoride was synthesized by the following method in accordance with the method mentioned in H. D. Nguyen, C. C. Lin, R. S. Liu, Angew. Chem. Volume 54, 37, p.10862(2015).

[0073] First, 35 ml of a 48% by mass hydrofluoric acid solution was charged in a PFA container having an internal volume of 0.1 L. Next, while stirring the hydrofluoric acid solution, 1.2 g of SiO.sub.2 was added and dissolved. Further, 0.3 g of K.sub.2MnF.sub.6 was added to this solution and dissolved.

[0074] Subsequently, 3.5 g of KF was slowly added to the solution over 15 minutes to obtain crystals. The thus obtained crystals were washed with a 20% by mass hydrofluoric acid solution and acetone, and then dried at 70° C. for 6 hours. As a result, K.sub.2SiF.sub.6:Mn.sup.4+ as a Mn-activated complex fluoride was obtained.

Example 1

[0075] Bismuth fluoride (BiF.sub.3) (0.15 g) was added to 16.6 ml of a 43% by mass hydrofluoric acid, followed by stirring for 5 minutes to prepare a suspension (hydrofluoric acid: bismuth=1,408:1 (mixing ratio on a mass basis)). Next, while stirring this suspension, 5.3 g of K.sub.2SiF.sub.6:Mn.sup.4+ was added, followed by stirring for additional 10 minutes.

[0076] After completion of the stirring, the suspension was left to stand for 10 minutes to precipitate a dispersed solid. Then, suction filtration was performed to collect the residue. After adding ethanol to this residue, suction filtration was performed again to remove the supernatant, and this operation was repeated to wash the residue. The washed residue was collected and dried under a nitrogen atmosphere at a drying temperature of 105° C. to evaporate ethanol. As a result, a red phosphor according to Example 1 was fabricated.

Example 2

[0077] In this Example, the amount of bismuth fluoride added was changed from 0.15 g to 0.05 g (hydrofluoric acid:bismuth=423:1 (mixing ratio on a mass basis)). A red phosphor according to Example 2 was fabricated in the same manner as in Example 1, except for the above. [0077]

Example 3

[0078] In this Example, the amount of bismuth fluoride added was changed from 0.15 g to 0.015 g (hydrofluoric acid:bismuth=141:1 (mixing ratio on a mass basis)). A red phosphor according to Example 3 was fabricated in the same manner as in Example 1, except for the above. [0078]

Example 4

[0079] In this Example, the amount of bismuth fluoride added was changed from 0.15 g to 0.60 g (hydrofluoric acid:bismuth=35:1 (mixing ratio on a mass basis)). A red phosphor according to Example 4 was fabricated in the same manner as in Example 1, except for the above. [0079]

Example 5

[0080] In this Example, the amount of bismuth fluoride added was changed from 0.15 g to 0.90 g, and the amount of a 43% by mass hydrofluoric acid was changed from 16.6 ml to 21.5 ml (hydrofluoric acid:bismuth=35:1 (mixing ratio on a mass basis)). A red phosphor according to Example 5 was fabricated in the same manner as in Example 1, except for the above. [0080]

Example 6

[0081] In this Example, bismuth fluoride was changed to an aqueous solution of bismuth nitrate having a concentration of 40% by mass, and the amount added was changed from 0.15 g to 0.56 g (hydrofluoric acid:bismuth=140:1 (mixing ratio on a mass basis)). A red fluorescent substance according to Example 6 was fabricated in the same manner as in Example 1 except for above.[0081]

Example 7

[0082] In this Example, the concentration of a hydrofluoric acid was changed from 43% by mass to 35% by mass, and the amount of bismuth fluoride added was changed from 0.15 g to 0.015 g (hydrofluoric acid:bismuth=1408:1 (mixing ratio on a mass basis)). A red phosphor according to Example 7 was fabricated in the same manner as in Example 1, except for the above. [0082]

Comparative Example 1

[0083] In the present Comparative Example, the above-mentioned K.sub.2SiF.sub.6:Mn.sup.4+ was used as the red phosphor.

(Evaluation of Red Phosphor)

[0084] The red phosphors according to Examples 1 to 7 and Comparative Example 1 were evaluated by the methods mentioned below.

<Molar Ratio of Mn and Content of Bismuth>

[0085] The manganese concentration and bismuth content of the red phosphors of Examples 1 to 7 and Comparative Example 1 were measured by energy dispersive X-ray spectrometry (EDX). The EDX measurement is a measurement method in which fluorescent X-rays generated when irradiating a sample with X-rays are measured, and elements constituting the sample and the concentration are analyzed.

[0086] The red phosphors of Examples 1 to 7 and Comparative Example 1 were placed on a sample stage of an EDX measuring device, respectively, and the manganese concentration and bismuth content were calculated. As the EDX measuring device, JSF-7800F schottky field emission scanning electron microscope (trade name, manufactured by JEOL, Ltd.) was used. The measurement conditions were as follows: an acceleration voltage of 15 kV, an irradiation current of 1.0000 nA and an energy range of 0 to 20 keV.

[0087] As a result of the measurement, the molar ratio of the total number of mols of Si and Mn, Mn (Mn/(Si+Mn)), in the red phosphor was 0.054, 0.054, 0.055, 0.054, 0.054, 0.055, 0.055, respectively, in case of the red phosphors of Examples 1 to 7, and was 0.055 in case of the red phosphor of Comparative Example 1.

[0088] In case of the red phosphors of Examples 1 to 7, the bismuth content was 4.1% by weight, 1.3% by weight, 0.4% by weight, 10.7% by weight, 14.9% by weight, 4.0% by weight and 0.4% by weight, respectively. In case of the red phosphor of Comparative Example 1, the bismuth content was less than the detection limit (0.01% by weight).

<Evaluation of Optical Properties of Red Phosphor>

[0089] In order to evaluate the optical properties of each of the red phosphors of Examples 1 to 7 and Comparative Example 1, the absorptivity and internal quantum efficiency of each red phosphor were determined.

[0090] The absorptivity and internal quantum efficiency were measured using a blue LED spot illuminator (trade name: TSPA22X8-57B, manufactured by AS ONE CORPORATION) and a spectroradiometer (trade name: SR-UL2, manufactured by TOPCON CORPORATION). That is, a white plate (BaSO.sub.4, manufactured by JASCO Corporation) which reflects almost 100% of excitation light is set on the sample stage and the spectral radiance of excitation light (wavelength: 449 nm) was measured, and then a peak value thereof (Ex1) was measured.

[0091] Subsequently, a sample of the red phosphor of any one of Examples 1 to 7 or Comparative Example 1 was packed in the recess of the sample stage, and a spectral radiance peak value (Em) of fluorescence under irradiation with excitation light and the unabsorbed component of an excitation light peak value (Ex2) was measured, respectively.

[0092] The absorptivity a of each of the red phosphors of Examples 1 to 7 and Comparative Example 1 was calculated using the following mathematical formula (1). The results are shown in Table 1.

Absorptivityα(%)=(Ex1−Ex2)/Ex1×100  (1)

[0093] The internal quantum efficiency η of each of the red phosphors of Examples 1 to 7 and Comparative Example 1 was calculated using the following mathematical formula (2). The results are shown in Table 1.

Internal quantum efficiencyη(%)=Em/(Ex1−Ex2)×100   (2)

<Evaluation of Durability of Red Phosphor>

[0094] The durability test was performed as follows. First, 0.3 g of each of the red phosphors of Examples 1 to 7 or Comparative Example 1 was placed in a PFA tray, which was set in a thermo-hygrostat controlled at a temperature of 80° C. and a relative humidity of 80%, followed by storage for 88 hours. Then, the absorptivity a and internal quantum efficiency η were determined by the above-mentioned methods, respectively. The absorptivity a and internal quantum efficiency η after storage of each red phosphor for 168 hours under an environment of a temperature of 80° C. and a relative humidity of 80% were also determined.

[0095] Furthermore, an index of the durability of the red phosphor under high-temperature and high-humidity environments was calculated from the values of the internal quantum efficiency before and after the durability test of each red phosphor, based on the following mathematical formula (3). The results are shown in Table 1.

(Durability index)=(internal quantum efficiency after durability test)/internal quantum efficiency before durability test)×100  (3)

[0096] Note that “after endurance test” in mathematical formula (3) means the case after storage for 88 hours under an environment of a temperature of 80° C. and a relative humidity of 80%, and the case after storage for 168 hours under the same environment.

(Results)

[0097] As shown in Table 1, inclusion of bismuth was confirmed in the red phosphors of Examples 1 to 7 in which the surface was treated with the treatment liquid containing bismuth fluoride. It was also confirmed that the red phosphors of Examples 1 to 7 exhibited improved durability under high-temperature and high-humidity environments as compared with the red phosphors of Comparative Example 1 which was not subjected to a surface treatment.

TABLE-US-00001 TABLE 1 Initial optical properties Durability 0 Hour 88 Hours 168 Hours Bi Internal Internal Internal content Mn quantum Absorp- quantum Durability Absorp- quantum Durability (% by molar Absorptivity efficiency tivity efficiency index tivity efficiency index weight) ratio (%) (%) (%) (%) (%) (%) (%) (%) Example 1 4.1 0.054 77 88 79 86 98.8 79 83 94.3 Example 2 1.3 0.054 78 87 79 86 98.8 79 84 96.6 Example 3 0.4 0.055 79 86 79 86 100 79 85 98.8 Example 4 10.7 0.054 75 86 75 83 97.1 75 80 93.9 Example 5 14.9 0.055 66 84 67 81 96.5 66 78 92.8 Example 6 4.0 0.054 74 88 76 85 96.8 75 82 93.7 Example 7 0.4 0.055 79 86 79 86 100 79 85 99.1 Comparative N.D 0.055 80 84 80 83 98.8 80 76 90.5 Example 1