Red phosphor element, and manufacturing method of red phosphor element

Abstract

To provide a red phosphor element having humidity resistance, and a manufacturing method of the red phosphor element.SOLUTION: The red phosphor element according to one embodiment of the invention comprises a phosphor layer formed of Eu:(CaxSr1-x)S (where 0≤x≤1) monocrystalline phosphor and at least including a light irradiation surface serving as cleavage surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a red phosphor element and a method for manufacturing the red phosphor element. [Background technology]

[0002] Quasi-white light sources that combine solid-state light sources and phosphors have rapidly expanded their market share in recent years and have become indispensable in real life. However, the combination of a blue semiconductor light source and a yellow phosphor, which is often used to construct quasi-white light sources, lacks red components and has poor color rendering properties. To improve color rendering properties, the use of a red phosphor is expected. Conventional red phosphors are disclosed, for example, in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-033202 [Patent Document 2] Special Publication No. 2002-527570 Summary of the Invention [Problem to be solved by the invention]

[0004] However, europium-activated calcium sulfide phosphor (Eu:CaS), which is used as a material for red phosphors, has poor moisture resistance and is prone to degradation by moisture, resulting in a decrease in luminescence intensity. When a red phosphor is used to improve color rendering, degradation of the red phosphor can cause a shift in the color of the white light source. To solve this problem, Patent Documents 1 and 2, for example, disclose the application of a water-resistant coating to red phosphor powder. However, the coating requires complex process management, which increases manufacturing costs. Therefore, it would be desirable to provide a red phosphor element capable of improving moisture resistance without the application of a coating, and a method for manufacturing the red phosphor element. [Means for solving the problem]

[0005] The red phosphor element according to one embodiment of the present invention is x Sr 1-x )S (where 0≦x≦1) single crystal phosphor, and at least the light irradiation surface is a cleavage plane of the phosphor layer.

[0006] A method for manufacturing a red phosphor element according to an embodiment of the present invention includes the following two steps. (1) Raw materials containing (Eu, Ca, S), (Eu, Sr, S) or (Eu, Ca, Sr, S) are melted at a temperature above the melting point of the raw materials and slowly cooled to obtain Eu:(Ca x Sr 1-x )S (where 0≦x≦1) forming a bulk phosphor containing a single crystal phosphor. (2) By cleaving the phosphor bulk body, a phosphor layer is formed in which at least the light-irradiated surface is the cleavage surface. [Effects of the Invention]

[0007] In the red phosphor element according to one embodiment of the present invention, the phosphor layer is x Sr 1-x )S (where 0≦x≦1) single crystal phosphor. In this phosphor layer, at least the light irradiation surface is a cleavage plane. This makes the proportion of crystal defects in the light irradiation surface smaller than the proportion of crystal defects present on the surface of the phosphor powder. As a result, the moisture resistance of the light irradiation surface can be improved beyond that of the phosphor powder without applying a coating.

[0008] In a method for manufacturing a red phosphor element according to an embodiment of the present invention, a raw material containing (Eu,Ca,S), (Eu,Sr,S) or (Eu,Ca,Sr,S) is melted at a temperature equal to or higher than the melting point of the raw material and slowly cooled to obtain Eu:(Ca x Sr 1-x)S (where 0≦x≦1) single crystal phosphor is formed. Then, by cleaving the phosphor bulk, a phosphor layer is formed in which at least the light irradiation surface is the cleavage surface. This makes the proportion of crystal defects in the light irradiation surface smaller than the proportion of crystal defects present on the surface of the phosphor powder. As a result, the moisture resistance of the light irradiation surface can be improved beyond that of the phosphor powder without applying a coating. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a cross-sectional configuration of a red phosphor element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a modified example of the cross-sectional structure of the red phosphor element of FIG. [Figure 3] FIG. 3 is a diagram showing an example of a manufacturing process for the phosphor layer of FIG. 1 and FIG. [Figure 4] FIG. 4 is a diagram showing a schematic configuration example of an FZ (Floating Zone) melting apparatus that can be used to manufacture the phosphor layer of FIGS. [Figure 5] FIG. 5 is a diagram showing an example of an XRD (X-ray diffraction) pattern of the phosphor layer of FIG. 1 and FIG. [Figure 6] FIG. 6 is a diagram showing a modified example of the manufacturing process of the phosphor layer shown in FIGS. [Figure 7] FIG. 7 is a graph showing the wavelength dependence of the transmittance of a phosphor layer that has been annealed without adding Eu and a phosphor layer that has not been annealed. [Figure 8] FIG. 8 is a graph showing the wavelength dependence of the transmittance of a phosphor layer with Eu added that has been annealed and that has not been annealed. [Figure 9] FIG. 9 is a diagram showing an example of the difference in transmittance before and after annealing at a wavelength of 400 nm. [Figure 10] FIG. 10 is a graph showing an example of the internal quantum efficiency of the phosphor layer when the annealing temperature, annealing time, and annealing atmosphere are changed. [Figure 11] FIG. 11 is a graph showing the wavelength dependence of the transmittance of a film that has been annealed in an inert atmosphere and a film that has not been annealed. [Figure 12] FIG. 12 is a graph showing the wavelength dependence of the transmittance of a film that has been annealed in a sulfur atmosphere and a film that has not been annealed. [Figure 13] FIG. 13 is a diagram showing an example of the difference in transmittance before and after annealing at a wavelength of 400 nm. [Figure 14] FIG. 14 is a diagram showing an example of the absorptance and internal quantum efficiency of a raw material powder according to a comparative example, and an example of the absorptance and internal quantum efficiency before and after annealing according to an example. [Figure 15] FIG. 15 is a graph showing an example of the test time dependency of the internal quantum efficiency maintenance rate of the phosphor layer according to Example 1. In FIG. [Figure 16] FIG. 16 is a graph showing an example of the test time dependency of the internal quantum efficiency maintenance rate of the phosphor layer according to Example 2. In FIG. [Figure 17] FIG. 17 is a diagram showing an example of the lattice constant of the raw material powder according to the comparative example and an example of the lattice constant of the phosphor layer according to the third example. [Figure 18] FIG. 18 is a diagram illustrating an example of the wavelength distribution of the fluorescent light emitted from the phosphor layer according to Example 3. As shown in FIG. [Figure 19] FIG. 19 is a diagram showing an example of the internal quantum efficiency of the phosphor layer according to Example 3 before and after annealing. [Figure 20] FIG. 20 is a graph showing an example of the test time dependency of the internal quantum efficiency maintenance rate of the phosphor layer according to Example 3. In FIG. [Figure 21] FIG. 21 is a graph showing an example of the test time dependency of the internal quantum efficiency maintenance rate of the phosphor layer according to Example 4. In FIG. [Figure 22] FIG. 22 is a graph showing an example of the test time dependency of the internal quantum efficiency maintenance rate of the phosphor layer according to the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] <1. Background> Quasi-white light sources, which combine solid-state light sources and phosphors, have rapidly expanded their market share in recent years and have become indispensable in real life. However, the combination of blue semiconductor light sources and yellow phosphors, which is often used to create quasi-white light sources, lacks red components and has poor color rendering. To improve color rendering, the use of red phosphors is expected.

[0011] Europium-activated calcium sulfide phosphor (Eu:CaS), which is used as a material for red phosphors, exhibits a deep red color, a narrow fluorescence half-width, and high color purity, making it a promising phosphor suitable for blue excitation light. Furthermore, the emission wavelength of Eu:CaS can be controlled by substituting some or all of the Ca sites with Sr or Ba. However, alkaline earth sulfides generally have poor moisture resistance and are prone to degradation by moisture, resulting in a deterioration in emission intensity. Therefore, no practically usable alkaline earth sulfides have been reported. This is disclosed, for example, in the non-patent document "Yasushi Ito, et al.: 'A phosphor sheet and a backlight system providing wider color gamut for LCDs,' JSID, vol. 22, Issue 8 (2014)."

[0012] Furthermore, CaS is characterized by hydrolysis, decomposing into calcium hydroxide and hydrogen sulfide, and as the reaction progresses further it turns into calcium carbonate, which turns white and no longer emits fluorescence. Generally, when attempting to obtain white light with good color rendering using a blue solid-state light source such as a light-emitting diode or laser diode, a yellow phosphor is often used in combination with a red phosphor. Even if the yellow phosphor has no weather resistance issues, if the red phosphor deteriorates due to hydrolysis, the color of the white light source will shift toward blue-green over time.

[0013] For example, when powdered Eu:CaS was subjected to a storage reliability test under high-temperature, high-humidity conditions of 85°C and 85% RH, it was confirmed that the internal quantum efficiency decreased to 72% after 20 hours compared to before the storage reliability test. Furthermore, it was confirmed that the fluorescence intensity decreased to 70% after 20 hours compared to before the storage reliability test. This decrease in internal quantum efficiency and fluorescence intensity can also be caused by atmospheric humidity. Therefore, powdered Eu:CaS presents a problem of limited usage environments. Similarly, alkaline earth sulfide phosphors containing Eu:CaS also present a problem of limited usage environments.

[0014] Patent Documents 1 and 2, for example, disclose that applying a water-resistant coating to alkaline earth sulfide phosphor powder prevents the powder from deteriorating. However, coating requires complex process management, which increases manufacturing costs. Therefore, it is desirable to provide a red phosphor element that can improve moisture resistance without applying a coating, and a method for manufacturing the red phosphor element. Below, we will explain in detail the measures for improving moisture resistance without applying a coating.

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is one specific example of the present invention, and the present invention is not limited to the following embodiment. Furthermore, the present invention is not limited to the arrangement, dimensions, dimensional ratios, etc. of each component shown in each drawing.

[0016] <2. Embodiment> [composition] A red phosphor device 1 according to an embodiment of the present invention will be described. FIG. 1 shows a cross-sectional configuration example of the red phosphor device 1. The red phosphor device 1 includes, for example, a phosphor layer 10 and a heat sink 20 as shown in FIG. 1. The phosphor layer 10 has a surface on the side opposite to the heat sink 20 (light irradiation surface S1) and a surface on the heat sink 20 side (back surface S2). The heat sink 20 is bonded to the back surface S2 of the phosphor layer 10. Thereby, the heat generated in the phosphor layer 10 is dissipated to the outside through the heat sink 20. The heat sink 20 is composed of a material having higher heat dissipation than the phosphor layer 10, and includes, for example, a metal material such as Cu or CuW, or a non-metal material such as diamond, SiC, AlN, BeO, CBN, or DLC.

[0017] The phosphor layer 10 is formed of a CaS (calcium sulfide) single crystal doped with Eu (europium) (Eu:CaS single crystal phosphor), a SrS (strontium sulfide) single crystal doped with Eu (Eu:SrS single crystal phosphor), or a CaSrS (calcium strontium sulfide) single crystal doped with Eu (Eu:(Ca x Sr 1-x )S (where 0 < x < 1) single crystal phosphor). That is, the phosphor layer 10 is formed of a Eu:(Ca x Sr 1-x )S (where 0 ≤ x ≤ 1) single crystal phosphor. In the phosphor layer 10, at least the light irradiation surface S1 is a cleavage plane. In the phosphor layer 10, the light irradiation surface S1 and the back surface S2 may be cleavage planes. The cleavage plane of the phosphor layer 10 is a {100} plane. In the phosphor layer 10, a surface (side surface) different from the light irradiation surface S1 and the back surface S2 may be a cleavage plane or a non-cleavage plane. The phosphor layer 10 is capable of generating red fluorescent light having a peak in the red wavelength region when irradiated with laser light in the blue wavelength region (excitation light in the blue wavelength region) with respect to the light irradiation surface S1. The phosphor layer 10 may be a layer annealed at a temperature of 1000 °C or higher.

[0018] In the phosphor layer 10, the cleavage plane has significantly fewer crystal defects than a non-cleavage plane (e.g., the surface of Eu:CaS powder). The crystal structure of CaS is cubic. Therefore, by exposing the {100} plane of CaS, a surface with minimal lattice defects can be obtained. This means that the reactivity of the cleavage plane with atmospheric moisture is extremely low.

[0019] The size of the phosphor layer 10 (light irradiation surface S1) is larger than the irradiation spot diameter of the excitation light irradiated onto the phosphor layer 10. The thickness of the phosphor layer 10 is, for example, thick enough to allow the excitation light to pass through and not leak out from the back surface. The thickness of the phosphor layer 10 may be thin enough to allow the excitation light to pass through and leak out from the back surface. In this case, however, it is preferable that a reflective film capable of reflecting the excitation light and fluorescent light with high reflectance is formed on the surface of the heat sink 20. Examples of such a reflective film include a metal film such as Ag, or a dielectric multilayer film.

[0020] When the red phosphor element 1 is a reflective element that utilizes fluorescent light emitted from the light irradiation surface S1, the heat sink 20 is preferably attached to the back surface S2 of the phosphor layer 10, for example, as shown in Fig. 1. On the other hand, when the red phosphor element 1 is a transmissive element that utilizes fluorescent light emitted from the back surface S2, the heat sink 20 is preferably attached to the side surface S3 of the phosphor layer 10, avoiding the central portions of the light irradiation surface S1 and the back surface S2 of the phosphor layer 10, for example, as shown in Fig. 2. In this case, it is preferable that both the light irradiation surface S1 and the back surface S2 of the phosphor layer 10 are cleavage planes.

[0021] FIG. 3 shows an example of a manufacturing process for the phosphor layer 10.

[0022] First, raw materials are prepared (step S101). The raw materials are, for example, Eu:CaS powder or powder containing Eu:CaS. The raw materials may be, for example, a mixture of compounds containing Ca, S, and Eu separately. The raw materials may be, for example, a mixture containing CaS, CaSO4, CaCO3, CaO, S, Eu2(SO4)3, and Eu2O3. The raw materials may be, for example, an Eu:CaS bulk formed using a liquid-phase method or a solid-phase reaction method. The purity and fluorescent properties of Eu:CaS in the Eu:CaS bulk are not particularly limited. It is preferable that the purity of Eu:CaS in the Eu:CaS bulk be as high as possible, and that the fluorescent properties of Eu:CaS in the Eu:CaS bulk be as good as possible.

[0023] The raw material may be, for example, Eu:SrS powder or a powder containing Eu:SrS. The raw material may be, for example, a mixture of compounds containing Sr, S, and Eu separately. The raw material may be, for example, a mixture containing SrS, SrSO4, SrCO3, SrO, S, Eu2(SO4)3, and Eu2O3. The raw material may be, for example, an Eu:SrS bulk formed using a liquid-phase method or a solid-phase reaction method. The purity and fluorescent properties of Eu:SrS in the Eu:SrS bulk are not particularly limited. It is preferable that the purity of Eu:SrS in the Eu:SrS bulk be as high as possible, and that the fluorescent properties of Eu:SrS in the Eu:SrS bulk be as good as possible.

[0024] The raw material is, for example, Eu:(Ca x Sr 1-x )S powder (but 0 <x<1)、または、Eu:(Ca x Sr 1-x) It may be a powder containing S (where 0 < x < 1). The raw material may be, for example, a mixture of compounds separately containing Ca, Sr, S, and Eu. The raw material may be, for example, a mixture containing CaS, CaSO4, CaCO3, CaO, SrS, SrSO4, SrCO3, SrO, S, Eu2(SO4)3, and Eu2O3. The raw material may be, for example, Eu:(Ca x Sr 1-x )S (where 0 < x < 1) bulk. Eu:(Ca x Sr 1-x )S (where 0 < x < 1) in the bulk, regarding the purity and fluorescence characteristics of Eu:(Ca x Sr 1-x )S (where 0 < x < 1), is not particularly limited. For Eu:(Ca x Sr 1-x )S (where 0 < x < 1) in the bulk, regarding the purity and fluorescence characteristics of Eu:(Ca x Sr 1-x )S (where 0 < x < 1), it is preferably as high as possible, and for Eu:(Ca x Sr 1-x )S (where 0 < x < 1) in the bulk, regarding the fluorescence characteristics of Eu:(Ca x Sr 1-x )S (where 0 < x < 1), it is preferably as good as possible.

[0025] <00The raw material may be Eu:CaS powder with an internal quantum efficiency (86%) and Eu concentration (0.107 at%). This internal quantum efficiency is an absolute value measured using a JASCO FP-8550 spectrophotometer and a standard phosphor (Standard Phosphor Red: Lot. No. NSR1310) manufactured by Sialon Corporation as a reference. When using powder as the raw material, the powder may be compacted by pressure molding to make it easier to handle. One-way pressing using a metal mold or cold isostatic pressing (CIP) using a rubber mold can be used for the pressing. The pressing conditions may be arbitrary, as long as they result in a compact that maintains a density sufficient for the phosphor layer 10 formation process. For example, the raw material is placed in a rubber tube and subjected to CIP at a pressure of 80 MPa for two minutes, forming the raw material into a cylindrical rod that does not easily crumble. The compact obtained by pressing may be subjected to a firing process at any temperature, atmosphere, and time to improve strength, reduce impurities, and reduce internal moisture, etc. In this way, the raw material rod M1 is produced.

[0026] When a bulk body is used as the raw material, processes such as CIP, which are required when a powder is used as the raw material, can be omitted, and the raw material rod M1 can be produced by processing the bulk body into a rod shape by cutting and polishing.

[0027] Next, the raw material rod M1 is melted at a temperature equal to or higher than the melting point of the raw material (step S102). Subsequently, the molten portion of the raw material rod M1 is slowly cooled to form a single crystal (step S103). For example, if the raw material contains CaS, the raw material is melted at a temperature equal to or higher than the melting point of CaS (approximately 2400°C to 2500°C). To prevent unwanted chemical reactions during single crystal production, the melting is preferably performed in an inert gas atmosphere. Alternatively, to prevent desulfurization from the raw material, the melting is preferably performed in a sulfur atmosphere. Examples of the inert gas include argon gas and nitrogen gas. The melting method is not particularly limited. For example, the floating zone melting (hereinafter abbreviated as FZ) method can be used. When using the FZ method, for example, the FZ melting apparatus 100 shown in FIG. 4 can be used. The FZ method has the great advantage of easy control of the growth atmosphere and the ability to grow crystals without using a crucible. Generally, in the growth method using a crucible, the crucible for melting the CaS powder needs to be made of an ultra-high melting point metal that can withstand temperatures of 2400°C to 2500°C and is inert to sulfur even at high temperatures, and it is very difficult to prepare such a crucible.

[0028] As shown in FIG. 4, the FZ melting apparatus 100 includes a chamber 110. The chamber 110 is formed, for example, of a transparent quartz tube. The chamber 110 contains a feedstock rod M1 prepared by the above-described method, a seed crystal rod M2 made of the same single crystal as the single crystal of the phosphor layer 10, a chuck 120 to which the feedstock rod M1 is attached, and a chuck 130 to which the seed crystal rod M2 is attached. The feedstock rod M1 and the seed crystal rod M2 are both positioned on an axis AX defined by the chucks 120 and 130, with a small gap between the tip of the feedstock rod M1 and the tip of the seed crystal rod M2. The seed crystal rod M2 is attached to the chuck 130 so that the Miller indices of the crystal plane of the seed crystal rod M2 along the axis AX are {100}.

[0029] A heating light source is provided outside the chamber 110. The heating light source is composed of, for example, a pair of xenon lamps 140 and a spheroidal mirror 150. The spheroidal mirror 150 is positioned so that one of the two foci of the spheroid is located at the tip of the feed rod M1. The xenon lamp 140 is positioned at the focal point outside the chamber 110. As shown in FIG. 4, the FZ melting apparatus 100 may include, as a heating light source, a pair of xenon lamps 140 and a spheroidal mirror 150, or multiple pairs of xenon lamps 140 and a spheroidal mirror 150. For example, a four-elliptical mirror floating zone melting apparatus (model FZ-T-12000-X-VIII-VPO-PC-OH) manufactured by Crystal System Co., Ltd. can be used as the FZ melting apparatus 100. Further provided outside the chamber 110 are a vacuum pump that evacuates the gas inside the chamber 110 and a gas supply source that supplies gas G into the chamber 110. The gas G is composed of, for example, sulfur gas or an inert gas (for example, argon gas).

[0030] In the FZ melting apparatus 100, the gas in the chamber 110 is evacuated using a vacuum pump, and then gas G is supplied into the chamber 110 using a gas supply source at a rate of, for example, 3 to 10 liters per minute. With gas G being supplied into the chamber 110, the xenon lamp 140 is turned on to heat the tip of the feed rod M1, which is located near the focal point of the spheroid mirror 150 in the chamber 110. This causes the tip of the feed rod M1 to begin to melt. The chuck 130 is then operated to bring the tip (melt portion) of the feed rod M1 and the tip of the seed crystal rod M2 into contact with each other, forming a molten zone (melt LQ). The chucks 120 and 130 are then operated to rotate the feed rod M1 and the seed crystal rod M2 in opposite directions, for example, at a rate of 4 to 20 rpm. Next, the feed rod M1 and the seed crystal rod M2 are moved downward relative to the heating light source by operating the chucks 120 and 130. This causes a new single crystal to grow at the tip of the seed crystal rod M2. The downward movement speed of the feed rod M1 and the seed crystal rod M2 is set to, for example, within the range of 2 mm / h to 20 mm / h.

[0031] When the remaining length of the feedstock rod M1 becomes short, the chucks 120 and 130 are operated to stop the downward movement of the feedstock rod M1. Furthermore, the current (light intensity) of the xenon lamp 140 is gradually reduced to reduce the size of the molten zone (melt LQ), and finally, the tip of the feedstock rod M1 and the tip of the seed crystal rod M2 are separated. The single crystal bulk formed at the tip of the seed crystal rod M2 is then slowly cooled, and the seed crystal rod M2 is removed from the chuck 130. The single crystal bulk formed at the tip of the seed crystal rod M2 is then cleaved to obtain a thin plate of single crystal phosphor (step S104). The single crystal phosphor thus obtained is used as the phosphor layer 10. At this time, both the top and bottom surfaces of the single crystal phosphor are cleavage planes. Figure 5 shows the results of XRD analysis of the single crystal phosphor by irradiating the cleavage plane with X-rays. As shown in FIG. 5, two sharp peaks were observed in the diffraction intensity, which indicates that a highly crystalline single crystal phosphor was obtained.

[0032] The single crystal phosphor obtained in this way may have some dark areas (unevenness). This unevenness is mostly distributed in the center of the crystal and may interfere with fluorescence. To clarify whether this unevenness is due to the added ions or the parent crystal, CaS single crystals were grown using the FZ method without adding Eu. Black or dark red coloration was observed in the grown crystals. This coloration may absorb fluorescence and lead to reduced efficiency. Furthermore, even if blackening is not observed, sufficient characteristics may not be obtained due to various reasons such as compositional misalignment, lattice distortion, or residual stress.

[0033] To solve these problems, the single crystal phosphor may be annealed at a temperature of 1000°C or higher (step S105 in Figure 6). We prepared CaS single crystals without Eu doping and CaS single crystals with Eu doping, both of which were not annealed and annealed, and measured the transmission spectra of these single crystals. The results are shown in Figures 7, 8, and 9.

[0034] Figure 7 shows that the transmission spectrum of the unannealed CaS single crystal without Eu addition contains an absorption band with a peak at approximately 520 nm from 300 nm to 700 nm, and that this absorption band is eliminated by annealing. Figure 8 shows that the transmittance is low from 450 nm to 600 nm due to the absorption band of divalent Eu ions, but in the wavelength range from 300 nm to 450 nm, where transmittance is slightly higher, annealing increases the transmittance, similar to that of CaS single crystals. Figure 9 shows that the difference in transmittance at 400 nm before and after annealing shows a 12% increase regardless of whether Eu is added, indicating that the black or dark-red discoloration in Eu:CaS is eliminated, just like in CaS.

[0035] FIG. 10 shows the measured values ​​of internal quantum efficiency when a single crystal phosphor formed using the FZ melting apparatus 100 of FIG. 4 was annealed in the temperature range of 800°C to 1200°C. FIG. 10 also shows the measured values ​​of internal quantum efficiency when sulfur gas and an inert gas were used as the gas G used in the FZ melting apparatus 100 of FIG. 4. It can be seen from FIG. 10 that annealing at 1000°C or higher can improve the internal quantum efficiency compared to when no annealing was performed or when annealing was performed at a low temperature (800°C). It can also be seen from FIG. 10 that annealing at 1100°C or higher can improve the internal quantum efficiency with a shorter annealing time.

[0036] FIG. 11 shows the transmission spectrum of a single crystal phosphor formed using the FZ melting apparatus 100 of FIG. 4 after annealing in an inert atmosphere at 1100°C for four hours. For comparison, FIG. 11 also shows the transmission spectrum of the single crystal phosphor before annealing. FIG. 12 shows the transmission spectrum of a single crystal phosphor formed using the FZ melting apparatus 100 of FIG. 4 after annealing in a sulfur atmosphere at 1100°C for four hours. For comparison, FIG. 12 also shows the transmission spectrum of the single crystal phosphor before annealing. FIG. 13 shows the difference in transmittance at 400 nm before and after annealing.

[0037] It can be seen from Figures 11 and 13 that annealing in an inert atmosphere can cause precipitates to form on the surface, making the surface cloudy and reducing transmittance. Figures 12 and 13 show that when annealing in a sulfur atmosphere is performed, the transmittance decreases slightly, but no precipitates are observed on the surface, and it can be seen that transparency is not impaired compared to when annealing in an inert atmosphere.

[0038] Figure 14 shows the absorptance and internal quantum efficiency of single-crystal phosphors annealed in an inert atmosphere and a sulfur atmosphere, compared with the absorptance and internal quantum efficiency of single-crystal phosphors not annealed and the absorptance and internal quantum efficiency of the raw material powder. Figure 14 confirms that annealing a single-crystal phosphor in an inert atmosphere or a sulfur atmosphere significantly improves the internal quantum efficiency. Figure 14 also confirms that annealing in an inert atmosphere results in absorptance and internal quantum efficiency similar to those obtained when annealing in a sulfur atmosphere. In other words, annealing in an inert atmosphere results in inferior transmittance compared to annealing in a sulfur atmosphere, but results in internal quantum efficiency (emission characteristics) equivalent to those obtained when annealing in a sulfur atmosphere.

[0039] Next, Examples 1 to 5 and Comparative Example 1 will be described.

[0040] Example 1 3g to 10g of Eu:CaS powder raw material was prepared. The purity of this raw material was 99.9% or higher. Next, the prepared Eu:CaS powder raw material was uniformly packed into a latex sleeve with an inner diameter of 5mm and a length of 300mm, one end of which was sealed. The sleeve's inlet was then sealed, and the material was pressurized at 80MPa for 1 minute or more using the cold isostatic pressing (CIP) method. After the pressure was reduced, a solidified, elongated cylindrical rod was removed from the latex sleeve, yielding an Eu:CaS raw material rod. A Eu:CaS seed crystal rod was also prepared, with a Eu:CaS single crystal attached to the tip.

[0041] Next, the Eu:CaS feed rod and Eu:CaS seed crystal rod were attached to a four-elliptical mirror floating zone melting apparatus (hereinafter referred to as FZ apparatus) manufactured by Crystal System Co., Ltd. The Eu:CaS feed rod was attached to the upper axis, and the Eu:CaS seed crystal rod was attached to the lower axis so that the Miller indices of the crystal plane in the direction of the lower axis were {100}. The Eu:CaS feed rod and Eu:CaS seed crystal rod were covered with a transparent quartz tube. After evacuating the air from the transparent quartz tube, high-purity argon gas was flowed into the transparent quartz tube at a flow rate of 3 to 10 liters per minute.

[0042] Next, the xenon lamp of the FZ apparatus was turned on. After turning it on, the voltage applied to the lamp was gradually increased, and the current was increased to heat the tip of the Eu:CaS feedstock rod. When the tip of the Eu:CaS feedstock rod exceeded the melting point of Eu:CaS and melted into droplets, the distance between the tip of the Eu:CaS feedstock rod and the Eu:CaS seed crystal rod was narrowed, and the tip of the Eu:CaS seed crystal rod was also melted. The tip of the Eu:CaS feedstock rod and the Eu:CaS seed crystal rod were then brought into contact with each other to form a molten zone. The Eu:CaS feedstock rod and the Eu:CaS seed crystal rod were rotated in opposite directions within a range of 4 rpm to 20 rpm. The Eu:CaS feedstock rod and the Eu:CaS seed crystal rod were then moved downward relative to the xenon lamp, allowing a new single crystal to grow at the tip of the Eu:CaS seed crystal rod. The downward moving speed of the Eu:CaS raw material rod and the Eu:CaS seed crystal rod was set within the range of 2 mm / h to 20 mm / h.

[0043] When the remaining length of the Eu:CaS feed rod became too short, the descent of the Eu:CaS feed rod and Eu:CaS seed crystal rod was stopped, and the applied voltage of the xenon lamp was gradually reduced to reduce the molten zone. Finally, the Eu:CaS feed rod and Eu:CaS seed crystal rod were separated. The xenon lamp was then turned off, and the Eu:CaS seed crystal rod was cooled to room temperature before being removed from the FZ apparatus. The Eu:CaS seed crystal rod removed from the FZ apparatus had a slightly rounded square columnar shape, and the Miller indices of the longitudinal crystal plane of the Eu:CaS seed crystal rod were {100}.

[0044] Next, the single crystal bulk formed at the tip of the Eu:CaS seed crystal rod was cleaved to produce thin plate-shaped Eu:CaS single crystal phosphors. Specifically, a sharp blade was applied to the single crystal bulk formed at the tip of the Eu:CaS seed crystal rod, perpendicular to the longitudinal direction of the Eu:CaS seed crystal rod. Next, when force was applied to the blade, the Eu:CaS single crystal cleaved parallel to the {100} plane, splitting it into two pieces. The cleaved surface was a bright red color. By repeating the same procedure, a large number of thin, circular Eu:CaS single crystal phosphors with a thickness of less than 1 mm were obtained.

[0045] The Eu:CaS single crystal phosphor obtained in this way was subjected to a storage test under high-temperature and humidity conditions of 85°C and 85% RH, and the change in internal quantum efficiency before and after the storage test was measured. The evaluation was performed using a JASCO FP-8550. Previous experiments have shown that this measuring device has a peak-to-peak error of approximately 3%. From this reliability evaluation test, as shown in Figure 15, it was confirmed that after 1000 hours of testing, the internal quantum efficiency of the Eu:CaS single crystal phosphor decreased by only 10% compared to the internal quantum efficiency before the test. Therefore, Figure 15 indicates that the internal quantum efficiency of the Eu:CaS single crystal phosphor remained almost unchanged even after 1000 hours of testing.

[0046] Example 2 A Eu:CaS raw material rod was obtained in the same manner as in Example 1. Also, a Eu:CaS seed crystal rod was prepared, with a Eu:CaS single crystal as a seed crystal placed at the tip.

[0047] Next, an Eu:CaS feedstock rod and an Eu:CaS seed crystal rod were attached to the FZ apparatus. The Eu:CaS feedstock rod was attached to the upper axis, and the Eu:CaS seed crystal rod was attached to the lower axis so that it formed an angle of several degrees. Subsequently, a new single crystal was grown at the tip of the Eu:CaS seed crystal rod using the same method as in Example 1. The Eu:CaS seed crystal rod removed from the FZ apparatus had an elliptical cylindrical shape with an elliptical cross section, with steps in various places on the side. The surface of the side where the steps occurred was a {100} crystal plane, and the single crystal bulk formed at the tip of the seed crystal rod was a single crystal that inherited the crystalline structure of the seed crystal.

[0048] Next, the single-crystal bulk formed at the tip of the Eu:CaS seed crystal rod was cleaved to produce thin-plate Eu:CaS single-crystal phosphors. Specifically, a sharp blade was applied to the step on the single-crystal bulk formed at the tip of the Eu:CaS seed crystal rod, perpendicular to the longitudinal direction of the Eu:CaS seed crystal rod. Next, force was applied to the blade, causing the Eu:CaS single crystal to cleave parallel to the {100} plane and split into two pieces. The cleavage was at an angle of several dozen degrees from the longitudinal direction of the Eu:CaS seed crystal rod. The cleavage plane was a vivid red color. By repeating this process, numerous thin-plate oval-shaped Eu:CaS single-crystal phosphors with thicknesses of less than 1 mm were obtained.

[0049] The Eu:CaS single crystal phosphor thus obtained was subjected to a storage test under high-temperature and humidity conditions of 85°C and 85% RH, and the change in internal quantum efficiency before and after the storage test was measured. An FP-8550 manufactured by JASCO Corporation was used for the evaluation. As shown in Figure 16, this reliability evaluation test confirmed that after 200 hours of testing, the internal quantum efficiency of the Eu:CaS single crystal phosphor had decreased by only 10% compared to the internal quantum efficiency before the test. Therefore, Figure 16 indicates that the internal quantum efficiency of the Eu:CaS single crystal phosphor remained almost unchanged even after 200 hours of testing.

[0050] Example 3 8.670 g of Eu:CaS powder raw material was prepared. Further, 1.197 g of SrS powder raw material without Eu addition was prepared so that the element ratio of Ca to Sr was 9:1. The 8.670 g of Eu:CaS powder raw material and the 1.197 g of SrS powder raw material were dry-mixed using a mortar and a pestle. The mixed powder raw material was uniformly packed into a latex sleeve with an inner diameter of 5 mm and a length of 300 mm with one end sealed. Thereafter, in the same procedure as in Example 1, a Eu:(Ca x Sr 1-x )S (where x = 0.9) raw material rod was obtained. Also, a Eu:(Ca x Sr 1-x )S (where 0 < x < 1) single crystal having a Eu:(Ca x Sr 1-x )S (where 0 < x <​​​​​​​​​​​​​​​​​​​​​​​​​​​)S (where 0 < x < 1) For single crystal phosphors, it can be confirmed that the peak wavelength of the fluorescent light shifts to the shorter wavelength side than the peak wavelength of the fluorescent light obtained from Eu:CaS single crystal phosphors. This means that a part of the Ca sites is substituted with Sr. Also, as shown in Fig. 19, in the Eu:CaSrS single crystal phosphor, an improvement in the quantum efficiency can be confirmed by performing annealing treatment.

[0052] Eu:(Ca x Sr 1-x )S (where 0 < x < 1) For single crystal phosphors, a storage test was conducted under high humidity and high temperature of 85 °C and 85% RH, and the change in the internal quantum efficiency before and after the storage test was measured. An FP - 8550 manufactured by JASCO Corporation was used for the evaluation. From this reliability evaluation test, as shown in Fig. 20, after 20 hours of the test time, for Eu:(Ca x Sr 1-x )S (where 0 < x < 1) single crystal phosphors, it can be confirmed that the internal quantum efficiency has decreased by only within 3% compared to the internal quantum efficiency before the test. Therefore, from Fig. 20, it can be seen that even after 20 hours of the test time, the internal quantum efficiency of Eu:(Ca x Sr 1-x )S (where 0 < x < 1) single crystal phosphors has hardly changed.

[0053] (Example 4) An Eu:CaS raw material rod was obtained in the same manner as in Example 1 except that the inner diameter of the latex sleeve was 7 mm. Also, an Eu:CaS seed crystal rod with an Eu:CaS single crystal serving as a seed crystal placed at the tip was prepared. Further, in the same manner as in Example 1, a circular Eu:CaS single crystal phosphor in the form of a thin plate with a thickness of 1 mm or less was obtained. On the cleavage plane, the outer edge part was brightly red, but the central part was dark red.

[0054] The Eu:CaS single crystal phosphors obtained in this way were subjected to a storage test under high-temperature and humidity conditions of 85°C and 85% RH, and the change in internal quantum efficiency before and after the storage test was measured. An FP-8550 manufactured by JASCO Corporation was used for the evaluation. As shown in Figure 21, this reliability evaluation test confirmed that after 7 hours of testing, the internal quantum efficiency of the Eu:CaS single crystal phosphors had decreased by only 3% or less compared to the internal quantum efficiency before the test. Therefore, Figure 21 indicates that even for single crystals that showed black or dark-red coloring inside the crystals, the internal quantum efficiency of the Eu:CaS single crystal phosphors remained almost unchanged after 7 hours of testing.

[0055] Example 5 The Eu:CaS single crystal phosphor obtained in Example 1 was annealed using the following procedure. A three-zone horizontal electric furnace, capable of controlling the annealing atmosphere using a transparent quartz furnace tube, was used for the annealing. The heating time, holding temperature and time, and cooling time were controlled using a program controller. The heating time to the annealing holding temperature was approximately 1 hour. The holding time was 2 to 16 hours, with the holding temperature ranging from 800 to 1200°C. The cooling time was set to 2 hours, but in the latter half of the cooling process, when the cooling program setting was below approximately 600°C, the actual temperature inside the furnace did not follow the set temperature due to the large heat capacity of the furnace. The sulfide sample was either embedded in Eu:CaS powder in a magnetic crucible or placed on platinum foil in the magnetic crucible. High-purity argon gas was flowed at a flow rate of 1 to 2 liters per minute during the heat treatment. The results are shown in Figure 10.

[0056] (Comparative Example 1) As Comparative Example 1, a powdered Eu:CaS phosphor was obtained commercially. As described on page 289 of Inorganic Phosphors Composition Preparation and Optical Properties (by William M. Yen and Marvin J. Weber), the powdered Eu:CaS phosphor was obtained by annealing raw materials, CaCO3, Eu2O3, and NH4Cl, in a reducing atmosphere and a hydrogen sulfide atmosphere at temperatures ranging from 1100°C to 1200°C. In addition to this method, other methods for preparing raw materials for phosphors based on CaS, such as those using CaS, CaSO4, EuS, and Eu(NO3)3, are described on pages 141-142 of Ohmsha's Phosphor Handbook. The internal quantum efficiency of the obtained powdered Eu:CaS phosphor was 91%. The particle size of the obtained powdered Eu:CaS phosphor was 10.3 μm.

[0057] A storage test was conducted on the powdered Eu:CaS phosphor under high temperature and humidity conditions of 85°C and 85% RH, and the change in internal quantum efficiency before and after the storage test was measured. An FP-8550 manufactured by JASCO Corporation was used for the evaluation. As shown in Figure 22, this reliability evaluation test confirmed that the internal quantum efficiency of the powdered Eu:CaS phosphor decreased to 80% after 20 hours of testing.

[0058] [effect] Next, the effects of the red phosphor element 1 and the manufacturing method thereof will be described.

[0059] In the red phosphor element 1 according to this embodiment, the phosphor layer 10 is made of Eu:(Ca x Sr 1-x )S (where 0≦x≦1) single crystal phosphor. In the phosphor layer 10, at least the light irradiation surface S1 is a cleavage plane. This makes the proportion of crystal defects contained in the light irradiation surface S1 smaller than the proportion of crystal defects present on the surface of the phosphor powder. As a result, the moisture resistance of the light irradiation surface S1 can be improved to be greater than that of the phosphor powder without applying a coating.

[0060] In the red phosphor element 1 according to this embodiment, when the light irradiation surface S1 is irradiated with laser light in the blue wavelength range, red fluorescent light having a peak in the red wavelength range is generated. As a result, for example, a white light source can be formed by using a blue semiconductor light source as an excitation light source and the red phosphor element 1 and a yellow phosphor as phosphors. In this case, at least the light irradiation surface S1 of the red phosphor element 1 is a cleavage plane, and the proportion of crystal defects contained in the light irradiation surface S1 is smaller than the proportion of crystal defects present on the surface of the phosphor powder. Therefore, the red phosphor element 1 has high moisture resistance, which prevents a decrease in the light intensity of the red fluorescent light emitted from the red phosphor element 1. This prevents a change in the color of the white light source.

[0061] In the red phosphor element 1 according to this embodiment, the phosphor layer 10 is a layer that has been annealed at a temperature of 1000°C or higher. This reduces crystal defects at least on the light irradiation surface S1 of the phosphor layer 10 compared to when the annealing process is not performed. As a result, the moisture resistance of the light irradiation surface S1 can be further improved compared to the moisture resistance of the phosphor powder without applying a coating.

[0062] In the red phosphor element 1 according to this embodiment, the light irradiation surface S1 (cleavage plane) is a {100} plane. This makes the proportion of crystal defects contained in the light irradiation surface S1 smaller than the proportion of crystal defects present on the surface of the phosphor powder. As a result, the moisture resistance of the light irradiation surface S1 can be improved to be greater than that of the phosphor powder without applying a coating.

[0063] In the red phosphor element 1 according to this embodiment, a heat sink 20 is provided in contact with the surface (rear surface S2) of the phosphor layer 10 opposite to the light irradiation surface S1. This allows heat generated from the phosphor layer 10 to be dissipated to the outside via the heat sink 20. As a result, an excessive increase in the temperature of the phosphor layer 10 can be prevented, and a decrease in luminous efficiency that occurs at high temperatures can be suppressed.

[0064] In a method for manufacturing a red phosphor element according to an embodiment of the present invention, a raw material containing (Eu,Ca,S), (Eu,Sr,S) or (Eu,Ca,Sr,S) is melted at a temperature equal to or higher than the melting point of the raw material and slowly cooled to obtain Eu:(Ca x Sr 1-x )S (where 0≦x≦1) single crystal phosphor is formed. Then, by cleaving the phosphor bulk, a phosphor layer is formed in which at least the light irradiation surface is the cleavage surface. This makes the proportion of crystal defects in the light irradiation surface smaller than the proportion of crystal defects present on the surface of the phosphor powder. As a result, the moisture resistance of the light irradiation surface can be improved beyond that of the phosphor powder without applying a coating.

[0065] The present invention is applicable to various fields such as laser displays (laser projectors, laser TVs, head-mounted displays, etc.), laser lighting (microscopes, headlamps, indoor indirect lighting, plant factories, etc.), projection mapping, and medicine (laser scalpels, etc.). [Explanation of symbols]

[0066] 1...red phosphor element, 10...phosphor layer, 20...heat sink, S1...light irradiation surface, S2...back surface.

Claims

1. Eu: (Ca ｘ Sr １－ｘ ) S (where 0≦x≦1) single crystal phosphor, and at least the light irradiation surface is a cleavage plane. Red phosphor element.

2. The phosphor layer is capable of generating red fluorescent light having a peak in a red wavelength range when the light irradiation surface is irradiated with laser light in a blue wavelength range. The red phosphor element according to claim 1 .

3. The phosphor layer is a layer that has been annealed at a temperature of 1000°C or higher. The red phosphor element according to claim 1 .

4. The cleavage plane is a {100} plane. The red phosphor element according to claim 1 .

5. The light-emitting device further includes a heat dissipation layer that is in contact with the surface of the phosphor layer opposite to the light irradiation surface and has a higher heat dissipation property than the phosphor layer. The red phosphor element according to claim 1 .

6. A raw material containing (Eu, Ca, S), (Eu, Sr, S) or (Eu, Ca, Sr, S) is melted at a temperature equal to or higher than the melting point of the raw material and slowly cooled to obtain Eu:(Ca ｘ Sr １－ｘ ) S (where 0≦x≦1) forming a bulk phosphor containing a single crystal phosphor; cleaving the phosphor bulk body to form a phosphor layer having at least the light irradiation surface as a cleavage surface; Contains A method for manufacturing a red phosphor element.

7. and melting the raw material using a floating zone melting method. The method for manufacturing the red phosphor element according to claim 6 .

8. annealing the phosphor layer at a temperature of 1000° C. or higher. The method for manufacturing the red phosphor element according to claim 6 .

Images