JP7519743B2 - Wavelength conversion member and light emitting device - Google Patents

Description

The present invention relates to a wavelength conversion member and a light emitting device.

Halogen lamps, which have a wide wavelength distribution, are used as light sources in various analytical equipment, medical equipment, and general lighting fields. However, halogen lamps have disadvantages in terms of the impact they generate on the surrounding area and their short lifespan. On the other hand, in recent years, semiconductor light-emitting devices such as LEDs (Light Emitting Diodes) and LDs (Laser Diodes) have been attracting attention due to their long lifespan, low power consumption, and fast lighting speed. These semiconductor light-emitting devices have the advantage of emitting light in a specific wavelength range, but it has been difficult to emit light over a wide band.

Patent Document 1 discloses a light-emitting diode device in which a light-emitting diode element arranged on a semiconductor substrate, a lens holder with a cone-shaped recess arranged to surround the light-emitting diode element, and a phosphor layer made of phosphor particles molded with epoxy resin provided inside the lens holder are stacked in multiple layers, with the red phosphor layer, green phosphor layer, and blue phosphor layer stacked in order from the side closest to the light-emitting element to the side with the longest peak wavelength of the secondary light. It is described that this configuration makes it easy to set the color balance because the light emitted from the phosphor layer closest to the light-emitting element is not absorbed by the phosphor layer above it.

JP 2006-261554 A

However, the technology described in Patent Document 1 involves stacking multiple phosphor layers, which results in a thick phosphor layer overall, and there are still issues with performance degradation due to heat generation and making the device more compact.

The present invention was made in consideration of these circumstances, and aims to provide a compact wavelength conversion member that can efficiently obtain light over a wide wavelength range and has excellent color uniformity, as well as a light-emitting device using the same.

(1) In order to achieve the above object, the wavelength conversion member of the present invention comprises a base material containing an inorganic material and transmitting light, and a phosphor section provided on the base material, in which two or more phosphor layers formed of phosphor particles and a translucent ceramic that bonds the phosphor particles to each other are laminated, the phosphor section having an entrance surface set on either the base material side or the surface side of the phosphor section located opposite the base material side, and an exit surface set on the other side, the emission peak wavelength of the phosphor particles in one phosphor layer of the phosphor section is longer than the emission peak wavelength of the phosphor particles in another phosphor layer located closer to the exit surface than the one phosphor layer, and at least one of the phosphor layers is a mixed layer containing two or more types of the phosphor particles.

In this way, by stacking the phosphor layers from the entrance surface side to the exit surface side, starting with the phosphor layer containing phosphor particles with a long emission peak wavelength, the light converted by the phosphor layer on the entrance surface side is less likely to be absorbed by the phosphor layer above it, making it possible to appropriately control the color uniformity, and by making at least one phosphor layer a mixed layer containing two or more types of phosphor particles, it is possible to make the phosphor layers thinner and improve the emission intensity.

(2) In addition, the wavelength conversion member of the present invention is characterized in that the average particle diameters of the two or more types of phosphor particles in the mixed layer are different. This allows the thickness of the mixed layer to be made thinner, and the luminous intensity to be further improved.

(3) In addition, in the wavelength conversion member of the present invention, the thickness of each of the phosphor layers is 1 to 6 times the maximum average particle diameter of the phosphor particles contained in each of the phosphor layers. In this way, by making the thickness (average film thickness) of each of the stacked phosphor layers 1 to 6 times the average particle diameter of the phosphor particles contained therein, the thickness of each phosphor layer and the thickness of the entire phosphor section can be reduced, and the accumulation of heat generated in the phosphor layer can be suppressed. This makes it possible to maintain the fluorescent performance even when irradiated with high-intensity light from a light source. Furthermore, peeling of the phosphor section can be prevented by making the layers thinner.

(4) In addition, the wavelength conversion member of the present invention is characterized in that the absorptance of the absorption spectrum of the phosphor particles with a long emission peak wavelength contained in the mixed layer does not exceed 30% at the emission peak wavelength of the fluorescence spectrum of the phosphor particles with a short emission peak wavelength. In the mixed layer, secondary excitation occurs in which the light converted by the phosphor particles with a short emission peak wavelength is used to fluoresce the phosphor particles with a long emission peak wavelength, and the emission intensity on the short wavelength side becomes small. However, by selecting and mixing a combination of phosphor particles such that the absorptance of the absorption spectrum of the phosphor particles with a long emission peak wavelength does not exceed 30% at the emission peak wavelength of the fluorescence spectrum of the phosphor particles with a short emission peak wavelength, this effect can be reduced and color uniformity can be more appropriately controlled.

(5) In addition, in the wavelength conversion member of the present invention, the thickness of at least one of the phosphor layers is thinner than the thickness of other phosphor layers located on the emission surface side of the phosphor layer. In this way, by increasing the thickness of each phosphor layer from the entrance surface side toward the emission surface side, the required amount of light emission can be obtained in each phosphor layer in accordance with the gradual decrease in the amount of excitation light in the phosphor section, and color uniformity can be more appropriately controlled.

(6) In addition, in the wavelength conversion member of the present invention, the phosphor layer closest to the incident surface side is the mixed layer. Since the phosphor layer on the incident surface side of each phosphor layer has a relatively low density of phosphor particles, by making the phosphor layer on the incident surface side a mixed layer, it is possible to make the layer thinner than when the other phosphor layers are mixed layers, and the luminous intensity can be further improved.

(7) The light-emitting device of the present invention is characterized by comprising a light-emitting element that emits excitation light in a specific range of wavelengths, and a wavelength conversion member according to any one of (1) to (6) above. This allows the color uniformity to be appropriately controlled, and at least one layer can be a mixed layer in which two or more types of phosphor particles are mixed, making it possible to make the phosphor layer thinner and improving the emission intensity.

According to the present invention, it is possible to configure a wavelength conversion member and a light emitting device that can appropriately control color uniformity and can improve the emission intensity by making at least one phosphor layer a mixed layer in which two or more types of phosphor particles are mixed, thereby making it possible to make the phosphor layer thinner.

FIG. 1 is a schematic diagram illustrating an example of a light emitting device of the present invention. 1 is a schematic diagram illustrating an example of a wavelength conversion member of the present invention. 4A, 4B, and 4C are cross-sectional views showing a process for producing a wavelength conversion member. 1 is a table showing the absorptance at the fluorescence peak wavelengths of any two combinations of phosphor particles used in Examples and Comparative Examples. 1 is a table showing the emission intensities of light at specific wavelengths, color balance evaluations, and total emission intensities of wavelength conversion members of Examples and Comparative Examples.

As a result of intensive research, the inventors discovered that when constructing a phosphor section in which multiple phosphor layers are stacked, by making at least one phosphor layer a mixed layer containing two or more types of phosphor particles, it is possible to appropriately control the color uniformity while making the phosphor layer thinner and improving the luminous intensity, and thus completed the present invention.

That is, the wavelength conversion member of the present invention includes a base material that contains an inorganic material and transmits light, and a phosphor section that is provided on the base material and has two or more stacked phosphor layers formed of phosphor particles and a translucent ceramic that bonds the phosphor particles to each other, and the phosphor section has an entrance surface set on either the base material side or the surface side of the phosphor section located opposite the base material side, and an exit surface set on the other side, the emission peak wavelength of the phosphor particles in one phosphor layer of the phosphor section is longer than the emission peak wavelength of the phosphor particles in another phosphor layer located closer to the exit surface than the one phosphor layer, and at least one of the phosphor layers is a mixed layer containing two or more types of the phosphor particles.

The following describes an embodiment of the present invention with reference to the drawings. To facilitate understanding, the same reference numbers are used for the same components in each drawing, and duplicate descriptions are omitted. Note that in the configuration diagrams, the size of each component is shown conceptually and does not necessarily represent the actual dimensional ratio.

[Configuration of the Light Emitting Device]
Fig. 1 is a schematic diagram showing an example of a light emitting device. As shown in Fig. 1, the light emitting device 10 includes a light emitting element 50 and a wavelength conversion member 100, and emits irradiation light by combining a plurality of converted lights generated by excitation with light source light in the wavelength conversion member 100. Alternatively, the light source light transmitted through the wavelength conversion member 100 and the plurality of converted lights may be combined to form the irradiation light. The irradiation light may be, for example, white light.

The light-emitting element 50 may be an LED (Light Emitting Diode) or an LD (Laser Diode). An LED generates light source light having a specific range of wavelengths depending on the design of the light-emitting device 10. For example, an LED generates ultraviolet light. When an LD is used, coherent light with little variation in wavelength and phase can be generated. The light-emitting element 50 is not limited to these, but is preferably one that generates ultraviolet light, blue light, or green light, and is particularly preferably one that generates ultraviolet light.

[Configuration of wavelength conversion member]
FIG. 2 is a schematic diagram showing an example of a wavelength conversion member. The wavelength conversion member 100 has a phosphor section 120 formed on a base material 110. The wavelength conversion member 100 absorbs and excites the light source light irradiated from the light source while sequentially transmitting the light source light irradiated from the light source to generate light of different wavelengths. For example, the wavelength conversion member 100 irradiated with ultraviolet light source light can emit converted light of red light, green light, and blue light converted by the phosphor section 120, and these can be combined to form a white radiation light. In addition, the wavelength conversion member 100 irradiated with blue light source light can transmit the blue light source light, and emit converted light of red light, yellow light, and green light converted by the phosphor section 120, and the converted light and the light source light can be combined to form a white radiation light. In this way, by combining light of multiple colors, it is possible to emit radiation light with a good color balance having a wide wavelength distribution. In addition, it is possible to convert light of various colors according to the design.

The substrate 110 contains an inorganic material and transmits light. The substrate 110 is made of a light-transmitting material such as sapphire or glass. From the viewpoint of luminous intensity, it is preferable that at least the portion through which light transmits is made of a material that does not easily absorb light from the light source. In addition, since the temperature increases when high-energy light is irradiated, it is preferable that the thermal conductivity is high. For this reason, the substrate 110 is preferably made of sapphire. In addition, the substrate 110 is preferably formed in a plate shape.

The phosphor section 120 is provided on the substrate 110, and is formed by stacking two or more phosphor layers 130. The phosphor section 120 has an incident surface 122 set on either the substrate 110 side or the surface side of the phosphor section 120 located opposite the substrate 110 side, and an exit surface 124 set on the other side. In the example of FIG. 1 and FIG. 2, the substrate 110 side is set as the incident surface 122, and the surface side of the phosphor section 120 is set as the reflecting surface 124. When light is incident from the substrate side, heat can be dissipated to the substrate, especially for the light emitted by long-wavelength phosphors that generate a lot of heat, so that the light emission amount is less likely to be quenched by temperature and can be kept high. When light is incident from the surface side of the phosphor section, in cases where it is not desired to expose the phosphor section to the atmosphere, such as when using a phosphor that deteriorates due to oxidation, the phosphor can be directly sealed on the light-emitting element side and the substrate can be used as a lid, simplifying the structure of the light-emitting device. In the example of FIG. 2, the phosphor section 120 is formed by stacking three phosphor layers 130, namely phosphor layers 130a, 130b, and 130c.

The thickness (average film thickness) of the phosphor section 120 is preferably 150 μm or less, and more preferably 100 μm or less. This allows the heat generated in the phosphor section 120 to be efficiently conducted to the substrate 110, preventing the temperature rise of the phosphor section 120. As a result, the fluorescent performance can be maintained even when irradiated with high-intensity light from a light source. In other words, even when a high-energy density laser is used as the light source light, by forming a thin phosphor section 120, temperature quenching due to heat generation (heat storage) of the phosphor particles 132 can be suppressed. In addition, the thickness of the phosphor section 120 is preferably 10 μm or more. This allows the phosphor section 120 to be not too thin, thereby suppressing a decrease in luminous efficiency.

Thermal resistance, which indicates the difficulty of heat transfer, depends on the thickness when the thermal resistivity or thermal conductivity and area of the phosphor part are constant, and the thicker it is, the higher the thermal resistance. When irradiated with a laser, the smaller the thermal resistance, i.e., the thinner the thickness, the easier it is to transfer heat and the less likely heat storage occurs, making it possible to suppress temperature quenching due to heat generation (heat storage).

Each phosphor layer 130 forming the phosphor section 120 is formed of phosphor particles 132 and translucent ceramics 134. The translucent ceramics 134 bonds the phosphor particles 132 together, the phosphor particles 132 and the base material 110, or adjacent phosphor layers 130 together. This allows efficient heat dissipation when irradiated with high-energy-density light because the phosphor particles 132 are bonded to the base material 110, which functions as a heat dissipation material, and temperature quenching of the phosphor can be suppressed. Furthermore, for efficient heat dissipation, it is preferable that each of the above bonds be chemical bonds.

Among the phosphor layers 130, the emission peak wavelength of the phosphor particles 132 of one phosphor layer is longer than the emission peak wavelength of the phosphor particles 132 of the other phosphor layers located on the emission surface 124 side than the phosphor layer of the first phosphor layer (the phosphor layer in question). In this way, by stacking the phosphor layers 130 from the incident surface 122 side toward the emission surface 124 side, starting with the phosphor layer 130 containing the phosphor particles 132 with the long emission peak wavelength, the light converted by the phosphor layer 130 on the incident surface 122 side is not easily absorbed by the phosphor layer 130 above it, so that the color uniformity (color balance) can be appropriately controlled. In the example of FIG. 2, the phosphor layer 130a contains phosphor particles 132a and 132b, the phosphor layer 130b contains phosphor particles 132c, and the phosphor layer 130c contains phosphor particles 132d. Therefore, for example, if the emission peak wavelengths of phosphor particles 132a, 132b, 132c, and 132d are represented as A, B, C, and D, respectively, then A>C>D and B>C>D hold true.

At least one phosphor layer 130 is a mixed layer containing two or more types of phosphor particles 132. This allows the thickness of the phosphor layer 130 as a mixed layer to be thinner than the sum of the thicknesses of the phosphor layers 130 when separate phosphor layers 130 are formed, thereby improving the luminous intensity. It is preferable that the two or more types of phosphor particles 132 contained in the mixed layer are phosphor particles of different types having different emission peak wavelengths. In the example of FIG. 2, phosphor particles 132a, 132b, 132c, and 132d are each different types of phosphor particles. And phosphor layer 130a is a mixed layer containing phosphor particles 132a and 132b, which are different types of phosphor particles.

When two or more phosphor layers are laminated, it is often necessary to transmit the excitation light to obtain a specific luminescent color, and fillers that do not contribute to luminescence may be added to the phosphor layers in addition to the translucent ceramics. Adding fillers increases the film thickness, which reduces the luminescence intensity and luminescence efficiency. In the present invention, at least one phosphor layer is a mixed layer in which two or more types of phosphor particles are mixed, which reduces the number of layers and reduces the amount of filler added, and also reduces the amount of translucent ceramics. This makes it possible to make the phosphor layers thinner, which contributes to improving the luminescence efficiency. The mixed layer may be a mixture of three or more types of phosphor particles.

In the mixed layer, it is preferable that the average particle diameters of two or more types of phosphor particles 132 are different. This allows the layer thickness of the mixed layer to be thinner and the luminous intensity to be improved compared to the case where phosphor particles 132 of the same particle diameter are mixed. The different particle diameters preferably mean, for example, that one average particle diameter is in the range of 1.5 to 2.0 times the average particle diameter of the other. In this specification, the average particle diameter refers to the volume-based median diameter (D50). The median diameter (D50) can be measured using a laser diffraction/scattering type particle size distribution measuring device in dry or wet measurement.

The thickness of each phosphor layer 130 is preferably 1 to 6 times the maximum value of the average particle diameter of the phosphor particles 132 contained in each phosphor layer 130. In this way, by making the thickness (average film thickness) of each phosphor layer 130 to be stacked 1 to 6 times the average particle diameter of the phosphor particles 132 contained therein, the thickness of each phosphor layer 130 and the thickness of the entire phosphor section 120 can be reduced, and the accumulation of heat generated in the phosphor layer 130 can be suppressed. This makes it possible to maintain the fluorescent performance even when irradiated with light from a light source with a high intensity. In addition, peeling of the phosphor section 120 can be prevented by making the layer thinner. The maximum value is used in the case of a mixed layer containing two or more types of phosphor particles 132. For a phosphor layer 130 containing one type of phosphor particles 132, the average particle diameter of the phosphor particles 132 is used.

It is preferable that the absorptance of the absorption spectrum of the phosphor particles 132 with a long emission peak wavelength contained in the mixed layer does not exceed 30% at the emission peak wavelength of the fluorescence spectrum of the phosphor particles with a short emission peak wavelength. In the mixed layer, secondary excitation occurs in which the light converted by the phosphor particles with a short emission peak wavelength is used to fluoresce the phosphor particles with a long emission peak wavelength, and the emission intensity on the short wavelength side becomes small. However, by selecting and mixing a combination of phosphor particles such that the absorptance of the absorption spectrum of the phosphor particles with a long emission peak wavelength does not exceed 30% at the emission peak wavelength of the fluorescence spectrum of the phosphor particles with a short emission peak wavelength, this effect can be reduced and color uniformity can be more appropriately controlled. This absorptance can be measured using a fluorescence spectrophotometer or a microspectrophotometer.

For example, if the absorptance of the absorption spectrum of phosphor particles with a long emission peak wavelength contained in the mixed layer is 30% at the emission peak wavelength of the fluorescence spectrum of phosphor particles with a short emission peak wavelength, when secondary excitation occurs once in a certain optical path in the mixed layer, the intensity of the light on the short wavelength side in that optical path decreases to 70%. Also, when secondary excitation occurs twice, the intensity of the light on the short wavelength side in that optical path decreases to 49% (70% x 70%). Therefore, it is preferable that the absorptance of the absorption spectrum of phosphor particles with a long emission peak wavelength contained in the mixed layer is as small as possible at the emission peak wavelength of the fluorescence spectrum of phosphor particles with a short emission peak wavelength, but if the value does not exceed 30%, light with an intensity of about 50% or more can be extracted in that optical path even if secondary excitation occurs twice.

There is a trade-off between the decrease in luminescence intensity due to secondary excitation caused by providing a mixed layer and the increase in luminescence intensity due to the thinner layer, but by appropriately setting various conditions such as the thickness of the phosphor layer, the amount of phosphor particles, and the types of phosphor particles combined in the mixed layer, it is possible to increase the luminescence intensity compared to when a mixed layer is not provided.

The thickness of at least one phosphor layer is preferably thinner than the thickness of other phosphor layers located on the emission surface side of the phosphor layer, and is preferably not thicker than the thickness of other phosphor layers located on the incidence surface side of the phosphor layer. In this way, by making the thickness of each phosphor layer thinner on the incidence surface side and thicker on the emission surface side, the required amount of light emission can be obtained in each phosphor layer in accordance with the gradual decrease in the amount of excitation light in the phosphor section, and color uniformity can be more appropriately controlled. Note that phosphor layers of the same thickness may be present. In other words, it is preferable that the thickness of the phosphor layer increases monotonically in a broad sense from the incidence surface side to the emission surface side, and that phosphor layers of different thicknesses are present.

For example, the phosphor particles 132 may be a yttrium aluminum garnet phosphor doped with cerium (Ce) (YAG phosphor, YAG:Ce, or simply YAG) as a yellow phosphor particle. Also, a lutetium aluminum garnet phosphor doped with cerium (LuAG phosphor, LuAG:Ce, or simply LuAG) as a green phosphor particle. Also, a nitride phosphor called S-CASN ((Sr,Ca)AlSiN ₃ :Eu) may be used as a red phosphor particle.

In addition, the phosphor particles can be selected from the following materials depending on the design of the color to be emitted. For example, blue phosphors _such as _BaMgAl10O17 : _{Eu, ZnS:Ag, Cl, Eu, BaAl2S4:Eu, or CaMgSi2O6 : Eu ,} yellow or green phosphors such as _Zn2SiO4 : _Mn , (Y,Gd) _BO3 :Tb, ZnS:Cu, Al, (M1) _{2SiO4 :} Eu, (M1)(M2) _2S :Eu, (M3) _{3Al5O12 :} Ce, SiAlON:Eu, CaSiAlON:Eu, (M1) _Si2O2N :Eu _, or (Ba,Sr,Mg) _2SiO4 : _Eu , Mn, and _{the like .} Examples of the phosphor include yellow, orange, or red phosphors such as (Y,Gd) _BO3 :Eu, _Y2O2S :Eu, (M1) _2Si5N8 :Eu, (M1) _{AlSiN3 :} Eu, or _YPVO4 :Eu. In the above chemical formula, M1 includes at least one of the group consisting of Ba _, Ca _, Sr, and Mg, M2 includes at least one of Ga and Al, and M3 includes at least one of the group consisting of Y, Gd, Lu, and Te. The above phosphor particles are examples, and the phosphor particles used in the wavelength conversion member are not necessarily limited to the above.

The average particle diameter of the phosphor particles 132 is preferably 5 μm or more and 20 μm or less. Because it is 5 μm or more, the luminous intensity of the converted light is increased, and therefore the luminous intensity of the wavelength conversion member 100 is increased. In addition, because it is 20 μm or less, the temperature of each phosphor particle 132 can be kept low, and thermal quenching can be suppressed.

The thickness of the phosphor part of the wavelength conversion member, the thickness of the phosphor layer, and the average particle diameter of the phosphor particles can also be measured by analyzing SEM images. In the following description of the analysis of SEM images, the thickness of the phosphor layer includes the thickness of the phosphor part. The thickness of the phosphor layer in the analysis of SEM images is measured by taking an SEM image of the cross section in the direction perpendicular to the planar direction of the substrate, for example, at 1000 times magnification, performing image analysis such as binarization on the obtained SEM image, determining the range of the image recognized as the phosphor layer from the image, calculating the thickness in the perpendicular direction at equal intervals, and calculating the average value of the average thickness of the phosphor part or phosphor layer. Note that the images used to calculate the average thickness of the phosphor layer are taken from multiple cross-sectional images (e.g., three or more) of the phosphor layer so as to obtain an overall average value.

The average particle diameter of the phosphor particles in the analysis of the SEM image can be obtained by, for example, obtaining a SEM image of the cross section at 1000 times magnification for a cross section in a direction perpendicular to the planar direction of the substrate, performing image analysis such as binarization on the obtained SEM image, calculating the cross-sectional area of 100 or more particles recognized as phosphor particles from the image, and determining the average particle diameter from the cumulative distribution. Note that the images used to calculate the cross-sectional area of 100 or more particles recognized as phosphor particles from the image are obtained by obtaining cross-sectional images (e.g., three or more) of multiple locations in the phosphor layer so that the particle diameter of the phosphor particles contained in the phosphor layer is the overall average particle diameter. The difference between the average particle diameter of the phosphor particles thus obtained and the average particle diameter as the median diameter (D50) of the phosphor particles specified at the time of manufacturing the wavelength conversion member is sufficiently small by statistically calculating and measuring the number of cross-sectional images and the number of phosphor particles.

The translucent ceramics 134 are formed by hydrolysis or oxidation of an inorganic binder, and are made of an inorganic material having translucency. The translucent ceramics 134 are made of, for example, silica (SiO ₂ ) and aluminum phosphate. Since the translucent ceramics 134 are made of an inorganic material, they do not change in quality even when irradiated with high-energy light such as that from an LD. Furthermore, since the translucent ceramics 134 are translucent, they can pass light from the light source and converted light without reducing the emission intensity.

Note that a translucent material is one that has the property that when light in the visible light wavelength range (λ = 380-780 nm) is incident perpendicularly onto a 0.5 mm target material, the radiant flux of the light that exits from the other side exceeds 80% of the incident light.

This wavelength conversion member and light emitting device can improve the emission intensity while appropriately controlling color uniformity. The wavelength conversion member and light emitting device of the present invention are suitable for use in various analytical devices and medical devices.

[Method of producing wavelength conversion member]
3(a), (b), and (c) are cross-sectional views showing the manufacturing process of the wavelength conversion member of the present invention. First, an inorganic binder, a solvent, and a plurality of types of phosphor particles are prepared. The inorganic binder is preferably an organic silicate such as ethyl silicate. By using the organic silicate, the phosphor particles are dispersed throughout the printing paste, and a printing paste with an appropriate viscosity can be prepared. For example, when ethyl silicate is used as the inorganic binder, the mass of ethyl silicate is 70 wt% or more and 100 wt% or less, preferably 80 wt% or more and 90 wt% or less, relative to the mass of water and catalyst. In addition, the inorganic binder may be obtained by reacting at room temperature or by heat treating at a temperature of 500°C or less a raw material containing at least one of a group consisting of a silicon oxide precursor that becomes silicon oxide by hydrolysis or oxidation, a silicic acid compound, silica, and amorphous silica. Examples of silicon oxide precursors include those mainly composed of perhydropolysilazane, ethyl silicate, and methyl silicate. As the solvent, a high boiling point solvent such as butanol, isophorone, α-terpineol, or glycerin can be used.

In addition, a filler made of an inorganic material may be added to control the filling rate and light scattering properties of the phosphor layer. It is preferable that the average particle size of the filler is equal to or smaller than the average particle size of the phosphor particles contained in the phosphor layer.

Different types of phosphor particles are used for each phosphor layer to be stacked. For example, particles such as YAG, LuAG, and S-CASN can be used. The type and amount of phosphor particles are adjusted according to the color and color balance of the light to be irradiated with the light from the light source. In this case, two or more different types of phosphor particles are used to form the mixed layer.

As shown in FIG. 3(a), the inorganic binder, solvent, and phosphor particles are mixed to prepare a paste (ink) 410. A ball mill or the like can be used for mixing. Two or more types of phosphor particles are mixed into the paste for producing the mixed layer. Meanwhile, a base material 110 made of an inorganic material is prepared. The base material can be glass, sapphire, or the like.

Next, as shown in FIG. 3(b), the obtained paste 410 is applied to the substrate 110 using a screen printing method so that the paste 410 will have a predetermined average film thickness after heat treatment. Screen printing can be performed by pressing the paste 410 with an ink squeegee 510 against a screen 520 stretched over a frame. Other methods besides screen printing include a spray method, a dispenser drawing method, and an inkjet method, but the screen printing method is preferred for stably forming a thin phosphor layer.

Then, the printed paste 410 is dried to produce the phosphor layer. Drying is preferably performed at 100°C to 150°C for 20 minutes to 60 minutes. Then, paste 410 that will become the next phosphor layer is printed on the dried phosphor layer, and dried in the same manner as before to produce the next phosphor layer. This process is repeated to stack a predetermined number of phosphor layers, producing the phosphor section 120.

After the last phosphor layer is dried, as shown in FIG. 3(c), the solvent is removed by heat treatment in a furnace 600, and the organic matter in the inorganic binder is removed to oxidize the main metal in the inorganic binder (to _SiO2 if the main metal is Si), and the adjacent phosphor layers and the phosphor layers are bonded to the substrate 110. The heat treatment temperature is preferably 150° C. or higher and 500° C. or lower, and the heat treatment time is preferably 0.5 hours or higher and 2.0 hours or lower. The heating rate is preferably 50° C./h or higher and 200° C./h or lower. The firing atmosphere is preferably a non-oxidizing atmosphere such as a nitrogen atmosphere in order to suppress oxidation of the substrate.

In this way, a wavelength conversion member can be obtained. A light emitting device can then be produced by appropriately positioning the wavelength conversion member relative to a light source such as an LED.

[Examples and Comparative Examples]
(Sample Preparation Method)
The following five types of phosphor particles were prepared.
(1) CASN phosphor (Denka RE-660AMD) with a peak emission wavelength of 660 nm, average particle size of 15 μm
(2) α-sialon (Denka YL-600B) with a peak emission wavelength of 600 nm, average particle size of 15 μm
(3) Silicate phosphor (Tokyo Chemical 2E50B700C2) with a peak emission wavelength of 520 nm, average particle size of 15 μm
(4) Aluminate phosphor (Tokyo Chemical BMD-LED) with a peak emission wavelength of 450 nm, average particle size of 10 μm
(5) Sulfide phosphor (ZnS:Eu) showing an emission peak wavelength of 420 nm, average particle size of 10 μm

Apart from preparing the samples, the absorptivity of the phosphor particles prepared above was confirmed. Figure 4 is a table showing the absorptivity of any two combinations of phosphor particles used in the examples and comparative examples. That is, Figure 4 shows the extent to which the phosphor particles with a long emission peak wavelength absorb incident light of the same wavelength as the emission peak wavelength of the phosphor particles with a short emission peak wavelength in any two combinations of phosphor particles used in the examples and comparative examples, and shows the absorptivity of the absorption spectrum at a specific wavelength. The values in Figure 4 represent the attenuation rate of the incident light as a percentage. From this result, it can be seen that, among the phosphor particles (1) to (5), the combinations of phosphor particles with absorptivity not exceeding 30% are (1) and (2), (1) and (3), (2) and (3), and (4) and (5). That is, it was found that these are preferable combinations to be used in a mixed layer.

A sapphire substrate was prepared as a flat plate measuring 20 mm x 20 mm x 2.0 mm thick. A paste containing any of the above phosphor particles was screen-printed onto the substrate, and each phosphor layer was produced by applying the paste and drying it at 100°C for 20 minutes. This process was repeated to produce a phosphor part with stacked phosphor layers. Finally, the sample was completed by heating the sample to 350°C at 150°C/h in a nitrogen atmosphere furnace and baking it for 30 minutes. The conditions for the phosphor part of each sample were as follows. The amount (concentration) of phosphor particles contained in each phosphor layer of each sample was appropriately adjusted so that white light was irradiated.

Example 1
First layer (light-emitting element side): A phosphor layer made of a mixture of phosphor particles (1) and (2) and having a thickness of 25 μm. Second layer: A phosphor layer made of phosphor particles (3) and having a thickness of 25 μm. Third layer: A phosphor layer made of phosphor particles (4) and having a thickness of 25 μm. Fourth layer (outer surface side): A phosphor layer made of phosphor particles (5) and having a thickness of 35 μm. The thickness of the phosphor part was 110 μm.

Example 2
First layer (light-emitting element side): A mixture of phosphor particles (1) and (2) to form a phosphor layer having a thickness of 20 μm. Second layer: A phosphor layer having a thickness of 20 μm, made of phosphor particles (3). Third layer: A phosphor layer having a thickness of 20 μm, made of phosphor particles (4). Fourth layer (outer surface side): A phosphor layer having a thickness of 35 μm. The thickness of the phosphor part was 95 μm.

Example 3
First layer (light-emitting element side): A phosphor layer made of a mixture of phosphor particles (1) and (2) and having a thickness of 20 μm. Second layer: A phosphor layer made of phosphor particles (3) and having a thickness of 20 μm. Third layer (outer surface side): A phosphor layer made of phosphor particles (4) and (5) and having a thickness of 35 μm. The thickness of the phosphor part was 75 μm.

Example 4
First layer (light-emitting element side): A 20 μm-thick phosphor layer formed by mixing phosphor particles (1) + (2) Second layer: A 25 μm-thick phosphor layer formed by mixing phosphor particles (3) and (4) + (5) Third layer (outer surface side): A 30 μm-thick phosphor layer formed by mixing phosphor particles (4) + (5) The thickness of the phosphor part was 75 μm.

Example 5
First layer (light-emitting element side): A phosphor layer having a thickness of 35 μm, formed by mixing phosphor particles (1)+(2)+(3). Second layer: A phosphor layer having a thickness of 25 μm, formed by phosphor particles (4). Third layer (outer surface side): A phosphor layer having a thickness of 35 μm, formed by phosphor particles (5). The thickness of the phosphor part was 95 μm.

(Comparative Example 1)
1st layer (light-emitting element side): phosphor particle (1), phosphor layer having a thickness of 35 μm 2nd layer: phosphor particle (2), phosphor layer having a thickness of 35 μm 3rd layer: phosphor particle (3), phosphor layer having a thickness of 35 μm 4th layer: phosphor particle (4), phosphor layer having a thickness of 35 μm 5th layer (outer surface side): phosphor particle (5), phosphor layer having a thickness of 35 μm The thickness of the phosphor part was 175 μm.

(Comparative Example 2)
First layer (light-emitting element side): phosphor particle (1), phosphor layer having a thickness of 20 μm Second layer: phosphor particle (2), phosphor layer having a thickness of 20 μm Third layer: phosphor particle (3), phosphor layer having a thickness of 20 μm Fourth layer: phosphor particle (4), phosphor layer having a thickness of 20 μm Fifth layer (outer surface side): phosphor particle (5), phosphor layer having a thickness of 20 μm The thickness of the phosphor part was 100 μm.

(Sample Evaluation Method)
Each completed sample was subjected to emission spectrum testing using a spectrometer with excitation by a UV LED package with a peak wavelength of 365 nm, resulting in an input power of 0.8 W.

Figure 5 is a table showing the emission intensity (light amount) for each emission peak wavelength of the phosphor particles used in Examples 1 to 5 and Comparative Examples 1 and 2, the value obtained by dividing the maximum emission intensity by the minimum emission intensity (MAX/MIN), the judgment results, and the total emission intensity (total fluorescence). The emission intensity is shown as a relative value. In addition, the judgment results of the color balance are shown as follows: samples with a MAX/MIN value of 3 or less are considered to have passed, and are indicated with a circle; samples with a value greater than 3 are considered to have failed, and are indicated with a cross.

Example 1 is an example in which the first layer is a mixed layer in which phosphor particles (1) and (2) are mixed. Example 1 has excellent color balance and high luminous intensity. Example 2 is an example in which the thickness of the phosphor layers from the first to third layers is thin, with the same configuration as Example 1. Example 2 has better color balance and higher luminous intensity than Example 1.

Example 3 is an example in which the first layer is a mixture of phosphor particles (1) and (2), and the third layer is a mixture of phosphor particles (4) and (5). Example 3 has excellent color balance and the emission intensity is greater than Examples 1 and 2. Example 4 is an example in which the thickness of the phosphor layer is gradually increased from the first layer to the third layer, with the same configuration as Example 3. Example 4 has the same color balance as Example 3, and the emission intensity is further increased.

In Example 5, the first layer is a mixed layer made of three types of phosphor particles, phosphor particles (1), (2), and (3). Example 5 has a particularly excellent color balance and a sufficiently high emission intensity.

In Comparative Example 1, no mixed layer was provided, and all the phosphor layers had the same thickness. In Comparative Example 1, the emission intensity of light in the short wavelength region was particularly low, and the color balance was poorer than in the Examples. The emission intensity was also low compared to the Examples. In Comparative Example 2, the thickness of each phosphor layer was made thinner in the same configuration as Comparative Example 1. In Comparative Example 2, the emission intensity was increased compared to Comparative Example 1, but was not greater than in the Examples. The color balance was further worse than in Comparative Example 1. It is presumed that the color balance can be improved in Comparative Example 2 by, for example, increasing the thickness of the fourth and fifth phosphor layers, but in that case, it is presumed that the emission intensity would be reduced and would not be the same as in the Examples.

These results demonstrate that the wavelength conversion material and light emitting device of the present invention can adequately control color uniformity and improve light emission intensity.

The present invention is not limited to the above-described embodiment, and it goes without saying that it covers various modifications and equivalents that fall within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for convenience of explanation and may be changed as appropriate.

REFERENCE SIGNS LIST 10 Light emitting device 50 Light source 100 Wavelength conversion member 110 Base material 120 Phosphor portion 122 Incident surface 124 Emitting surface 130, 130a, 130b, 130c Phosphor layer 132, 132a, 132b, 132c, 132d Phosphor particle 134 Light-transmitting ceramic 410 Paste 510 Ink squeegee 520 Screen 600 Furnace

Claims (6)

A wavelength conversion member,
A substrate that contains an inorganic material and transmits light;
a phosphor section provided on the base material, in which two or more phosphor layers each formed of phosphor particles and a translucent ceramic that bonds the phosphor particles to each other are laminated,
The phosphor section has an incident surface set on either the substrate side or a surface side of the phosphor section located opposite to the substrate side, and an exit surface set on the other side,
an emission peak wavelength of the phosphor particles in one phosphor layer of the phosphor section is longer than an emission peak wavelength of the phosphor particles in another phosphor layer located closer to the light exit surface than the one phosphor layer;
At least one of the phosphor layers is a mixed layer containing two or more types of phosphor particles,
A wavelength conversion member , characterized in that at least one of the phosphor layers has a thickness smaller than that of another phosphor layer located closer to the light exit surface than the phosphor layer . The wavelength conversion member according to claim 1, characterized in that the different types of phosphor particles in the mixed layer have different average particle sizes. The wavelength conversion member according to claim 1 or 2, characterized in that the thickness of each of the phosphor layers is 1 to 6 times the maximum average particle size of the phosphor particles contained in each of the phosphor layers. A wavelength conversion member according to any one of claims 1 to 3, characterized in that the absorptance of the absorption spectrum of the phosphor particles with a long emission peak wavelength contained in the mixed layer does not exceed 30% at the emission peak wavelength of the fluorescence spectrum of the phosphor particles with a short emission peak wavelength. 5. The wavelength conversion member according to claim 1, wherein the phosphor layer located closest to the incident surface side is the mixed layer. A light emitting device, comprising:
A light emitting element that emits excitation light in a specific range of wavelengths;
A light emitting device comprising: the wavelength conversion member according to claim 1 .

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