JP2015050124A - Light emitting device - Google Patents

Abstract

Provided is a reflection type light emitting device which has a reflection layer structure with high incidence without dependence on an incident angle, and thereby can achieve high luminance. The light emitting device of the present invention has a refractive index lower than the refractive index of the material constituting the phosphor layer 2 between the light emitting side of the phosphor layer 2 and the reflective layer 4 provided on the opposite side. A total reflection film 6 made of a material is provided. Preferably, between the reflective layer 4 and the total reflection film 6, an increased reflection film 5 made of an optical multilayer film is provided. The total reflection film 6, the increased reflection film 5, and the reflection layer 4 can be formed by sequentially forming on the surface of the phosphor layer 2. Of the light emitted from the phosphor layer 2, light incident on the total reflection film 6 at an angle greater than the critical angle is totally reflected. Thereby, the reflectance as the reflection layer 4, the reflective reflection film 5, and the total reflection film 6 as a whole can be improved. [Selection] Figure 1

Description

  The present invention relates to a light emitting device in which a light source such as an LD (laser diode) or an LED (light emitting diode) is combined with a phosphor that absorbs light from the light source and emits fluorescence.

  A light emitting device combining a solid light source such as an LD and an LED and a phosphor has a wide range of applications such as general illumination and a headlamp of an automobile as a high luminance light source.

  As a method for increasing the brightness of a light source, a reflection type device has been proposed (Patent Document 1). In a reflection type light emitting device, an optical semiconductor and a phosphor layer are arranged spatially separated, and light emission from the phosphor layer side is used in a reflection method. In order to reflect light emitted from the phosphor layer, techniques such as bonding the phosphor layer to a highly reflective metal substrate such as aluminum and coating the substrate with silver (Ag) having a high light reflectivity are adopted. Yes. Such a reflective light emitting device can use both light emitted from a phosphor layer excited by excitation light from a solid-state light source and reflected light of excitation light reflected by the phosphor layer. Brightness is achieved.

JP 2012-64484 A

  Light emitted from the phosphor layer is light traveling in all directions, and is incident on the reflection surface of the reflection substrate (reflection layer) at any incident angle. Therefore, it is desirable that the material used for the reflective layer has no angle dependency. Silver is an excellent material with a high reflectivity of 98% or more over a wavelength range of 500 nm to 800 nm at all incident angles, and absorbs several percent of light in the visible light region.

  On the other hand, it is known that the dielectric multilayer film increases the reflectivity, and there is a method of increasing the reflectivity by forming the dielectric multilayer film on the reflective layer made of a metal film such as aluminum. However, such a reflection-enhancing film has a property that the reflectance at a high incident angle, particularly at an incident angle of 70 degrees or more, rapidly decreases. For this reason, in the reflection type light-emitting device, if a reflection-increasing film is provided between the phosphor layer and the silver reflection film, the reflectance at a high incident angle is lowered, so that high brightness cannot be achieved. .

  An object of the present invention is to provide a reflection type light emitting device that has a reflection layer structure with high reflectivity and has no angle dependency, thereby achieving high luminance.

  In order to solve the above problems, the light emitting device of the present invention is refracted more than the refractive index of the material constituting the reflective layer between the reflective layer provided on the opposite side of the light emitting side of the phosphor layer and the phosphor layer. A total reflection film made of a low-rate material is provided.

  That is, the light-emitting device of the present invention includes a light source that emits excitation light, a phosphor layer that receives excitation light from the light source, enters the excitation light, and emits light having a wavelength different from that of the excitation light, and excitation of the phosphor layer A light emitting device having a reflective layer disposed on the side opposite to the light incident surface, wherein the refractive index is lower than the refractive index of the phosphor layer between the reflective layer and the phosphor layer, and a critical angle And a total reflection film that totally reflects light incident at the above angle.

  The suitable aspect of the light-emitting device of this invention further has a reflection enhancement film between the total reflection film and the reflection layer.

  By interposing a total reflection film between the reflection layer and the phosphor layer, the amount of light absorbed by the reflection layer can be reduced, and the luminance of the light emitter can be increased. In particular, when a reflection-increasing film is provided between the reflection layer and the total reflection film, the reflection coefficient is increased for incident light below the critical angle where the reflection film is not totally reflected by the total reflection film, and the total reflection film is increased. Since the reflection angle dependency of the reflective film is complemented, further increase in luminance can be achieved.

Sectional drawing which shows 1st embodiment of the light-emitting device of this invention. The figure explaining the optical path of the light in the light-emitting device of 1st embodiment. The graph which shows the incident angle dependence of the reflectance in 1st embodiment The figure explaining the simulation method of the reflectance of FIG. The figure which shows an example of the manufacturing method of the light-emitting device of 1st embodiment. Sectional drawing which shows 2nd embodiment of the light-emitting device of this invention. The graph which shows the angle dependence of the reflectance in 2nd embodiment

Hereinafter, embodiments of a light emitting device of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an overall configuration of a light-emitting device common to the embodiments. This light-emitting device includes a solid-state light source 1 that emits light of a predetermined wavelength, a phosphor layer 2 that emits light having a wavelength different from that of the excitation light, using the light from the solid-state light source 1 as excitation light, a substrate 3, and a support (not shown) It is comprised from the structure and the optical member added as needed. A reflective layer 4 is provided between the phosphor layer 2 and the substrate 3, and a surface opposite to the reflective layer side of the phosphor layer 2 is a light emitting surface (light emitting surface). In the light emitting device of the embodiment, the solid light source 1 is arranged with respect to the phosphor layer 2 so that excitation light is incident on the light emitting surface of the phosphor layer 2 from an oblique direction.

In the light emitting device according to the present embodiment, a reflective reflection film 5 and a total reflection film 6 are further provided in order from the reflective layer 4 between the phosphor layer 2 and the reflective layer 4. Although omitted in FIG. 1, a wall material such as a white resin for preventing light leakage from the side surface of each layer may be provided on the side surface of the layer above the reflective layer 4. As the wall material, a so-called white resin material in which a scattering material such as TiO ₂ , BN, Al ₂ O ₃ , ZnO, BaSO ₄ , or SiO ₂ is dispersed in a resin such as a silicone resin or an epoxy resin is used. it can.

  As the solid-state light source 1, a light emitting diode (LED) or a laser diode (LD) having an emission wavelength in the ultraviolet light to blue light region can be used. Since the present invention is particularly effective for a light-emitting device using a light source having a high excitation term intensity, it is preferable to use a laser diode. Specifically, a laser diode that is composed of an InGaN-based or GaN-based semiconductor and emits blue light having a wavelength of 450 nm can be given.

The phosphor layer 2 is a layer including a phosphor that emits light having a longer wavelength than the excitation light using the light emitted from the solid light source 1 as excitation light. Specifically, for red, CaAlSiN ₃ : Eu ²⁺ , (Ca, Sr) AlSiN ₃ : Eu ²⁺ , Ca ₂ Si ₅ N ₈ : Eu ²⁺ , (Ca, Sr) ₂ Si ₅ N ₈ : Eu ²⁺ , KSiF ₆ : Mn ⁴⁺ , KTiF ₆ : Mn ⁴⁺ etc. For yellow, Y ₃ Al ₅ O ₁₂ : Ce ³⁺ (YAG), (Si, Ba) ₂ SiO ₄ : Eu ²⁺ , Ca _x (Si, Al) ₁₂ (O, N) ₁₆ : Eu ²⁺ etc. For green, Lu ₃ Al ₅ O ₁₂ : Ce ³⁺ , Y ₃ (Ga, Al) ₅ O ₁₂ : Ce ³⁺ , Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ^{3+ _{, CaSc 2 O 4: Eu 2+}} , (Ba, Sr) 2 SiO 4: Eu 2+, Ba 3 Si 6 O 12 N 2: Eu 2+, (Si, Al) 6 (O, N) 8: Eu 2+ It can be used in the phosphor. These can be used alone or in combination of two or more. When the laser blue light and the yellow phosphor are combined, the light emitted from the light source device 1 is white light.

As the form of the phosphor layer 2, a phosphor powder dispersed in glass or resin, a glass phosphor in which a luminescent center ion is added to a glass matrix, phosphor ceramics, or the like can be used. Specifically, the phosphor powder is dispersed in glass or resin. Specifically, the phosphor powder described above is contained in a glass containing components such as P ₂ O ₃ , Si ₂ , B ₂ O ₃ , and Al ₂ O _3. Are dispersed. As the glass phosphor, oxynitride glass such as Ca—Si—Al—O—N or Y—Si—Al—O—N added with Ce ³⁺ or Eu ²⁺ as an activator (emission center ion). Examples include phosphors. Examples of the phosphor ceramic include a sintered body having the phosphor composition described above and substantially free of a resin component.

  Among these, phosphor ceramics which are sintered bodies of phosphor powder are preferable. Since phosphor ceramics have high thermal conductivity, it is possible to reduce a phenomenon (temperature quenching) in which light emission of the phosphor is weakened by heat. Among the phosphor ceramics, those having high translucency, which hardly contain pores or grain boundary impurities that cause light scattering in the sintered body, are particularly preferable. The pores of the sintered body can be reduced by selecting the flux used when manufacturing the sintered body and adjusting the pressure and temperature during sintering. In addition, the value of specific gravity of the phosphor ceramic can be used as an index for evaluating the remaining amount of pores, and it is particularly desirable that the value is 95% or more with respect to the theoretical value for calculating the value. By using phosphor ceramics with high translucency, the light extraction efficiency from the fluorescent layer can be increased without losing excitation light or fluorescence by diffusion.

  In FIG. 1, a flat phosphor layer 2 having a uniform thickness is shown, but the phosphor layer 2 is not a flat plate, for example, a spherical shape, a light emitting surface and / or a side opposite to the light emitting surface. It can take various shapes such as a convex or concave surface. Moreover, although it does not specifically limit about a flat thing, It is preferable that thickness is 50 micrometers or more and 300 micrometers or less. By setting it as such a range, sufficient brightness | luminance can be obtained and the loss of the light from a side surface can be suppressed. The thickness is preferably 100 μm or more and 150 μm or less. For other shapes, it is preferable that the thickness is in a range inferred from the thickness of the flat plate.

  The light emitting surface of the phosphor layer 2, that is, the surface on which the excitation light from the solid light source 1 is incident is subjected to a treatment for preventing reflection of the excitation light or a known antireflection film (not shown). Can be provided.

  The substrate 3 functions as a support substrate for the phosphor layer 2 and also functions as a heat dissipation substrate that releases heat generated by the phosphor to the outside. For this reason, it is preferable to form the substrate 3 from a material having both high heat transfer characteristics and workability. Specifically, ceramics such as oxide ceramics and non-oxide ceramics (nitride ceramics), metals such as Al, Cu, Ti, Si, Ag, Au, Ni, Mo, W, Fe, Pd or the like Including alloys can be used. A metal is particularly preferable in terms of high heat transfer characteristics.

  The surface of the substrate 3 may be subjected to surface treatment as necessary, such as plating, sputtering film formation, and vapor deposition film formation. In particular, the surface of the phosphor layer side surface may be subjected to surface treatment for enhancing the adhesion with the reflective layer or the like. Further, the outer surface may have a fin shape in order to improve heat dissipation.

  The substrate 3 is bonded to the phosphor layer 2 and the like by the bonding layer 7. The bonding layer 7 is preferably made of a material having good heat resistance and thermal conductivity. Specifically, an organic adhesive such as silicone resin, an inorganic adhesive such as glass, a low melting point metal such as AuSn or solder, or a metal braze can be used. When a reflective layer 4 described later is formed on the phosphor layer 2 and this reflective layer 4 is bonded to the substrate 3, the bonding layer 7 does not need to be translucent, but the surface of the substrate 3. Is also used as the reflective layer 4, or when the reflective layer 4 is formed on the surface of the substrate 3, the bonding layer 7 is preferably made of a translucent material such as transparent silicone resin or glass.

  The reflection layer 4 reflects the light generated by the phosphor layer 2 or the light transmitted through the phosphor layer 2 to the light emitting surface side of the phosphor layer 2 and is opposite to the light emitting surface of the phosphor layer 2. It is formed by forming a film on the side or on the surface of the substrate 3. When the substrate 3 itself is made of a highly reflective material, the surface of the substrate 3 can also serve as the reflective layer 4. As a material of the reflective layer 4 formed by film formation, a metal such as Al, Ag, or Au is used. In particular, Ag having no wavelength dependency and high reflectance is preferable. The reflective layer 4 can be formed by an electron beam evaporation (EB) method, a sputtering method, or the like. The thickness of the reflective layer 4 is preferably 50 nm or more, more preferably 100 nm or more. About the upper limit of the thickness, even if the thickness is increased, the effect obtained is not changed, and only the film formation time is increased.

The reflective layer 4 can be provided with a protective film (not shown) for protecting the metal film as necessary. As the protective film, a metal film such as Ti or a metal oxide film such as TiO ₂ is used, and these films can be formed by a known film formation technique such as an EB method or a sputtering method. The thickness of the protective film may be the same as or thinner than the thickness of the reflective layer 4.

The increased reflection film 5 is an optical multilayer film in which low-refractive index materials and high-refractive index materials are alternately stacked, and the thickness of each layer is adjusted to ¼ of the wavelength λ of incident light so that the number of layers is sufficient. As a result, incident light is hardly transmitted and reflected light can be obtained. Therefore, the thickness of the layer is adjusted in consideration of the light from the solid light source 1 and the wavelength of fluorescence, and is specifically about 10 nm to 100 nm. The total thickness is preferably about 0.01 μm to 3 μm. As a low refractive index material, for example, Na ₅ Al ₃ F ₁₄ (thiolite) (n = 1.33), AlF ₃ (n = 1.36), CaF ₂ (n = 1.38), SiO ₂ (n = 1.45), Al ₂ O ₃ (n = 1.64), etc. are used. As a high refractive index material, CeO ₂ (n = 2.13), Ta ₂ O ₅ (n = 2.20), Ti ₃ O ₅ (n = 2.31), TiO ₂ (n = 2.35). Nb ₂ O ₅ (n = 2.37) or the like is used. The reflective film 5 can be formed by sequentially depositing these materials by a method such as sputtering or vacuum deposition.

The total reflection film 6 is a layer that is in direct contact with the phosphor layer 2 and is made of a material having a refractive index smaller than the refractive index of the phosphor layer 2. The refractive index difference between the material constituting the total reflection film 6 and the phosphor layer is preferably 0.1 or more, more preferably 0.2 or more. Since the refractive index of YAG as a typical phosphor is 1.85, the refractive index is preferably 1.65 or less. As such a low refractive index material, specifically, Na ₅ Al ₃ F ₁₄ (thiolite) (n = 1.33), AlF ₃ (n = 1.36), MgF ₂ (n = 1.38) , CaF ₂ (n = 1.43), SiO ₂ (n = 1.45), Al ₂ O ₃ (n = 1.64), or the like can be used. Of these, SiO ₂ is preferable from the viewpoint of film formability. From the viewpoint of performance including total reflectivity, MgF ₂ is preferable.

  The thickness of the total reflection film 6 is not limited, but is preferably 300 nm or more, more preferably 500 nm or more. Moreover, it is preferably 2 μm or less, more preferably 1 μm or less. The total reflection film 6 can be formed by a method such as sputtering or vacuum deposition in the same manner as the increased reflection film 5.

As shown in FIG. 2, the light emitted from the phosphor layer 2 has no directivity and travels in all directions, so that the incident angle of light incident on the total reflection film 6 is distributed from 0 degrees to 90 degrees. Here, since the refractive index of the total reflection film 6 is lower than that of the phosphor layer 2, light having an incident angle equal to or greater than the critical angle θ _T among the light incident on the total reflection film 6 from the phosphor layer 2 is totally reflected. When the refractive index of the phosphor layer 2 is n1 and the refractive index of the total reflection film 6 is n2, the critical angle θ _T is sin (θ _T ) = n2 / n1 according to Snell's law.
It is represented by For example, when the phosphor layer 2 is YAG (n = 1.85) and the total reflection film 6 is SiO ₂ (n = 1.45), the critical angle θ _T is 51.6 degrees. That is, light having an incident angle of 51.6 degrees or more is totally reflected.

  Light having an incident angle smaller than the critical angle is incident on the total reflection film 6. Here, when the total reflection film 6 is made of a material having a good light transmittance, the total reflection film 6 is transmitted. The light transmitted through the total reflection film 6 is incident on the enhanced reflection film 5. The light incident on the increased reflection film 5 undergoes multiple reflections and travels in the transmission direction when passing through the optical multilayer film, and becomes almost zero, and the reflected light becomes reflected light through the total reflection film 6. Return to. Since the reflectance of the increased reflection film 5 is highly wavelength-dependent, light other than a predetermined wavelength passes through the increased reflection film 5 and reaches the reflection layer 4, but is reflected by the reflection layer 4.

  As described above, the total reflection film 6 totally reflects light having a large incident angle out of the light emitted from the phosphor layer 2 to prevent the light from going to the reflection reflection film 5 and the reflection layer 4. The reflection function can be sufficiently exerted. The light transmitted through the increased reflection film 5, that is, light having a wavelength with low reflection characteristics of the increased reflection film 5 is reflected by the reflection layer 4. As a result, high reflectivity can be achieved for the total reflection film 6, the increased reflection film 5, and the reflection layer 4 as a whole.

FIG. 3 shows the result of simulating the reflection characteristics of these optical films. In the simulation, the medium 41 shown in FIG. 4 is YAG (1.85), the total reflection film 42 is SiO ₂ (1.45), the enhanced reflection film 43 is a multilayer film (six layers) of SiO ₂ / Ta ₂ O ₅ , Assuming that the reflective layer 44 is set to silver, a measuring instrument is present in the medium 41, the peak wavelength of the fluorescence spectrum of YAG is set to the reference wavelength 510 nm of the incident light, and the incident angle θ ranges from 0 to 90 degrees. The reflectance in the range (average value of P wave and S wave) is calculated. Further, it was assumed that there was no scattering in each layer, and the interface was assumed to be a mirror surface (no irregularities). In FIG. 3, the broken line is the reflectance of only silver, the dotted line is the reflectance when the increased reflection film is provided on the silver, and the solid line is the reflectance when the increased reflection film / total reflection film is provided on the silver. is there.

  As shown in FIG. 3, when the incident angle is in the range of 0 to 70 degrees, the reflectivity when the reflection-increasing film is provided on the silver is higher than the reflectivity of silver alone. The reflectance decreases. This is due to the fact that the thickness (ideally λ / 4) of the multilayer film constituting the enhanced reflection film varies depending on the incident angle. On the other hand, when a total reflection film is further provided on the increased reflection film, light having an incident angle greater than the critical angle is totally reflected, so that the incident angle is not affected by the reflectance of the increased reflection film. A high reflectance can be maintained even at 70 degrees or more.

  Next, an example of a method for manufacturing the light emitting device of this embodiment will be described. As shown in FIG. 5, the manufacturing process is roughly divided into a phosphor layer manufacturing process 501, a phosphor layer forming process 502, and a substrate bonding process 503.

An embodiment of a manufacturing method using Ce: YAG will be described.
<Manufacture of phosphor layer>
The raw material powders of yttrium nitrate (hexahydrate), aluminum nitrate (9 hydrate), and cerium nitrate (hexahydrate) were weighed in a stoichiometric ratio, and then water was added and stirred to dissolve. To this aqueous solution, an aqueous ammonium hydrogen carbonate solution was added dropwise to form a precipitate, which was left for 3 hours when the pH reached 8.5. The produced precipitate was separated by centrifugation (3000 rpm, 5 minutes × 3 times), and the precipitate was dried at 100 ° C. for 12 hours. The dried product was crushed using a mortar and pestle and then calcined at 900 ° C. for 2 hours. The fired product was crushed with a mortar and pestle, and then uniaxial mold molding was performed using a mold having a predetermined shape at 30 MPa. Further, cold isostatic pressing (CIP) was performed at 150 MPa to obtain a molded body, which was fired in a nitrogen atmosphere at 1700 ° C. to obtain a sintered body, and the sintered body was polished and mirror-finished.

<Film formation on phosphor layer>
A total reflection film and an increased reflection film were formed on the mirror-finished phosphor layer by the EB method. The total reflection film was SiO ₂ and the film thickness was 1000 nm. The increased reflection film is a multilayer film of SiO ₂ and Ta ₂ O ₅ , the number of layers is 6, and the thickness of the layers is 260 nm. Note that the thickness of the film and the thickness of the layer can be easily and accurately controlled by controlling the film formation time. On the phosphor layer on which the total reflection film and the increased reflection film were laminated, an Ag alloy reflection film (150 nm) and a Ti protective film (50 nm) were sequentially formed by sputtering.

<Bonding to substrate>
A metal (Al) substrate 3 having a predetermined size was prepared, and a silicone resin serving as a bonding layer was applied thereon by a dispensing method. Next, the protective film surface formed on the phosphor layer was placed on the resin coating solution and pressurized, and then heated at 150 ° C. for 4 hours to cure the silicone resin.

  The manufacturing method described above is an example, and the manufacturing method of the light emitting device of the present embodiment is not limited to the above method, conditions, and numerical values.

  According to the light emitting device of the present embodiment, the optical reflection layer and the total reflection film are provided in order from the reflection layer between the reflection layer that reflects the light from the phosphor layer and the phosphor layer. Since the film (total reflection film, increased reflection film, and reflection layer) supplements the respective reflection characteristics and has high reflectivity that does not depend on the incident angle, the luminance of the light emitting device can be improved.

<Second embodiment>
The light emitting device of this embodiment is provided with a total reflection film made of a material having a refractive index smaller than the refractive index of the material constituting the phosphor layer between the phosphor layer and the reflective layer. It is the same as the form. However, in the light emitting device of this embodiment, as shown in FIG. 6, the increased reflection film provided between the reflection layer and the total reflection film in the first embodiment is omitted. In FIG. 6, the same elements as those of FIG.

  Even in the light emitting device of the present embodiment, the light incident on the total reflection film 6 at the incident angle greater than the critical angle among the light emitted from the phosphor layer 2 is totally reflected as in the first embodiment. The light incident on the reflection film 6 is directed directly to the reflection layer 4, reflected at the interface with the reflection layer 4, transmitted through the total reflection film 6 and the phosphor layer 2, and emitted from the emission surface of the phosphor layer 2.

  FIG. 7 shows the result of simulating the reflection characteristics by the optical film of this embodiment. The simulation conditions are the same as in the first embodiment. In FIG. 7, the broken line indicates the reflectance of only silver, and the solid line indicates the reflectance when a total reflection film is provided on the silver. For reference, the reflectivity when a reflective film is provided on silver is indicated by a dotted line, and the reflectivity when a reflective film / total reflective film is provided on silver (the first embodiment) is indicated by a dashed line. Show.

  As shown in the figure, the reflectance at a relatively low incident angle is low compared to the case where an increased reflection film is provided, but in the range of the incident angle greater than the critical angle of the total reflection film, the effect of improving the reflectivity by the total reflection film Was confirmed.

  According to the present invention, a high-luminance light-emitting device is provided. This light-emitting device can be used as a high-luminance light source, and can also be applied to a vehicular lamp or a general lighting device.

DESCRIPTION OF SYMBOLS 1 ... Solid light source, 2 ... Phosphor layer, 3 ... Substrate, 4 ... Reflective layer, 5 ... Increasing reflection film, 6 ... Total reflection film, 7 ... Bonding layer .

Claims (6)

  A light source that emits excitation light, a phosphor layer that receives excitation light from the light source and emits light having a wavelength different from that of the excitation light, and a reflection layer disposed on the opposite side of the excitation light incident surface of the phosphor layer A light-emitting device comprising: a total reflection that between the reflection layer and the phosphor layer has a refractive index lower than that of the phosphor layer and totally reflects light incident at an angle greater than a critical angle; A light-emitting device comprising a film. The light-emitting device according to claim 1,
A light-emitting device further comprising an increased reflection film between the total reflection film and the reflection layer. The light-emitting device according to claim 2,
The light-emitting device, wherein the increased reflection film is an optical multilayer film formed by alternately laminating a film of a low refractive index material and a film of a high refractive index material. The light-emitting device according to any one of claims 1 to 3,
A light emitting device, wherein a difference in refractive index between the phosphor layer and the total reflection film is 0.2 or more. The light-emitting device according to claim 4,
The total reflection film is made of SiO ₂ or MgF ₂ . The light-emitting device according to claim 1, wherein the light source emits a blue laser.

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