Patent Description:
In recent years, a light source including a light emitting element and a wavelength conversion member has been developed. The wavelength conversion member has phosphor particles embedded in a matrix. The phosphor particles are irradiated with light from the light emitting element as excitation light, and light having a wavelength longer than the wavelength of the excitation light is radiated from the phosphor. It has been attempted to increase the luminance and output of light in this type of light source.

Patent Literature <NUM> discloses an LED sealing resin body in which a phosphor is dispersed in a silicone resin. Patent Literature <NUM> discloses a wavelength conversion member in which glass is used as a material for the matrix. Patent Literature <NUM> discloses a wavelength conversion member in which zinc oxide (ZnO) is used as a material for the matrix. ZnO is superior to a silicone resin in heat resistance. ZnO is an inorganic material having a refractive index close to the refractive index of a number of phosphors and exhibits excellent translucency and thermal conductivity. According to the wavelength conversion member of Patent Literature <NUM>, light scattering at the interface between the phosphor particles and the ZnO matrix is suppressed and high light output can be achieved.

The wavelength conversion member of Patent Literature <NUM> has room for improvement from the viewpoint of reliability.

An object of the present discloser is to provide a wavelength conversion member exhibiting high reliability.

The present invention is defined by the features described in the independent claims. Additional embodiments are defined in the dependent claims.

According to the technology of the present disclosure, it is possible to provide a wavelength conversion member exhibiting high reliability.

In the wavelength conversion member of Patent Literature <NUM>, ZnO contained in the matrix reacts with corrosive gas in the air in some cases. The reaction between ZnO and corrosive gas proceeds with time. As the above reaction proceeds with time, the chromaticity of light radiated from the wavelength conversion member changes with time in some cases.

The wavelength conversion member according to the invention is defined in claim <NUM>.

Accordingly, the first protective layer suppresses permeation of corrosive gas in the air. For this reason, ZnO contained in the matrix of the phosphor layer hardly reacts with the corrosive gas. In other words, it is possible to suppress that the reaction between ZnO and the corrosive gas proceeds with time. By this, a change in chromaticity of light radiated from the wavelength conversion member with time is sufficiently suppressed. In other words, the wavelength conversion member exhibits high reliability.

Moreover, with ZnO of the wavelength conversion member being c-axis-oriented polycrystalline ZnO, light scattering in the phosphor layer is further suppressed. Hence, high light output can be achieved in the wavelength conversion member.

Furthermore, the strength of the wavelength conversion member is improved by the second protective layer. The permeation of corrosive gas can also be further suppressed by the second protective layer.

In a first optional aspect of the present disclosure, for example, the first protective layer of the wavelength conversion member is in contact with the phosphor layer. Accordingly, , a change in chromaticity the of light radiated from the wavelength conversion member with time is sufficiently suppressed.

In a second optional aspect of the present disclosure, for example, the phosphor layer of the wavelength conversion member further has filler particles. Accordingly, the wavelength conversion member radiates light having a required chromaticity.

In a third optional aspect of the present disclosure, for example, the thickness of the first protective layer of the wavelength conversion member is in a range of <NUM> to <NUM>. Accordingly, the first protective layer is sufficiently thin and a high luminous efficiency can be thus achieved.

The light source according to the present invention as defined in claim <NUM> includes a light emitting element and the wavelength conversion member according to the invention or one of its optional aspects that receives excitation light emitted from the light emitting element and radiates fluorescence.

Accordingly, it is possible to provide a light source in which a change in the chromaticity of light with time is sufficiently suppressed. In other words, the light source exhibits high reliability.

Hereinafter, examples for illustrative purposes and embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following exemplary embodiments.

As illustrated in <FIG>, wavelength conversion member <NUM> according to the first example includes substrate <NUM>, phosphor layer <NUM>, and first protective layer <NUM>. While this first example does not fully implement the claimed invention and mainly serves for illustrative purposes, parts of the disclosure herein may be used in connection with the claimed invention as will be described further below. Substrate <NUM> supports phosphor layer <NUM> and first protective layer <NUM>. Phosphor layer <NUM> is disposed on substrate <NUM>. Phosphor layer <NUM> covers the entire surface of substrate <NUM>. Phosphor layer <NUM> may only partially cover the surface of substrate <NUM>. The lower surface of phosphor layer <NUM> is in contact with the upper surface of substrate <NUM>.

First protective layer <NUM> is disposed on phosphor layer <NUM>. Phosphor layer <NUM> is disposed between substrate <NUM> and first protective layer <NUM>. In other words, substrate <NUM>, phosphor layer <NUM>, and first protective layer <NUM> are arranged in the thickness direction of wavelength conversion member <NUM> in this order. First protective layer <NUM> covers the entire surface of phosphor layer <NUM>. First protective layer <NUM> may only partially cover the surface of phosphor layer <NUM>. The lower surface of first protective layer <NUM> is in contact with the upper surface of phosphor layer <NUM>.

Phosphor layer <NUM> has matrix <NUM> and phosphor particles <NUM>. Phosphor layer <NUM> may further have filler particles <NUM>. Matrix <NUM> exists between the respective particles. The respective particles are embedded in matrix <NUM>. In other words, the respective particles are dispersed in matrix <NUM>.

When wavelength conversion member <NUM> is irradiated with excitation light having a first wavelength band, wavelength conversion member <NUM> converts a part of the excitation light into light having a second wavelength band and radiates the light. Wavelength conversion member <NUM> radiates light having a wavelength longer than the wavelength of the excitation light. The second wavelength band is a band different from the first wavelength band. However, a part of the second wavelength band may overlap the first wavelength band. The light radiated from wavelength conversion member <NUM> may include not only the light radiated from phosphor particles <NUM> but also the excitation light itself.

Substrate <NUM> has substrate main body <NUM> and thin film <NUM>. The thickness of substrate <NUM> is, for example, thicker than the thickness of phosphor layer <NUM>. Substrate main body <NUM> contains at least one selected from the group consisting of sapphire (Al<NUM>O<NUM>), gallium nitride (GaN), aluminum nitride (AIN), silicon, aluminum, glass, quartz (SiO<NUM>), silicon carbide (SiC), and zinc oxide. For example, substrate main body <NUM> may or may not exhibit translucency with respect to the excitation light and the light radiated from phosphor particles <NUM>. Substrate main body <NUM> may have a mirror-polished surface.

The surface of substrate main body <NUM> may be covered with an antireflective film, a dichroic mirror, a metal reflective film, a reflection enhancing film, a protective film, and the like. The antireflective film is a film for preventing reflection of excitation light. The dichroic mirror can be composed of a dielectric multilayer film. The metal reflective film is a film for reflecting light and is fabricated of a metal material such as silver or aluminum. The reflection enhancing film can be composed of a dielectric multilayer film. The protective film can be a film for physically or chemically protecting these films.

Thin film <NUM> functions as a ground layer for forming phosphor layer <NUM>. When matrix <NUM> of phosphor layer <NUM> is crystalline, thin film <NUM> functions as a seed crystal in the crystal growth process of matrix <NUM>. In other words, thin film <NUM> is a single crystalline thin film or a polycrystalline thin film. When matrix <NUM> is composed of single crystalline ZnO or polycrystalline ZnO, thin film <NUM> can be a single crystalline ZnO thin film or a polycrystalline ZnO thin film. However, thin film <NUM> may be omitted in a case in which substrate main body <NUM> can exert the function of the seed crystal. For example, when substrate main body <NUM> is composed of crystalline GaN or crystalline ZnO, matrix <NUM> composed of crystalline ZnO can be formed directly on substrate main body <NUM>.

In phosphor layer <NUM>, phosphor particles <NUM> are dispersed in matrix <NUM>. In <FIG>, phosphor particles <NUM> are separated from each other. Filler particles <NUM> are also separated from phosphor particles <NUM>. However, phosphor particles <NUM> may be in contact with each other or filler particles <NUM> may be in contact with phosphor particles <NUM>. A plurality of filler particles <NUM> may be in contact with phosphor particles <NUM>. Phosphor particles <NUM> and filler particles <NUM> may be stacked like a stone wall.

Phosphor particles <NUM> receive excitation light and radiate fluorescence. The material for phosphor particles <NUM> is not particularly limited. Various fluorescent substances can be used as the material for phosphor particles <NUM>. Specifically, fluorescent substances such as Y<NUM>Al<NUM>O<NUM>:Ce(YAG), Y<NUM>(Al,Ga)<NUM>O<NUM>:Ce(GYAG), Lu<NUM>Al<NUM>Ol<NUM>:Ce(LuAG), (Si,Al)<NUM>(O,N)<NUM>:Eu(β-SiAlON), (La,Y)<NUM>Si<NUM>N<NUM>:Ce(LYSN, La<NUM>Si<NUM>N<NUM>:Ce(LSN), Lu<NUM>CaMg<NUM>Si<NUM>O<NUM>:Ce(LCMS), Sr<NUM>SiO<NUM>:Eu, (Ba,Sr)Si<NUM>O<NUM>N<NUM>:Eu, Ca<NUM>Sc<NUM>Si<NUM>O<NUM>:Ce, and CaSi<NUM>O<NUM>N<NUM>:Eu can be used. Phosphor particles <NUM> may include plural kinds of phosphor particles having different compositions. The material for phosphor particles <NUM> is selected in accordance with the chromaticity of light that should be radiated from wavelength conversion member <NUM>.

The average particle diameter of phosphor particles <NUM> is, for example, in a range of <NUM> to <NUM>. The average particle diameter of phosphor particles <NUM> can be specified by the following method, for example. First, the cross section of wavelength conversion member <NUM> is observed under a scanning electron microscope. In the electron microscope image attained, the area of specific phosphor particle <NUM> is calculated by image processing. The diameter of a circle having the same area as the calculated area is regarded as the particle diameter (diameter of particle) of specific phosphor particle <NUM>. The particle diameters of an arbitrary number (for example, <NUM>) of phosphor particles <NUM> are calculated, and the average value of the calculated values is regarded as the average particle diameter of phosphor particles <NUM>. In the present disclosure, the shape of phosphor particles <NUM> is not limited. The shape of phosphor particles <NUM> may be a spherical shape, a scaly shape, or a fibrous shape. In the present disclosure, the method for measuring the average particle diameter is not limited to the above method.

Matrix <NUM> contains ZnO. ZnO is suitable as the material for matrix <NUM> from the viewpoints of transparency and thermal conductivity. ZnO exhibits high thermal conductivity. Hence, when ZnO is used as the material for matrix <NUM>, the heat of phosphor layer <NUM> can be easily released to the outside (mainly to substrate <NUM>). Matrix <NUM> may contain ZnO as a main component. The "main component" means a component that is contained in matrix <NUM> in the greatest amount as a weight ratio. Matrix <NUM> may be composed substantially of ZnO. "To be composed substantially of" means to exclude other components which alter the essential features of the mentioned compound. However, matrix <NUM> may contain impurities in addition to ZnO.

In detail, ZnO as the material for matrix <NUM> is single crystalline ZnO or c-axis-oriented polycrystalline ZnO. ZnO has a wurtzite crystal structure. "c-axis-oriented ZnO" means that the plane parallel to the principal surface (the surface having the largest area) of substrate <NUM> is the c-plane. When matrix <NUM> contains c-axis-oriented polycrystalline ZnO, light scattering is suppressed inside phosphor layer <NUM> and high light output can be achieved.

C-axis-oriented polycrystalline ZnO includes a plurality of columnar crystal grains oriented in the c-axis. In c-axis-oriented polycrystalline ZnO, there are few crystal grain boundaries in the c-axis direction. The "columnar crystal grains are oriented in the c-axis" means that the growth of ZnO in the c-axis direction is faster than the growth of ZnO in the a-axis direction and vertical ZnO crystal grains are formed on substrate <NUM>. The c-axis of ZnO crystal grain is parallel to the normal direction of substrate <NUM>. Alternatively, the inclination of the c-axis of ZnO crystal grain with respect to the normal direction of substrate <NUM> is <NUM>° or less. Here, the fact that "inclination of c-axis is <NUM>° or less" means that the distribution of inclination of the c-axis is <NUM>° or less but does not necessarily mean that the inclination of the c-axis of all crystal grains is <NUM>° or less. The "inclination of c-axis" can be evaluated by the half-value width of the c-axis by the X-ray rocking curve method. In detail, the half-value width of the c-axis by the X-ray rocking curve method is <NUM>° or less. Patent Literature <NUM> (International Publication No. <CIT>) discloses a matrix composed of c-axis-oriented polycrystalline ZnO in detail.

In phosphor layer <NUM>, filler particles <NUM> are dispersed in matrix <NUM>. When filler particles <NUM> are irradiated with excitation light, filler particles <NUM> do not radiate fluorescent light or radiate only fluorescent light with an negligible intensity. The material, shape, and added amount of filler particles <NUM> are appropriately adjusted in accordance with the required chromaticity.

Filler particles <NUM> are, for example, inorganic particles and typically contain a metal oxide. Filler particles <NUM> may be composed substantially of a metal oxide. A number of metal oxides are chemically stable and hardly radiate fluorescence and thus are suitable as materials for filler particles <NUM>. In an example, filler particles <NUM> contain at least one selected from Al<NUM>O<NUM> particles, SiO<NUM> particles, or TiO<NUM> particles.

The average particle diameter of filler particles <NUM> is, for example, in a range of <NUM> to <NUM>. The average particle diameter of filler particles <NUM> is, for example, smaller than the average particle diameter of phosphor particles <NUM>. The ratio (D2/D1) of average particle diameter D2 of filler particles <NUM> to average particle diameter D1 of phosphor particles <NUM> is, for example, in a range of <NUM> to <NUM>. The average particle diameter of filler particles <NUM> can be measured by the same method as the method for the average particle diameter of phosphor particles <NUM>. The shape of filler particles <NUM> may be a spherical shape, a scaly shape, or a fibrous shape. The volume of phosphor particles <NUM> is defined as V1. The volume of filler particles <NUM> is defined as V2. At this time, the value of V2/(V1 + V2) is, for example, in a range of <NUM> to <NUM>.

First protective layer <NUM> contains at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM>. These compounds hardly react with corrosive gas in the air. The corrosive gas is, for example, gas containing at least one selected from the group consisting of H<NUM>S, Cl<NUM>, NO<NUM>, and SO<NUM>. First protective layer <NUM> hardly reacts with the corrosive gas. First protective layer <NUM> suppresses permeation of corrosive gas. Hence, ZnO contained in matrix <NUM> hardly reacts with the corrosive gas. In other words, it is possible to suppress that the reaction between ZnO and the corrosive gas proceeds with time. By this, a change in chromaticity of light radiated from wavelength conversion member <NUM> with time is sufficiently suppressed. In other words, wavelength conversion member <NUM> exhibits high reliability.

First protective layer <NUM> may contain at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM> as a main component. First protective layer <NUM> may contain any one selected from the group consisting of ZnClz, ZnS, and ZnSO<NUM> as a main component. First protective layer <NUM> may be composed substantially of at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM>. However, first protective layer <NUM> may contain impurities in addition to these compounds.

The thickness of first protective layer <NUM> is, for example, thinner than the thickness of phosphor layer <NUM>. The thickness of first protective layer <NUM> is, for example, in a range of <NUM> to <NUM>. As first protective layer <NUM> is thinner, a higher luminous efficiency can be achieved. The thickness of first protective layer <NUM> may be less than or equal to <NUM> or less than or equal to <NUM>.

The fact that wavelength conversion member <NUM> includes first protective layer <NUM> can be confirmed by performing elemental analysis of the surface of wavelength conversion member <NUM>. Elemental analysis can be performed using, for example, an electron beam microanalyzer. The fact that wavelength conversion member <NUM> includes first protective layer <NUM> can be confirmed by observing the surface of wavelength conversion member <NUM> under a laser microscope. The thickness of first protective layer <NUM> can be measured using, for example, an electron beam microanalyzer.

Next, a method for manufacturing wavelength conversion member <NUM> will be described.

First, a mixed sol containing a precursor such as zinc alkoxide, phosphor particles <NUM>, and filler particles <NUM> is prepared. The mixed sol is applied to substrate <NUM> so that a coating film is formed on substrate <NUM>. Examples of the method for forming a coating film include a printing method. Phosphor layer <NUM> is obtained by gelling and firing the coating film.

In a case in which matrix <NUM> is single crystalline ZnO or c-axis-oriented polycrystalline ZnO, matrix <NUM> can be formed on substrate <NUM> by a solution growth method. First, substrate <NUM> is prepared. A crystalline ZnO thin film is formed on substrate main body <NUM> as thin film <NUM>. As a method for forming the ZnO thin film, vacuum film forming methods such as an electron beam vapor deposition method, a reactive plasma vapor deposition method, a sputtering method, and a pulse laser accumulation method are used. Thin film <NUM> can be a single crystalline ZnO thin film or a polycrystalline ZnO thin film. Next, a layer containing phosphor particles <NUM> and filler particles <NUM> is formed on substrate <NUM> (on thin film <NUM>). For example, a dispersion containing phosphor particles <NUM> and filler particles <NUM> is prepared. Substrate <NUM> is disposed in the dispersion, and phosphor particles <NUM> and filler particles <NUM> are deposited on substrate <NUM> by electrophoresis. By this, a layer containing phosphor particles <NUM> and filler particles <NUM> can be formed on substrate <NUM>. It is also possible to form a layer containing phosphor particles <NUM> and filler particles <NUM> on substrate <NUM> by disposing substrate <NUM> in the dispersion and precipitating phosphor particles <NUM> and filler particles <NUM>. It is also possible to form a layer containing phosphor particles <NUM> and filler particles <NUM> on substrate <NUM> using a coating solution containing phosphor particles <NUM> and filler particles <NUM> by a thin film forming method such as a printing method.

Next, matrix <NUM> is formed between the particles by a solution growth method using a solution containing Zn. Phosphor layer <NUM> is thus obtained. As the solution growth method, chemical bath deposition performed at the atmospheric pressure, hydrothermal synthesis performed at a pressure higher than the atmospheric pressure, and electrochemical deposition in which a voltage or a current is applied, and the like are used. As the solution for crystal growth, for example, an aqueous solution of zinc nitrate containing hexamethylenetetramine is used. Crystalline matrix <NUM> is epitaxially grown on thin film <NUM>. Phosphor layer <NUM> is thus obtained.

Next, phosphor layer <NUM> is placed in an atmosphere of sample gas. The sample gas contains at least one selected from the group consisting of H<NUM>S, Cl<NUM>, and SO<NUM>. ZnO contained in matrix <NUM> reacts with the sample gas in the vicinity of the surface of phosphor layer <NUM>. First protective layer <NUM> is thus formed. At this time, first protective layer <NUM> formed is in close contact with the surface of phosphor layer <NUM>. In other words, a gap is hardly formed between first protective layer <NUM> and phosphor layer <NUM>. Hence, reflection of light is suppressed at the interface between first protective layer <NUM> and phosphor layer <NUM>. First protective layer <NUM> is, for example, transparent and hardly absorbs visible light. In other words, high light output is achieved according to wavelength conversion member <NUM> fabricated by the above method. First protective layer <NUM> suppresses permeation of the sample gas. Hence, ZnO contained in matrix <NUM> hardly reacts with the sample gas after first protective layer <NUM> is formed.

The concentration of each of H<NUM>S, Cl<NUM>, and SO<NUM> in the sample gas may be in a range of <NUM> vol ppm to <NUM> vol ppm. The period during which phosphor layer <NUM> and the sample gas should be in contact with each other may be in a range of <NUM> day to <NUM> days. The temperature of the sample gas when the sample gas is brought into contact with phosphor layer <NUM> may be in a range of <NUM> to <NUM>.

First protective layer <NUM> may be fabricated by depositing at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM> on phosphor layer <NUM>. Examples of the method for depositing these compounds include a sputtering method, an ion plating method, an electron beam vapor deposition method, a vacuum vapor deposition method, a chemical vapor deposition method, and a chemical vapor phase deposition method.

As illustrated in <FIG>, wavelength conversion member <NUM> according to a second example includes second protective layer <NUM>. While this second example does not fully implement the claimed invention and mainly serves for illustrative purposes, parts of the disclosure herein may be used in connection with the claimed invention as will be described further below. The structure of wavelength conversion member <NUM> is the same as the structure of wavelength conversion member <NUM> of the first example except second protective layer <NUM>. Accordingly, elements common to wavelength conversion member <NUM> of the first example and wavelength conversion member <NUM> of the present example are denoted by the same reference numerals, and the description of the elements may be omitted. In other words, the following description regarding the respective examples can be applied to each other as long as there is no technical contradiction. Furthermore, the respective examples may be combined with each other as long as there is no technical contradiction.

Second protective layer <NUM> is disposed on phosphor layer <NUM> and first protective layer <NUM>. In detail, substrate <NUM>, phosphor layer <NUM>, first protective layer <NUM>, and second protective layer <NUM> are arranged in the thickness direction of wavelength conversion member <NUM> in this order. Second protective layer <NUM> covers the entire surface of phosphor layer <NUM>. Second protective layer <NUM> may only partially cover the surface of phosphor layer <NUM>. In wavelength conversion member <NUM>, the upper surface of first protective layer <NUM> is in contact with the lower surface of second protective layer <NUM>. Second protective layer <NUM> may not be disposed on first protective layer <NUM>. Second protective layer <NUM> may be disposed between phosphor layer <NUM> and first protective layer <NUM>.

Second protective layer <NUM> contains at least one selected from the group consisting of a silicone resin, a hybrid organic-inorganic material, and glass. The strength of wavelength conversion member <NUM> is improved by second protective layer <NUM>. The permeation of corrosive gas can also be further suppressed by second protective layer <NUM>. Second protective layer <NUM> may contain at least one selected from the group consisting of a silicone resin, a hybrid organic-inorganic material, and glass as a main component. The hybrid organic-inorganic material may be, for example, polysilsesquioxane having a siloxane bond. Second protective layer <NUM> may be composed substantially of glass. The thickness of second protective layer <NUM> is, for example, thinner than the thickness of phosphor layer <NUM>. The thickness of second protective layer <NUM> is, for example, in a range of <NUM> to <NUM> pm.

The method for fabricating second protective layer <NUM> is not particularly limited. For example, in a case in which second protective layer <NUM> contains a silicone resin, second protective layer <NUM> can be fabricated by the following method. First, a dispersion containing a silicone resin is prepared. The dispersion is applied to first protective layer <NUM> so that a coating film is formed on first protective layer <NUM>. Second protective layer <NUM> is formed by drying the coating film.

In a case in which second protective layer <NUM> contains a hybrid organic-inorganic material, second protective layer <NUM> can be fabricated by the following method. First, polysilsesquioxane is dissolved in benzyl alcohol, and a dispersion containing these is prepared. The dispersion is applied to first protective layer <NUM> so that a coating film is formed on first protective layer <NUM>. Second protective layer <NUM> is obtained by thermally curing the coating film.

In a case in which second protective layer <NUM> contains glass, second protective layer <NUM> can be fabricated by the following method. First, a sol containing a precursor such as silicon alkoxide is prepared. The sol is applied to first protective layer <NUM> so that a coating film is formed on first protective layer <NUM>. Second protective layer <NUM> is obtained by gelling and firing the coating film.

When second protective layer <NUM> is disposed between phosphor layer <NUM> and first protective layer <NUM>, first protective layer <NUM> is fabricated by, for example, depositing at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM> on second protective layer <NUM>.

As illustrated in <FIG>, wavelength conversion member <NUM> according to the present exemplary embodiment includes phosphor layer <NUM>, first protective layer <NUM>, and second protective layer <NUM>. The material for first protective layer <NUM> is the same as the material for first protective layer <NUM> described in the previous example. The material for second protective layer <NUM> is the same as the material for second protective layer <NUM> described in the previous example. Second protective layer <NUM> has a plurality of pinholes <NUM>. Pinholes <NUM> are through holes which penetrate second protective layer <NUM> in the thickness direction. The plurality of pinholes <NUM> overlap the upper surface of phosphor layer <NUM>. A plurality of first protective layers <NUM> are disposed on phosphor layer <NUM> in the plurality of pinholes <NUM>. In other words, the plurality of first protective layers <NUM> are in contact with phosphor layer <NUM> through the plurality of pinholes <NUM>. The lower surface of second protective layer <NUM> and each lower surface of the plurality of first protective layers <NUM> are in contact with the upper surface of phosphor layer <NUM>. In wavelength conversion member <NUM>, the each thickness of the plurality of first protective layers <NUM> is thinner than the thickness of second protective layer <NUM>.

The diameters of the plurality of pinholes <NUM> in plan view may be each in a range of <NUM> to <NUM>. The diameters of the plurality of pinholes <NUM> can be measured by, for example, observing the surface of second protective layer <NUM> under an electron microscope.

In wavelength conversion member <NUM>, each of second protective layer <NUM> and the plurality of first protective layers <NUM> can be fabricated as follows. First, second protective layer <NUM> is disposed on phosphor layer <NUM>. For the fabrication of second protective layer <NUM>, the method described above can be utilized. Second protective layer <NUM> fabricated by the method described above usually has the plurality of pinholes <NUM>. The plurality of pinholes <NUM> may be formed by irradiating second protective layer <NUM> with an ion beam. Phosphor layer <NUM> is exposed to the outside through the plurality of pinholes <NUM>.

Next, phosphor layer <NUM> on which second protective layer <NUM> is disposed is placed in an atmosphere of sample gas. ZnO contained in matrix <NUM> reacts with the sample gas in the vicinity of the surface of phosphor layer <NUM> exposed to the outside. The plurality of first protective layers <NUM> are thus formed in the plurality of pinholes <NUM> of second protective layer <NUM>.

As illustrated in <FIG>, light source <NUM> includes wavelength conversion member <NUM> (<NUM>, <NUM>) and light emitting element <NUM>. Phosphor layer <NUM> of wavelength conversion member <NUM> is located between light emitting element <NUM> and substrate <NUM> of wavelength conversion member <NUM>. Light source <NUM> is a reflective light source. Wavelength conversion member <NUM> described with reference to <FIG> and wavelength conversion member <NUM> described with reference to <FIG> can also be used instead of wavelength conversion member <NUM>. While using wavelength conversion member <NUM> described with reference to <FIG> or wavelength conversion member <NUM> described with reference to <FIG> does not fully implement the claimed invention but mainly serves for illustrative purposes, using wavelength conversion member <NUM> described with reference to <FIG> represents an exemplary embodiment of the claimed light source. A combination of these wavelength conversion members <NUM>, <NUM>, and <NUM> can also be used in light source <NUM>.

Light emitting element <NUM> radiates excitation light. Light emitting element <NUM> is typically a semiconductor light emitting element. The semiconductor light emitting element is, for example, a light emitting diode (LED), a super luminescent diode (SLD), or a laser diode (LD).

Light emitting element <NUM> may be composed of one LD or a plurality of LDs. The plurality of LDs may be optically coupled with each other. Light emitting element <NUM> radiates blue-violet light, for example. In the present disclosure, blue-violet light is light having a peak wavelength in a range of <NUM> to <NUM>.

Light source <NUM> further includes optical system <NUM>. Optical system <NUM> may be located on the optical path of the excitation light radiated from light emitting element <NUM>. Optical system <NUM> includes optical components such as a lens, a mirror, and an optical fiber.

As illustrated in <FIG>, lighting system <NUM> of the present exemplary embodiment includes light source <NUM> and optical component <NUM>. Optical component <NUM> is a component for guiding light radiated from light source <NUM> forward, and specifically, is a reflector. Optical component <NUM> has, for example, a metal film of Al, Ag or the like or an Al film having a protective film formed on the surface. Filter <NUM> may be provided in front of light source <NUM>. Filter <NUM> absorbs or scatters blue light so that coherent blue light from the light emitting element of light source <NUM> is not directly emitted to the outside. Lighting system <NUM> may be so-called reflector type or projector type. Lighting system <NUM> is, for example, a headlamp for vehicle.

The present disclosure will be specifically described based on Examples. However, the present disclosure is not limited by the following Examples at all.

First, a crystalline ZnO thin film was formed on the substrate main body. As the substrate main body, an Ag mirror with protective film (manufactured by KEIHIN KOMAKU KOGYO CO. ) was used. The protective film was SiO<NUM>. Phosphor particles were disposed on the ZnO thin film. The material for the phosphor particles was YAG (manufactured by NEMOTO & CO.

Next, a crystalline ZnO matrix was formed on the ZnO thin film by a solution growth method. A phosphor layer containing phosphor particles embedded in a ZnO matrix was thus formed. As the solution for crystal growth, an aqueous solution of zinc nitrate containing hexamethylenetetramine was used. The concentration of hexamethylenetetramine in the aqueous solution was <NUM> mol/L. The concentration of zinc nitrate in the aqueous solution was <NUM> mol/L. In this manner, a wavelength conversion member of Sample <NUM> was obtained.

A phosphor layer was fabricated on the substrate by the same method as in Sample <NUM>. Next, the phosphor layer was placed in an atmosphere of sample gas. The sample gas contained H<NUM>S, Cl<NUM>, and SO<NUM>. The concentration of H<NUM>S in the sample gas was <NUM> vol ppm. The concentration of Cl<NUM> in the sample gas was <NUM> vol ppm. The concentration of SO<NUM> in the sample gas was <NUM> vol ppm. The temperature of the sample gas was <NUM>. The humidity of the sample gas was <NUM>% RH. The phosphor layer and the sample gas were in contact with each other for <NUM> days. In this manner, a wavelength conversion member of Sample <NUM> was obtained.

The surface of the wavelength conversion member of each of Samples <NUM> and <NUM> was observed under a laser microscope. As the laser microscope, LEXT OLS4100 (manufactured by Olympus Corporation) was used. The laser microscope images attained are illustrated in <FIG>. As can be seen from <FIG>, the surface of the wavelength conversion member of Sample <NUM> was different from the surface of the wavelength conversion member of Sample <NUM>. From this, it is inferred that the wavelength conversion member of Sample <NUM> includes the first protective layer.

The wavelength conversion member of Sample <NUM> was analyzed using an electron beam microanalyzer. As the electron beam microanalyzer, JXA-8900R (manufactured by JEOL Ltd. ) was used. The analysis results are illustrated in <FIG>. In <FIG>, a graph showing the detection result of S atom and a graph showing the detection result of Cl atom are displayed side by side. The horizontal axis of the graph indicates the distance from the detection unit of the electron beam microanalyzer in the thickness direction of the wavelength conversion member. The vertical axis of the graph indicates the intensity of the detection signal. As can be seen from <FIG>, S atom and Cl atom were detected in a range surrounded by a broken line. The range surrounded by a broken line was <NUM>. In other words, the first protective layer of the wavelength conversion member of Sample <NUM> had a thickness of <NUM>.

A wavelength conversion member of Sample <NUM> was obtained by the same method as in Sample <NUM> except that the composition of the phosphor layer was changed. Specifically, Al<NUM>O<NUM> particles as filler particles were added to the phosphor layer. The volume ratio of the phosphor particles to the filler particles was adjusted so that the required chromaticity of light was attained. The ratio of the volume of the phosphor particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The ratio of the volume of the filler particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. Next, the wavelength conversion member obtained was irradiated with excitation light. LD was used as an excitation light source. The wavelength of the excitation light was <NUM>. The energy density of the excitation light was <NUM> kW/mm<NUM>. At this time, the luminescence intensity of light radiated from the wavelength conversion member and the CIE chromaticity coordinates of the light were measured using a luminance meter. As the luminance meter, an imaging color luminance meter LumiCam1300 (manufactured by Instrument Systems) was used. The color temperature of light was calculated based on the CIE chromaticity coordinates attained. Furthermore, the temperature of the surface of the phosphor layer contained in the wavelength conversion member was measured by infrared thermography. As the infrared thermography, FLIR T640 (manufactured by FLIR Systems Japan) was used. The results attained are presented in Table <NUM>.

A first protective layer was fabricated on the phosphor layer by the same method as in Sample <NUM> except that the composition of the phosphor layer was changed. In detail, the volume ratio of the phosphor particles to the filler particles was adjusted so that the required chromaticity of light was attained. The ratio of the volume of the phosphor particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The ratio of the volume of the filler particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. Next, a sol containing tetraethyl orthosilicate was prepared. The sol was applied to the first protective layer so that a coating film was formed on the first protective layer. The coating film was gelled and fired to cure the coating film, and a second protective layer was thus formed on the first protective layer. Firing was performed at <NUM> for <NUM> hours. The second protective layer was composed of glass. In this manner, a wavelength conversion member of Sample <NUM> was obtained. The wavelength conversion member of Sample <NUM> was irradiated with excitation light by the same method as in Sample <NUM>. At this time, the luminescence intensity of the light radiated from the wavelength conversion member, the CIE chromaticity coordinates of the light, the color temperature of the light, and the temperature of the surface of the phosphor particles contained in the wavelength conversion member were measured or calculated. The results attained are presented in Table <NUM>.

A phosphor layer was fabricated on the substrate by the same method as in Sample <NUM> except that the composition of the phosphor layer was changed. Specifically, Al<NUM>O<NUM> particles as filler particles were added to the phosphor layer. The volume ratio of the phosphor particles to the filler particles was adjusted so that the required chromaticity of light was attained. The ratio of the volume of the phosphor particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The ratio of the volume of the filler particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. Next, a second protective layer was fabricated on the phosphor layer. The second protective layer was fabricated by the same method as in Sample <NUM>. Next, the phosphor layer was placed in an atmosphere of sample gas. The composition of the sample gas, the temperature of the sample gas, the humidity of the sample gas, and the period during which the phosphor layer was in contact with the sample gas were the same as those in Sample <NUM>. A plurality of first protective layers were thus formed on the phosphor layer in a plurality of pinholes of the second protective layer. In this manner, a wavelength conversion member of Sample <NUM> was obtained. The wavelength conversion member of Sample <NUM> was irradiated with excitation light by the same method as in Sample <NUM>. At this time, the luminescence intensity of the light radiated from the wavelength conversion member, the CIE chromaticity coordinates of the light, the color temperature of the light, and the temperature of the surface of the phosphor particles contained in the wavelength conversion member were measured or calculated. The results attained are presented in Table <NUM>.

A wavelength conversion member of Sample <NUM> was obtained by the same method as in Sample <NUM> except that the composition of the phosphor layer was changed. Specifically, Al<NUM>O<NUM> particles as filler particles were added to the phosphor layer. The volume ratio of the phosphor particles to the filler particles was adjusted so that the required chromaticity of light was attained. The ratio of the volume of the phosphor particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The ratio of the volume of the filler particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The wavelength conversion member of Sample <NUM> was irradiated with excitation light by the same method as in Sample <NUM>. At this time, the luminescence intensity of the light radiated from the wavelength conversion member, the CIE chromaticity coordinates of the light, the color temperature of the light, and the temperature of the surface of the phosphor particles contained in the wavelength conversion member were measured or calculated. The results attained are presented in Table <NUM>.

First, a mixed sol containing tetraethyl orthosilicate, phosphor particles, and filler particles was prepared. The material for the phosphor particles was YAG (manufactured by NEMOTO & CO. The filler particles were Al<NUM>O<NUM> particles. Next, the mixed sol was applied to the substrate so that a coating film was formed on the substrate. As the substrate, an Ag mirror with protective film (manufactured by KEIHIN KOMAKU KOGYO CO. ) was used. Next, the phosphor layer was formed by drying and firing the coating film. In this manner, a wavelength conversion member of Sample <NUM> was obtained. The phosphor layer of the wavelength conversion member of Sample <NUM> had a glass matrix instead of a ZnO matrix. The glass matrix contained silicone as a main component. The ratio of the volume of the phosphor particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The ratio of the volume of the filler particles to the total value of the volume of the phosphor particles and the volume of the filler particles was <NUM> vol%. The wavelength conversion member of Sample <NUM> was irradiated with excitation light by the same method as in Sample <NUM>. At this time, the luminescence intensity of the light radiated from the wavelength conversion member, the CIE chromaticity coordinates of the light, the color temperature of the light, and the surface temperature of the phosphor particles contained in the wavelength conversion member were measured or calculated. The results attained are presented in Table <NUM>.

The wavelength conversion member of each of Samples <NUM> to <NUM> was placed in an atmosphere of corrosive gas. The corrosive gas contained H<NUM>S, Cl<NUM>, NO<NUM>, and SO<NUM>. The concentration of H<NUM>S in the corrosive gas was <NUM> vol ppm. The concentration of Clz in the corrosive gas was <NUM> vol ppm. The concentration of NO<NUM> in the corrosive gas was <NUM> vol ppm. The concentration of SO<NUM> in the corrosive gas was <NUM> vol ppm. The temperature of the corrosive gas was <NUM>. The humidity of the corrosive gas was <NUM>% RH. The wavelength conversion member and the corrosive gas were in contact with each other for <NUM> days.

The wavelength conversion member of each of Samples <NUM> to <NUM> was irradiated with excitation light after being in contact with the corrosive gas. At this time, the CIE chromaticity coordinates of light radiated from the wavelength conversion member was measured using a luminance meter. The color temperature of light was calculated based on the CIE chromaticity coordinates attained. The results attained are presented in Table <NUM>.

In Table <NUM>, it was judged that the characteristics of the wavelength conversion member were practically sufficient (o) in a case in which the temperature of the phosphor surface was less than or equal to <NUM> and the change in color temperature of light before and after contact with the corrosive gas was in a range of <NUM>. It was judged that the characteristics of the wavelength conversion member were insufficient (x) in a case in which the temperature of the phosphor surface or the change in color temperature of light did not satisfy the above requirement.

<FIG> illustrate changes in CIE chromaticity coordinates of light radiated from the wavelength conversion members of Samples <NUM>, <NUM> and <NUM>, respectively. In the graph of each of <FIG>, a square mark indicates the CIE chromaticity coordinates of light radiated from the wavelength conversion member before being brought into contact with the corrosive gas. A circular mark indicates the CIE chromaticity coordinates of light radiated from the wavelength conversion member after being brought into contact with the corrosive gas. The color temperature range of <NUM> to <NUM> is surrounded by a closing line. A dotted line indicates the relation between the chromaticity and color temperature of the light radiated from a black body.

As can be seen from <FIG>, the chromaticity of light radiated from the wavelength conversion member of Sample <NUM> hardly changed before and after contact with the corrosive gas. In other words, the wavelength conversion member of Sample <NUM> exhibited high reliability. The wavelength conversion member of Sample <NUM> also exhibited high reliability in the same manner as in Sample <NUM>.

As can be seen from <FIG>, the change in color temperature of light before and after contact with the corrosive gas was in a range of <NUM> in the wavelength conversion member of Sample <NUM>. In other words, the wavelength conversion member of Sample <NUM> exhibited practically sufficient reliability.

As can be seen from <FIG>, the chromaticity of light radiated from the wavelength conversion member of Sample <NUM> greatly changed before and after contact with the corrosive gas. The reliability of the wavelength conversion member of Sample <NUM> was inferior to the reliability of the wavelength conversion member of Samples <NUM> to <NUM>.

As can be seen from the results in Table <NUM>, the temperature (<NUM>) of the surface of the phosphor contained in the wavelength conversion member of Sample <NUM> was higher than the temperature of the surface of Samples <NUM> to <NUM>. The luminescence intensity of the light radiated from the wavelength conversion member decreases in a case in which the temperature of the surface of the phosphor is high. The luminescence intensity of the light radiated from the wavelength conversion member of Sample <NUM> was lower than the luminescence intensity in Samples <NUM> to <NUM>.

Claim 1:
A wavelength conversion member (<NUM>) comprising:
a substrate (<NUM>),
a phosphor layer (<NUM>) formed on the substrate (<NUM>), the phosphor layer (<NUM>) having a matrix (<NUM>) containing ZnO and phosphor particles (<NUM>) embedded in the matrix (<NUM>);
a first protective layer (<NUM>) that contains at least one selected from the group consisting of ZnCl<NUM>, ZnS, and ZnSO<NUM>, and covers the phosphor layer (<NUM>);
a second protective layer (<NUM>) that contains at least one selected from the group consisting of a silicone resin, a hybrid organic-inorganic material, and glass and covers the phosphor layer (<NUM>), the second protective layer (<NUM>) having a plurality of pinholes (<NUM>); and
wherein a plurality of the first protective layers (<NUM>) are disposed on the phosphor layer (<NUM>) in the plurality of the pinholes (<NUM>), and
the ZnO is c-axis-oriented polycrystalline ZnO.