Patent Description:
A phosphor formed of YAG-based single crystal is known (see, e.g., <CIT>). According to <CIT>, the phosphor formed of the single crystal has excellent temperature characteristics in that a decrease in fluorescence intensity associated with temperature increase is less than ceramic powder phosphor.

Also, a light-emitting device is known which uses a particulate single crystal phosphor obtained by pulverizing a YAG-based single crystal ingot (see, e.g., <CIT> and <CIT>). <CIT> discloses a single-crystal phosphor which can exhibit excellent properties under high-temperature conditions; and a light-emitting device in which the phosphor is used. As one embodiment, a single-crystal phosphor is provided, which has a chemical composition represented by the compositional formula: (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM> ≤ x ≤ <NUM>, <NUM> ≤ y ≤ <NUM>, <NUM> ≤ z ≤ <NUM>, -<NUM> ≤ a ≤ <NUM>). <CIT>discloses a YAG-based single crystal phosphor which produces fluorescence of a non-conventional color; and a phosphor-containing member and a light emitting device, each of which is provided with this single crystal phosphor. Provided as one embodiment is a single crystal phosphor which has a composition represented by composition formula (Y<NUM>-a-bLuaCeb)<NUM>+cAl<NUM>-cO1<NUM> (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM> and -<NUM> ≤ c ≤ <NUM>), and which has an emission spectrum having CIE chromaticity coordinates x and y satisfying the relation -<NUM>. 4377x + <NUM> ≤ y ≤ -<NUM>. 4585x + <NUM> when the peak wavelength of the excitation light is <NUM> at the temperature of <NUM>. <NPL>, discloses single crystal phosphor plates (SCPPs) using Czochralski grown Ce and Gd-doped Y<NUM>Al<NUM>O<NUM> (Ce,Gd:YAG) single crystal in a new concept of white LED. The new concept realizes epoxy resin free package and eliminates photodegradation issue. SCPP showed superior stability under the high temperatures, irradiation and current. Quantum efficiency of SCPP was found to be as high as <NUM>%.

It is an object of the invention to further improve the emission intensity and emission properties under high-temperature conditions of a particulate YAG-based or LuAG-based single crystal phosphor by optimizing a composition in the state of particles, and thereby to provide a phosphor-including member comprising a particulate phosphor that includes a YAG-based or LuAG-based single crystal and that is excellent in emission intensity and, particularly, excellent in emission properties under high-temperature conditions, as well as a production method thereof, , and a light-emitting device or projector including the phosphor-including member.

The present invention is defined in independent claims <NUM> and <NUM>. The dependent claims define embodiments of the invention.

According to an embodiment of the invention, a phosphor-including member comprising a particulate phosphor can be provided that includes a YAG-based or LuAG-based single crystal and that is excellent in external quantum efficiency and excellent in emission properties under high-temperature conditions, as well as a production method thereof, and a light-emitting device or projector including the phosphor-including member.

The single crystal phosphor in the first embodiment is a YAG-based or LuAG-based single crystal phosphor of which base crystal is a Y<NUM>Al<NUM>O<NUM> (YAG)-based crystal or a Lu<NUM>Al<NUM>O<NUM> (LuAG)-based crystal and which has a composition represented by a compositional formula (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, -<NUM>≤a≤<NUM>). Lu and Gd here are components which are substituted in the Y site but do not serve as emission centers. Ce is a component which can be substituted in the Y site and can serve as an emission center (an activator).

Meanwhile, of the above-mentioned composition of the single crystal phosphor, some atoms may be in different positions in the crystal structure. Also, although the composition ratio of O in the above compositional formula is <NUM>, the above-mentioned composition also includes compositions with an O composition ratio slightly different from <NUM> due to presence of inevitably mixed oxygen or oxygen deficiency. Also, the value of "a" in the compositional formula is a value which inevitably varies in the production of the single crystal phosphor, but variation within the numerical range of about -<NUM> ≦a≦ <NUM> has little effect on physical properties of the single crystal phosphor.

Also, the phosphor in the first embodiment is characterized in that Group II elements such as Ba or Sr and Group XVII elements such as F or Br are not contained and purity is high. These characteristics allow the phosphor to have higher brightness and longer life.

The reason why the numerical value of z representing the Ce concentration in the compositional formula is in a range of <NUM> ≦z≦ <NUM> is as follows: when the numerical value of z is less than <NUM>, there is a problem that absorption by the particulate single crystal phosphor is reduced and external quantum efficiency is thus reduced, resulting in a decrease in emission intensity. On the other hand, when z is more than <NUM>, high-temperature characteristics of the particulate single crystal phosphor degrade. For example, the internal quantum efficiency of phosphor at, e.g., <NUM>°C becomes less than <NUM>. The Ce concentration of <NUM> ≦z≦<NUM> is an optimized range for the particulate single crystal phosphor and is different from a Ce concentration range suitable for, e.g., a plate-shaped single crystal phosphor.

Also, the phosphor in the first embodiment is a particulate single crystal phosphor having a particle diameter (D<NUM>) of not less than <NUM> µm. D<NUM> here is a particle diameter at <NUM> vol% in the cumulative distribution.

When the particle diameter is increased, the surface area relative to volume is reduced and external quantum efficiency is thereby improved.

Also, in case that particulate phosphor is sealed with a transparent sealing member, the volume ratio of the phosphor to the material of the sealing member increases with increasing the particle diameter of the phosphor. Sealing material generally has a lower thermal conductivity than phosphor and thus causes thermal resistance to increase. Therefore, by increasing the volume ratio of the phosphor to the material of the sealing member, it is possible to reduce thermal resistance of the whole (the sealing member including the phosphor).

Meanwhile, known YAG polycrystalline phosphors are synthesized by solid-state reaction of oxide powder raw materials such as Y<NUM>O<NUM>, Al<NUM>O<NUM> and CeO<NUM>, and it is thus difficult to produce phosphor with a large particle diameter of not less than about <NUM> to <NUM> µm. On the other hand, the single crystalline YAG phosphor in the first embodiment is made by pulverizing a melt-grown ingot of single crystal phosphor, and thus can have even a particle diameter of not less than <NUM> µm.

In pulverizing the ingot, it is possible to use known pulverizing equipment such as roller mill, ball mill or jet mill. A mortar and pestle may be used when pulverizing a small amount. A material of the members coming into a contact with YAG, such as mills or balls, of the pulverizing equipment is preferably a material with high hardness, is most preferably a single crystalline YAG in view of contamination, but may be high-purity aluminum in view of productivity.

<FIG> is a graph showing a relation between particle diameter (D<NUM>) of YAG phosphor and thermal resistance. In the graph shown in <FIG>, a point plotted at D<NUM> of <NUM> µm is data from a known sintered YAG phosphor, and other points are data from a particulate single crystalline YAG phosphor in the first embodiment (obtained by pulverizing a region of a single crystal phosphor ingot in which composition distribution is in a range from (Y<NUM>Ce<NUM>)<NUM>Al<NUM>Ox to (Y<NUM>Ce<NUM>)<NUM>Al<NUM>Ox). The vertical axis in <FIG> is thermal resistance of <NUM> µm-thick films containing the respective fluorescent bodies sealed with a SiO<NUM>-based inorganic sealing material and indicates a relative value when the thermal resistance value of the sealing film with the known sintered YAG phosphor is defined as <NUM>. The thickness of the sealing film containing a phosphor with D<NUM> of <NUM> µm is <NUM> µm.

As shown in <FIG>, for example, thermal resistance can be reduced less than that of when containing the known YAG sintered phosphor by adjusting a particle diameter (D<NUM>) of the phosphor to <NUM> µm and can be reduced to half or less than half the thermal resistance of when containing the known YAG phosphor by adjusting to <NUM> µm. The present inventors also conducted experiments and confirmed that thermal resistance of a <NUM> µm-thick single crystalline YAG plate not containing a binder such as inorganic sealing material is about <NUM>, and a particulate phosphor when having a particular size of about <NUM> to <NUM> µm can realize thermal resistance substantially equivalent to that of the single crystalline YAG plate.

Also, a decrease in fluorescence intensity associated with temperature increase is smaller in the YAG-based single crystal phosphor than in the YAG-based polycrystalline phosphor made by the sintering method, etc., as described previously. The small decrease in fluorescence intensity results from a small decrease in internal quantum efficiency. The same applies to the LuAG-based single crystal phosphor.

The phosphor in the first embodiment is more suitable for use under high-temperature conditions due to having excellent emission properties under high-temperature conditions which are inherent to the YAG-based or LuAG-based single crystal phosphor, as well as due to having an effect of reducing thermal resistance of a phosphor-including member by controlling the particle diameter. The phosphor can be very functional when used in, e.g., a light-emitting device having very high brightness per unit area, such as laser projector or laser headlight using laser light as excitation light. Also, since the phosphor in the first embodiment is in the form of particles, it is effective to increase light scattering and it is thereby possible to realize more uniform emission intensity and emission color.

Meanwhile, the known YAG-based or LuAG-based powder phosphor is polycrystalline powder made by the sintering method and has a particle diameter D<NUM> = <NUM> to <NUM> µm. Since YAG-based or LuAG-based compounds have very high melting points, D<NUM> of not less than <NUM> µm is very difficult to achieve by the sintering method, which is based on the solid-state reaction, due to temporal and qualitative limits.

Also, when the phosphor in the first embodiment is used for white lighting, etc., the particle diameter (D<NUM>) is preferably not more than <NUM> µm. This is because when more than <NUM> µm, yellow as a fluorescent color of the phosphor becomes too intense and it may be difficult to obtain white light with a desired chromaticity.

The particulate phosphor is obtained by pulverizing a single crystal phosphor ingot grown by a method in which a crystal is pulled upward from a source melt, such as CZ method (Czochralski method), EFG method (Edge-Defined Film-Fed Growth Method) or Bridgman method.

Next, an example of a method for producing the phosphor in the first embodiment will be described in detail. A single crystal phosphor is grown by the CZ method in the following example.

Firstly, powders of Y<NUM>O<NUM>, Lu<NUM>O<NUM>, Gd<NUM>O<NUM>, CeO<NUM> and Al<NUM>O<NUM> each having a high purity (not less than <NUM>%) are prepared as starting materials and are dry-blended, thereby obtaining a mixture powder. Meanwhile, the raw material powders of Y, Lu, Gd, Ce and Al are not limited to those mentioned above. Also, when producing a single crystal phosphor not containing Lu or Gd, the raw material powders thereof are not used.

<FIG> is a schematic cross-sectional view showing how a single crystal phosphor ingot is pulled upward in the CZ method. A crystal growth system <NUM> is provided primarily with an iridium crucible <NUM>, a ceramic cylindrical container <NUM> housing the crucible <NUM>, and a high-frequency coil <NUM> wound around the cylindrical container <NUM>.

The obtained mixture powder is loaded into the crucible <NUM>, a high-frequency energy of <NUM> kW is supplied to the crucible <NUM> by the high-frequency coil <NUM> in a nitrogen atmosphere to generate an induced current, and the crucible <NUM> is thereby heated. The mixture powder is melted and a melt <NUM> is thereby obtained.

Next, a seed crystal <NUM> which is a YAG single crystal is prepared, the tip thereof is brought into contact with the melt <NUM>, and the seed crystal <NUM> is pulled upward at a pulling rate of not more than <NUM> mm/h and rotated simultaneously at a rotation speed of <NUM> rpm at a pull-up temperature of not less than <NUM>° C, thereby growing a single crystal phosphor ingot <NUM> oriented to the <<NUM>> direction. The single crystal phosphor ingot <NUM> is grown in a nitrogen atmosphere at atmospheric pressure in a state that nitrogen is being supplied at a flow rate of <NUM> L/min into the cylindrical container.

The single crystal phosphor ingot <NUM> formed of a single crystal having a composition represented by the compositional formula (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, -<NUM>≤a≤<NUM>) is thereby obtained. The size of the single crystal phosphor ingot <NUM> is, e.g., about <NUM> cm in diameter and about <NUM> cm in length.

In the YAG-based or LuAG-based single crystal phosphor, Ce has a significantly larger ionic radius than Y in the YAG-based or LuAG-based single crystal as a base crystal and is thus less likely to be incorporated into the crystal. Therefore, when the YAG-based or LuAG-based single crystal phosphor is grown by a pulling-up method such as CZ (Czochralski) method, the Ce concentration in the source melt increases as the crystal grows, hence, the YAG-based or LuAG-based single crystal phosphor has a Ce concentration distribution gradient such that the Ce concentration decreases toward the direction of pulling up the crystal. In other words, the Ce concentration in the YAG-based or LuAG-based single crystal phosphor increases from the seed (the seed crystal) toward the tail.

<FIG> is a schematic diagram illustrating the grown single crystal phosphor ingot <NUM>. In the single crystal phosphor ingot <NUM>, the Ce concentration increases from the seed crystal <NUM> toward a tail <NUM>.

In the first embodiment, a region of the single crystal phosphor ingot <NUM> in which z representing the Ce concentration in the compositional formula is, e.g., <NUM>≤z≤<NUM> is cut out as a pulverizing region <NUM>. In the pulverizing region <NUM>, z representing the Ce concentration in the compositional formula is distributed continuously between <NUM> and <NUM> along the pull-up direction of the single crystal phosphor ingot <NUM>. To be precise, this continuity of Ce concentration distribution is relevant to the effective segregation coefficient defined by <FIG> and Formula <NUM> (see below) described in "<NPL>". The Ce concentration is measured by the ICP-MS method, etc.<MAT>.

In the formula <NUM>, "Ccrystal" represents Ce concentration in crystal, "Cmelt" represents initial Ce concentration in melt, "keff" represents effective segregation coefficient, and "g" represents solidification rate (weight of crystal/initial weight of melt).

Next, the pulverizing region <NUM> is pulverized and the particulate phosphor is obtained. Needless to say, this particulate phosphor has the same composition as the pulverizing region <NUM>.

When z in the compositional formula of the pulverizing region <NUM> is, e.g., <NUM>≤z≤<NUM> and is continuously distributed in the range of not less than <NUM> and not more than <NUM>, z in the compositional formula of each particle of the particulate phosphor obtained by pulverizing the pulverizing region <NUM> is <NUM>≤z≤<NUM>, and z in the compositional formula of the particulate phosphor group is continuously distributed in the range of not less than <NUM> and not more than <NUM>.

Emission color of phosphor changes depending on the Ce concentration. In detail, as the Ce concentration increases, the CIE chromaticity (x, y) shift from, e.g., yellow region to red region when the phosphor does not contain Lu in the Y site, and shift green region to yellow region when Lu is contained in the Y site.

Thus, when the Ce concentration of the compositional formula of the particulate single crystal phosphor group is continuously distributed in a predetermined range, the full width at half maximum of emission spectrum increases and color rendering properties are improved as compared to when the Ce concentration is constant.

Preferably, z in the compositional formula of each particle of the particulate phosphor is <NUM>≤z≤<NUM>, and z in the compositional formula of the particulate phosphor group is continuously distributed in the range of not less than <NUM> and not more than <NUM>. More preferably, z in the compositional formula of each particle of the particulate phosphor is <NUM>≤z≤<NUM>, and z in the compositional formula of the particulate phosphor group is continuously distributed in the range of not less than <NUM> and not more than <NUM>.

In general, Ce-containing powder phosphor made by the sintering method, etc., also has a certain level of Ce concentration distribution. However, this distribution is due to deviation from a desired Ce concentration and is normal distribution. On the other hand, the Ce concentration distribution in the particulate single crystal phosphor obtained by pulverizing a single crystal phosphor ingot in the first embodiment is not normal distribution.

Also, the pulverizing region <NUM> does not need to be the nearly entire region of the single crystal phosphor ingot <NUM>. When z in the compositional formula of the single crystal phosphor ingot <NUM> is, e.g., <NUM> in a portion close to an end on the seed crystal <NUM> side and <NUM> in a portion close to an end on the tail <NUM> side, a region with z distributed in a range of not less than <NUM> and not more than <NUM> may be cut out as the pulverizing region <NUM> from the single crystal phosphor ingot <NUM>. The particulate single crystal phosphor obtained from the pulverizing region <NUM> in this case has the CIE chromaticity (x, y) closer to red than the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of not less than <NUM> and not more than <NUM>.

Then, the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of, e.g., not less than <NUM> and not more than <NUM> has the CIE chromaticity (x, y) closer to green than the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of not less than <NUM> and not more than <NUM>.

Furthermore, the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of, e.g., not less than <NUM> and not more than <NUM> has the CIE chromaticity (x, y) between the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of not less than <NUM> and not more than <NUM> and the particulate single crystal phosphor obtained from the pulverizing region <NUM> with z distributed in a range of not less than <NUM> and not more than <NUM>.

Also, if a difference between the maximum value and the minimum value of z in the compositional formula of the pulverizing region <NUM> is not less than <NUM>, it is effective to increase the full width at half maximum of fluorescence spectrum and it is also possible to increase the usable region of the single crystal phosphor ingot <NUM>, allowing for reduction of the production cost of the phosphor.

Furthermore, absorption by the particulate single crystal phosphor obtained by pulverizing a single crystal phosphor ingot can be significantly improved by treating with hydrofluoric acid.

<FIG> is a graph showing changes in absorption before and after treating a particulate single crystal phosphor (obtained by pulverizing a region of a single crystal phosphor ingot in which composition distribution is in a range from (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>Ox to (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>Ox) with hydrofluoric acid.

In detail, in the hydrofluoric acid treatment, a surface of the particulate single crystal phosphor is etched with <NUM>% hydrofluoric acid at <NUM>°C for one hour.

<FIG> shows that absorption by the particulate single crystal phosphor is significantly improved by the hydrofluoric acid treatment. Based on the fact that external quantum efficiency largely related to emission intensity of phosphor is indicated by a value obtained by multiplying internal quantum efficiency by absorption, it can be said that emission intensity of the particulate single crystal phosphor is significantly improved by the hydrofluoric acid treatment.

<FIG> are SEM (Scanning Electron Microscope) images showing the particulate single crystal phosphor respectively before and after hydrofluoric acid treatment.

The single crystal phosphor after hydrofluoric acid treatment shown in <FIG> consists of particles each having rounded edges and has more curved surfaces than the single crystal phosphor before hydrofluoric acid treatment shown in <FIG>. It is considered that since the surfaces of the particles of the single crystal phosphor are curved as such, light reflection at the surface is reduced and absorption is improved. It is also considered that pulverizing has an effect of removing a crystal defect layer formed on the phosphor surface. Also, the rounded shape of the phosphor has such an effect that dispersibility when being dispersed in an inorganic sealing material is increased, the density of the phosphor in the film is improved, and thermal resistance is reduced.

The second embodiment of the invention is a light-emitting device using the single crystal phosphor in the first embodiment.

<FIG> is a schematic diagram illustrating a light source unit of a laser headlight <NUM> as a light-emitting device in the second embodiment. The laser headlight <NUM> has three laser diodes <NUM> each having a collimating lens <NUM>, a condenser lens <NUM> for condensing blue laser light emitted from the laser diodes <NUM>, a phosphor-including member <NUM> absorbing light condensed by the condenser lens <NUM> and emitting fluorescent light, and a mirror <NUM> reflecting the fluorescent light emitted from the phosphor-including member <NUM> and distributing light toward the front of the laser headlight <NUM>. The laser headlight <NUM> is configured that white light is obtained by mixing blue light emitted from the laser diodes <NUM> and yellow light emitted from the phosphor-including member <NUM>.

<FIG> are a cross sectional view and a plan view showing the phosphor-including member <NUM> in the second embodiment. The phosphor-including member <NUM> has a substrate 24a, a sealing material 24b formed on a surface of the substrate 24a, and a particulate phosphor 24c sealed in the sealing material 24b.

The substrate 24a is a substrate having a highly reflective surface, such as mirror substrate. Also, the substrate 24a is preferably connected to a highly thermally conductive radiator formed of Cu or Al, etc. The planar shape of the substrate 24a is not specifically limited.

The sealing material 24b is formed of a transparent inorganic material such as glass, SiO<NUM>-based or Al<NUM>O<NUM>-based material, and thus has excellent heat resistance as compared to a sealing material formed of an organic material such as silicone. The planar shape of the sealing material 24b may be a square as shown in <FIG>, or may be a circle as shown in <FIG>.

The phosphor 24c is a phosphor formed of a particulate YAG-based or LuAG-based single crystal in the first embodiment, i.e., is a particulate phosphor which is formed of a single crystal having a composition represented by the compositional formula (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, -<NUM>≤a≤<NUM>) and has a particle diameter (D<NUM>) of not less than <NUM> µm.

The phosphor 24c is also a particulate phosphor group of which z in the compositional formula is, e.g., <NUM>≤z≤<NUM> and is continuously distributed between <NUM> and <NUM>.

Thus, the phosphor 24c has excellent emission properties under high-temperature conditions and can stably and efficiently emit fluorescent light even when the high-power laser diodes <NUM> are used as sources of excitation light.

The third embodiment of the invention is a projector using the single crystal phosphor in the first embodiment.

<FIG> is a schematic diagram illustrating a configuration of a projector <NUM> in the third embodiment. The projector <NUM> has a blue laser diode <NUM> as a light source, a phosphor-including member <NUM> which is excited by absorbing a portion of blue light emitted from the laser diode <NUM> and passing through a condenser lens <NUM> and emits yellow fluorescent light, a lens <NUM> for aligning the traveling direction of white light obtained by combining the yellow fluorescent light emitted from the phosphor-including member <NUM> and blue light transmitted without being absorbed by the phosphor-including member <NUM>, a dichroic mirror 35a filtering white light passing through the lens <NUM> to allow for transmission of blue light and reflect the other light, a dichroic mirror 35b filtering the light reflected by the dichroic mirror 35a to allow for transmission of red light and reflect green light as the other light, a mirror 36a reflecting the blue light transmitted through the dichroic mirror 35a, mirrors 36b and 36c reflecting the red light transmitted through the dichroic mirror 35b, a liquid-crystal panel 37a driven and controlled to form a desired image and allowing the blue light reflected by the mirror 36a to be transmitted in a desired pattern, a liquid-crystal panel 37b driven and controlled to form a desired image and allowing the green light reflected by the dichroic mirror 35b to be transmitted in a desired pattern, a liquid-crystal panel 37c driven and controlled to form a desired image and allowing the red light reflected by the mirror 36c to be transmitted in a desired pattern, a prism <NUM> synthesizing the blue, green and red lights transmitted through the liquid-crystal panels 37a, 37b and 37c, and a lens <NUM> for spreading out the light synthesized by the prism <NUM> and emitting the light as an image onto an external screen <NUM>.

The lens <NUM>, the dichroic mirrors 35a, 35b, the mirrors 36a, 36b, 36c, the liquid-crystal panels 37a, 37b, 37c and the prism <NUM> constitute an image-forming section which forms an image by processing fluorescent light emitted from the phosphor-including member <NUM> and light emitted from the laser diode <NUM> in the projector <NUM>. That is, the projector <NUM> is configured that an image formed by the image-forming section using fluorescent light emitted from the phosphor-including member <NUM> is projected onto the external screen <NUM>.

<FIG> are plan views showing the phosphor-including member <NUM> in the third embodiment. The phosphor-including member <NUM> has a disc-shaped transparent substrate 33a, an annular sealing material 33b formed on a surface of the transparent substrate 33a along the outer periphery thereof, and a particulate phosphor 33c sealed in the sealing material 33b.

The transparent substrate 33a is formed of, e.g., sapphire having a high thermal conductivity and is placed inside the projector <NUM> so as to be rotatable in the circumferential direction.

The sealing material 33b is formed of a transparent inorganic material such as glass, SiO<NUM>-based or Al<NUM>O<NUM>-based material, and thus has excellent heat resistance as compared to a sealing material formed of an organic material such as silicone.

The phosphor 33c is a phosphor formed of a particulate YAG-based or LuAG-based single crystal in the first embodiment, i.e., is a particulate phosphor which is formed of a single crystal having a composition represented by the compositional formula (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, -<NUM>≤a≤<NUM>) and has a particle diameter (D<NUM>) of not less than <NUM> µm.

The phosphor 33c is also a particulate phosphor group of which z in the compositional formula is, e.g., <NUM>≤z≤<NUM> and is continuously distributed between <NUM> and <NUM>.

Thus, the phosphor 33c has excellent emission properties under high-temperature conditions and can stably and efficiently emit fluorescent light even when the high-power laser diode <NUM> is used as a source of excitation light.

Also, since the phosphor-including member <NUM> rotates when the projector <NUM> is in operation, an illuminated position 33d of the blue light emitted from the laser diode <NUM> changes constantly, allowing heat rise in the phosphor-including member <NUM> to be prevented. Therefore, operation under high-temperature conditions is further stabilized.

Also, since the phosphor 33c is excellent in emission properties at high temperature, a phosphor-including member of stationary type can be used in some cases in place of the rotary type as is the phosphor-including member <NUM>. It is difficult to use the known polycrystalline phosphors in such a way since thermal quenching occurs unless having excellent emission properties at high temperature.

Also, such stationary phosphor-including member may be of transmissive type as is the phosphor-including member <NUM> using a transparent substrate, or may be of reflective type. The reflective phosphor-including member has, e.g., the same structure as the phosphor-including member <NUM> shown in <FIG>. In this case, a highly-reflective metal substrate such as Ag or Al substrate is preferably used as the substrate 24a. Alternatively, a surface of a metal substrate may be coated with a highly-reflective Ag- or Al-based material, etc..

Meanwhile, in the projector <NUM>, the light-emitting element used as a light source may be an LED in place of the laser diode <NUM>. However, the effect by the phosphor-including member <NUM>, i.e., excellent emission properties under high-temperature conditions, is exerted more significantly when using a high-power laser diode.

Also, although the projector <NUM> is a projector having a configuration in which a spectrum of yellow emission from phosphor is dispersed into green spectrum and red spectrum, the single crystal phosphor in the first embodiment can be used in a projector having a configuration in which green spectrum is directly extracted from a spectrum of green emission from phosphor. Also, the single crystal phosphor in the first embodiment can be used regardless of the configuration of the image-forming section of the projector.

According to the embodiment, it is possible to obtain a particulate phosphor which is formed of a YAG-based or LuAG-based single crystal and has excellent external quantum efficiency and excellent emission properties under high-temperature conditions. Also, by using such particulate phosphor, it is possible to manufacture light-emitting device and projector which are excellent in operating performance and reliability.

Ce concentration distribution in the single crystal phosphor ingot <NUM> of the first embodiment was examined in Example <NUM>.

Table <NUM> below is data from the single crystal phosphor ingot <NUM> grown by the CZ method and containing Lu in the Y site and shows a relation among distance from an interface with the seed crystal <NUM> in a direction parallel to the growth direction, value of z representing the Ce concentration in the compositional formula, CIE chromaticity coordinate x, and CIE chromaticity coordinate y.

Table <NUM> shows that as the distance from the interface with the seed crystal <NUM> increases, the Ce concentration increases and the fluorescent color shifts from green to yellow.

Temperature dependence of emission properties of the phosphor-including member shown in <FIG> was examined in Example <NUM>.

In the phosphor-including member in Example <NUM>, an Al substrate was used as the substrate, a SiOx-based inorganic sealing material was used as the sealing material, and the particulate single crystal phosphor in the first embodiment having a particle diameter (D<NUM>) of about <NUM> µm was used as the phosphor.

<FIG> is a schematic diagram illustrating a configuration of a test optical system in Example <NUM>. The test optical system has a blue laser diode array <NUM> as a light source, a phosphor-including member <NUM> which is excited by absorbing a portion of blue light emitted from the laser diode array <NUM> and passing through a condenser lens <NUM> and emits yellow fluorescent light, a dichroic mirror <NUM> filtering white light obtained by combining the yellow fluorescent light emitted from the phosphor-including member <NUM> and blue light reflected without being absorbed by the phosphor-including member <NUM> to allow for transmission of blue light and reflect yellow fluorescent light, a photodiode <NUM> receiving yellow light and generating photocurrent, and a light shielding plate <NUM> allowing the photodiode <NUM> to receive only the light reflected by the dichroic mirror <NUM>.

<FIG> is a graph showing a relation between output of the laser diode array <NUM> and surface temperature of phosphor sealed in three types of phosphor-including members <NUM> having different sealing-member thicknesses when the known YAG-based polycrystalline phosphor is used as the phosphor contained in the phosphor-including members <NUM>.

<FIG> is a graph showing a relation between output of the laser diode array <NUM> and fluorescence intensity of the three types of phosphor-including members <NUM> having different sealing-member thicknesses when the known YAG-based polycrystalline phosphor is used as the phosphor contained in the phosphor-including members <NUM>.

The particle diameter (D<NUM>) of the known YAG-based polycrystalline phosphor pertaining to <FIG> is <NUM> µm. Then, the thicknesses of the sealing materials of the three types of phosphor-including members <NUM> are <NUM> µm, <NUM> µm and <NUM> µm.

<FIG> is a graph showing a relation between output of the laser diode array <NUM> and surface temperature of phosphor sealed in three types of phosphor-including members <NUM> having different sealing-member thicknesses when a YAG-based single crystal phosphor in the first embodiment (obtained by pulverizing a region of a single crystal phosphor ingot in which composition distribution is in a range of (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>Ox from (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>Ox) is used as the phosphor contained in the phosphor-including members <NUM>.

<FIG> is a graph showing a relation between output of the laser diode array <NUM> and fluorescence intensity of the three types of phosphor-including members <NUM> having different sealing-member thicknesses when the YAG-based single crystal phosphor in the first embodiment (obtained by pulverizing a region from a single crystal phosphor ingot in which composition distribution is in a range of (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>Ox to (Y<NUM>Lu<NUM>Ce<NUM>)<NUM>Al<NUM>. <NUM>Ox) is used as the phosphor contained in the phosphor-including members <NUM>.

The particle diameter (D<NUM>) of the YAG-based single crystal phosphor pertaining to <FIG> is <NUM> µm. Then, the thicknesses of the sealing materials of the three types of phosphor-including members <NUM> are <NUM> µm, <NUM> µm and <NUM> µm.

When comparing <FIG>, it is clear that the slope of the increase in surface temperature of phosphor with respect to output of the laser diode array <NUM> is smaller (i.e., thermal resistance is smaller) in the YAG-based single crystal phosphor in the first embodiment than in the known YAG-based polycrystalline phosphor.

Also, while the slope of the temperature increase of the known YAG-based polycrystalline phosphor becomes sharper with decreasing internal quantum efficiency when the surface temperature exceeds about <NUM> to <NUM>°C, the slope of the temperature increase of the YAG-based single crystal phosphor in the first embodiment is substantially constant up to about <NUM>°C.

In consequence, the maximum value of fluorescence intensity of the known YAG-based polycrystalline phosphor was <NUM> when the thickness of the sealing material was <NUM> µm, but the maximum value of fluorescence intensity of the YAG-based single crystal phosphor in the first embodiment was <NUM> when the thickness of the sealing material was <NUM> µm, as shown in <FIG> and <FIG>. Fluorescence intensity of the YAG-based single crystal phosphor in the first embodiment, when the thickness of the sealing material was <NUM> µm, was not saturated even when output of the laser diode array <NUM> was increase to 78W, and it is expected that higher fluorescence intensity can be obtained.

The invention is not intended to be limited to the embodiments and Examples, and the various kinds of modifications can be implemented without departing from the gist of the invention. For example, although a headlight has been described in the second embodiment as an example of the light-emitting device using the phosphor in the first embodiment and light-emitting elements, the light-emitting device is not limited thereto.

Also, a binder for binding particles of the phosphor may be used in place of the sealing material used to seal the particulate phosphor in the embodiments and Examples. The phosphor particles bound by the binder, when used in a reflective phosphor-including member in the embodiments and Examples, are arranged on a substrate having a highly reflective surface, such as mirror substrate. Also, the phosphor particles bound by the binder has enough strength to self-stand. Therefore, the particles bonded into a plate shape can be used alone as a transmissive phosphor-including member, but may be arranged on a highly thermally conductive transparent substrate such as sapphire substrate to dissipate heat. The binder is formed of an inorganic material such as SiO<NUM>-based or Al<NUM>O<NUM>-based material.

Also, the invention according to claims is not to be limited to the embodiments and Examples described above. Further, it should be noted that all combinations of the features described in the embodiments and Examples are not necessary to solve the problem of the invention.

Claim 1:
A phosphor-including member (<NUM>, <NUM>), comprising:
a particulate phosphor (24c, 33c) consisting of a group of YAG-based or LuAG-based single crystal phosphor particles containing Ce and each of the particles has a composition represented by a compositional formula (Y<NUM>-x-y-zLuxGdyCez)<NUM>+aAl<NUM>-aO<NUM> (<NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, -<NUM>≤a≤<NUM>); and
a sealing member (24b, 33b) comprising a transparent inorganic material sealing the particulate phosphor and having a lower thermal conductivity than the particulate phosphor or comprising a binder formed of an inorganic material and binding the particles of the particulate phosphor,
wherein the particulate phosphor (24c, 33c) has a particle diameter (D50) in a range of not less than <NUM> and not more than <NUM>.