Fluorescent wheel and lighting device

Abstract

Fluorescent wheel (10c), comprising: a substrate (11); and a plurality of phosphor layers (12) arranged separately from one another on the substrate (11) along a circumferential direction, wherein each of the plurality of phosphor layers (12) comprises a first fluorescence emitter (12a) and a second fluorescence emitter (12b) arranged side by side along the circumferential direction and emitting fluorescence of different colors from each other, wherein the fluorescence efficiency of the second fluorescence emitter (12b) when the second fluorescence emitter (12b) is irradiated with excitation light is lower than the fluorescence efficiency of the first fluorescence emitter (12a) when the first fluorescence emitter (12a) is irradiated with the excitation light, wherein, in plan view, a bare portion (13) is arranged adjacent to the second fluorescence emitter (12b) in the circumferential direction, wherein the bare portion (13) is a portion of the substrate at which no phosphor layer (12) is arranged, wherein the phosphor wheel (10c) rotates so as to cause the second fluorescence emitter (12b) to be irradiated with the excitation light immediately after the bare section (13), wherein the substrate (11) is light-reflecting and at least a portion of the bare portion (13) reflects the excitation light, wherein the bare portion (13) comprises a first bare portion (13a) and a second bare portion (13b) arranged side by side along the circumferential direction, the first bare section (13a) reflects the excitation light, the second bare section (13b) allows the excitation light to pass through, in plan view, the second bare portion (13b) is arranged in the circumferential direction adjacent to the second fluorescence emitter (12b), and when the substrate (11) is rotated, the second fluorescence emitter (12b) is irradiated with the excitation light immediately after the second bare section (13b), wherein the substrate (11) comprises a light-transmitting substrate body (11a) and a totally reflective film (11e), and the plurality of phosphor layers (12) are arranged separately from one another along the circumferential direction on the totally reflective film (11e), and wherein the second bare portion (13b) of the light-reflecting phosphor wheel (10c) is a region of the substrate (11) from which the totally reflecting film (11e) is removed.

Description

[Technical Field]The present invention relates to a phosphor wheel and a lighting device including the phosphor wheel.[Prior Art]In recent years, a light source device in which a solid-state light emitting element that emits laser light and a light wave conversion device including a phosphor have been proposed. Patent Document (PTL) 1 discloses a projector light source device including a phosphor wheel as a light wave conversion device. In this connection, Patent Document (PTL) 2 discusses a light module for generating wavelength-converted light in the red spectral region by a wavelength conversion element, and a method for generating wavelength-converted light in the red spectral region and a method for providing a wavelength conversion element. Patent Document (PTL) 3 relates to a wavelength conversion element, a light source device, and a projector, and more particularly to a phosphor wheel for generating fluorescent light. Patent Document (PTL) 4 describes a wavelength conversion element including phosphors and the like for use in projectors, and Patent Document (PTL) 5 relates to an illumination system for a projector.[Document List][Patent Document][PTL 1] JP 2012-123 179 A[PTL 2] DE 102013215981 A1[PTL 3] US 2012 / 0 106 126 A1[PTL 4] DE 10 2015 113 692 A1[PTL 5] DE 10 2012 100 446 A1[Summary of the Invention][Technical Problem]In phosphor wheels, it is a challenge to reduce the thermal effect on a phosphor layer comprising a relatively heat sensitive phosphor.The present invention provides a phosphor wheel capable of reducing the thermal effect on a phosphor layer including a relatively heat-sensitive phosphor, and a lighting device including the phosphor wheel.[Solution of Problem]A phosphor wheel according to an aspect of the present invention includes: a substrate; and a plurality of phosphor layers arranged separately from each other on the substrate along a circumferential direction. Each of the plurality of phosphor layers includes a first fluorescence emitter and a second fluorescence emitter that are arranged side by side along the circumferential direction and emit fluorescence having colors different from each other. The fluorescence efficiency of the second fluorescence emitter when the second fluorescence emitter is irradiated with excitation light is lower than the fluorescence efficiency of the first fluorescence emitter when the first fluorescence emitter is irradiated with the excitation light. In plan view, a bare portion is disposed adjacent to the second fluorescent emitter in the circumferential direction, the bare portion being a portion of the substrate where no phosphor layer is disposed. The phosphor wheel rotates to cause the second fluorescent emitter to be irradiated with the excitation light immediately after the bare portion. The substrate is light reflecting and at least a portion of the bare portion reflects the excitation light. The bare portion includes a first bare portion and a second bare portion that are arranged side by side along the circumferential direction. The first bare portion reflects the excitation light, and the second bare portion transmits the excitation light. In the plan view, the second bare portion is arranged adjacent to the second fluorescence emitter in the circumferential direction. When the substrate is rotated, the second fluorescent emitter is irradiated with the excitation light immediately after the second bare portion. The substrate includes a light transmissive substrate body and a total reflective film, and the plurality of phosphor layers are arranged on the total reflective film separately from each other along the circumferential direction. The second bare portion of the light reflecting phosphor wheel is a region of the substrate where the total reflecting film is removed.An illumination device according to an aspect of the present invention includes the phosphor wheel; an excitation light source that irradiates the phosphor wheel with the excitation light; and a motor that rotates the phosphor wheel so as to cause the second fluorescence emitter to be irradiated with the excitation light immediately after the bare portion.[Advantageous Effects of the Invention]The present invention provides a phosphor wheel that reduces the thermal effect on a phosphor layer comprising a relatively heat-sensitive phosphor, and an illumination device comprising the phosphor wheel.[Brief Description of Drawings]FIG. 1 is a schematic diagram showing a configuration of a lighting device according to an embodiment; FIG. 2 is a plan view of a phosphor wheel according to the embodiment; FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. 2 ; FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. 2 ; FIG. 5 is a schematic cross-sectional view taken along line V-V in FIG. 2 ; FIG. 6 is a diagram for explaining the amount of heat generated in the phosphor wheel according to the embodiment; FIG. 7 is a plan view for explaining the rotation direction of the phosphor wheel according to the embodiment; FIG. 8 is a plan view of a phosphor wheel according to a variation 1; FIG. 9 is a schematic cross-sectional view taken along line IX-IX in FIG. 8 ; FIG. 10 is a schematic cross-sectional view of a light reflecting phosphor wheel according to a variation 2; and FIG. 11 is a schematic cross-sectional view of a second bare portion of a light reflecting phosphor wheel according to a variation 3.[Description of Embodiment]An embodiment will be described below with reference to the drawings. It should be noted that the following embodiment describes a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, etc. indicated in the following embodiment describe a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, etc. indicated in the following embodiment are merely examples and do not limit the present invention. Further, among the structural elements in the following embodiment, those not recited in any of the independent claims representing the most generic concepts are described as optional structural elements.It should also be noted that each figure is a schematic illustration and is not necessarily a precise illustration. Further, in the figures, the same reference numerals are assigned to substantially the same structural elements, and redundant description may be omitted or simplified.Further, some of the figures referred to for explanation of the following embodiment have coordinate axes. The positive side of the Z axis may be referred to as the top side (top) and the negative side of the Z axis may be referred to as the bottom side (bottom). In other words, the Z-axis direction is a direction orthogonal to the substrate included in the phosphor wheel. Further, the X-axis direction and the Y-axis direction are perpendicular to each other on a plane (horizontal plane) orthogonal to the Z-axis direction. The X-Y plane is a plane parallel to the main surfaces of the substrate incorporated in the phosphor wheel. For example, in the following embodiment, "plan view" means a view in the Z-axis direction.(EMBODIMENT)[Structure of Lighting Apparatus]The configuration of a lighting device according to the embodiment will be described below. FIG. 1 is a schematic diagram showing the configuration of the lighting device according to the embodiment.The lighting device 100 according to the embodiment illuminates an interior space or an exterior space. As shown in FIG. 1, the illumination device 100 includes a phosphor wheel 10, an excitation light source 20, and a motor 30. unlike a projector, for example, the illumination device 100 does not include a pixel such as a micromirror array or a liquid crystal panel.The phosphor wheel 10 is a light wave conversion device that converts excitation light (blue laser light) emitted from the excitation light source 20 into white light and outputs the white light. The phosphor layer 12 included in the phosphor wheel 10 emits fluorescence when irradiated with the excitation light. At this time, the phosphor wheel 10 rotates about the rotation axis J by the power of the motor 30 while the phosphor layer 12 is irradiated with the excitation light to prevent a specific point on the phosphor layer 12 from being intensively irradiated with the excitation light. This prevents decomposition of the phosphor included in the phosphor layer 12 due to the heat generated by the irradiation with the excitation light.The phosphor layer 12 includes a first fluorescence emitter 12 aand a second fluorescence emitter 12 bwhich emit fluorescence having colors different from each other. The first fluorescence emitter 12 aconverts at least a part of the excitation light with which the first fluorescence emitter 12 ais irradiated into yellow fluorescence and emits the yellow fluorescence. The second fluorescence emitter 12 bconverts at least a part of the excitation light with which the second fluorescence emitter 12 bis irradiated into a red fluorescence and emits the red fluorescence. As described, the color of the fluorescence emitted by the first fluorescence emitter 12 aand the color of the fluorescence emitted by the second fluorescence emitter 12 bare different. In particular, the fluorescence peak wavelength of the first fluorescence emitter 12 ais shorter than the fluorescence peak wavelength of the second fluorescence emitter 12 b.The phosphor wheel 10 has a bare portion 13 in which no phosphor layer is disposed. The blank portion 13 transmits the excitation light (blue laser light) emitted from the excitation light source 20.While the phosphor wheel 10 rotates by the power of the motor 30, the first fluorescence emitter 12 a, the blank portion 13, and the second fluorescence emitter 12 bare sequentially irradiated with the excitation light emitted from the excitation light source 20. As a result, white light is emitted from the phosphor wheel 10. The color temperature of the white light is 3000 K, for example.The excitation light source 20 irradiates the phosphor wheel 10 with the excitation light. The excitation light source 20 is, for example, a semiconductor laser that emits blue laser light as excitation light. In other words, the excitation light is blue light. The emission peak wavelength (emission center wavelength) of the excitation light source 20 is, for example, at least 440 nm and at most 470 nm. The excitation light source 20 is specifically a CAN-encapsulated element, but may be a chip-type element. It should be noted that the excitation light source 20 may be a light source that emits blue-violet laser light or ultraviolet laser light.The motor 30 rotates the phosphor wheel 10 about the rotation axis J. The motor 30 is, for example, an outer rotor motor, but is not particularly limited.[Detailed Construction of Phosphor Wheel]Next, the detailed structure of the phosphor wheel 10 will be described. The detailed structure of the phosphor wheel 10 represents a basic shape not according to the invention, which is configured in more detail by the variation 3 according to the invention. FIG. 2 is a plan view of the phosphor wheel 10. FIG. 3 is a schematic cross-sectional view taken along the line III-III in FIG. 2, FIG. 4 is a schematic cross-sectional view taken along the line IV-IV in FIG. 2, FIG. 5 is a schematic cross-sectional view taken along the line V-V in FIG. 2, It should be noted that in FIGS. 3 to 5, the thickness, etc., of each structural element relative to the thickness, etc., of the other structural elements need not be accurate.The phosphor wheel 10 is a light transmissive phosphor wheel that transmits a part of the excitation light entering through the second main surface 11 dof the substrate 11 and allows a part of the excitation light to exit through the first main surface 11 cof the substrate 11. Another part of the excitation light is emitted from the phosphor wheel 10 after being subjected to wavelength conversion. Accordingly, white light is emitted as a whole. As shown in FIGS. 2 to 5, the phosphor wheel 10 includes the substrate 11 and a plurality of phosphor layers 12.The substrate 11 is transparent. The substrate 11 specifically includes a substrate body 11 aand a dichroic mirror layer 11 b. The substrate 11 has a first main surface 11 cand a second main surface 11 don a side of the substrate 11 opposite to the first main surface 11 c. A circular opening 15 is formed in the center of the substrate 11 for connection to the motor 30.The substrate body 11 ais a circular plate having a positive side surface of the Z axis on which the dichroic mirror layer 11 bis formed and a negative side surface of the Z axis (second main surface 11 dof the substrate 11) serving as an input surface of the excitation light. Specifically, the substrate body 11 ais a sapphire substrate. The substrate body 11 amay be another light transmissive substrate, such as a light transmissive ceramic substrate formed of polycrystalline alumina or aluminum nitride, a transparent glass substrate, a crystal substrate, or a transparent resin substrate.The dichroic mirror layer 11 bis a thin film having characteristics of transmitting light having wavelengths in the blue region and reflecting light having wavelengths longer than the wavelengths in the blue region. That is, the dichroic mirror layer 11 bhas characteristics of transmitting the excitation light emitted by a laser light source and reflecting the fluorescence emitted by the phosphor layers 12. By having the dichroic mirror layer 11 b, it is possible to increase the light emission efficiency of the phosphor wheel 10.The plurality of phosphor layers 12 are arranged separately from each other on the first main surface 11 c(on the dichroic mirror layer 11 b) of the substrate 11 along the circumferential direction about the rotation axis J. In the present embodiment, two phosphor layers 12 are disposed on the first main surface 11 cof the substrate 11; however, three or more phosphor layers 12 may be disposed.By disposing the plurality of phosphor layers 12 separately from each other as described, heat generated by irradiation with the excitation light can be dissipated more effectively than when the phosphor layers 12 are formed in a ring shape with no space therebetween. The heat dissipation prevents the substrate 11 from being deformed, and prevents the phosphor layers 12 from being peeled off, for example.In plan view, each of the plurality of phosphor layers 12 has a band (arc) shape along the circumferential direction. Each of the plurality of phosphor layers 12 includes the first fluorescence emitter 12 aand the second fluorescence emitter 12 b, which are arranged side by side along the circumferential direction and emit fluorescence having colors different from each other.First, the first fluorescent emitter 12a will be described mainly with reference to Fig. 3. The first fluorescence emitter 12 aincludes a base material 12 cand first phosphor particles 14 a. For example, the first fluorescent emitter 12 ais formed by printing a paste formed of the base material 12 cincluding first phosphor particles 14 aon the substrate 11. The thickness of the first fluorescence emitter 12 ais, for example, at least 20 μm and at most 200 μm. It should be noted that the first fluorescent emitter 12 amay be molded in advance using, for example, a molding die, and the first fluorescent emitter 12 amay be attached to the substrate 11 after the molding using, for example, a resin. Further, the first fluorescent emitter 12 amay be a sintered body.The base material 12 cis formed of an inorganic material such as glass or an organic-inorganic hybrid material. By using the base material 12 cincluding an inorganic material as described, heat dissipation of the phosphor wheel 10 can be improved.The first phosphor particles 14 aare dispersed in the first fluorescence emitter 12 a(base material 12 c), and emit light when excited by blue laser light emitted by the laser light source. That is, the first phosphor particles 14 aemend fluorescence when excited by the excitation light. The particle size (especially the median size (d50) or the average size. The same applies below) of the first phosphor particles 14 ais, for example, at least 1 μm and at most 40 μm.Specifically, the first phosphor particles 14 aare formed of a yellow yttrium aluminum garnet (YAG) phosphor, such as a Y 3( Al, Ga) 5 O 12: Ce phosphor, and emit fluorescence. That is, the fluorescence emitted by the first fluorescence emitter 12 ais yellow light. The first phosphor particles 14 amay be a lutetium aluminum garnet (LuAG) phosphor, such as a Lu 3 Al 5 O 12: Ce phosphor. The first fluorescence emitter 14 acan be a green phosphor. In the example shown in FIG. 3, the first fluorescent emitter 12 aincludes one type of phosphor, i.e., the first phosphor particles 14 a; however, the first fluorescent emitter 12 amay include two or more types of phosphor.It should be noted that the yellow phosphor has a fluorescence peak wavelength of, for example, at least 570 nm and at most 590 nm, and the green phosphor has a fluorescence peak wavelength of, for example, at least 495 nm and at most 570 nm.First, the second fluorescent emitter 12b will be described mainly with reference to Fig. 4. The second fluorescence emitter 12 bincludes a base material 12 cand second phosphor particles 14 b. For example, the second fluorescent emitter 12 bis formed by printing a paste formed of the base material 12 cincluding second phosphor particles 14 bon the substrate 11. The thickness of the second fluorescence emitter 12 bis, for example, at least 20 μm and at most 200 μm. It should be noted that the second fluorescent emitter 12 bmay be molded in advance using, for example, a molding die, and the second fluorescent emitter 12 bmay be attached to the substrate 11 after the molding using, for example, a resin. Further, the second fluorescent emitter 12 bmay be a sintered body.The base material 12 cis formed of an inorganic material such as glass or an organic-inorganic hybrid material. By using the base material 12 cincluding an inorganic material as described, heat dissipation of the phosphor wheel 10 can be improved.The second phosphor particles 14 bare dispersed in the second fluorescence emitter 12 b(base material 12 c), and emit light when excited by blue laser light emitted by the laser light source. That is, the second phosphor particles 14 bemission fluorescence when excited by the excitation light. The particle size of the second phosphor particles 14 bis, for example, at least 1 μm and at most 40 μm. It should be noted that the second fluorescent emitter 12 bmay be molded in advance using, for example, a molding die, and the second fluorescent emitter 12 bmay be attached to the substrate 11 after the molding using, for example, a resin.Specifically, the second phosphor particles 14 bare formed of a red phosphor such as a CaAISiN 3: Eu phosphor, or a (Sr, Ca)AlSiN 3: Eu phosphor, and emit a red fluorescence. That is, the fluorescence emitted by the second fluorescence emitter 12 bis red light. In the example shown in FIG. 4, the second fluorescent emitter 12 bincludes one type of phosphor, i.e., the second phosphor particles 14 b; however, the second fluorescent emitter 12 bmay include two or more types of phosphor. It should be noted that the red phosphor has a fluorescence peak wavelength of, for example, at least 600 nm and at most 750 nm.As shown in FIG. 2, in plan view, a bare portion 13, which is a portion of the substrate 11 where no phosphor layer is disposed, is located between one phosphor layer 12 and another phosphor layer 12 in the circumferential direction. In other words, the bare portion 13 is continuous with the second fluorescent emitter 12 bin the circumferential direction. As shown in FIG. 5, the bare portion 13 is where nothing is disposed on the substrate 11. The blank portion 13 allows the excitation light to pass therethrough as it is.[Rotation Direction of Phosphor Wheel]As described above, the first fluorescent emitter 12 aincludes the first phosphor particles 14 aformed of the yellow YAG phosphor, whereas the second fluorescent emitter 12 bincludes the second phosphor particles 14 bformed of a red phosphor such as a CaAlSiN 3: Eu phosphor or a (Sr, Ca)AlSiN 3: Eu phosphor. Such second phosphor particles 14 b(red phosphor) have a fluorescence emission efficiency lower than that of the above-described first phosphor particles 14 a(yellow phosphor), and are more heat-sensitive than the first phosphor particles 14 a. That is, the fluorescence emission efficiency of the second fluorescence emitter 12 bwhen the second fluorescence emitter 12 bis irradiated with the excitation light is lower than the fluorescence emission efficiency of the first fluorescence emitter 12 awhen the first fluorescence emitter 12 ais irradiated with the excitation light, and the second fluorescence emitter 12 bis more heat-sensitive than the first fluorescence emitter 12 a. It should be noted that the fluorescence efficiency is expressed as, for example, (intensity (power) of fluorescence output when the phosphor is irradiated with excitation light) / intensity (power) of excitation light with which the phosphor is irradiated).Here, the amount of heat generated as a result of irradiation of the phosphor wheel 10 with the excitation light is shown in FIG. 6. FIG. 6 is a diagram for explaining the amount of heat generated in the phosphor wheel 10.As shown in (a) of FIG. 6, heat is generated during a period in which the first fluorescent emitter 12 aof the phosphor wheel 10 is irradiated with the excitation light as a result of excitation and emission of fluorescence of the first phosphor particles 14 aincluded in the first fluorescent emitter 12 a. As shown in (b) of FIG. 6, during a period in which the bare portion 13 of the phosphor wheel 10 is irradiated with the excitation light, no phosphor is excited, and thus the amount of heat generated is very small.In contrast, as shown in (c) of FIG. 6, heat is generated during a period in which the second fluorescent emitter 12 bof the phosphor wheel 10 is irradiated with the excitation light as a result of excitation and emission of fluorescence of the second phosphor particles 14 bincluded in the second fluorescent emitter 12 b. At this time, the fluorescence efficiency of the second phosphor particles 14 bis lower than that of the first phosphor particles 14 a. As such, the amount of heat generated in the period during which the second fluorescent emitter 12 bis irradiated with the excitation light is larger than the amount of heat generated in the period during which the first fluorescent emitter 12 ais irradiated with the excitation light.The direction of rotation of the phosphor wheel 10 is set so as to reduce the thermal effect on the second fluorescent emitter 12 b. Specifically, the rotation direction is set such that the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the bare portion 13 is irradiated with the excitation light, which generates a smaller amount of heat. FIG. 7 is a plan view for explaining the rotational direction of the phosphor wheel 10. FIG. 7 is a plan view of the phosphor wheel 10 viewed from the first main surface 11 cside (positive Z-axis side) of the substrate 11.As shown in FIG. 7, the first fluorescent emitter 12 a, the second fluorescent emitter 12 b, and the bare portion 13 of the phosphor wheel 10 are arranged in the clockwise direction in the stated order when viewed from the first main surface 11 cside of the substrate 11.When such a phosphor wheel 10 is rotated clockwise about the rotation axis J in a view from the first main surface 11 cside of the substrate 11, the first fluorescence emitter 12 apasss through the irradiation position P of the excitation light ((a) of FIG. 7 ) and the bare portion 13 passes through the irradiation position P of the excitation light ((b) of FIG. 7 ). After the bare portion 13, the second fluorescence emitter 12 bpasss through the irradiation position P of the excitation light ((c) of FIG. 7 ). That is, when the phosphor wheel 10 (substrate 11) is rotated, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the bare portion 13.In the described manner, the phosphor wheel 10 rotates to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the bare portion 13. With the phosphor wheel 10, irradiation of the second fluorescent emitter 12 bwith the excitation light starts in a state where the amount of heat generated is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b.It should be noted that the first fluorescence emitter 12 a, the second fluorescence emitter 12 b, and the bare portion 13 of the phosphor wheel 10 may be arranged counterclockwise as viewed from the first main surface 11 cside of the substrate 11 in the stated order. In this case, when the phosphor wheel 10 is rotated counterclockwise about the rotation axis J as viewed from the first main surface 11 cside of the substrate 11, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the bare portion 13.[Variation not according to the invention 1]In the above embodiment, the entire blank portion 13 transmits the excitation light; however, this is only required for at least a portion of the blank portion 13 to transmit the excitation light. For example, the blank portion 13 may include a portion that blocks the excitation light. FIG. 8 is a plan view of a phosphor wheel according to variation 1 not according to the present invention.The bare portion 13 of the phosphor wheel 10 ashown in FIG. 8 includes a first bare portion 13 aand a second bare portion 13 bwhich are adjacent to each other along the circumferential direction.The first bare portion 13 ais a region that transmits the excitation light, and the cross-sectional view of the first bare portion 13 ais as shown in FIG. 5. In contrast, the second bare portion 13 bblocks the excitation light. FIG. 9 is a schematic cross-sectional view of the second bare portion 13 b(taken along line IX-IX in FIG. 8 ).As shown in FIG. 9, the second bare portion 13 bis formed by the light shield 13 cdisposed on the first main surface 11 cside of the substrate 11. Any article may serve as the light shield 13 c, as long as it blocks light. For example, a light reflector that reflects the excitation light is used as the light shield 13 c. The light shield 13 cmay be disposed on the second main surface 11 d. It should be noted that, unlike the excitation light that irradiates the first bare portion 13 a, the excitation light that irradiates the second bare portion 13 bdoes not become a leakage light.As shown in FIG. 8, the first fluorescent emitter 12 a, the second fluorescent emitter 12 b, the second bare portion 13 b, and the first bare portion 13 aof the phosphor wheel 10 aare arranged in the clockwise direction in the stated order when viewed from the first main surface 11 cside of the substrate 11. That is, in the phosphor wheel 10 a, the second bare portion 13 bis disposed adjacent to the second fluorescent emitter 12 bin the circumferential direction in plan view. Therefore, when the phosphor wheel 10 ais viewed clockwise from the first main surface 11 cside, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the second bare portion 13 b.In the described manner, the phosphor wheel 10 arotates to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the second bare portion 13 b. During a period in which the second bare portion 13 bis irradiated with the excitation light, no phosphor is excited, and thus the amount of heat generated is very small. Accordingly, in the phosphor wheel 10 a, irradiation of the second fluorescent emitter 12 bstarts with the excitation light in a state where the amount of generated heat is small. As a result, the thermal effect on the second fluorescent emitter 12b is reduced.[Variation not according to the invention 2]Although the phosphor wheel 10 and the phosphor wheel 10 aare light transmissive phosphor wheels, the present invention may be implemented as a light reflective phosphor wheel. FIG. 10 is a schematic cross-sectional view of a light reflecting phosphor wheel. It should be noted that, since the basic structure of the light reflecting phosphor wheel 10 bis identical to that of the phosphor wheel 10, the following description is mainly directed to the aspects of the light reflecting phosphor wheel 10 bwhich are different from those of the phosphor wheel 10, and the aspects already discussed above will not be described or shown.The light reflecting phosphor wheel 10 bdiffers from the phosphor wheel 10 in that the substrate 11 is light reflecting and non-light transmissive. For example, as shown in FIG. 10, the light reflecting substrate 11 is implemented by including, in place of the dichroic mirror layer 11 b, the total reflecting film 11 ehaving a high reflection in the visible light region on the substrate body 11 a. In this case, the substrate body 11 amay be formed of a material that is not light transmissive. The light reflecting substrate 11 can be implemented by forming the substrate body 11 aitself from a light reflecting material. In this case, the total reflection film 11 emay be omitted.In the light reflecting phosphor wheel 10 b, the excitation light enters from the first main surface 11 cside, and exiting light is emitted toward the first main surface 11 cside. For example, the first fluorescence emitter 12 aconverts at least a portion of the excitation light with which the first fluorescence emitter 12 ais irradiated into a yellow fluorescence. A part of the yellow fluorescence and a part of the excitation light not subjected to wavelength conversion are reflected by the total reflective film 11 e.Further, although not shown, the second fluorescence emitter 12 bof the light reflecting phosphor wheel 10 bconverts at least a part of the excitation light with which the second fluorescence emitter 12 bis irradiated into red fluorescence. A part of the red fluorescence and a part of the excitation light that are not subjected to wavelength conversion are reflected by the total reflective film 11 e. Although not shown, no phosphor layer is disposed in the bare portion 13 of the light reflecting phosphor wheel 10 b, and the excitation light irradiating the bare portion 13 is reflected by the total reflecting film 11 e.For example, as in FIG. 7, the first fluorescent emitter 12 a, the second fluorescent emitter 12 b, and the bare portion 13 of the light reflecting phosphor wheel 10 bare also arranged clockwise when viewed from the first main surface 11 cside of the substrate 11.When the light reflecting phosphor wheel 10 bis rotated clockwise about the rotation axis J in a view from the first main surface 11 cside of the substrate 11, the blank portion 13 passes through the irradiation position of the excitation light after the first fluorescence emitter 12 apass through the irradiation position of the excitation light. After the bare portion 13, the second fluorescence emitter 12 bpasss through the irradiation position of the excitation light. That is, when the light reflecting phosphor wheel 10 bis rotated, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the bare portion 13.In the described manner, the light reflecting phosphor wheel 10 brotates to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the bare portion 13. Also in the light reflecting phosphor wheel 10 b, irradiation of the second fluorescent emitter 12 bwith the excitation light starts in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b.[Inventive Variation 3]In the light reflecting phosphor wheel 10 b, it is only necessary that at least a portion of the bare portion 13 reflect the excitation light. For example, the blank portion 13 may include a first blank portion 13 athat reflects the excitation light and a second blank portion 13 bthat transmits the excitation light. FIG. 11 is a schematic cross-sectional view of the second bare portion 13 bof a light reflecting phosphor wheel. It should be noted that since the basic structure of the light reflecting phosphor wheel 10 cis identical to that of the phosphor wheel 10 b, the following description is mainly directed to the aspects of the light reflecting phosphor wheel 10 cdifferent from those of the phosphor wheel 10 b, and the aspects already discussed above will not be described or shown.The second bare portion 13 bof the light reflecting phosphor wheel 10 cshown in FIG. 11 is a portion of the substrate 11 where an opening 13 dis formed. It should be noted that the excitation light that irradiates the second bare portion 13 bof the light reflecting phosphor wheel 10 cis not reflected, and thus becomes no exiting light.As in FIG. 8, the first fluorescent emitter 12 a, the second fluorescent emitter 12 b, the second bare portion 13 band the first bare portion 13 aof the light reflecting phosphor wheel 10 care also arranged in the clockwise direction in the stated order when viewed from the first main surface 11 cside of the substrate 11. That is, also in the light reflecting phosphor wheel 10 c, the second bare portion 13 bis disposed adjacent to the second fluorescent emitter 12 bin the circumferential direction in plan view.Therefore, when the light reflecting phosphor wheel 10 cis rotated clockwise as viewed from the first main surface 11 cside, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the second bare portion 13 b.In the described manner, the light reflecting phosphor wheel 10 crotates to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the second bare portion 13 b. During a period in which the second bare portion 13 bis irradiated with the excitation light, no phosphor is excited, and thus the amount of heat generated is very small. Accordingly, in the light reflecting phosphor wheel 10 c, irradiation of the second fluorescent emitter 12 bwith the excitation light starts in a state where the amount of generated heat is small. As a result, the thermal effect on the second fluorescent emitter 12b is reduced.It should be noted that the second bare portion 13 bof the light reflecting phosphor wheel 10 cmay not be the portion of the substrate 11 where the opening 13 dis formed. In this connection, the substrate body 11 ais light transmissive, and the second bare portion 13 bof the light reflective phosphor wheel 10 cis a region of the substrate 11 where the total reflective film 11 eis removed. For the second bare portion 13 bof the light reflecting phosphor wheel 10 c, it is only necessary to transmit the excitation light.[Advantageous Effects, etc.]As described so far, the phosphor wheel 10 includes the substrate 11 and a plurality of phosphor layers 12 arranged on the substrate 11 separately from each other in the circumferential direction. Each of the plurality of phosphor layers 12 includes a first fluorescence emitter 12 aand a second fluorescence emitter 12 barranged side by side along the circumferential direction and emitting fluorescence having colors different from each other. The fluorescence efficiency of the second fluorescence emitter 12 bwhen the second fluorescence emitter 12 bis irradiated with excitation light is lower than the fluorescence efficiency of the first fluorescence emitter 12 awhen the first fluorescence emitter 12 ais irradiated with the excitation light. In plan view, the bare portion 13 is located adjacent to the second fluorescence emitter 12 bin the circumferential direction. The bare portion 13 is a portion of the substrate 11 where no phosphor layer is disposed. The phosphor wheel 10 rotates so as to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the bare portion 13. The substrate is light reflecting and at least a portion of the bare portion reflects the excitation light. The bare portion includes a first bare portion and a second bare portion that are arranged side by side along the circumferential direction. The first bare portion reflects the excitation light, and the second bare portion transmits the excitation light. In the plan view, the second bare portion is arranged adjacent to the second fluorescence emitter in the circumferential direction. When the substrate is rotated, the second fluorescent emitter is irradiated with the excitation light immediately after the second bare portion. The substrate includes a light transmissive substrate body and a total reflective film, and the plurality of phosphor layers are arranged on the total reflective film separately from each other along the circumferential direction. The second bare portion of the light reflecting phosphor wheel is a region of the substrate where the total reflecting film is removed.Thereby, the irradiation of the second fluorescent emitter 12 bstarts with the excitation light in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b. That is, a phosphor wheel 10 is provided that can reduce the thermal effect on the phosphor layers including the relatively heat-sensitive phosphor. Further, by disposing the plurality of phosphor layers 12 separately from each other, it is possible to dissipate the heat generated when the phosphor layers 12 are irradiated with the excitation light.Further, in the phosphor wheel 10 or the phosphor wheel 10 anot according to the present invention, the substrate 11 is light transmissive, and at least a portion of the bare portion 13 transmits the excitation light.This provides a light transmissive phosphor wheel 10 (or phosphor wheel 10 a) not according to the present invention, which can reduce the thermal effect on the phosphor layers including the relatively heat sensitive phosphor.Further, in the phosphor wheel 10 anot according to the present invention, the blank portion 13 includes the first blank portion 13 aand the second blank portion 13 bwhich are adjacent to each other in the circumferential direction. The first blank portion 13 atransmits the excitation light, and the second blank portion 13 bblocks the excitation light. In plan view, the second bare portion 13 bis arranged adjacent to the second fluorescence emitter 12 bin the circumferential direction. When the substrate 11 is rotated, the second fluorescent emitter 12 bis irradiated with the excitation light immediately after the second bare portion 13 b.Thereby, the irradiation of the second fluorescent emitter 12 bstarts with the excitation light in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b. That is, a phosphor wheel 10 anot according to the present invention is provided that can reduce the thermal effect on the phosphor layers including the relatively heat-sensitive phosphor.Further, in the phosphor wheel 10 bor the phosphor wheel 10 c, which is not according to the present invention, the substrate 11 is light-reflecting, and at least a portion of the bare portion 13 reflects the excitation light.Thereby, a light-reflecting phosphor wheel 10 b(or phosphor wheel 10 c) not according to the present invention is provided, which can reduce the thermal effect on the phosphor layers including the relatively heat-sensitive phosphor.Further, in the phosphor wheel 10 caccording to the present invention, the blank portion 13 includes the first blank portion 13 aand the second blank portion 13 bdisposed side by side in the circumferential direction. The first blank portion 13 areflects the excitation light and the second blank portion 13 btransmits the excitation light. In plan view, the second bare portion 13 bis arranged adjacent to the second fluorescence emitter 12 bin the circumferential direction. When the substrate 11 is rotated, the fluorescent emitter 12 bis irradiated with the excitation light immediately after the second bare portion 13 b.Thereby, the irradiation of the second fluorescent emitter 12 bstarts with the excitation light in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b. That is, there is provided a phosphor wheel 10 cin accordance with the present invention which can reduce the thermal effect on the phosphor layers including the relatively heat-sensitive phosphor.Further, in the phosphor wheel 10 caccording to the present invention, the second bare portion 13 bmay be a portion of the substrate 11 where an opening is formed.Thereby, by forming an opening in the substrate 11, the second bare portion 13 bcan be easily formed.Further, the excitation light is blue light, the fluorescence emitted by the first fluorescence emitter 12 ais yellow light, and the fluorescence emitted by the second fluorescence emitter 12 bis red light.Thereby, irradiation of the second fluorescent emitter 12 bincluding the red phosphor starts with the excitation light in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 bincluding the red phosphor.Further, the illumination device 100 includes the phosphor wheel 10 c; the excitation light source 20 that irradiates the phosphor wheel 10 with the excitation light; and a motor that rotates the phosphor wheel 10 cin such a manner as to cause the second fluorescent emitter 12 bto be irradiated with the excitation light immediately after the bare portion 13.Thereby, the irradiation of the second fluorescent emitter 12 bstarts with the excitation light in a state where the amount of generated heat is small, thereby reducing the thermal effect on the second fluorescent emitter 12 b. That is, there is provided an illumination device 100 that can reduce the thermal effect on the phosphor layers including the relatively heat-sensitive phosphor.(OTHER EMBODIMENTS)Although an embodiment has been described above, the present invention is not limited to the above embodiment.For example, in the above embodiment, the first fluorescent emitter includes a yellow phosphor or a green phosphor and the second fluorescent emitter includes a red phosphor. However, the second fluorescent emitter is only required to have a low fluorescent efficiency relative to the fluorescent efficiency of the first fluorescent emitter, and the phosphor included in the first fluorescent emitter and the phosphor included in the second fluorescent emitter are not particularly limited.Further, although the excitation light source has been described as a semiconductor laser in the above embodiment, the excitation light source may be a laser other than a semiconductor laser. The laser light source may be, for example, a solid state laser such as a YAG laser, a liquid laser such as a dye laser, or a gas laser such as an Ar ion laser, a He-Cd laser, a nitrogen laser, or an excimer laser. Further, the illumination device may include a plurality of excitation light sources. The illumination device may include, as the excitation light source, a solid-state light emitting element other than the semiconductor laser, such as a light emitting diode (LED) light source, an organic electroluminescence (EL) element, or an inorganic EL element.The present invention also includes embodiments obtained by applying various modifications to the embodiment and any variation that can be provided by a person skilled in the art, as well as embodiments obtained by arbitrarily combining structural elements and functions of the embodiments without departing from the spirit of the present invention.[List of Reference Numerals]10, 10 a, 10 b, 10 cphosphor wheel 11 substrate 12 phosphor layer 12 afirst fluorescent emitter 12 bsecond fluorescent emitter 13 blank portion 13 afirst blank portion 13 bsecond blank portion 13 dopening 20 excitation light source 30 motor 100 lighting device

Claims

A phosphor wheel (10c) comprising: a substrate (11); and a plurality of phosphor layers (12) arranged separately from each other on the substrate (11) along a circumferential direction, each of the plurality of phosphor layers (12) comprising a first fluorescence emitter (12a) and a second fluorescence emitter (12b) arranged side by side along the circumferential direction and emitting fluorescence having colors different from each other, wherein the fluorescence efficiency of the second fluorescence emitter (12b) when the second fluorescence emitter (12b) is irradiated with excitation light is lower than the fluorescence efficiency of the first fluorescence emitter (12a) when the first fluorescence emitter (12a) is irradiated with the excitation light, wherein, in plan view, a blank portion (13) is arranged adjacent to the second fluorescence emitter (12b) in the circumferential direction, wherein the blank portion (13) is a portion of the substrate where no phosphor layer (12) is disposed, the phosphor wheel (10c) rotates so as to cause the second fluorescent emitter (12b) to be irradiated with the excitation light immediately after the blank portion (13), the substrate (11) being light reflecting, and at least a portion of the blank portion (13) reflecting the excitation light, the blank portion (13) including a first blank portion (13a) and a second blank portion (13b) disposed side by side along the circumferential direction, the first blank portion (13a) reflecting the excitation light, the second blank portion (13b) transmitting the excitation light, the second blank portion (13b) being disposed adjacent to the second fluorescent emitter (12b) in the circumferential direction in plan view, and when the substrate (11) is rotated, the second fluorescent emitter (12b) is irradiated with the excitation light immediately after the second bare portion (13b), wherein the substrate (11) includes a light-transmissive substrate body (11a) and a total reflection film (11e), and the plurality of phosphor layers (12) are arranged separately from each other along the circumferential direction on the total reflection film (11e), and wherein the second bare portion (13b) of the light reflection phosphor wheel (10c) is a region of the substrate (11) where the total reflection film (11e) is removed.The phosphor wheel (10c) according to claim 1, wherein the excitation light is blue light, the fluorescence emitted by the first fluorescence emitter (12a) is yellow light, and the fluorescence emitted by the second fluorescence emitter (12b) is red light.An illumination device (100) comprising: the phosphor wheel (10c) according to claim 1 or 2; an excitation light source (20) that irradiates the phosphor wheel (10c) with the excitation light; and a motor (30) that rotates the phosphor wheel (10c) to cause the second fluorescence emitter (12b) to be irradiated with the excitation light immediately after the bare portion (13).

Images