This invention relates to fluorescent wheels for projectors and light-emitting devices for projectors.
To reduce projector size, there have recently been proposed light-emitting devices in which an LED (light emitting diode) and a phosphor are used. For example, Patent Literature 1 discloses a projector in which use is made of a light-emitting device including: a light source configured to emit ultraviolet light; and a phosphor layer configured to convert the ultraviolet light from the light source into visible light. In Patent Literature 1, a fluorescent wheel is used which is produced by providing an annular phosphor layer on an annular rotatable transparent substrate.
Light-emitting devices in which conventional fluorescent wheels are used have the problem that their luminescence intensity is insufficient.
An object of the present invention is to provide a fluorescent wheel for a projector capable of increasing the luminescence intensity and a light-emitting device for a projector using the same.
A fluorescent wheel for a projector according to the present invention includes: an annular transparent substrate including a first principal surface located on a side where excitation light enters and a second principal surface located on a side where the excitation light exits; a phosphor layer provided on the second principal surface of the transparent substrate and including an inorganic binder and a phosphor dispersed in the inorganic binder; and a filter layer provided on the first principal surface of the transparent substrate or between the second principal surface of the transparent substrate and the phosphor layer and configured to transmit the excitation light and reflect fluorescence emitted from the phosphor layer.
The phosphor layer is preferably provided in an annular shape.
The transparent substrate preferably has a thickness of 2.0 mm or less.
The phosphor layer preferably has, in a circumferential direction, a width equal to or more than six times a spot diameter of the excitation light.
The excitation light is, for example, blue light. Furthermore, the fluorescence is, for example, green light, yellow light or red light.
The filter layer is preferably a bandpass filter capable of transmitting 95% or more of light in a wavelength range of 410 to 450 nm and reflecting 95% or more of light in a wavelength range of 500 to 750 nm.
The inorganic binder is, for example, glass.
The difference in refractive index between the transparent substrate and the inorganic binder is preferably 0.4 or less.
The phosphor layer may be divided into a plurality of regions along a circumferential direction thereof and the plurality of regions may contain different types of phosphors.
A light-emitting device for a projector according to the present invention includes the above-described fluorescent wheel for a projector according to the present invention and a light source capable of irradiating the phosphor layer of the fluorescent wheel with the excitation light.
The present invention can increase the luminescence intensity of the light-emitting device for a projector.
Hereinafter, a description will be given of preferred embodiments. However, the following embodiments are simply illustrative and the present invention is not intended to be limited to the following embodiments. In the drawings, elements having substantially the same functions may be referred to by the common references.
In a first embodiment, a filter layer is provided on a first principal surface of a transparent substrate.
In this embodiment, the phosphor layer 12 is composed of an inorganic binder and a phosphor dispersed in the inorganic binder. In this embodiment, an inorganic phosphor is used as the phosphor.
No particular limitation is placed on the type of the inorganic binder so long as it can be used as a dispersion medium for the phosphor, such as an inorganic phosphor. Examples that can be cited include glasses, such as borosilicate-based glasses and phosphate-based glasses. Note that the softening point of the glass is preferably 250° C. to 1000° C. and more preferably 300° C. to 850° C.
Alternatively, a transparent inorganic material for use in a sol-gel method can be used as the inorganic binder. An example of such a transparent inorganic material that can be cited is polysilazane. Polysilazane is capable of reacting on moisture in the air to generate ammonia and become condensed to form a SiO2 network. With the use of the transparent inorganic material, the phosphor layer 12 can be formed at relatively low temperatures (room temperature to 200° C.). Other transparent inorganic materials that can be cited include those which contain an alcohol-soluble organic silicon compound or other metal compounds (organic or inorganic) and form a SiO2 network, like glass, at relatively low temperatures in the presence of a catalyst. When such a transparent inorganic material is used together with a metal alkoxide as an organometallic compound and an alcohol as a catalyst, hydrolysis and dehydration are promoted, resulting in the formation of a SiO2 network.
No particular limitation is placed on the type of the phosphor so long as it can emit fluorescence upon entry of the excitation light 1. Specific examples of the phosphor that can be cited include one or more selected from the group consisting of, for example, oxide phosphor, nitride phosphor, oxynitride phosphor, chloride phosphor, oxychloride phosphor, sulfide phosphor, oxysulfide phosphor, halide phosphor, chalcogenide phosphor, aluminate phosphor, halophosphoric acid chloride phosphor, and garnet-based compound phosphor. With the use of blue light as excitation light, a phosphor capable of emitting as fluorescence, for example, green light, yellow light or red light can be used.
The content of the phosphor in the phosphor layer 12 is preferably in a range of 5 to 80% by volume, more preferably in a range of 10 to 75% by volume, and still more preferably in a range of 20 to 70% by volume.
The thickness of the phosphor layer 12 is preferably small to the extent that the excitation light 1 can be surely absorbed into the phosphor. The reason for this is that if the phosphor layer 12 is too thick, scattering and absorption of light in the phosphor layer 12 may become too much, so that the efficiency of emission of fluorescence may be low. Specifically, the thickness of the phosphor layer 12 is preferably 1 mm or less, more preferably 0.5 mm or less, and still more preferably 0.3 mm or less. The lower limit of the thickness of the phosphor layer 12 is generally about 0.03 mm.
The filter layer 13 is a filter layer configured to transmit the excitation light 1 and reflect the fluorescence emitted from the phosphor layer 12. In this embodiment, the filter layer 13 is a bandpass filter formed of a dielectric laminated film. The dielectric laminated film herein is a so-called dielectric multi-layer and is formed of a laminate of high-refractive index films and low-refractive index films. An example of the dielectric laminated film that can be used as the bandpass filter is a film in which high-refractive index films made of niobium oxide, titanium oxide, lanthanum oxide, tantalum oxide, yttrium oxide, gadolinium oxide, tungsten oxide, hafnium oxide, aluminum oxide, silicon nitride or other materials and low-refractive index films made of silicon oxide or other materials are alternately deposited.
With the use of blue light as the excitation light, an example of the filter layer 13 that can be used is a bandpass filter capable of transmitting 95% or more of light in a wavelength range of 410 to 450 nm and reflecting 95% or more of light in a wavelength range of 500 to 750 nm.
The geometric thickness of the filter layer 13 is appropriately adjusted within a range of 80 to 10000 nm according to the desired property. If the geometric thickness of the filter layer 13 is too small, the function of selectively transmitting desired visible light is less likely to be obtained. On the other hand, if the geometric thickness of the filter layer 13 is too large, the stress generating in the filter layer 13 becomes large, so that cracks may occur or the filter layer 13 may be peeled from the substrate.
When the filter layer 13 is formed of a multi-layer in which high-refractive index films and low-refractive index films are alternately deposited, the number of films deposited is appropriately adjusted within a range of 8 to 100.
No particular limitation is placed on the type of the transparent substrate 11 so long as it can transmit excitation light applied from a light source. Therefore, the term “transparent” of the transparent substrate 11 means being transparent to excitation light. Examples of the transparent substrate 11 that can be used include inorganic substrates, such as a glass substrate, a crystallized glass substrate and a ceramic substrate, and resin substrates. With the use of an inorganic substrate as the transparent substrate 11, the phosphor layer 12 can be formed directly on top of (inorganically bonded to) the transparent substrate 11 by applying an inorganic binder containing a phosphor on the surface of the transparent substrate 11 and subjecting them to heat treatment. The fluorescent wheel 10 thus produced is composed only of inorganic materials and, therefore, has excellent thermal resistance. Other than the above, examples of a method for forming the phosphor layer 12 on top of the transparent substrate 11 include the method of spraying an inorganic binder in slurry form containing a phosphor on the surface of the transparent substrate 11 and the method of screen-printing the inorganic binder in slurry form on the surface of the transparent substrate 11. The phosphor layer 12 and the transparent substrate 11 may be bonded together with a heat-resistant resin or glass.
In this embodiment, the thickness t of the transparent substrate 11 shown in
If the difference in refractive index between the transparent substrate 11 and the phosphor layer 12 is made small, it can be suppressed that while the excitation light 1 having permeated the transparent substrate 11 enters the phosphor layer 12, it is reflected at the interface between the transparent substrate 11 and the phosphor layer 12. Therefore, the amount of excitation light 1 entering the phosphor layer 12 can be increased. An example of a method for making the difference in refractive index between the transparent substrate 11 and the phosphor layer 12 small when a glass substrate is used as the transparent substrate 11 is the method of making the difference in refractive index between glass for use in the glass substrate and an inorganic binder in the phosphor layer 12 small. The difference in refractive index between the transparent substrate 11 and the inorganic binder in the phosphor layer 12 is preferably 0.4 or less.
Excitation light 1 emitted from the light source 20 passes through the filter layer 13 and the transparent substrate 11 of the fluorescent wheel 10 and then enters the phosphor layer 12. The excitation light 1 having entered the phosphor layer 12 excites the phosphor, so that fluorescence 2 is emitted from the phosphor. Specific examples of the light source 20 that can be cited include an LED light source and a laser light source.
In the case of using as the light source 20 a light source emitting blue light as excitation light, for example, a phosphor capable of being excited by blue light to emit yellow light, green light or red light can be used as the phosphor for the phosphor layer 12. It is possible to extract, from the light emitted from the phosphor layer 12, only part thereof having a desired wavelength using a filter as necessary. An annular filter may be attached to the rotary shaft 22 and rotated in synchronism with the fluorescent wheel 10 to filter the emitted light.
In this embodiment, the fluorescent wheel 10 is configured to rotate circumferentially. Therefore, the region being subjected to the excitation light 1 from the light source 20 keeps moving, so that even if it is subjected to the excitation light 1 and heated, the heat is immediately released. Thus, the temperature rise of the fluorescent wheel 10 can be suppressed.
Using glass substrates having a thickness of 0.55 mm as transparent substrates 11, a fluorescent wheel 10 provided with a filter layer 13 on the incident surface (first principal surface 11a) of the transparent substrate 11 and a fluorescent wheel not provided with any filter layer 13 were produced.
As phosphor layers 12, two types of phosphor layers were formed: a phosphor layer in which a phosphor capable of being excited by blue light to emit green light as fluorescence was used; and a phosphor layer in which a phosphor capable of being excited by blue light to emit yellow light as fluorescence was used. Therefore, a total of four types of fluorescent wheels were produced.
Light having a wavelength of 445 nm was applied as excitation light 1 and the intensity of fluorescence emitted from the phosphor layer 12 was measured with an integrating sphere having a 13 mm diameter opening, disposed above the phosphor layer 12.
In a second embodiment, a filter layer is provided between a second principal surface of a transparent substrate and a phosphor layer.
Examples of the transparent substrate 11, the phosphor layer 12, and the filter layer 13 that can be used in this embodiment are the same as those in the first embodiment.
Furthermore, in this embodiment, since the filter layer 13 is provided between the transparent substrate 11 and the phosphor layer 12, it can be suppressed that the fluorescence 2 emitted from the phosphor layer 12 enters the transparent substrate 11. In the first embodiment, as shown in
The fluorescent wheel according to this embodiment can also be used for the light-emitting device shown in
Using glass substrates having a thickness of 0.55 mm as transparent substrates 11, the following fluorescent wheels were produced:
a fluorescent wheel according to the first embodiment in which a filter layer 13 was provided on the incident surface (first principal surface 11a) of a transparent substrate 11;
a fluorescent wheel according to the second embodiment in which a filter layer 13 was provided between a transparent substrate 11 and a phosphor layer 12; and
a fluorescent wheel for comparison in which no filter layer 13 was provided.
The filter layers 13 used were those having a spectral property shown in
Light having a wavelength of 436 nm was applied and light emitted from each fluorescent wheel was focused on a photoreceiver using a lens and measured.
In the fluorescent wheels 10 according to the above embodiments, a phosphor of the same type is contained in the whole area of the phosphor layer 12. However, the present invention is not limited to this form. As in an embodiment to be described below, the phosphor layer 12 may be divided into a plurality of regions along the circumferential direction thereof and the plurality of regions may contain different types of phosphors.
Although in the embodiment shown in
Also when the phosphor layer 12 is divided into a plurality of regions along the circumferential direction, the luminescence intensity of fluorescence emitted from each of the first regions 12a, the second regions 12b, and the third regions 12c can be increased by providing the filter layer 13 on the first principal surface 11a of the transparent substrate 11 or between the second principal surface 11a thereof and the phosphor layer 12. Alternatively, any one of the first region 12a, the second region 12b, and the third region 12c may be a region not provided with the phosphor layer 12.
1 . . . excitation light
2 . . . fluorescence
10 . . . fluorescent wheel
11 . . . transparent substrate
11
a . . . first principal surface
11
b . . . second principal surface
12 . . . phosphor layer
12
a to 12c . . . first to third regions
13 . . . filter layer
14 . . . phosphor
20 . . . light source
21 . . . motor
22 . . . rotary shaft
31 . . . light-emitting device for projector
Number | Date | Country | Kind |
---|---|---|---|
2013-234799 | Nov 2013 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2014/078566 | 10/28/2014 | WO | 00 |