JP2020095065A - Light emitting element and light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce light density quenching due to irradiated excitation light in a light emitting element that emits fluorescence. A light emitting element (10) emits fluorescence based on a predetermined excitation light. The light emitting element includes a phosphor layer (11) and an object layer (12). The fluorescent material layer contains a fluorescent material (13) that emits fluorescence. The object layer has a refractive index (n2) different from the refractive index (n1) in the phosphor layer. A plurality of phosphor layers and object layers are alternately laminated. In the periodic structure (5) including the laminated phosphor layer and the object layer, the phosphor layer and the object layer are periodic so that the peak of the intensity distribution of the electric field when the excitation light is incident is located on the object layer. Is located in. [Selection diagram] Fig. 3

Description

The present disclosure relates to a light emitting element and a light emitting device that emit fluorescence based on excitation light.

Non-Patent Document 1 discloses a technique using a one-dimensional photonic crystal in order to enhance fluorescence emission based on excitation light. The one-dimensional photonic crystal of Non-Patent Document 1 is configured by repeatedly stacking a layer containing a quantum dot phosphor and a layer made of another material, and an electric field of excitation light inside each phosphor layer. It is designed to be stronger than another adjacent layer. As a result, a large fluorescence emission intensity can be obtained even when excitation light having a low intensity is used.

K. Min, et al, "Enhanced fluorescence from CdSe/ZnS quantum dot nanophosphors embedded in a one-dimensional phoenic4,5,15,14,15,14,15,14,14,15,14,14,15,14,15,14,14,14,14,14,14,14,14,14,14,14,14,14,15,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14.

The present disclosure provides a light-emitting element and a light-emitting device that can reduce light density quenching due to excitation light applied to a light-emitting element that emits fluorescence.

A light emitting element according to an aspect of the present disclosure emits fluorescence based on predetermined excitation light. The light emitting element includes a phosphor layer and an object layer. The phosphor layer includes a phosphor that emits fluorescence. The object layer has a refractive index different from that of the phosphor layer. A plurality of phosphor layers and object layers are alternately laminated. In a periodic structure including a stacked phosphor layer and object layer, the phosphor layer and the object layer are periodically arranged so that the peak of the intensity distribution of the electric field when excitation light enters is located in the object layer. ing.

A light emitting device according to one aspect of the present disclosure includes an excitation light source and a light emitting element. The excitation light source emits a predetermined excitation light. The light emitting element includes a periodic structure in which a plurality of phosphor layers, each including a phosphor layer containing a phosphor that emits fluorescence based on excitation light, and an object layer having a refractive index lower than that of the phosphor layer are alternately stacked. .. The periodic structure includes a first photonic band that defines a light dispersion relationship and a second photonic band that defines a light dispersion relationship with a photonic band gap and a larger angular frequency than the first photonic band. Have. The excitation light has an angular frequency near the band edge in the second photonic band.

According to the light emitting device and the light emitting device according to the present disclosure, when excitation light enters the light emitting device, the peak position of the electric field intensity is outside the phosphor layer. Thereby, the light density quenching due to the excitation light with which the light emitting element is irradiated can be reduced.

FIG. 3 is a diagram showing a configuration of a projector according to the first embodiment of the present disclosure. FIG. 2 is a diagram showing a configuration of a light emitting element according to Embodiment 1. FIG. 3 is a diagram for explaining the function of the light emitting element according to the first embodiment. Graph for explaining the relation of light dispersion in the photonic crystal of the light emitting device Graph showing simulation result of electric field analysis for light emitting element FIG. 3 is a diagram for explaining a modification of the light emitting element according to the first embodiment. The figure which illustrates the structure of the light emitting element which concerns on other embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed description of well-known matters or duplicate description of substantially the same configuration may be omitted. This is to prevent the following description from being unnecessarily redundant and to facilitate understanding by those skilled in the art.

It should be noted that the applicant provides the accompanying drawings and the following description for those skilled in the art to fully understand the present disclosure, and is not intended to limit the subject matter described in the claims by these. Absent.

(Embodiment 1)
In the first embodiment, the light emitting element and the light emitting device according to the present disclosure will be described using an application example to a projector.

[1. Constitution]
The configurations of the light emitting device and the light emitting element according to this embodiment will be described below.

[1-1. About projector]
The light emitting device according to the present disclosure is used, for example, as a light source in a projector. The configurations of the projector and the light emitting device according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of a projector 1 in this embodiment.

As shown in FIG. 1, the projector 1 includes a light emitting device 2, a light guide optical system 3, a DMD (digital mirror device) 49, and a projection lens 51. The projector 1 projects projection light showing an image on a screen or the like. The light emitting device 2 emits yellow light, for example. The projector 1 further includes, for example, a blue light source (not shown) that emits blue light, and uses the yellow light from the light emitting device 2 and the blue light to generate projection light.

The light emitting device 2 includes an excitation light source 41, a collimating lens system 42, a dichroic mirror 43, a condensing optical system 44, and a phosphor wheel 20. The light emitting device 2 uses the phosphor wheel 20 to perform wavelength conversion from excitation light of blue light to fluorescence of yellow light, for example.

In this embodiment, the excitation light source 41 emits blue light having a wavelength of 450 nm as excitation light. The excitation light source 41 is composed of, for example, a plurality of semiconductor lasers (LD). The excitation light source 41 is not limited to the LD, and may be configured by various light source elements such as LEDs.

The collimating lens system 42 includes a plurality of lenses such as a collimating lens, and is arranged between the excitation light source 41 and the phosphor wheel 20. The collimator lens system 42 collimates the light incident on the light emitting element 10.

The dichroic mirror 43 has an optical characteristic of transmitting blue light and reflecting yellow light, for example. The dichroic mirror 43 is arranged to face the excitation light source 41 via the collimating lens system 42, the phosphor wheel 20, and the condensing optical system 44.

The condensing optical system 44 includes, for example, a plurality of optical lenses. The condensing optical system 44 is arranged so that the focal position is located on the main surface of the phosphor wheel 20. The focus position of the condensing optical system 44 may be near the main surface of the phosphor wheel 20.

In the light emitting device 2, the excitation light emitted from the excitation light source 41 is collimated by the collimator lens system 42 as shown in FIG. 1, and corresponds to the focal position of the condensing optical system 44 on the main surface of the phosphor wheel 20. The position is illuminated. The optical system inside the light emitting device 2 is not limited to the above configuration, and may be set as appropriate.

The phosphor wheel 20 includes a light emitting element 10 that emits fluorescence based on excitation light, a base material 21 having a main surface, and a rotating device 22 including a motor and the like. The light emitting element 10 is provided on the main surface of the base material 21. The rotation device 22 rotationally drives the base material 21 with the main surface as a rotation surface. The phosphor wheel 20 rotates the irradiation position of the excitation light in the light emitting element 10 on the base material 21, and converts the excitation light into fluorescence while cooling the light emitting element 10.

The light emitting device 10 according to the present embodiment can reduce light density quenching, which decreases internal quantum efficiency in conversion of excitation light into fluorescence when the light intensity of the excitation light is increased. The configuration of the light emitting element 10 will be described later.

In the present embodiment, the phosphor wheel 20 is a transmissive type and emits the converted fluorescence in the same direction as the incident direction of the excitation light. The fluorescent light (yellow light) emitted from the phosphor wheel 20 is incident on the dichroic mirror 43 in a parallelized state by moving backward through the condensing optical system 44. The light emitting device 2 reflects the yellow light after the wavelength conversion by the dichroic mirror 43 and emits it to the light guide optical system 3.

The light guide optical system 3 includes a condenser lens 45, a rod integrator 46, a relay lens 47, a field lens 48, and a total reflection prism 50. The light guide optical system 3 collects the yellow light from the light emitting device 2 on the rod integrator 46 by the condensing lens 45, and the rod integrator 46 combines the yellow light and the separately supplied blue light into white light. The combined white light is guided to the DMD 49 via the relay lens 47, the field lens 48, and the total reflection prism 50.

The DMD 49 spatially modulates the white light guided from the light guiding optical system 3 to generate projection light so as to represent a video based on a video signal from the outside. The projector 1 is not limited to the DMD 49, and various spatial light modulators such as a liquid crystal panel may be used.

The projection lens 51 projects the projection light generated by the DMD 49 to the outside of the projector 1. As a result, a desired image is displayed based on the projection light from the projector 1. At this time, the upper limit of the brightness of the image is defined by the light output from the light emitting device 2 or the like.

In the projector 1 as described above, it is required to increase the brightness of the projection light. In order to increase the brightness of the projector 1, the light intensity of the excitation light from the excitation light source 41 is increased in order to increase the light output of the light emitting device 2.

The conventional projector has a problem that when the light intensity of the excitation light is increased, the conversion efficiency of the excitation light into the fluorescence is reduced due to the influence of the light density quenching. Therefore, in the light emitting device 2 according to the present embodiment, the light emitting element 10 reduces the light density quenching due to the excitation light emitted from the excitation light source 41. Hereinafter, the configuration of the light emitting element 10 according to the present embodiment will be described.

[1-2. Configuration of light emitting element]
The configuration of the light emitting element 10 according to the first embodiment will be described with reference to FIG. FIG. 2 is a diagram showing a configuration of the light emitting element 10 according to the present embodiment.

The light emitting element 10 according to the present embodiment is configured by stacking a multilayer film on the base material 21 of the phosphor wheel 20 (FIG. 1). FIG. 2 shows a cross-sectional structure of the light emitting element 10.

Hereinafter, the thickness direction of the light emitting element 10 will be referred to as the X direction, and two directions along the main surface of the light emitting element 10 that are orthogonal to each other will be referred to as the Y direction and the Z direction. In addition, the excitation light is assumed to be incident from the −X side of the light emitting element 10.

As shown in FIG. 2, the light emitting element 10 includes a plurality of phosphor layers 11, a plurality of low refractive index layers 12, a substrate 16, and a dichroic filter 17.

The phosphor layer 11 includes a phosphor that emits fluorescence (yellow light) by being excited by incident excitation light (blue light). The refractive index n1 of the phosphor layer 11 is, for example, n1=1.8, and the thickness TH1 of the phosphor layer 11 is, for example, TH1=75 nm.

In the present embodiment, the phosphor layer 11 is made of a nanocomposite material containing the quantum dots 13 that form particles of the phosphor. The quantum dots 13 are composed of, for example, CdSe, CuInS ₂ . According to the phosphor layer 11 in the present embodiment, by controlling the density of the quantum dots 13 and the like, it is possible to obtain desired physical properties such as the refractive index n1.

The low refractive index layer 12 is made of various materials that transmit excitation light (for example, PMMA or CA resin). The refractive index n2 of the low refractive index layer 12 is, for example, n2=1.5, and the thickness TH2 of the low refractive index layer 12 is, for example, TH2=72 nm. The low refractive index layer 12 may be composed of a nanocomposite material. The low refractive index layer 12 is an example of the object layer in this embodiment.

In the light emitting element 10 according to the present embodiment, as shown in FIG. 2, a plurality of phosphor layers 11 and low refractive index layers 12 are alternately laminated. The plurality of phosphor layers 11 and the plurality of low refractive index layers 12 that are stacked together form a photonic crystal 5. The number of the phosphor layers 11 and the number of the low refractive index layers 12 in the photonic crystal 5 are, for example, 10 layers or more, for example, several hundred layers.

In the light emitting device 10 according to the present embodiment, for example, a photonic crystal in which the phosphor layers 11 and the low refractive index layers 12 set to the thicknesses TH1 and TH2 and the refractive indices n1 and n2 as described above are periodically arranged. The periodic structure of No. 5 controls the intensity distribution of the excitation light and reduces the light density quenching. The photonic crystal 5 is an example of the periodic structure in this embodiment. Details of the photonic crystal 5 will be described later.

The substrate 16 is, for example, a sapphire substrate. The substrate 16 may be fixed on the main surface of the base material 21 of the phosphor wheel 20 (FIG. 1), or may be configured integrally with the base material 21.

The dichroic filter 17 is a dielectric multilayer film and has optical characteristics of transmitting a wavelength band of excitation light (for example, blue light) and reflecting a wavelength band of fluorescence (for example, yellow light). The dichroic filter 17 is provided on the surface of the substrate 16 on which the excitation light enters.

[2. motion]
The operations of the light emitting device 2 and the light emitting element 10 according to the present embodiment will be described below.

In the light emitting device 2 (FIG. 1) according to this embodiment, the excitation light source 41 irradiates the light emitting element 10 with excitation light. As shown in FIG. 2, the excitation light from the excitation light source 41 enters in the +X direction from the −X side of the light emitting element 10. The excitation light passes through the dichroic filter 17 in the light emitting element 10 and propagates so as to sequentially pass through the phosphor layer 11 and the low refractive index layer 12 that are stacked as a plurality of photonic crystals 5. Each time the excitation light propagates through the phosphor layer 11, it is absorbed by the quantum dots 13 of the phosphor and converted into fluorescence.

As shown in FIG. 2, the converted fluorescent light in the light emitting element 10 includes light emitted from the +X side in the +X direction and light emitted from the +X side due to the fluorescent light in the −X direction that is reflected by the dichroic filter 17. There are two types of light. That is, the light emitting element 10B emits the converted light so that the light is transmitted from the +X side based on the excitation light that is incident from the −X side. The light emitting device 2 outputs the fluorescence (yellow light) emitted from the light emitting element 10.

[2-1. About light emitting element]
The light emitting device 10 according to the present embodiment has a function of controlling the electric field distribution of the excitation light by the periodic structure of the photonic crystal 5 when converting the excitation light into fluorescence in the light emitting device 2 as described above. The function of the light emitting element 10 will be described with reference to FIG.

FIG. 3 shows the spatial distribution of the electric field intensity distributed inside the photonic crystal 5 when the excitation light enters the light emitting element 10. Hereinafter, it is assumed that the excitation light is a TE wave propagating in the X direction and that the transverse wave component of the electric field vibrates in the Y direction. In FIG. 3, the horizontal axis represents the position in the X direction, and the vertical axis represents the intensity of the Y component Ey of the electric field (that is, the light intensity of the TE wave).

When the excitation light enters the light emitting element 10, the excitation light is distributed as a wave having a wave number kx corresponding to the frequency of the excitation light according to the light dispersion relationship defined by the periodic structure of the photonic crystal 5. At this time, as shown in FIG. 3, periodic peaks (maximum values) and valleys (minimum values) are formed in the distribution of the electric field intensity of the excitation light. Here, in the vicinity of the peak of the electric field intensity of the excitation light, the light intensity of the excitation light becomes larger than that of the surroundings, and it is considered that the influence of the light density quenching is great.

Therefore, in the present embodiment, the photonic crystal 5 is configured such that the periodic peaks of the electric field intensity Ey ² of the excitation light inside the photonic crystal 5 are located in the low refractive index layer 12, respectively. At this time, a periodic valley having, for example, an electric field intensity Ey ² is located in each phosphor layer 11 (FIG. 3 ).

According to the light emitting element 10 as described above, when the light emitting element 10 is irradiated with the excitation light, the electric field intensity Ey ² in the phosphor layer 11 becomes lower than the peak value inside the light emitting element 10, and may occur at the peak value. The light density extinction in the light emitting element 10 can be reduced more than the light density extinction. Thereby, when the light intensity of the excitation light output from the excitation light source 41 is increased, the loss due to the light density quenching can be reduced, and the conversion efficiency of the excitation light into the fluorescence in the light emitting device 2 can be improved.

[2-1-1. About photonic crystals]
Details of the photonic crystal 5 for realizing the functions of the light emitting element 10 as described above will be described with reference to FIG.

FIG. 4 is a graph for explaining a light dispersion relationship in the photonic crystal 5 of the light emitting element 10. The horizontal axis of FIG. 4 is the wave number kx in the X direction (see FIG. 2). The vertical axis of FIG. 4 is the wavelength λ. Curves C1 and C2 show the relationship of light dispersion in the photonic crystal 5.

In the light emitting device 10 (FIG. 2) according to the present embodiment, the light dispersion relationship is defined in the photonic crystal 5 by the following formula due to the periodic structure of the phosphor layer 11 and the low refractive index layer 12. It

上式（１）において、ａは蛍光体層１１の厚さを表すパラメータであり、ｂは低屈折率層１２の厚さを表すパラメータであり、ｃは（真空中又は空気中の）光速である。また、変数ｋ１ｘは上式（２）のとおり蛍光体層１１の屈折率ｎ１と光の角振動数ω（周波数の２π倍）とに依存し、変数ｋ２ｘは上式（３）のとおり低屈折率層１２の屈折率ｎ２と光の角振動数ωとに依存する。

In the above equation (1), a is a parameter representing the thickness of the phosphor layer 11, b is a parameter representing the thickness of the low refractive index layer 12, and c is the speed of light (in vacuum or in air). is there. Also, the variable k1x depends on the refractive index n1 of the phosphor layer 11 and the angular frequency ω of light (2π times the frequency) as in the above equation (2), and the variable k2x has a low refractive index as in the above equation (3). It depends on the refractive index n2 of the refractive index layer 12 and the angular frequency ω of light.

Equation (1) substitutes the electromagnetic wave solution corresponding to the periodic structure of the photonic crystal 5 based on Bloch's theorem in the wave equation (Maxwell equation) of the electromagnetic wave propagating in the X direction, and also expands the dielectric constant by Fourier series. It is obtained by things.

In the photonic crystal 5, the wave number kx corresponding to the angular frequency ω of light becomes a complex number according to the equation (1), and a frequency section that does not exist in a real number, that is, a photonic band gap occurs (see FIG. 4 ). The photonic crystal 5 has first and second photonic bands that define the dispersion relation of light having the angular frequency ω of light outside the photonic band gap based on the equation (1).

In the photonic crystal 5, the first photonic band associates the angular frequency ω of light below the photonic band gap with the real wave number kx. The second photonic band associates the angular frequency ω of light with the photonic band gap or more with the real wave number kx.

In FIG. 4, the curve C1 corresponds to the first photonic band. The curve C2 corresponds to the second photonic band. In FIG. 4, since the wavelength λ (=2πc/ω) is used on the vertical axis, the curve C1 of the first photonic band is above the curve C2 of the second photonic band.

The minimum value of the curve C1 of the first photonic band represents the photonic band edge (PBE) on the first photonic band side, that is, the band edge in the first photonic band. Further, the maximum value of the curve C2 of the second photonic band represents PBE on the second photonic band side, that is, the band edge in the second photonic band.

In this embodiment, the angular frequency (or equivalently the wavelength) of the excitation light emitted from the excitation light source 41 of the light emitting device 2 (FIG. 1) and the vicinity of the PBE on the second photonic band side are matched. , Photonic crystal 5 (FIG. 4). The vicinity of the PBE is, for example, a frequency position where the reflectance is minimum in the frequency spectrum of the light reflectance of the photonic crystal 5, and is within a range including the frequency position adjacent to the PBE.

According to the configuration of the photonic crystal 5 described above, when light having the same angular frequency as the excitation light is distributed inside the photonic crystal 5, the peak of the electric field intensity is located in the low refractive index layer 12 as described above. (See FIG. 3). With such a configuration, the thicknesses TH1 and TH2 of the layers 11 and 12 and the refractive indices n1 and n1 are set so that the angular frequency near PBE based on the equation (1) matches the angular frequency of the excitation light used as the reference. Obtained by setting n2. The values of the various parameters TH1, TH2, n1, and n2 can be appropriately selected within the range where the above relationship is established from the equation (1). Further, the frequency of the excitation light used as the reference may be set appropriately.

Further, since the angular frequency of the excitation light is near the minimum angular frequency position of the reflectance spectrum in the vicinity of PBE, it is possible to reduce the loss due to the reflection when the excitation light is incident on the light emitting element 10. The efficiency of conversion from light to fluorescence can be improved.

[2-2. About simulation]
With respect to the light emitting element 10 based on the photonic crystal 5 as described above, a simulation performed by the inventor of the present application will be described with reference to FIG.

FIG. 5 is a graph showing the results of an electric field analysis simulation in the photonic crystal 5 of the light emitting device 10. The vertical axis of FIG. 5 represents the time T in terms of distance using the speed of light c (cT [μm]), and the horizontal axis represents the electric field strength Ey ² in arbitrary units.

In the analysis simulation of FIG. 5, the intensity of the electric field when the excitation light (TE wave) is incident on the photonic crystal 5 of the light emitting device 10 according to this embodiment is simulated by the FDTD method. At this time, the assumption was used that the excitation light was not attenuated by fluorescence emission. In such a simulation model of the photonic crystal 5, when the transmitted light, the reflected light, and the light passing through the predetermined position inside the phosphor layer 11 are numerically calculated, the time change of the electric field intensity Ey ² is shown in FIG. The result is as follows.

According to FIG. 5, the electric field intensity Ey ² of the excitation light is reduced to about 20% of the transmitted light inside the phosphor layer 11. According to the above assumption, the light incident on the simulation model of the photonic crystal 5 is transmitted without being absorbed. From this, it is considered that the curve of the transmitted light in FIG. 5 corresponds to the electric field intensity Ey ² generated in the conventional phosphor structure (for example, bulk structure) that does not use the periodic structure like the photonic crystal 5 in the present embodiment. Be done. Therefore, it was confirmed that the photonic crystal 5 in the present embodiment can reduce the light intensity of the excitation light in the phosphor layer 11 as compared with the conventional structure.

[3. Effect, etc.]
As described above, the light emitting element 10 according to the present embodiment emits fluorescence based on the excitation light set in advance. The light emitting element 10 includes a phosphor layer 11 and a low refractive index layer 12 as an object layer. The phosphor layer 11 includes fluorescent quantum dots 13 that emit fluorescence. The low refractive index layer 12 has a refractive index n2 different from the refractive index n1 of the phosphor layer 11. A plurality of phosphor layers 11 and low refractive index layers 12 are alternately laminated. In the photonic crystal 5 which is a periodic structure including the laminated phosphor layer 11 and the low refractive index layer 12, the peak of the intensity distribution of the electric field when excitation light is incident is located in the low refractive index layer 12. The phosphor layers 11 and the low refractive index layers 12 are periodically arranged.

According to the light emitting element 10 described above, the peak position of the electric field intensity is outside the phosphor layer 11 when the excitation light enters the light emitting element 10. Thereby, the light density quenching due to the excitation light with which the light emitting element 10 is irradiated can be reduced.

In the present embodiment, the photonic crystal 5 defines a first photonic band that defines the light dispersion relationship and a second photonic band that defines the light dispersion relationship of a frequency that is larger than the first photonic band by a photonic band gap. With a photonic band. Based on such a photonic band structure, the distribution of the electric field intensity of the excitation light can be controlled and the light density quenching can be reduced.

Further, in the present embodiment, the refractive index n2 of the low refractive index layer 12 is lower than the refractive index n1 of the phosphor layer 11. The band edge in the second photonic band has a frequency near the frequency of the excitation light (FIG. 4). When the refractive index is n2<n1, the light density quenching in the light emitting element 10 can be reduced by setting the PBE on the second photonic band side near the frequency of the excitation light.

Further, in the present embodiment, in the periodic structure, at least 10 layers each of the phosphor layer 11 and the low refractive index layer 12 are laminated. Thereby, the periodic structure functions as the photonic crystal 5, and the distribution of the electric field strength can be controlled.

In addition, in the present embodiment, the light emitting device 2 includes the light emitting element 10 and the excitation light source 41 that irradiates the light emitting element 10 with excitation light. The light emitting element 10 includes a photonic crystal 5. The photonic crystal 5 is a periodic structure in which a plurality of phosphor layers 11 and low refractive index layers 12 having a refractive index n2 lower than the refractive index n1 of the phosphor layers 11 are alternately laminated. The photonic crystal 5 has a first photonic band and a second photonic band. The excitation light has a frequency near the band edge in the second photonic band.

According to the light emitting device 2 described above, in the light emitting element 10 that emits fluorescence, it is possible to reduce the light density quenching due to the excitation light with which the light emitting element 10 is irradiated.

(Modification)
The light emitting device 10 according to the first embodiment includes the photonic crystal 5. In the light emitting device according to the present disclosure, a periodic structure such as the photonic crystal 5 may be partially provided. This modification will be described with reference to FIG.

FIG. 6 is a diagram for explaining a light emitting element 10A according to a modified example of the first embodiment. As shown in FIG. 6, the light emitting device 10A according to this modification includes a photonic crystal 5 and a bulk structure 6. The bulk structure 6 is made of, for example, a material similar to that of the phosphor layer 11 of the photonic crystal 5 or a material having similar fluorescence characteristics. The photonic crystal 5 is stacked on the −X side of the bulk structure 6 (excitation light incident side).

In the light emitting device 2, it is considered that the light density quenching by the excitation light is remarkable on the incident side of the excitation light in the light emitting element 10A. Therefore, in the light emitting device 10A according to the present modification, the photonic crystal 5 is provided on the incident side of the excitation light, and the bulk phosphor (bulk structure 6) is used for the remaining part.

As an example, in the photonic crystal 5, the phosphor layer 11 and the low refractive index layer 12 are laminated in 200 layers, respectively, and the thickness TH1 of the phosphor layer 11 per layer is TH1=70 nm, and the absorptance α of the phosphor is α= Consider the case of 1000 cm ⁻¹ . In this case, the total thickness of the phosphor layer 11 in the photonic crystal 5 is 14 μm. In this case, assuming that the light intensity of the excitation light before entering the light emitting element 10A is I0, the light intensity after the excitation light propagates inside the photonic crystal 5 can be calculated by the following equation.

I0*exp(-0.0014*1000)=0.247*I0 (4)
According to the above equation (4), the light intensity after propagating inside the photonic crystal 5 is attenuated by about 1/4. Therefore, by providing the photonic crystal 5 on the −X side of the bulk structure 6 as described above, when the excitation light enters the bulk structure 6 through the photonic crystal 5, the light intensity of the excitation light is about 1 or less. It can be reduced to /4 times.

In the bulk structure 6, since the light intensity of the excitation light is reduced via the photonic crystal 5, the influence of the light density quenching is suppressed, and the excitation light can be efficiently absorbed and converted into fluorescence. .. The thickness of the bulk structure 6 may be appropriately set in consideration of the light intensity of the excitation light reduced by the photonic crystal 5 to a thickness at which the excitation light is assumed to be sufficiently absorbed. (For example, 100 μm to 200 μm).

As described above, the light emitting device 10A according to the present modification further includes the bulk structure 6 made of a phosphor that emits fluorescence. The photonic crystal 5, which is a periodic structure, is provided on the incident side (−X side) of the excitation light with respect to the bulk structure 6. Thereby, the light density quenching can be reduced in the photonic crystal 5, and the excitation light can be efficiently converted into fluorescence in the bulk structure 6 as well.

(Other embodiments)
As described above, the first embodiment and its modifications have been described as examples of the technique disclosed in the present application. However, the technique in the present disclosure is not limited to this, and is also applicable to the embodiment in which changes, replacements, additions, omissions, etc. are appropriately made. Further, it is also possible to combine the respective constituent elements described in each of the above-described embodiments to form a new embodiment. Therefore, other embodiments will be exemplified below.

In each of the above embodiments, the light emitting element 10 in the transmissive phosphor wheel 20 has been described, but the light emitting element according to the present disclosure is not limited to the transmissive phosphor wheel, but can be applied to a reflective phosphor wheel. The reflective light emitting element 10B will be described with reference to FIG.

FIG. 7: is a figure which illustrates the structure of the light emitting element 10B which concerns on other embodiment. In the light emitting device 10B of this example, in the same configuration as that of the first embodiment (FIG. 2), the substrate 16 and the dichroic filter 17 provided on the −X side are omitted, and instead, the metal substrate 15 and the adhesive layer 14 are provided on the +X side. Is provided. The metal substrate 15 is made of, for example, silver, and forms a reflection surface that reflects light such as fluorescence on the side (+X side) opposite to the excitation light incident side (−X side) in the light emitting element 10B. The adhesive layer 14 is made of various adhesives and bonds the photonic crystal 5 and the metal substrate 15 together.

In the light emitting element 10B of this example, the light propagating in the +X direction is reflected by the reflection surface of the metal substrate 15, and the propagation direction becomes the −X direction. Therefore, when the excitation light is incident in the +X direction from the −X side as in the first embodiment, the fluorescence converted from the excitation light is emitted in the −X direction of the light emitting element 10. The reflective surface of the light emitting element 10B may be formed by metal coating or the like.

As described above, the light emitting element 10B of the present example is further provided with the reflection surface that reflects light on the side (+X side) opposite to the excitation light incident side (−X side). As a result, the light emitting element 10B emits the converted light so as to reflect the incident excitation light.

In each of the above embodiments, the low refractive index layer 12 is used as the object layer in the light emitting devices 10 to 10B. In the light emitting device according to the present disclosure, the object layer is not limited to the low refractive index layer 12, and may be a high refractive index layer having a refractive index higher than that of the phosphor layer 11.

In this case, a photonic crystal having a periodic structure of the phosphor layer 11 and the high refractive index layer is configured so that the vicinity of PBE on the first photonic band side matches the excitation light (see FIG. 4). Thereby, in the photonic crystal, the peak of the intensity distribution of the electric field when the excitation light is incident can be set to be located in the high refractive index layer.

As described above, the refractive index of the object layer may be higher than that of the phosphor layer 11. In this case, the band edge in the first photonic band has a frequency near the frequency of the excitation light. Thereby, the light density quenching in the light emitting element 10 can be reduced by using the high refractive index layer.

Further, in each of the above-described embodiments, quantum dots are used as the phosphors in the phosphor layer 11 in the light emitting elements 10 to 10B. In the present disclosure, the phosphor in the phosphor layer or the like is not limited to quantum dots, and various phosphor materials may be used, such as YAG.

Further, in each of the above-described embodiments, an example has been described in which the light emitting device 2 converts the excitation light of blue light into fluorescence and outputs yellow light. The light emitting device according to the present disclosure is not limited to this. For example, the light emitting device may convert a part of the excitation light of blue light into yellow light and combine the remaining blue light to generate white light. In this case, a separate blue light source can be omitted in the projector 1.

Further, in the present disclosure, the excitation light is not limited to blue light and may be light in various wavelength bands. Further, the fluorescence is not limited to yellow light and may be light in various wavelength bands. As described above, the light emitting device according to the present disclosure may output various kinds of light based on various kinds of excitation light.

Further, in each of the above-described embodiments, an application example in which the light emitting device 2 is applied to the projector 1 has been described. The light emitting device according to the present disclosure is applicable not only to the projector 1 but also to various techniques using fluorescence emission based on excitation light.

Further, in each of the above-described embodiments, the light emitting device 2 includes the light emitting element 10 incorporated in the phosphor wheel 20. The light emitting device according to the present disclosure may include the light emitting element according to the present disclosure without being incorporated in the phosphor wheel. For example, the rotating device 22 may be omitted in the light emitting device 2 when the light emitting element is not particularly required to be cooled or when it can be cooled by another mechanism.

As described above, the embodiments have been described as examples of the technology according to the present disclosure. To that end, the accompanying drawings and detailed description are provided.

Therefore, among the constituent elements described in the accompanying drawings and the detailed description, not only constituent elements essential for solving the problem but also constituent elements not essential for solving the problem in order to exemplify the above technology. Can also be included. Therefore, it should not be immediately recognized that the non-essential components are essential, because the non-essential components are described in the accompanying drawings and the detailed description.

Further, since the above-described embodiments are for exemplifying the technique of the present disclosure, various changes, substitutions, additions, omissions, etc. can be made within the scope of the claims or the scope of equivalents thereof.

The present disclosure is applicable to various technologies that use fluorescence emission based on excitation light, and is applicable to, for example, a projector.

10, 10A, 10B Light emitting element 11 Phosphor layer 12 Low refractive index layer 13 Quantum dot 2 Light emitting device 41 Excitation light source 5 Photonic crystal

Claims (9)

A light-emitting element that emits fluorescence based on predetermined excitation light,
A phosphor layer containing a phosphor that emits the fluorescence,
An object layer having a refractive index different from the refractive index of the phosphor layer,
The phosphor layers and the object layer are alternately laminated,
In the periodic structure including the laminated phosphor layer and object layer, the phosphor layer and the object layer are arranged so that the peak of the intensity distribution of the electric field when the excitation light is incident is located in the object layer. Light-emitting elements that are physically arranged. The periodic structure includes a first photonic band that defines a dispersion relation of light, and a second photonic band that defines a dispersion relation of light whose frequency is larger than that of the first photonic band by a photonic band gap. The light emitting device according to claim 1, comprising: The refractive index in the object layer is lower than the refractive index in the phosphor layer,
The light emitting device according to claim 2, wherein the angular frequency of the photonic band edge in the second photonic band has a value near the angular frequency of the excitation light. The refractive index in the object layer is higher than the refractive index in the phosphor layer,
The light emitting device according to claim 2, wherein a band edge in the first photonic band has an angular frequency near the angular frequency of the excitation light. Further comprising a bulk structure composed of the phosphor that emits the fluorescence,
The light emitting device according to claim 1, wherein the periodic structure is provided closer to an incident side of the excitation light than the bulk structure. The light emitting device according to claim 1, further comprising a reflecting surface that reflects light, which is provided on a side opposite to a side where the excitation light is incident. The light emitting device according to claim 1, wherein in the periodic structure, at least 10 layers of the phosphor layer and the object layer are laminated. A light-emitting element according to any one of claims 1 to 7,
A light emitting device comprising: an excitation light source that irradiates the light emitting element with the excitation light. An excitation light source that emits a predetermined excitation light,
Phosphor layers containing a phosphor that emits fluorescence based on the excitation light, and a plurality of object layers having a refractive index lower than the refractive index of the phosphor layers are alternately stacked, and light emission including a periodic structure is laminated. With elements,
The periodic structure defines a first photonic band that defines a light dispersion relationship, and a second photonic band that defines a light dispersion relationship at a higher angular frequency by a photonic band gap than the first photonic band. Has a band and
The excitation light is a light emitting device having an angular frequency near the band edge in the second photonic band.

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