Wavelength conversion component and lighting device using the same

Abstract

To provide a wavelength conversion device and an illumination device that can reduce color unevenness of outgoing light to be taken out as a whole.SOLUTION: A wavelength conversion device has: a plate-like phosphor part from one surface of which excitation light is made incident, and which includes a phosphor that is excited by the excitation light and emits fluorescent light; a plurality of first nano-antennas that are formed of transparent dielectric substance and provided periodically in a first area of the other surface on the opposite side of the one surface of the phosphor part; and a plurality of second nano-antennas that are formed of transparent dielectric substance and provided periodically in an area around the first area of the other surface. Each of the plurality of first nano-antennas has a larger diameter than that of each of the plurality of second nano-antennas in plan view seen from a direction perpendicular to the other surface.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wavelength conversion member and a lighting device using the same. [Background technology]

[0002] A device is disclosed that uses a nano-sized antenna array (hereinafter referred to as a nano-antenna) to collimate emitted light. For example, Patent Document 1 discloses a device having a light-emitting diode (LED), a phosphor layer provided on the upper surface of the LED, and a nano-antenna provided on the upper surface of the phosphor layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2022-69533 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In a device like the one described in Patent Document 1, when excitation light for exciting the phosphor in the phosphor layer is emitted from a light source, the relationship between the intensity of the excitation light passing through the phosphor layer and the intensity of the fluorescence produced by the excitation of the phosphor changes in the central and peripheral parts of the phosphor layer. This results in a problem where color unevenness occurs in the emitted light, which contains both fluorescence and excitation light.

[0005] This invention has been made in view of the above-mentioned problems, and aims to provide a wavelength conversion device and an illumination device that can reduce the color unevenness of the emitted light as a whole. [Means for solving the problem]

[0006] The wavelength conversion device according to the present invention comprises a flat phosphor portion containing a phosphor that emits fluorescence when excitation light is incident on it from one surface and excited by the excitation light; a plurality of first nanoantennas made of a transparent dielectric material periodically provided in one region on another surface of the phosphor portion opposite to the first surface; and a plurality of second nanoantennas made of a transparent dielectric material periodically provided in a region surrounding the first region on the other surface, wherein each of the plurality of first nanoantennas has a larger diameter in a plan view taken from a direction perpendicular to the other surface than each of the plurality of second nanoantennas. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic cross-sectional view showing the configuration of the lighting device according to Example 1. [Figure 2] This is a top view of the wavelength conversion device according to Example 1. [Figure 3] This is a cross-sectional view of the wavelength conversion device according to Example 1. [Figure 4A] This graph shows various diffraction lines when a nanoantenna is provided at a predetermined period in the wavelength conversion device according to Example 1. [Figure 4B] This graph shows various diffraction lines when a nanoantenna is provided at a predetermined period in the wavelength conversion device according to Example 1. [Figure 4C] This graph shows various diffraction lines when a nanoantenna is provided at a predetermined period in the wavelength conversion device according to Example 1. [Figure 4D] This graph shows various diffraction lines when a nanoantenna is provided at a predetermined period in the wavelength conversion device according to Example 1. [Figure 4E] This graph shows various diffraction lines when a nanoantenna is provided at a predetermined period in the wavelength conversion device according to Example 1. [Figure 5A] This figure shows the analysis results of the fluorescence intensity emitted through the nanoantenna in the wavelength conversion device according to Example 1. [Figure 5B]It is a diagram showing the analysis result of the intensity of fluorescence emitted through a nanoantenna in the wavelength conversion device according to Example 1. [Figure 5C] It is a diagram showing the analysis result of the intensity of fluorescence emitted through a nanoantenna in the wavelength conversion device according to Example 1. [Figure 5D] It is a diagram showing the analysis result of the intensity of fluorescence emitted through a nanoantenna in the wavelength conversion device according to Example 1. [Figure 5E] It is a diagram showing the analysis result of the intensity of fluorescence emitted through a nanoantenna in the wavelength conversion device according to Example 1. [Figure 6] It is a graph showing the penetration length of an evanescent wave with respect to the incident angle of fluorescence in the wavelength conversion device according to Example 1. [Figure 7] It is a graph showing the propagation length of an evanescent wave with respect to the incident angle of fluorescence in the wavelength conversion device according to Example 1. [Figure 8A] It is a diagram showing the analysis result of the intensity of fluorescence reflected by a nanoantenna in the wavelength conversion device according to Example 1. [Figure 8B] It is a diagram showing the analysis result of the intensity of fluorescence reflected by a nanoantenna in the wavelength conversion device according to Example 1. [Figure 8C] It is a diagram showing the analysis result of the intensity of fluorescence reflected by a nanoantenna in the wavelength conversion device according to Example 1. [Figure 9] It is a diagram showing the analysis result of the emission intensity of fluorescence with respect to the tilt angle of the side surface of the nanoantenna in the wavelength conversion device according to Example 1. [Figure 10] It is a diagram showing the analysis result of the emission intensity of excitation light with respect to the ratio of the diameter to the period of the nanoantenna in the wavelength conversion device according to Example 1. [Figure 11] It is a diagram showing the analysis result of the emission intensity of excitation light with respect to the height of the nanoantenna in the wavelength conversion device according to Example 1. [Figure 12] It is a cross-sectional view of the wavelength conversion device according to a modification of Example 1.

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the drawings, the same reference numerals are assigned to the same components, and the description of overlapping components will be omitted.

Embodiment

[0009] [Lighting device] FIG. 1 is a cross-sectional view schematically showing the configuration of a lighting device 100 according to Embodiment 1. The housing 11 is a box-shaped housing and has openings OP1 and OP2 on each of two opposing surfaces. The housing 11 has a support structure 11A protruding inward at a position between the opening OP1 and the opening OP2.

[0010] The light source 12 is a light source fixed in the opening OP1 and emitting light L1 of a specific wavelength toward the opening OP2. In other words, the opening OP2 is formed on the optical axis OA of the light L1.

[0011] The light source 12 is a laser light source having a light-emitting layer made of an indium gallium nitride (InGaN)-based semiconductor. Blue light with a peak wavelength of 450 nm is emitted from the light source 12 as the light L1. In this embodiment, the light L1 emitted from the light source 12 has a Gaussian distribution beam profile. That is, the intensity of the light L1 decreases as the radial distance from the center of the beam increases.

[0012] The condenser lens 13 is an optical lens supported by the support structure 11A so as to be located on the optical axis OA. The condenser lens 13 receives the light L1 emitted from the light source 12 and irradiates the light L2 obtained by condensing the light L1 toward the above-described opening OP2. The condenser lens 13 has a function as a beam shaping element that shapes the spot shape of the light emitted from the light source 12 into an elliptical or circular shape. The condenser lens 13 is, for example, an aspherical condenser lens.

[0013] The wavelength converter 14 is bonded to the outer surface of the housing 11 and covers the opening OP2 from the outside of the housing 11. The wavelength converter 14 is a wavelength converter that receives light L2 incident through the opening OP2 and emits fluorescence of a different wavelength from the light L2. That is, the wavelength converter 14 contains a phosphor that is excited by light L2 as excitation light, and emits fluorescence when the phosphor is excited. Hereinafter, light L2 will also be referred to as excitation light L2.

[0014] The wavelength converter 14 emits light L3, which includes the excitation light that passed through the wavelength converter 14 without contributing to fluorescence generation when it received the excitation light L2, and the fluorescence described above. The light L3 emitted from the wavelength converter 14 is taken out to the outside of the housing 11, for example, via an optical element such as a lens positioned above the wavelength converter 14.

[0015] [Wavelength conversion device of Example 1] The wavelength conversion device 14 according to Embodiment 1, provided in the above-mentioned lighting device 100, will be described below with reference to Figures 2 and 3. Figure 2 is a top view of the wavelength conversion device 14. Figure 2 shows a plan view of the main surface of the wavelength conversion device 14 that emits light L3 in Figure 1, viewed from a direction perpendicular to the main surface. Figure 3 is a cross-sectional view of the wavelength conversion device 14 along the line 3-3 in Figure 2.

[0016] The transparent support 16 is a flat, transparent member with a rectangular top surface. The transparent support 16 is made of a material with high thermal conductivity that is transparent to blue wavelength light and can transfer the heat generated in the wavelength conversion device 14 to the housing 11, such as sapphire (Al2O3) or gallium nitride (GaN).

[0017] The dichroic mirror 17 is a mirror made of a dielectric multilayer film formed across the upper surface of the transparent support 16. The dichroic mirror 17 is configured to transmit blue wavelength light and reflect the fluorescence wavelength light. That is, blue light incident on the dichroic mirror 17 via the transparent support 16 is transmitted through the dichroic mirror 17.

[0018] The phosphor portion 18 is a flat phosphor plate with a rectangular top surface shape that is bonded to the upper surface of the dichroic mirror 17. When viewed from above, the phosphor portion 18 has the same shape as the transparent support 16 and the dichroic mirror 17.

[0019] The phosphor portion 18 consists of a phosphor that emits yellow fluorescence when excited by blue light. The phosphor portion 18 is, for example, a single-phase transparent ceramic phosphor plate made of yttrium aluminum garnet (YAG:Ce) phosphor with cerium (Ce) as an activator.

[0020] When blue light is incident on the phosphor portion 18, some of it passes through the phosphor portion 18 as is, while the other portion excites the phosphor, and yellow fluorescence is emitted from the excited phosphor. The yellow fluorescence generated from the phosphor has a peak wavelength of 520-570 nm and a yellow emission spectrum consisting of a broad peak over 480 nm-700 nm.

[0021] Therefore, from the upper surface of the phosphor section 18, excitation light (blue light) that has passed through the phosphor section 18 without contributing to the generation of fluorescence, and fluorescence (yellow light) emitted from the phosphor excited by the excitation light L2 are emitted. As a result, the wavelength conversion device 14 extracts white light, which is a mixture of the blue light and yellow fluorescence emitted from the upper surface of the phosphor section 18.

[0022] The incident region IA at the center of the lower surface of the phosphor portion 18 is the region into which the excitation light L2, which has reached the wavelength conversion device 14 via the focusing lens 13, is incident. The incident region IA has a shape similar to, for example, the beam spot shape of the excitation light L2. In other words, the incident region IA is the region that includes the intensity center of the excitation light L2 on the lower surface of the phosphor portion 18.

[0023] As described above, in the illumination device 100, when the excitation light L2 is incident on the wavelength converter 14, it forms an elliptical or circular spot on the lower surface of the wavelength converter 14, so the incident region IA is an elliptical or circular region.

[0024] Specifically, in the incident region IA, when the light L2 has a Gaussian beam profile, the maximum peak intensity (I MAX ) to e 2 Strength divided by (I MAX / e 2 This is the region into which light of an intensity of ) or greater is incident. In other words, the beam spot diameter when defining the incident region IA described above is 1 / e 2 It is defined by width.

[0025] The first nanoantenna 21 is a frustoconical dielectric structure located in a region at the center of the upper surface of the phosphor portion 18, and is provided in multiple locations within the superimposed region A1, which is a circular region overlapping with the incident region IA in a plan view. Each of the first nanoantennas 21 is arranged in a triangular lattice pattern with a period P in the superimposed region A1 in a top view. The period P is, for example, 420 to 520 nm. Each of the first nanoantennas 21 is also provided at a height H from the upper surface of the phosphor portion 18. The height H is, for example, 225 to 325 nm.

[0026] The first nanoantenna 21 is made of a transparent dielectric material that does not easily absorb light in the visible light region and has a higher refractive index (>1.83) than YAG:Ce phosphors, such as titanium dioxide (TiO2), zirconium oxide (ZrO2), niobium pentoxide (Nb2O5), lanthanum oxide (La2O3), tantalum pentoxide (Ta2O5), hafnium oxide (HfO2), yttrium oxide (Y2O3), cerium oxide (CeO2), silicon carbide (SiC), diamond (C), and gallium oxide (Ga2O3). The scattering efficiency of the first nanoantenna 21 is higher when the refractive index difference with air is large, so a higher refractive index is preferable, and a refractive index of 1.9 or higher is particularly preferable.

[0027] The second nanoantenna 22 is a frustoconical dielectric structure located in the peripheral region A2, which is the area surrounding the superposition region A1 described above, on the upper surface of the phosphor portion 18. In other words, the second nanoantenna 22 is formed in the peripheral region A2, which is a non-superposition region that does not overlap with the incident region IA on the lower surface of the phosphor portion 18.

[0028] Each of the second nanoantennas 22 is arranged in a triangular lattice pattern in the peripheral region A2 with the same period P as the first nanoantenna 21 when viewed from above. Furthermore, each of the second nanoantennas 22 is provided at a height H from the upper surface of the phosphor portion 18, similar to the first nanoantenna 21.

[0029] The second nanoantenna 22, like the first nanoantenna 21, is composed of a transparent dielectric material such as TiO2, ZrO2, Nb2O5, La2O3, Ta2O5, HfO2, Y2O3, CeO2, SiC, C, and Ga2O3, which does not readily absorb light in the visible light region and has a higher refractive index (>1.83) than the YAG:Ce phosphor. The second nanoantenna 22 is preferable to have a high refractive index, particularly one of 1.9 or higher, because a larger refractive index difference with air increases the scattering efficiency.

[0030] In this embodiment, the diameter W1 of each base surface of the first nanoantenna 21 is larger than the diameter W2 of each base surface of the second nanoantenna 22. Specifically, for example, the ratio of diameter W1 to period P is 80% or more and 85% or less, and the ratio of diameter W2 to period P is 75% or more and less than 80%.

[0031] Note that the arrangement of the first nanoantenna 21 and the second nanoantenna 22 shown in Figures 2 and 3 is merely a schematic representation to illustrate the first nanoantenna 21 and the second nanoantenna 22. The phosphor portion 18 is, for example, 2 mm square, in which case more of the first nanoantenna 21 and the second nanoantenna 22 are provided than those shown in Figures 2 and 3.

[0032] [Narrowing of the light beam by nano-antennas] Here, we will explain the angle-narrowing effect of the nanoantenna on light. When fluorescence reaches the upper surface of the phosphor portion 18 at an angle greater than the critical angle, the fluorescence is totally reflected at the upper surface of the phosphor portion 18. When this total reflection occurs, an evanescent wave is generated that seeps from the upper surface of the phosphor portion 18 toward the low refractive index medium. This evanescent wave propagates along the upper surface of the phosphor portion 18, in other words, along the interface between the phosphor portion 18 and the air.

[0033] When the evanescent wave propagates along the upper surface of the phosphor portion 18 reaches the first nanoantenna 21 and the second nanoantenna 22, it is emitted in the form of visible light with the same wavelength as the fluorescence in a direction that matches the diffraction conditions determined by the period P.

[0034] This phenomenon causes fluorescence to be emitted within an angular range that matches the diffraction conditions, promoting the narrowing of the fluorescence emitted from the upper surface of the phosphor portion 18. Here, narrowing by nanoantennas refers to the fact that the first nanoantenna 21 and the second nanoantenna 22 increase the amount of fluorescence emitted at a light distribution angle of, for example, within ±30°.

[0035] [Intensity of excitation light transmitted through the phosphor portion] Here, the intensity of the excitation light transmitted through the phosphor section 18 will be explained using Figure 3. In the following explanation, it will be assumed that the wavelength converter 14 is attached to the lighting device 100.

[0036] As described above, the phosphor portion 18 is composed of a single-phase phosphor that is less prone to light scattering inside. Inside the single-phase phosphor, excitation light that enters the phosphor portion 18 and is emitted outward from the phosphor portion 18 without exciting the phosphor is hardly scattered within the phosphor portion 18. Therefore, excitation light that enters the phosphor portion 18 from its lower surface and passes through the phosphor portion 18 without contributing to the generation of fluorescence is emitted from the upper surface of the phosphor portion 18 while maintaining its directionality.

[0037] Therefore, the excitation light L21 traveling from within the phosphor portion 18 to the superimposed region A1 travels at an angle nearly perpendicular to the upper surface of the phosphor portion 18. Consequently, compared to the excitation light L22 traveling from within the phosphor portion 18 to the surrounding region A2 at an angle, the optical path length from the lower surface to the upper surface of the phosphor portion 18 is shorter, resulting in a higher proportion of the excitation light L21 being emitted without contributing to fluorescence generation.

[0038] In other words, the intensity of the excitation light emitted from the superimposed region A1 is higher than the intensity of the excitation light emitted from the surrounding region A2. Also, since excitation light L21 contributes less to fluorescence generation than excitation light L22, the intensity of the fluorescence emitted from the superimposed region A1 is lower than the intensity of the fluorescence emitted from the surrounding region A2.

[0039] On the other hand, the intensity of the excitation light emitted from the peripheral region A2 is lower than the intensity of the excitation light emitted from the superimposed region A1. Also, because excitation light L22 contributes more to fluorescence generation than excitation light L21, the intensity of the fluorescence emitted from the peripheral region A2 is higher than the intensity of the fluorescence emitted from the superimposed region A1.

[0040] Therefore, the intensity ratio of excitation light emitted from the superimposed region A1 to fluorescence differs from the intensity ratio of excitation light emitted from the surrounding region A2, which can cause color unevenness in the emitted light (white light) taken out from the wavelength converter 14.

[0041] According to this embodiment, by making the diameter W1 of the first nanoantenna 21 larger than the diameter W2 of the second nanoantenna 22, the excitation light L21 that propagates from within the phosphor portion 18 to the superimposed region A1 is less likely to be emitted from the superimposed region A1. In other words, it is possible to suppress an increase in the intensity of the excitation light L21. Consequently, the difference between the intensity of the excitation light L21 emitted from the superimposed region A1 and the intensity of the excitation light L22 emitted from the surrounding region A2 can be reduced.

[0042] Furthermore, according to this embodiment, by controlling the ratio of the diameter W1 to the period of the first nanoantenna 21 and the ratio of the diameter W2 to the period of the second nanoantenna 22, as well as the height H of the first nanoantenna 21 and the second nanoantenna 22, the difference between the intensity of fluorescence emitted from the superimposed region A1 and the intensity of fluorescence emitted from the surrounding region A2 can be reduced.

[0043] Therefore, according to this embodiment, it is possible to prevent a change in the relationship between the intensity of excitation light transmitted through the phosphor layer and the intensity of fluorescence produced by the excitation of the phosphor in the central and peripheral parts of the phosphor section 18, thereby reducing color unevenness of the emitted light taken out from the wavelength conversion device 14.

[0044] In this embodiment, the case in which the light L2 incident on the wavelength conversion device 14 has a Gaussian beam profile has been described, but the light L2 may have other beam profiles. For example, in the illumination device 100, an optical element such as a beam homogenizer may be used instead of the focusing lens 13 to shape the laser light (light L1) having a Gaussian distribution into light L2 having a top-hat distribution, and this may be incident on the wavelength conversion device 14.

[0045] In the above case, the size of the incident region IA corresponds to the spot diameter of the light L2 having a top-hat distribution. Note that the spot shape of the light L2 is not limited to a circle, and may be formed into a rectangle by the optical element described above. That is, the first nanoantenna 21 may be provided in the overlapping region A1 which has a rectangular shape on the upper surface of the phosphor portion 18.

[0046] In this embodiment, it is sufficient that the diameter W1 of the first nanoantenna 21 is larger than the diameter W2 of the second nanoantenna 22, and the diameter may be varied within the superimposed region A1 and the peripheral region A2, respectively. For example, the diameter W1 may be set to decrease as it moves from the center of the superimposed region A1 towards the peripheral region A2, or the diameter W2 may be set to decrease as it moves towards the outer edge of the phosphor portion 18 within the peripheral region A2.

[0047] In this embodiment, the case in which the phosphor portion 18 consists of a single-phase YAG:Ce phosphor has been described, but the phosphor portion 18 can be any configuration that does not easily cause light scattering inside it, for example, it may be a plate made of a resin or glass medium containing phosphor particles that emit yellow fluorescence.

[0048] In this embodiment, the lighting device 100 uses a laser light source that emits blue light as the light source 12, but a high-output-intensity LED light source may be used instead of the laser light source.

[0049] In this embodiment, the first nanoantenna 21 and the second nanoantenna 22 are provided on the upper surface of the phosphor portion 18 in a triangular lattice arrangement, but the arrangement is not limited to this. For example, the first nanoantenna 21 and the second nanoantenna 22 may be provided on the upper surface of the phosphor portion 18 in a square lattice arrangement.

[0050] In this embodiment, the wavelength conversion device 14 has been described in which a transparent support 16 is provided on the lower side of the phosphor portion 18 via a dichroic mirror 17. However, the wavelength conversion device 14 does not necessarily have to have a dichroic mirror 17 and a transparent support 16.

[0051] [Method for fabricating a wavelength conversion device] The method for fabricating the wavelength conversion device 14 in this embodiment will be described below with reference to Figure 3.

[0052] First, a dielectric layer made of a transparent dielectric such as TiO2 is formed on the upper surface of the phosphor portion 18 by electron beam deposition or sputtering. At this time, the thickness of the dielectric layer becomes the height H of the first nanoantenna 21 and the second nanoantenna 22.

[0053] Next, a metal film made of aluminum (Al) or the like is formed on the dielectric layer formed on the upper surface of the phosphor portion 18, and after applying a resist film made of resin on the metal film, a nano-antenna pattern is formed by nanoimprinting. That is, by varying the diameter of the master mold used for nanoimprinting to match the diameters W1 and W2 described above, the diameter of the nano-antenna formed on the upper surface of the phosphor portion 18 can be controlled.

[0054] Next, the patterned resist film is used as a mask for dry etching to etch the metal film. Subsequently, the metal film remaining after dry etching is used as a metal mask to dry etch the dielectric layer. In this case, if the metal film is made of Al and the transparent dielectric is made of TiO2, chlorine (Cl) and argon (Ar) etching gases are used for the metal film, and carbon tetrafluoride (CF4), Ar, and oxygen (O2) etching gases are used for the transparent dielectric.

[0055] Furthermore, in the above process, if the metal film is made of Al and the transparent dielectric is made of TiO2, dry etching of the dielectric layer using etching gases of CF4, Ar, and O2 will also partially etch the metal film. Therefore, if the thickness of the metal film on the dielectric layer is formed thinly beforehand, the metal film and dielectric layer will be removed from the edges of the dielectric layer during etching, making it possible to form nanoantennas with a conical or frustoconical shape using this method. In addition, the tilt angle of the pillar can be controlled by changing various etching conditions (bias, gas flow rate, pressure).

[0056] Next, the phosphor portion 18 on which the nanoantennas (first nanoantenna 21 and second nanoantenna 22) are formed is joined to the transparent support 16 via a dichroic mirror 17. In this joining process, it is desirable to transfer as much heat as possible generated in the phosphor portion 18 to the transparent support 16, so it is preferable to join them directly by, for example, surface-activated bonding or plasma-activated bonding without an adhesive. Through the above steps, the wavelength conversion device 14 according to the present invention can be manufactured.

[0057] [verification] The verification performed on the wavelength conversion device 14 of the present invention and the verification results will be described below with reference to Figures 4A to 11. In the following, the angle of fluorescence emitted vertically from the upper surface of the phosphor section 18 is set to 0°. Also, all nanoantennas formed on the upper surface of the phosphor section 18 have the same diameter W.

[0058] First, Figures 4A to 4E will be used to explain the preferred range of the period P of the nanoantenna formed on the upper surface of the phosphor portion 18. Figures 4A to 4E show various diffraction lines when the period P of the nanoantenna is set to a predetermined value. In Figures 4A to 4E, the horizontal axis represents the emission angle θ of the fluorescence emitted from the upper surface of the phosphor portion 18. em This shows the wavelength of light on the vertical axis.

[0059] Figures 4A to 4E model a nanoantenna made of TiO2 (refractive index 2.4) formed on the upper surface of a phosphor portion 18 made of YAG:Ce phosphor. Figures 4A to 4E show the emission angle θ under diffraction conditions where the diffraction order is expressed as (m1, m2 (m1, m2 are integers)). em The diffraction lines obtained by plotting the wavelengths calculated for each point are shown.

[0060] In Figures 4A to 4E, the solid line represents the diffraction line (YAG(1,0)) when the diffraction order is (m1,m2)=(1,0). The dashed line represents the diffraction line (YAG(1,-1)) when the diffraction order is (m1,m2)=(1,-1). The dashed line represents the diffraction line (YAG(-1,0)) when the diffraction order is (m1,m2)=(-1,0). The dotted line represents the diffraction line (Air(-1,0)) when the diffraction order is (m1,m2)=(-1,0).

[0061] Figure 4A shows various diffraction lines when the period P is 400 nm. Figure 4B shows various diffraction lines when the period P is 420 nm. Figure 4C shows various diffraction lines when the period P is 450 nm. Figure 4D shows various diffraction lines when the period P is 520 nm. Figure 4E shows various diffraction lines when the period P is 540 nm.

[0062] In Figures 4A to 4E, the shaded region A, indicated by the diffraction lines (YAG(1,0)) and (Air(-1,0)), is the area where fluorescence emitted via the nanoantenna is enhanced. Furthermore, the dotted region B, indicated by the diffraction lines (YAG(1,0)), (YAG(1,-1)), and (Air(-1,0)), is the region where fluorescence is enhanced via the nanoantenna, following region A.

[0063] In Figures 4A to 4E, the range indicated by the dashed lines represents the range in which yellow fluorescence (wavelength range 450 to 700 nm) is emitted at angles from 0° to 30°, that is, the range in which fluorescence is emitted at a narrow angle. Therefore, in Figures 4A to 4E, the more regions A and B are included within the dashed-line region, the higher the intensity of fluorescence emitted at a narrow angle. In particular, it is preferable that region A contains many lines (dashed line PW in the figure) that show the peak wavelength of yellow fluorescence (550 nm), which has high visual sensitivity at emission angles from 0° to 30°.

[0064] Referring to Figures 4A to 4E, in Figure 4A (period P: 400 nm), components on the lower wavelength side, which are smaller than the fluorescence peak wavelength, are enhanced, but components on the longer wavelength side, which are larger than the fluorescence peak wavelength, especially components with wavelengths exceeding 631 nm, are not enhanced as much.

[0065] In Figures 4B (period P: 420 nm), 4C (period P: 450 nm), and 4D (period P: 520 nm), more than half of the dashed line PW is contained within region A, so it is expected that the intensity of the emitted fluorescence will be high. In particular, in Figure 4C, since almost all of the dashed line PW is contained within region A, setting the period P to 450 nm will result in the emission of fluorescence with a narrow light distribution and high intensity.

[0066] In Figure 4E (period P: 540 nm), components on the longer wavelength side, which are greater than the fluorescence peak wavelength, are enhanced, but components on the lower wavelength side, which are less than the fluorescence peak wavelength, especially those below 468 nm, are less enhanced.

[0067] Therefore, as shown in Figures 4A to 4E, the period P of the nanoantenna is preferably 420 to 520 nm, and particularly preferably 450 nm.

[0068] Next, using Figures 5A to 5E, we will explain the preferred range of the ratio of the diameter W to the period P of the nanoantenna formed on the upper surface of the phosphor portion 18.

[0069] Figures 5A to 5E show the results of analyzing the intensity of fluorescence emitted within ±30° via a nanoantenna using the RCWA (Rigorous coupled wave analysis) method, when the ratio of the diameter W to the period P of the nanoantenna is set to a predetermined value. In Figures 5A to 5E, the horizontal axis represents the height of the nanoantenna, and the vertical axis represents the period of the nanoantenna.

[0070] In Figures 5A to 5E, the analysis is performed using a model in which nanoantennas made of TiO2 (refractive index 2.4) with heights H of 200 to 500 nm and periods P of 380 to 540 nm are arranged in a triangular lattice on the upper surface of a phosphor section 18 made of Ce:YAG phosphor. The wavelength of fluorescence emitted through the nanoantennas is set to 550 nm. The analysis is performed with period P at 20 nm intervals and height H at 50 nm intervals.

[0071] Figure 5A shows the fluorescence intensity when the ratio of the diameter W to the period P of the nanoantenna is 70%. Figure 5B shows the fluorescence intensity when the ratio of the diameter W to the period P of the nanoantenna is 75%.

[0072] Figure 5C shows the fluorescence intensity when the ratio of the diameter W to the period P of the nanoantenna is 80%. Figure 5D shows the fluorescence intensity when the ratio of the diameter W to the period P of the nanoantenna is 85%. Figure 5E shows the fluorescence intensity when the ratio of the diameter W to the period P of the nanoantenna is 90%.

[0073] In Figures 5A to 5E, the fluorescence intensity emitted when no nanoantennas are formed on the upper surface of the phosphor portion 18 is shown as 1 (darkest region), and the maximum fluorescence intensity when nanoantennas are formed is shown as 2 (brightest region). The preferred period range (420 to 520 nm) mentioned above is indicated by a dashed line.

[0074] Referring to Figures 5A to 5E, in Figures 5B, 5C, and 5D, fluorescence with a high intensity, for example, 1.8 or higher, is obtained within the preferred period P range described above. In particular, the highest intensity fluorescence is obtained when the ratio of the diameter W to the period P of the nanoantenna is 75%. On the other hand, in Figures 5A and 5E, it is more difficult to obtain fluorescence with a high intensity compared to Figures 5B, 5C, and 5D.

[0075] Therefore, as shown in Figures 5A to 5E, when the period P of the nanoantenna is 420 to 520 nm, the ratio of the diameter W to the period is preferably 75 to 80%, and particularly preferably 75%.

[0076] Next, the preferred height H of the nanoantenna formed on the upper surface of the phosphor portion 18 will be explained using Figures 5A to 5E and Figure 6.

[0077] Figure 6 is a graph showing the length of the evanescent wave seeping from the upper surface of the phosphor portion 18 when the incident angle of fluorescence incident on the upper surface of the phosphor portion 18 is changed. In Figure 6, the horizontal axis represents the incident angle of fluorescence to the upper surface of the phosphor portion 18, and the vertical axis represents the length of the evanescent wave seeping from the upper surface of the phosphor portion 18.

[0078] Figure 6 shows the length of the evanescent wave, generated by total internal reflection of fluorescence at the top surface of the phosphor portion 18, from the top intensity to 1 / e, for each fluorescence wavelength (500 nm, 550 nm, 600 nm, 650 nm). The evanescent wave's length d is calculated using the following formula 1.

[0079]

number

[0080] Here, wavelength λ is the wavelength of fluorescence, refractive index n1 is the refractive index of the phosphor (n1=1.83), refractive index n2 is the refractive index of air (n2=1), and the incident angle θ is the incident angle of fluorescence incident from inside the phosphor portion 18 to the upper surface of the phosphor portion 18, that is, to the interface between the phosphor portion 18 and the air.

[0081] As shown in Figure 6, the seepage length d increases as the incident angle θ decreases at all wavelengths. In particular, the change in seepage length d is larger in the range where the incident angle θ is less than 40° than in the range where the incident angle θ is 40° or greater.

[0082] In order to scatter and diffract the evanescent waves seeping from the upper surface of the phosphor portion 18 using a nanoantenna, it is preferable that the height H of the nanoantenna be equal to or greater than the seepage length d of the evanescent waves.

[0083] Therefore, as shown in Figure 6, for example, when the wavelength λ is 500 nm, if the height H of the nanoantenna is 225 nm, relative to the critical angle of 33.1° from the phosphor portion 18 to the air, the evanescent wave generated by fluorescence with an incident angle θ of 37° or more can be scattered and diffracted by the nanoantenna.

[0084] Furthermore, as shown in Figure 6, for example, if the wavelength λ is 650 nm, and the height H of the nanoantenna is 325 nm, then evanescent waves generated by fluorescence with an incident angle θ of 35° or more can be scattered and diffracted by the nanoantenna.

[0085] Based on the results shown in Figure 6 and Figures 5A to 5E, when the period P of the nanoantenna is 420 to 520 nm, taking into account the range in which fluorescence with a high intensity of 1.8 or higher can be obtained, it is preferable that the height H of the nanoantenna be 225 to 325 nm.

[0086] Next, using Figure 7, we will explain the results of further verification regarding the preferred range of diameter W with respect to the period P of the nanoantenna described above. Figure 7 is a graph showing the displacement length of the evanescent wave generated on the upper surface of the phosphor portion 18 when the incident angle of fluorescence incident on the upper surface of the phosphor portion 18 is changed.

[0087] In Figure 7, the horizontal axis represents the incident angle of fluorescence, and the vertical axis represents the travel length of the evanescent wave along the upper surface of the phosphor portion 18. Note that in Figure 7, the fluorescence wavelength is assumed to be 550 nm.

[0088] Here, we will explain the seepage length and migration length of the evanescent wave. As described above, when the evanescent wave propagating along the upper surface of the phosphor portion 18 reaches the first nanoantenna 21 and the second nanoantenna 22, it is emitted in the form of visible light with the same wavelength as the fluorescence in a direction that matches the diffraction conditions determined by the period P. This phenomenon causes fluorescence to be emitted in a narrow angular range that matches the diffraction conditions, promoting the narrowing of the angle of fluorescence emitted from the upper surface of the phosphor portion 18.

[0089] At this time, the penetration length d from the upper surface of the phosphor layer 18 when the evanescent wave generated on the upper surface of the phosphor layer 18 reaches 1 / e of its intensity in the height direction is expressed by the above-described mathematical formula 1.

[0090] Also, the Goos-Hänchen shift d, which is the moving length of the evanescent wave along the upper surface of the phosphor layer 18 GH is expressed by the following mathematical formulas 2 and mathematical formula 3 together with the above-described mathematical formula 1. Note that mathematical formula 2 is an expression representing the Goos-Hänchen shift of a p-wave in which the vibration direction of the evanescent wave is parallel to the upper surface of the phosphor layer 18, and mathematical formula 3 is an expression representing the Goos-Hänchen shift of an s-wave in which the vibration direction of the evanescent wave is perpendicular to the upper surface of the phosphor layer 18.

[0091]

Equation

[0092]

Equation

[0093] Referring to FIG. 7 again. In FIG. 7, the solid line indicates the Goos-Hänchen shift (d GH,s ) of the evanescent wave when the incident angle of fluorescence is changed in the above-described mathematical formula 2, and the broken line indicates the Goos-Hänchen shift (d GH,p ) when the incident angle of fluorescence is changed in the above-described mathematical formula 3.

[0094] From FIG. 7, the Goos-Hänchen shift of the evanescent wave has a value of 100 nm or more for both the p-wave and the s-wave. In particular, referring to the p-wave, the Goos-Hänchen shift becomes longer as the incident angle of fluorescence with respect to the upper surface of the phosphor layer 18 changes from 60°.

[0095] If the distance between adjacent nanoantennas on the upper surface of the phosphor portion 18 is greater than the Goose-Henschen shift described above, a large number of evanescent waves will return to the phosphor without reaching the nanoantennas, making it difficult to obtain fluorescence with high intensity. Therefore, it is preferable that the distance between adjacent nanoantennas be less than or equal to the Goose-Henschen shift.

[0096] Using the ratio of diameter W to period P obtained in Figures 5A to 5E, when the period P of a nanoantenna is 420 nm and the diameter W is 85% of the period P, the distance between adjacent nanoantennas is 63 nm. Furthermore, when the period P of a nanoantenna is 520 nm and the diameter W is 75% of the period P, the distance between adjacent nanoantennas is 130 nm.

[0097] Therefore, when the period P of the nanoantenna is 420-520 nm and the diameter W of the nanoantenna is 75-85% of the period P, most of the evanescent waves have a Goose-Henschen shift that is greater than the distance between adjacent nanoantennas. Thus, by configuring the period P and diameter W of the nanoantenna as described above, fluorescence is less likely to be reflected by the nanoantenna, and fluorescence with high intensity can be obtained.

[0098] Next, Figures 8A to 8C will be used to explain the preferred range for the ratio of the diameter W to the period P of the nanoantenna. Figures 8A to 8C show the results of analyzing the reflection intensity of fluorescence reflected into the phosphor portion 18 by the nanoantenna using the RCWA method, when the ratio of the diameter W to the period P of the nanoantenna is set to a predetermined value.

[0099] In Figures 8A-8C, the horizontal axis represents the height of the nanoantenna, and the vertical axis represents the period of the nanoantenna. The model used for the analysis is the same as the one described in Figures 5A-5E, and is therefore omitted here.

[0100] Figure 8A shows the fluorescence reflectance when the ratio of the diameter W to the period P of the nanoantenna is 70%. Figure 8B shows the fluorescence reflectance when the ratio of the diameter W to the period P of the nanoantenna is 80%. Figure 8C shows the fluorescence reflectance when the ratio of the diameter W to the period P of the nanoantenna is 90%. The dashed lines in the figures indicate the preferred ranges for the period P and height H of the nanoantenna as described above.

[0101] In Figures 8A to 8C, the reflection intensity of fluorescence in the dashed line range increases as the ratio of the diameter W to the period P of the nanoantenna increases. In other words, for example, when the ratio of the diameter W to the period P of the nanoantenna is 90%, much of the fluorescence incident on the phosphor portion 18 is reflected by the nanoantenna, which can reduce the intensity of the fluorescence emitted through the nanoantenna.

[0102] Therefore, as shown in Figures 8A to 8C, the ratio of the diameter W to the period P of the nanoantenna is preferably 70% or more and less than 90%, and in particular, taking into account the results in Figures 5A to 5E described above, it is preferable that the ratio be 75 to 85%.

[0103] Next, Figure 9 will be used to describe the preferred shape of the nanoantenna. Figure 9 is a graph showing the change in fluorescence intensity ratio when the tilt angle of the nanoantenna is changed.

[0104] In Figure 9, the horizontal axis shows the inclination angle of the side of the nanoantenna relative to the upper surface of the phosphor portion 18, and the vertical axis shows the intensity ratio of fluorescence emitted within ±30°. On the horizontal axis, the inclination angle when the nanoantenna has a cylindrical shape is shown as 90°. On the vertical axis, the intensity ratio of fluorescence with Lambertsian distribution within ±30° is shown as 1.00.

[0105] Figure 9 plots the fluorescence intensity ratios for a total of eight conditions, where the nanoantenna period P is set to 420 nm, 460 nm, 480 nm, and 500 nm, and the nanoantenna height H is set to 250 nm and 300 nm for each period P.

[0106] As shown in Figure 9, the proportion of fluorescence intensity emitted within ±30° increases as the tilt angle of the side of the nanoantenna decreases from 90°, that is, as the nanoantenna becomes more tapered and narrows upwards.

[0107] In particular, when the tilt angle is less than 75°, the proportion of fluorescence intensity increases under all of the conditions described above. Also, as shown in Figure 9, when the tilt angle is less than 50°, the proportion of fluorescence intensity emitted within ±30° decreases.

[0108] Therefore, to increase the fluorescence intensity ratio, it is preferable to set the tilt angle of the side surface of the nanoantenna to 50° or more and 75° or less. For example, when the height H of the nanoantenna is 250 to 300 nm, a nanoantenna with a tilt angle of 75° on the side surface has a frustoconical shape. On the other hand, a nanoantenna with a tilt angle of 50° to 60° on the side surface has a conical shape.

[0109] As described above, since the evanescent wave generated on the upper surface of the phosphor portion 18 moves along that upper surface, if the nanoantenna has a conical or frustoconical shape within the aforementioned angular range, the proportion of fluorescence extracted at a narrow angle can be increased compared to when the nanoantenna is cylindrical. In other words, it is preferable that the nanoantenna has a conical or frustoconical shape.

[0110] Finally, using Figures 10 and 11, we will explain the results of analyzing the intensity of blue light (excitation light) transmitted through the phosphor portion 18 using the RCWA method when the ratio of the diameter W to the period P of the nanoantenna and the height H of the nanoantenna are varied.

[0111] Figure 10 is a graph plotting the intensity of blue light emitted after passing through the phosphor portion 18 without contributing to fluorescence generation, when the ratio of the diameter W to the period P of the nanoantenna is 70%, 75%, 80%, and 85%, respectively.

[0112] Figure 10 shows the intensity when a nanoantenna made of TiO2 with a period P of 420 nm and a height H of 250 nm is provided on the upper surface of the phosphor portion 18, and blue light with a wavelength of 450 nm is emitted through the nanoantenna within ±10°.

[0113] As shown in Figure 10, the larger the ratio of the diameter W to the period P of the nanoantenna, the lower the intensity of the blue light emitted within ±10°. Therefore, as described above, by making the diameter W1 of the first nanoantenna 21 larger than the diameter W2 of the second nanoantenna 22, it is possible to suppress the increase in the intensity of the excitation light L21 emitted from the superimposed region A1.

[0114] Figure 11 is a graph plotting the intensity of blue light transmitted through the phosphor portion 18 and emitted without contributing to fluorescence generation, when the height H of the nanoantenna is set to 200 nm, 250 nm, 300 nm, and 350 nm, respectively.

[0115] Figure 11 shows the intensity when a nanoantenna made of TiO2 with a period P of 420 nm and a ratio of the nanoantenna diameter W to the period P of 75% is provided on the upper surface of the phosphor portion 18, and blue light with a wavelength of 450 nm is emitted through the nanoantenna within ±10°.

[0116] As shown in Figure 11, the higher the height H of the nanoantenna, the lower the intensity of the blue light emitted within ±10°. Therefore, by making the height H1 of the first nanoantenna 21 higher than the height H2 of the second nanoantenna 22, it is possible to suppress the increase in the intensity of the excitation light L21 emitted from the superimposed region A1.

[0117] [Modified example 1 of the wavelength conversion device] A modified example of the wavelength conversion device 14 according to Example 1 will be described below with reference to Figure 12. Figure 12 is a cross-sectional view of the wavelength conversion device 34 according to Modified Example 1, similar to Figure 3.

[0118] The wavelength conversion device 34 differs from that of Example 1 in that the height of the first nanoantenna 21 is different, but other aspects, such as the diameter W1 of the first nanoantenna 21 and the diameter W2 of the second nanoantenna 22, are the same as those of Example 1.

[0119] In this modified example 1, the height H1 of the first nanoantenna 21 is set to be higher than the height H2 of the second nanoantenna 22. For example, the height H1 is 300-325 nm and the height H2 is 225-250 nm.

[0120] As described above, the higher the height H of the nanoantenna, the lower the intensity of the excitation light (blue light) emitted within ±10°. Therefore, by making the height H1 of the first nanoantenna 21 located in the superposition region A1 higher than the height H2 of the second nanoantenna 22, it becomes more difficult for the excitation light L21 to be emitted from the superposition region A1. In other words, it is possible to suppress the increase in the intensity of the excitation light L21. Consequently, the difference between the intensity of the excitation light L21 emitted from the superposition region A1 and the intensity of the excitation light L22 emitted from the surrounding region A2 can be reduced.

[0121] Therefore, according to this modified example 1, similar to Example 1, it is possible to prevent a change in the relationship between the intensity of the excitation light transmitted through the phosphor layer and the intensity of the fluorescence produced by the excitation of the phosphor in the central and peripheral parts of the phosphor portion 18, and to reduce color unevenness of the emitted light taken out from the wavelength conversion device 14.

[0122] In this modified example 1, it is sufficient that the height H1 of the first nanoantenna 21 is higher than the height H2 of the second nanoantenna 22, and the height may be varied within the superimposed region A1 and the peripheral region A2, respectively. For example, the height H1 may be set to decrease as you move from the center of the superimposed region A1 towards the peripheral region A2, or the height H2 may be set to decrease as you move towards the outer edge of the phosphor portion 18 in the peripheral region A2.

[0123] In the modified example 1, when forming a first nanoantenna 21 and a second nanoantenna 22 of different heights on the upper surface of the phosphor portion 18, the above-described configuration can be obtained by etching the dielectric layer on the phosphor portion 18 before forming a metal film on the dielectric layer.

[0124] Specifically, by forming a dielectric film on the upper surface of the phosphor portion 18, then patterning the region corresponding to the first nanoantenna 21 using a resist, and then etching the dielectric film until it reaches a desired thickness, dielectric films of different heights can be formed.

[0125] After this step, the resist is removed with a remover, and the wavelength conversion device 34 in this modified example 1 can be manufactured by performing the same processing as the method for manufacturing the wavelength conversion device 14 in Example 1 described above.

[0126] [Modified example 2 of the wavelength conversion device] Furthermore, as a second modification of the wavelength conversion device 14 according to Example 1, similar to the first modification 1 described above, the height H1 of the first nanoantenna 21 is configured to be higher than the height H2 of the second nanoantenna 22, and the diameters W1 of the first nanoantenna 21 and W2 of the second nanoantenna 22 can be the same. For example, the height H1 is 300 to 325 nm and the height H2 is 225 to 250 nm.

[0127] As described above, the higher the height H of the nanoantenna, the lower the intensity of the excitation light (blue light) emitted within ±10°. Therefore, by making the height H1 of the first nanoantenna 21 located in the superposition region A1 higher than the height H2 of the second nanoantenna 22, it becomes more difficult for the excitation light L21 to be emitted from the superposition region A1. In other words, it is possible to suppress the increase in the intensity of the excitation light L21. Consequently, the difference between the intensity of the excitation light L21 emitted from the superposition region A1 and the intensity of the excitation light L22 emitted from the surrounding region A2 can be reduced.

[0128] Therefore, according to this modified example 2, similar to Example 1, it is possible to prevent a change in the relationship between the intensity of the excitation light transmitted through the phosphor layer and the intensity of the fluorescence produced by the excitation of the phosphor in the central and peripheral parts of the phosphor portion 18, and to reduce color unevenness of the emitted light taken out from the wavelength conversion device 14. [Explanation of Symbols]

[0129] 100 Lighting devices 11 cabinets 12 light source 13. Focusing lens 14, 34 wavelength conversion device 16 Transparent support 17 Dichroic Mirror 18. Phosphor section 21. The first nanoantenna 22. The second nanoantenna

Claims

1. A flat plate-shaped phosphor portion containing a phosphor that emits fluorescence when excited by excitation light incident on surface 1, A plurality of first nanoantennas made of a transparent dielectric material are periodically provided in a region of the other surface of the phosphor portion opposite to the first surface, The other surface comprises a plurality of second nanoantennas made of a transparent dielectric material, which are periodically provided in the region surrounding the first region, A wavelength conversion device characterized in that each of the plurality of first nanoantennas has a larger diameter in a plan view from a direction perpendicular to the other surface than each of the plurality of second nanoantennas.

2. A flat plate-shaped phosphor portion containing a phosphor that emits fluorescence when excited by excitation light incident on surface 1, A plurality of first nanoantennas made of a transparent dielectric material are periodically provided in a region of the other surface of the phosphor portion opposite to the first surface, The other surface comprises a plurality of second nanoantennas made of a transparent dielectric material, which are periodically provided in the region surrounding the first region, A wavelength conversion device characterized in that each of the plurality of first nanoantennas is at a greater height from the other surface than each of the plurality of second nanoantennas.

3. The wavelength conversion device according to claim 1 or 2, characterized in that each of the plurality of first nanoantennas and the plurality of second nanoantennas has a conical or frustum shape that tapers upward.

4. The wavelength conversion device according to claim 3, characterized in that each of the plurality of first nanoantennas and the plurality of second nanoantennas has a side surface that is inclined at 75° or less with respect to the other surface.

5. The wavelength conversion device according to claim 1 or 2, characterized in that the transparent dielectric is titanium oxide.

6. The transparent dielectric is titanium oxide, The wavelength conversion device according to claim 1, characterized in that each of the plurality of first nanoantennas and the plurality of second nanoantennas is arranged on the other surface with a period of 420 nm to 520 nm and has a diameter of 75% to 85% of the period.

7. The wavelength conversion device according to claim 5, characterized in that each of the plurality of first nanoantennas and the plurality of second nanoantennas has a height of 225 nm or more and 325 nm or less.

8. The wavelength conversion device according to claim 1 or 2, characterized in that the transparent dielectric has a refractive index greater than that of the phosphor portion.

9. The wavelength conversion device according to claim 1 or 2, characterized in that the phosphor portion consists of a single-phase phosphor plate.

10. The wavelength conversion device according to claim 9, characterized in that the phosphor consists of yttrium aluminum garnet with cerium as an activator.

11. The wavelength conversion device according to claim 1 or 2, characterized in that it includes a dichroic mirror provided in contact with the surface 1 of the phosphor portion, which transmits the excitation light and reflects the fluorescence.

12. The wavelength conversion device according to claim 11, characterized in that it includes a transparent member provided on the surface side of the 1 so as to sandwich the dichroic mirror together with the phosphor portion and which is transparent to the excitation light.

13. A wavelength conversion device according to claim 1 or 2, A light source that emits the excitation light toward the surface mentioned in 1, A lighting device characterized by having the following features.

14. The lighting device according to claim 13, characterized in that the region 1 includes the intensity center of the excitation light incident on the surface 1 in a plan view taken from a direction perpendicular to the other surface.

Images