Light reducing agent and light-emitting device including the same

Abstract

[Problem] The objective of the present invention is to provide a dimming agent and a light-emitting device, capable of limiting brightness without lowering the current value of a current being injected into an LED. [Solution] The invention is the dimming agent having a diffuse reflection intensity of 80% or lower at wavelengths from 400 nm to 750 nm, characterized by containing at least one among terbium, praseodymium, manganese, and titanium.

Description

Technical Field

[0001] The present invention relates to a light dimming agent and a light emitting device including the light dimming agent.

Background Art

[0002] LEDs with high efficiency have been developed for energy conservation. On the other hand, for example, LEDs used in dark environments such as in-vehicle applications need to be not too dazzling so as not to interfere with the driver's vision.

[0003] For example, Patent Document 1 describes an invention related to a dimming circuit that switches the emission luminance of an in-vehicle LED.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As shown in FIG. 10, since the brightness of the LED changes according to the injection current into the LED, it is possible to adjust the brightness by changing the injection current into the LED using a dimming circuit or the like as described in Patent Document 1 above. However, when the injection current into the LED is set to a low current, there is a problem that the emission wavelength of the blue LED fluctuates greatly. When the emission wavelength of the blue LED changes, it affects the variation in chromaticity when made white.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide a light dimming agent that can suppress brightness without reducing the current value of the current injected into the LED, and a light emitting device using the same.

Means for Solving the Problems

[0007] The present invention is made to achieve the above object, Contains an alkaline earth metal as a constituent element of the base material, and terbium, praseodymium, and manganese and provides a light reducing agent having a diffuse reflection intensity of 80% or less in the wavelength range of 400 nm to 750 nm, characterized by containing at least one of the following.

[0008] According to such a light reducing agent, without lowering the current value of the current injected into the LED, it becomes a light reducing agent for a light emitting device with the brightness suppressed low. For this reason, the change in the emission wavelength of the LED, that is, the change in chromaticity is suppressed, and it becomes a light emitting device suitable for use in a dark environment such as in-vehicle use.

[0009] At this time, the alkaline earth metal can be Contains as a constituent element of the base material, and the base material is composed of any one of an oxide, a halogen compound, an acid halide compound, an oxynitride, a nitride, and a sulfide a light reducing agent having a diffuse reflection intensity of 80% or less in the wavelength range of 400 nm to 750 nm, characterized by containing at least one of terbium, praseodymium, and manganese.

[0010] In this way, similar to the phosphor containing an alkaline earth metal, the base material of the light reducing agent can be designed. Also, Terbium, praseodymium, and manganese can be added like an activator of the phosphor. By designing the light reducing agent like a phosphor, it becomes possible to control the specific gravity and particle size, and it can be adjusted as a factor when uniformly dispersing with the phosphor.

[0011] At this time, the emission peak wavelength of the light emitting element is in the range of 380 to 490 nm, and a light emitting device including the above light reducing agent can be obtained.

[0012] Thereby, a light emitting device with various brightnesses (luminosities) can be provided, in which the brightness is suppressed without lowering the current value of the current injected into the LED.

[0013] Also, the emission peak wavelength of the light emitting element is in the range of 380 to 490 nm, and a light emitting device including the above light reducing agent and phosphor can be obtained.

[0014] According to such a light-emitting device, a light-emitting device with a low brightness can be obtained without reducing the current value of the current injected into the LED. Therefore, the change in the emission wavelength of the LED, that is, the change in chromaticity, is suppressed, and the light-emitting device is suitable for use in a dark environment such as in-vehicle use.

Effects of the Invention

[0015] As described above, by using the light-reducing agent of the present invention, a light-emitting device with a suppressed brightness can be obtained without reducing the current value of the current injected into the LED. In addition, by using a phosphor, light-emitting devices with various brightnesses can be provided not only in blue but also in green, yellow, red, and white.

Brief Description of the Drawings

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Modes for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0018] As described above, there has been a demand for a light-emitting device with reduced brightness without lowering the current value of the current injected into the LED.

[0019] As a result of intensive studies on the above problems, the inventors have found that a light-emitting device with reduced brightness can be provided without lowering the current value of the injection current into the LED by using a light-reducing agent having a diffuse reflection intensity of 80% or less in the wavelength range of 400 nm to 750 nm, which contains at least one of terbium, praseodymium, manganese, and titanium, and thus completed the present invention.

[0020] In addition, the inventors have found that a light-emitting device can be provided that includes a light-emitting element, the light-reducing agent according to claims 1 and 2 that absorbs part of the light from the light-emitting element, and a phosphor that absorbs part of the light from the light-emitting element and converts it into light having an emission peak wavelength different from the peak wavelength of the emission wavelength of the light-emitting element, and thus completed the present invention.

[0021] Hereinafter, it will be described with reference to the drawings.

[0022] As described above, a light-emitting device used in a dark environment, such as a white LED for vehicle use, is required to have a brightness that can be recognized under sunlight during the day and not be too dazzling at night. As an example of a white LED for night use, one with a luminous intensity of 300 mcd is the mainstream. However, especially those arranged near the driver are required to have a lower brightness in the market, with a luminous intensity of 120 mcd or less, particularly 100 to 10 mcd, from the perspective of safety at night. If such a light-emitting device with a luminous intensity of 120 mcd or less is to be achieved by lowering the injection current as in the prior art, the emission wavelength (peak wavelength) of the blue LED will vary as described above, and the chromaticity of the white LED will change.

[0023] Using conventional blue LEDs with low luminous efficiency is also a solution. However, as the technological trend is towards higher efficiency of blue LEDs, there is no manufacturer that can supply blue LEDs with low luminous efficiency, stable quality, and low cost. Therefore, there is a need for a technology to manufacture dim LEDs based on high-efficiency, high-quality, and low-cost blue LEDs that are widely distributed in the market.

[0024] As a result of intensive studies by the present inventor, a phosphor-converted white LED with a luminous intensity of 30 mcd or less can be obtained by using a light-emitting element, a light diffusing reflector with a diffusion reflection intensity of 80% or less in the wavelength range of 400 nm to 750 nm, which contains at least one of terbium, praseodymium, manganese, and titanium that absorbs part of the light from the light-emitting element, and a phosphor that absorbs part of the light from the light-emitting element and converts it into light with an emission peak wavelength different from the peak wavelength of the emission wavelength of the light-emitting element.

[0025] Although details will be described later, when the light diffusing reflector contains a trivalent rare earth element as a constituent element, the light diffusing effect of terbium and praseodymium is weak. Therefore, a host crystal containing a divalent alkaline earth metal is preferred.

[0026] Fig. 1 shows an example of a light-emitting device 100 according to the present invention. The light-emitting device 100 according to the present invention includes a light-emitting element 10 disposed on a substrate 40 and a light diffusing reflector 2 that absorbs part of the light from the light-emitting element 10. The light diffusing reflector 2 is dispersed in a resin layer 20 that functions as a resin encapsulant covering the light-emitting element 10 and is housed in a package 30. Additives such as Aerosil can be appropriately added to the resin layer 20 to enhance the dispersibility of the light diffusing reflector 2 and the like.

[0027] As the light-emitting element 10, one having a light emission peak wavelength in the range of 380 to 490 nm is used. Such a light-emitting element emits blue light, and a high-quality and low-cost one can be relatively easily obtained. The light-dimming agent 2 contains at least one of terbium, praseodymium, manganese, and titanium, and has a diffuse reflection intensity of 80% or less from a wavelength of 400 nm to 750 nm. By using such a light-dimming agent 2, a blue light-emitting device with reduced brightness can be obtained without lowering the current value of the current injected into the LED.

[0028] In addition, the phosphor 1 (1a, 1b) can be included in the resin layer 20. The inventors can produce a dim light-emitting device that exhibits various light-emitting colors such as green, yellow, and red, as well as white, by changing the emission wavelength of the phosphor 1.

[0029] In the experiments, examples, and comparative examples described below, as the light-emitting element 10, a blue LED with an output of 60 mcd and a dominant wavelength of 458 nm when a current of 5 mA was passed was used.

[0030] (Light-dimming agent) Next, the light-dimming agent will be described. First, the diffuse reflection spectrum of the currently used light-dimming agent is shown in FIG. 2. For comparison, the diffuse reflection spectrum of a commercially available product (Ba,Sr)2SiO4:Eu phosphor (hereinafter abbreviated as BOS phosphor) with a light emission peak wavelength of 530 nm is also shown in FIG. 2. It can be seen that the BOS phosphor selectively absorbs light of 500 nm or less, while the AlN light-dimming agent uniformly absorbs light of 400 nm to 750 nm.

[0031] However, the light absorption of the AlN light-dimming agent is not very strong. When trying to produce 30 mcd or less in a white LED, the amount of the AlN light-dimming agent used increases. However, when the powder concentration in the resin becomes high, the resin viscosity becomes high, making uniform coating difficult.

[0032] Therefore, an attempt was made to develop a new light-dimming agent. FIG. 3 shows the diffuse reflection spectrum of a powder with a dark body color. Terbium oxide (Tb4O7), praseodymium oxide (Pr4O11 ) Manganese dioxide (MnO2) is a material commonly used when manufacturing phosphors, and it is found that it has strong light absorption in a wide wavelength range of 400 nm to 750 nm. In addition, titanium is used as a raw material for phosphors, a photocatalyst, and a pigment in various compounds. Representative titanium black is titanium oxynitride, and it is also found that this also has strong light absorption in a wide wavelength range of 400 nm to 750 nm. For comparison, it is shown that carbon black powder used in automobile tires also has strong light absorption in a wide wavelength range of 400 nm to 750 nm.

[0033] When adding such a light-reducing agent with a dark body color to a white LED, it will be greatly light-reduced with a small amount of addition. From the workability during weighing, a light-reducing agent that can be added in a certain amount is required.

[0034] Furthermore, in order to uniformly disperse the phosphor and the light-reducing agent in the resin, it is preferable that the specific gravity and particle size of each particle can be adjusted.

[0035] (Specific gravity of light-reducing agent) The specific gravity of a substance is determined by the constituent elements, crystal structure, etc. Therefore, it is difficult to change the specific gravity of the phosphor while maintaining the light-emitting characteristics. As shown in Table 1, since the phosphor uses relatively heavy elements (for example, alkaline earth metals and rare earth elements), the specific gravity is heavy. AlN and Si3N4 powders with a similar body color use relatively light elements, so the specific gravity is light.

[0036] The specific gravity of each material referred from the Inorganic Crystal Structure Database (ICSD) is shown in Table 1.

Table 1

[0037] The specific gravity of the light-reducing agent can be adjusted by selecting the crystal matrix of the light-reducing agent.

[0038] (Light reduction rate) Moreover, by increasing the amount of the element to be doped, the light attenuation rate (absorption rate) can be increased.

[0039] The selection of the host material and the impurity doping can be carried out in the same design as the phosphor doped with the luminescence center (impurity), which is a major point.

[0040] (Particle size of the light attenuator) The particle growth of the phosphor can be controlled by the particle size of the raw materials used, the firing temperature and time, etc. By using the crystal host used in the phosphor as the light attenuator, the same production as the phosphor becomes possible. Therefore, the particle size of the light attenuator can be easily adjusted.

[0041] From the above, by adding elements (terbium, praseodymium, manganese, titanium) that cause light absorption to the same crystal host as the phosphor, white LEDs of 30 mcd or less can be provided.

[0042] Here, consider the valence of the element that causes light absorption.

[0043] Terbium oxide (Tb4O7) is a mixture of Tb2O3 and TbO2 and contains trivalent and tetravalent Tb. The body color is brownish. Trivalent Tb is well-known as the green phosphor for fluorescent lamps, LaPO4:Ce 3+ ,Tb 3+ (LAP). This green phosphor has a white body color and it can be seen that the light absorption in the visible light region is weak. From this, the visible light absorption of terbium oxide (Tb4O7) is considered to be due to tetravalent Tb.

[0044] On the other hand, praseodymium oxide (Pr4O 11 ) is also a mixture of Pr2O3 and PrO2 and contains trivalent and tetravalent Pr. The body color is dark gray. Pr in praseodymium fluoride (PrF3) is trivalent, and its powder has a green body color. Therefore, the black body color is considered to be due to tetravalent Pr.

[0045] Furthermore, Mn in manganese dioxide (MnO2) is tetravalent from the chemical formula. The body color is gray, and its light absorption is considered to be due to tetravalent Mn.

[0046] Terbium and praseodymium tend to be trivalent and tetravalent. When trivalent rare earth ions are included as constituent elements of the crystal matrix, terbium and praseodymium tend to exist as trivalent. Therefore, a crystal matrix containing divalent alkaline earth metals was selected.

[0047] (Preparation of light attenuator) Taking (Ba,Sr,Ca)2SiO4:Eu, which is well-known as a phosphor, as an example for explanation, crystal matrices such as (Ba,Sr,Ca)3SiO5 and (Ba,Sr,Ca)3MgSi2O8 are also acceptable. Moreover, it is not limited thereto.

Example

[0048] As raw materials for the light attenuator, barium carbonate (BaCO3), strontium carbonate (SrCO3), terbium oxide (Tb4O7), and silicon dioxide (SiO2) were used. The mixing ratios of the raw materials are shown below. Barium carbonate (BaCO3) 7.451 g Strontium carbonate (SrCO3) 9.000 g Terbium oxide (Tb4O7) 0.470 g Silicon dioxide (SiO2) 3.079 g After mixing the above raw materials with a ball mill, they were filled into an alumina crucible and fired at 1200 °C for 3 hours. (Ba,Sr)2SiO4:Eu 2+ When firing the phosphor, Eu 3+ →Eu 2+ Since a reduction reaction is required, a mixed gas of nitrogen and hydrogen is used. For Tb in this case 4+Since there was no need for a reduction reaction, firing was carried out in an air atmosphere. Further, the particle size was adjusted in the same manner as the phosphor to obtain a light-reducing agent.

Example

[0049] In the same manner as in Example 1, raw materials were mixed at the following mixing ratios. Barium carbonate (BaCO3) 16.904 g Terbium oxide (Tb4O7) 0.410 g Silicon oxide (SiO2) 2.687 g Thereafter, firing and particle size adjustment were carried out in the same manner to obtain a light-reducing agent.

Example

[0050] Similarly, raw materials were mixed at the following mixing ratios. Strontium carbonate (SrCO3) 16.095 g Terbium oxide (Tb4O7) 0.517 g Silicon oxide (SiO2) 3.389 g Thereafter, firing and particle size adjustment were carried out in the same manner to obtain a light-reducing agent.

[0051] (Comparative Example 1) Similarly, raw materials were mixed at the following mixing ratios. Barium carbonate (BaCO3) 7.487 g Strontium carbonate (SrCO3) 9.420 g Silicon oxide (SiO2) 3.094 g Thereafter, firing and particle size adjustment were carried out in the same manner to obtain a light-reducing agent.

[0052] (Measurement of Diffuse Reflection Spectrum) For the diffuse reflection spectrum, an integrating sphere unit of a spectrophotometer FP-6500 manufactured by JASCO Corporation was used. The reflection intensity with respect to Spectralon of a standard white plate was set to 100%, and the diffuse reflection spectrum of the prepared light-reducing agent was obtained.

[0053] Fig. 4 shows the diffuse reflection spectra of the light-reducing agents of Examples 1 to 3 and the powder of Comparative Example 1 not containing terbium. It can be seen that the light absorption of the light-reducing agent containing terbium is strong.

Example

[0054] Similar to Example 1, the raw materials were mixed in the following mixing ratio. Barium carbonate (BaCO3) 8.584 g Strontium carbonate (SrCO3) 7.416 g Terbium oxide (Tb4O7) 0.935 g Silicon oxide (SiO2) 3.065 g

[0055] Fig. 5 shows the powder diffuse reflection spectra of Example 1 and Example 4 with a light reducing agent and Comparative Example 1 without terbium. It can be seen that as the amount of terbium increases, the diffuse reflection intensity increases, that is, the light absorption becomes stronger.

[0056] The above examples were shown by taking (Ba,Sr)2SiO4 matrix as an example, but it can also be applied to other crystal matrices. In addition, not only terbium, but also doping with praseodymium, manganese, or titanium causes the same light absorption and can be used as a light reducing agent.

[0057] In the experiments, examples, and comparative examples described below, as the light emitting element 10, a blue light emitting element with an output of 60 mcd and a dominant wavelength of 458 nm when a current of 5 mA was passed was used.

[0058] (Comparative Example 2) The blue light emitting element 10 was covered with a sealing body 20 of a thermosetting silicone resin to fabricate a blue light emitting device 100A. The mixing ratio of the silicone resin is shown below. Silicone resin A (main agent) 0.5000 g Silicone resin B (hardening agent) 0.5000 g

Example

[0059] The blue light emitting element 10 was covered with a sealing body 20 of a thermosetting silicone resin containing the light reducing agent powder 2 of Example 4 to fabricate a blue light emitting device 100B. In order to prevent sedimentation of the light reducing agent, Aerosil was added to the sealing body 20. The mixing ratio of the materials is shown below. Silicone resin A (main agent) 0.5000 g Silicone resin B (hardener) 0.5000 g Aerosil 0.0150 g Light reducing agent of Example 4 0.3390 g

[0060] Table 2 shows the light emission characteristics of the light emitting devices of Comparative Example 2 and Example 5. Also, the emission spectra of the light emitting devices of Comparative Example 2 and Example 5 are shown in FIG. 6, and the normalized emission spectra are shown in FIG. 7. It can be seen that the blue light emitting device of Example 5 is sufficiently smaller than the comparative example.

Table 2

[0061] (Comparative Example 3) Blue light emitting element 10 and (Ba,Sr)2SiO4:Eu with an emission peak wavelength of 565 nm as phosphor 1a 2+ The phosphor (hereinafter referred to as BOS phosphor) was covered with a sealing body 20 of a thermosetting silicone resin to fabricate a white light emitting device 100. The compounding ratio of the materials is shown below. Silicone resin A (main agent) 0.5000 g Silicone resin B (hardener) 0.5000 g Aerosil 0.0150 g BOS phosphor (565 nm) 0.3308 g

[0062] (Comparative Example 4) A white light emitting device was fabricated in the same manner as in Comparative Example 3. AlN was used as a light reducing agent to reduce the brightness. Also, in order to match the white chromaticity, a BOS phosphor with an emission peak wavelength of 530 nm was used as phosphor 1b, and it was formulated so that the chromaticity was the same as that of Comparative Example 3. The compounding ratio of the materials is shown below. Silicone resin A (main agent) 0.5000 g Silicone resin B (hardener) 0.5000 g Aerosil 0.0150 g BOS phosphor (530 nm) 0.0093 g BOS phosphor (565 nm) 0.0699 g 0.3121 g of AlN

[0063] (Comparative Example 5) A white light-emitting device was fabricated in the same manner as in Comparative Example 4. Carbon black was used as a light-shielding agent to reduce the brightness. The mixing ratios of the materials are shown below. 0.5000 g of silicone resin A (main agent) 0.5000 g of silicone resin B (hardening agent) 0.0150 g of Aerosil 0.1624 g of BOS phosphor (565 nm) 0.0001 g of carbon black

Example

[0064] A white light-emitting device was fabricated in the same manner as in Comparative Example 5. The light-shielding agent of Example 4 was used to reduce the brightness. The mixing ratios of the materials are shown below. 0.5000 g of silicone resin A (main agent) 0.5000 g of silicone resin B (hardening agent) 0.0150 g of Aerosil 0.0242 g of BOS phosphor (530 nm) 0.1624 g of BOS phosphor (565 nm) 0.1581 g of the light-shielding agent of Example 4

Example

[0065] A white light-emitting device was fabricated in the same manner as in Example 6. The mixing ratios of the materials are shown below. 0.5000 g of silicone resin A (main agent) 0.5000 g of silicone resin B (hardening agent) 0.0150 g of Aerosil 0.0935 g of BOS phosphor (530 nm) 0.4480 g of BOS phosphor (565 nm) 0.3399 g of the light-shielding agent of Example 4

[0066] Table 3 shows the light emission characteristics of the light emitting devices of Comparative Examples 3, 4, 5 and Examples 6 and 7. Further, the light emission spectra of the light emitting devices of Comparative Example 3 and Example 6 are shown in Fig. 8, and the normalized light emission spectra are shown in Fig. 9. It can be seen that Example 6 can be sufficiently dimmed compared to Comparative Example 3.

Table 3

[0067] Here, consider the concentration of the powder 1 (1a, 1b) with respect to the sealing body 20. The powder concentration is expressed by the following formula. Powder concentration [%] = (powder weight [g]) / (powder weight [g] + sealing body weight [g]) Table 4 shows the phosphor concentration, light reducing agent concentration, and the total powder concentration obtained by adding the two of Comparative Examples 3, 4, 5 and Example 6.

Table 4

[0068] The light emission devices of Comparative Examples 3, 4 and Example 6 were placed in a thermo-hygrostat at 60 °C and 90% RH, and Table 5 shows the maintenance rate of the luminous intensity when energized.

Table 5

[0069] Compared with Comparative Example 5, in the case of black powder such as carbon black, a large amount of light reduction occurs even in a small amount. Also, since carbon black tends to aggregate, it is necessary to devise in manufacturing in order to disperse it uniformly.

[0070] Note that the present invention is not limited to the above-described embodiments. The above embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention. For example, regarding the light reducing agent in the examples, although an oxide matrix was described as an example, it goes without saying that it is also applicable to crystal matrices such as halogen compounds, acid halide compounds, oxynitrides, nitrides, and sulfides.

Industrial Applicability

[0071] It can be applied to a light-emitting device or the like that suppresses the brightness without reducing the current value of the current injected into the LED.

Explanation of Reference Numerals

[0072] 1, 1a, 1b... phosphor, 2... light reducing agent, 10... light-emitting element, 20... encapsulant, 30... package, 40... substrate, L... light, 100... light-emitting device.

Claims

1. comprising an alkaline earth metal as a constituent element of the base material, wherein the base material is composed of any one of an oxide, a halogen compound, an acid halide, an oxynitride, a nitride, and a sulfide, characterized by having a diffuse reflectance intensity of 80% or less in the wavelength range from 400 nm to 750 nm and containing at least one of terbium and praseodymium, a light reducing agent for a light emitting device that suppresses the chromaticity change of the output light while keeping the brightness low.

2. A light emitting device comprising a light emitting element and the light reducing agent according to claim 1 that absorbs a part of the light from the light emitting element.

3. A light emitting device comprising a light emitting element, the light reducing agent according to claim 1 that absorbs a part of the light from the light emitting element, and a phosphor that absorbs a part of the light from the light emitting element and converts it into light having an emission peak wavelength different from the peak wavelength of the emission wavelength of the light emitting element.

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