CN106062130A - Phosphor, light-emitting element, and light-emitting device - Google Patents

Abstract

The present invention relates to a phosphor having improved moisture resistance by modifying the particle surface of a Mn ⁴⁺ activated composite fluoride phosphor capable of realizing high-brightness red light emission, and excellent color rendering and stability by using the phosphor Light-emitting devices and light-emitting devices. The phosphor of the present invention is characterized in that it is represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , the element A is an alkali metal element containing at least K, and the element M is selected from Si, Ge, Sn, Ti, Zr and Hf One or more metal elements in, F is fluorine, Mn is manganese, wherein, the particle surface of the phosphor is modified so that the phosphor is dispersed in a methanol-water mixed solution whose mass ratio is 100 times (Water content: 10% by mass) and the fluorine content in the supernatant obtained after leaving still for 10 minutes became 2% by mass or less.

Description

Phosphor, light emitting element and light emitting device

technical field

The present invention relates to a phosphor that emits red light when excited by ultraviolet light or blue light, a light-emitting element using the phosphor, and a light-emitting device using the light-emitting element. More specifically, it relates to a Mn ⁴⁺ -activated composite fluoride phosphor whose moisture resistance is improved by modification of the particle surface, and a light-emitting element and a light-emitting device having excellent color rendering and stability by using the phosphor. Furthermore, the present invention also relates to a method for evaluating the moisture resistance of the Mn ⁴⁺ -activated composite fluoride phosphor.

Background technique

As white LEDs, white LEDs in which a blue LED chip and a yellow phosphor are combined to obtain pseudo-white light are widely used. However, although the white LED of this method falls into the white area as its chromaticity coordinate value, there are few light-emitting components such as the red area, so the visual effect of the object illuminated by the white LED is different from that of the object illuminated by natural light. very different. That is, the white LED has poor color rendering, which is an indicator of the naturalness of the visual effect of an object.

Therefore, white LEDs that improve color rendering by combining red phosphors, orange phosphors, and other red components in addition to yellow phosphors are being put into practical use.

As such a red phosphor, a nitride phosphor or an oxynitride phosphor activated with Eu ²⁺ is known. Typical phosphors include Sr ₂ Si ₅ N ₈ :Eu ²⁺ , CaAlSiN ₃ :Eu ²⁺ , (Ca,Sr)AlSiN ₃ :Eu ²⁺ , and the like.

However, for phosphors that activate Eu ²⁺ as the emission center ion, the half-value width of the emission spectrum is wide, so there is a tendency that the wavelength band beyond the human visible range contains many spectral components, and it is difficult to achieve high brightness.

In recent years, phosphors using Eu ³⁺ and Mn ⁴⁺ as luminescence center ions have been developed as red phosphors containing many spectral components in a region with a narrow half-value width of the emission spectrum and high visibility. Patent Documents 1 to 4 disclose a phosphor made by activating Mn ⁴⁺ with composite fluoride crystal K ₂ SiF ₆ and a light-emitting device using the phosphor. The phosphor can realize red emission with a narrow half-value width. The phosphor light-emitting device realizes excellent color rendering and color reproducibility.

prior art literature

patent documents

Patent Document 1: Japanese National Publication No. 2009-528429

Patent Document 2: International Publication No. 2009/110285 Pamphlet

Patent Document 3: Specification of US Patent No. 3576756

Patent Document 4: Japanese Patent Laid-Open No. 2012-224536

Contents of the invention

The problem to be solved by the invention

However, Mn ⁴⁺ -activated phosphors based on composite fluoride crystals have low stability, and in particular phosphors are easily hydrolyzed by contact with water or water vapor. Moreover, when hydrolysis occurs, not only the fluorescence characteristics are lowered, but also peripheral members may be corroded by fluorine ions and hydrogen fluoride generated along with the decomposition. Therefore, there is a problem in practical use of an LED light-emitting device in which a phosphor is dispersed in a sealing resin that cannot completely block water vapor from the viewpoint of durability and reliability.

solutions to problems

The inventors of the present invention conducted in-depth studies in view of the above problems, and found that by appropriately modifying the surface of the particles, the fluorine eluted in the supernatant when dispersed in a specific solution is reduced to a specified amount or less, and the moisture resistance can be significantly improved. Fluorescence characteristics are lowered, and the present invention has been accomplished.

That is, the main points of the phosphor of the present invention are represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , the element A is an alkali metal element containing at least K, and the element M is selected from Si, Ge, Sn, Ti, Zr and one or more metal elements in Hf, F is fluorine, and Mn is manganese, wherein the particle surface of the phosphor is modified so that the phosphor is dispersed in methanol-water with a mass ratio of 100 times The fluorine content in the supernatant liquid obtained after leaving still the mixed solution (water content: 10% by mass) for 10 minutes was 2% by mass or less.

In the phosphor, element A is preferably K, and element M is Si.

In addition, the gist of the light-emitting element of the present invention is that it includes the aforementioned phosphor and a light-emitting light source. Furthermore, the gist of the light-emitting device of the present invention is that it includes the above-mentioned light-emitting element.

Furthermore, the gist of the moisture resistance evaluation method of the present invention is that the phosphor is represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , the element A is an alkali metal element containing at least K, and the element M is selected from Si, Ge , Sn, Ti, Zr and more than one metal element in Hf, F is fluorine, and Mn is manganese, and the method comprises: measuring that the phosphor is dispersed in a methanol-water mixed solution ( The content of fluorine in the supernatant liquid obtained after standing still for 10 minutes in water content 10% by mass).

The effect of the invention

The phosphor of the present invention is a phosphor in which elution of fluorine in a specific solution is limited to a predetermined amount or less, and is remarkably excellent in moisture resistance.

Therefore, the light-emitting element and light-emitting device of the present invention using the phosphor have high color rendering and color reproducibility, little change over time, and a long life.

Description of drawings

FIG. 1 is a graph showing X-ray diffraction patterns of K ₂ SiF ₆ , Example 1, and Comparative Example 1.

FIG. 2 is a graph showing the excitation/fluorescence spectrum of the phosphor of Comparative Example 1. FIG.

detailed description

The present invention is a phosphor, which is represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , element A is an alkali metal element containing at least K, element M is selected from Si, Ge, Sn, Ti, Zr and Hf More than one metal element in, F is fluorine, Mn is manganese, wherein, the particle surface of the phosphor is modified so that the phosphor is dispersed in a methanol-water mixed solution whose mass ratio is 100 times (Water content: 10% by mass) and the fluorine content in the supernatant obtained after leaving still for 10 minutes became 2% by mass or less.

Here, the "particle surface" refers to the range covered by the surface modification, and is preferably a range from the surface of the phosphor (depth 0 μm) to a depth of 1.5 μm. When the range of modification is too deep, the absorption efficiency of the excitation light of the phosphor and the efficiency of outputting fluorescence from the phosphor may decrease.

In addition, "modification" typically includes a state in which fine particles of a Ca compound such as calcium fluoride are attached to the particle surfaces of the phosphor by treating the phosphor with a Ca source compound.

In the above general formula: A ₂ MF ₆ : Mn ⁴⁺ , Mn ⁴⁺ is an ion activated as a luminescent center, and is in solid solution in the form of replacing a part of the element M.

The element A is an alkali metal element containing at least K, preferably having a large K content. Specific examples of the element A include K alone, a combination of K and Na, a combination of K and Li, and a combination of K, Na, and Li. In order to obtain stronger luminous intensity, K alone is preferred.

The element M contains at least Si and is one or more metal elements selected from Si, Ge, Sn, Ti, Zr, and Hf. Specific examples of the element M include Si alone, Si and Ge, a combination of Si and Sn, a combination of Si and Ti, a combination of Si, Ge and Sn, a combination of Si, Ge and Ti, a combination of Si, Sn and Ti, Si Combination with Ge and Sn and Ti. The element M affects the excitation band of the phosphor. From the viewpoint of efficiently emitting blue light, Si alone is preferable.

The method for producing the phosphor before modifying the particle surface is not particularly limited, and known production methods such as those described in Patent Documents 1 to 4 can be used. Specifically, you can use:

A method in which a compound as a host crystal of a phosphor and a compound containing Mn ⁴⁺ as a luminescent center are dissolved in hydrofluoric acid, and the solvent is evaporated to dryness and re-precipitated (Patent Document 1);

A method of impregnating elemental metals such as silicon in a mixed solution of hydrofluoric acid and potassium permanganate (patent document 2);

・A method in which a poor solvent such as acetone or methanol is added to an aqueous solution of hydrofluoric acid in which the constituent elements of the composite fluoride phosphor are dissolved to precipitate the phosphor (Patent Document 3),

- A method of dissolving constituent elements of a composite fluoride phosphor in two or more hydrofluoric acids that do not precipitate solids, and mixing them to allow reaction and crystallization (Patent Document 4).

The Mn ⁴⁺ activated composite fluoride phosphors produced by these methods have solubility in water, react with water and hydrolyze to produce colored compounds such as manganese dioxide that absorb visible light, highly corrosive hydrogen fluoride. Hydrogen fluoride accelerates the deterioration of constituent members constituting the light-emitting element.

Moisture resistance can be remarkably improved by appropriately modifying the surface of the particles so that the amount of fluorine eluted in the supernatant when the phosphor is dispersed in a specific solution is reduced to a predetermined amount or less.

As a solution for investigating the elution amount of fluorine in the phosphor, a methanol-water mixed solution (water content: 10% by mass) having a mass ratio of 100 times was used. The fluorine content in the supernatant obtained after dispersing the phosphor sample in this solution and leaving it to stand for 10 minutes was investigated.

When the fluorine content in the supernatant is 2% by mass or less, an excellent effect of preventing hydrolysis, that is, excellent water resistance is exhibited.

As a method of modifying the phosphor to reduce the eluted amount of fluorine, typically, there is a method of treating the phosphor with a compound that is a Ca source to include a Ca-containing compound on the surface of the particles.

The means for adding the Ca-containing compound to the particle surface of the phosphor is not particularly limited as long as the Ca-containing compound generated from the Ca source can be physically or chemically attached to the surface of the phosphor particle, and it does not matter whether it is wet or dry. If the Ca-containing compound has low water solubility, calcium fluoride (CaF ₂ ) is preferably used regardless of whether it is crystalline or amorphous. Calcium fluoride not only has a very low solubility in water but is also difficult to dissolve in organic solvents such as hydrofluoric acid, acetone, methanol, and ethanol used in phosphor production, and is thus suitable as a Ca-containing compound.

A suitable example of attaching a Ca-containing compound to the particle surface of the phosphor is shown below.

First, phosphor particles are dispersed in an organic solvent alone or in a mixed liquid with hydrofluoric acid to prepare a suspension. As the organic solvent, acetone, methanol, and ethanol are preferable. Next, a solution obtained by dissolving a Ca source compound such as calcium nitrate is added to the suspension. As the solvent, there is water or an organic solvent. The Ca ions in the solution react with the hydrogen fluoride present in the suspension, and precipitate on the surface of the phosphor particles in the form of CaF ₂ .

Hydrogen fluoride as a reaction source of this reaction includes hydrogen fluoride generated by hydrolysis of the phosphor when an aqueous solution is added, residual hydrogen fluoride present in the phosphor, hydrofluoric acid added as a solvent, and the like. This reaction proceeds in a state where the phosphor is dispersed in a solvent, so it can also be carried out by adding a compound as a Ca source in the washing step after the composite fluoride crystal is precipitated during the production process of the phosphor.

The Ca-containing compound does not necessarily need to be present on the entire particle surface of the phosphor, and even if present in a part thereof, the moisture resistance can be improved.

The light-emitting device of the present invention has the aforementioned phosphor of the present invention and a light-emitting light source.

As a light emitting source, an ultraviolet LED or a visible light LED emitting light having a wavelength of 250 nm to 550 nm can be used, and among them, a blue LED light emitting element of 420 nm to 500 nm is preferable.

As the phosphor used in the light-emitting element, known phosphors may be used in combination in addition to the phosphor of the present invention. Higher color rendering and higher luminance can be obtained by appropriately combining the phosphor of the present invention with phosphors of other light-emitting colors such as green-emitting phosphors, yellow-emitting phosphors, and red-emitting phosphors.

The light-emitting device of the present invention uses the above-mentioned light-emitting element of the present invention, and examples thereof include backlights for liquid crystal panels, lighting devices, signals used for roads or railways, and projectors.

Example

Hereinafter, the present invention will be described in further detail by way of examples shown below.

＜Manufacture of raw material K ₂ MnF ₆ ＞

First, the production method of K ₂ MnF ₆ used as the Mn raw material of the phosphor in the following Examples and Comparative Examples will be described.

Concentration 40% by mass hydrofluoric acid 800ml is put into the beaker that the Teflon (registered trademark) of capacity 1 liter makes, make KHF ₂ powder (special grade reagent that Wako Pure Chemical Industries Co., Ltd. manufactures) 260g and potassium permanganate powder (Wako 12 g of reagents manufactured by Junyaku Kogyo Co., Ltd. (grade 1) were dissolved.

While stirring the hydrofluoric acid reaction solution with a magnetic stirrer, 8 ml of 30% hydrogen peroxide water (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise little by little. When the amount of hydrogen peroxide added exceeds a certain amount, yellow particles start to precipitate, and the color of the reaction solution changes from purple. After adding a certain amount of hydrogen peroxide water dropwise, after continuing to stir for a while, stop stirring to precipitate the precipitated particles. All the above reactions were carried out at room temperature.

After the particles are precipitated, the operations of removing the supernatant, adding methanol, stirring/standing, removing the supernatant, and adding methanol are repeated until the liquid becomes neutral. Then, precipitated particles were collected by filtration, dried, and methanol was completely evaporated to obtain 19 g of K ₂ MnF ₆ powder.

[Examples 1 to 3 and Comparative Example 1]

Examples 1-3 and Comparative Example 1 all relate to phosphors represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , element A is K, element M is Si, F is fluorine, and Mn is manganese, that is, K ₂ SiF ₆ : Phosphor represented by Mn ⁴⁺ . Comparative Example 1 is a conventional phosphor that does not contain a Ca-containing compound on the particle surface, and Examples 1 to 3 are phosphors that have been surface-modified by containing a Ca-containing compound on the particle surface.

＜Comparative example 1＞

At room temperature, 500 ml of hydrofluoric acid with a concentration of 48% by mass was put into a beaker made of Teflon (registered trademark) with a capacity of _{1 liter, and K SiF 6 powder} (manufactured by Wako Pure Chemical Industries, Ltd., grade: chemical Use) 50g and 5g of K ₂ MnF ₆ powder synthesized by the aforementioned method to prepare a suspension.

The Teflon (registered trademark) beaker containing the suspension was placed on a hot plate, and heated while stirring. Heating to about 80°C, holding it for a while, and checking the inside of the beaker revealed that the powder was completely dissolved and turned into a light brown solution. Further, this hydrofluoric acid aqueous solution was continuously heated to evaporate the solvent. Pale yellow crystals precipitated with the evaporation of the solvent. Heating was stopped in a state where the amount of solvent was considerably small, and cooled to room temperature. Thereafter, washing was performed with hydrofluoric acid and methanol at a concentration of 20% by mass, the solid portion was separated and recovered by filtration, and the residual methanol was evaporated and removed by drying. The phosphor after the drying treatment was classified using a nylon sieve with a mesh size of 75 μm, and only the phosphor that passed through the sieve was classified to obtain the phosphor K ₂ SiF ₆ :Mn ⁴⁺ of Comparative Example 1.

<Example 1>

20 g of the phosphor of Comparative Example 1 was added to 100 ml of a mixed solution of hydrofluoric acid and methanol at a concentration of 20% (volume ratio: 1:1) to prepare a suspension.

While stirring the suspension, 25 ml of a 0.6 mol% calcium nitrate aqueous solution was added. After the addition, it was further stirred for 10 minutes. After the stirring is completed, the operations of leaving the suspension to stand, precipitating the phosphor, removing the supernatant, adding methanol, stirring/standing, removing the supernatant, and adding methanol are repeated until the liquid becomes neutral .

Then, the precipitated particles were recovered by filtration, further dried, and the methanol was completely evaporated to obtain the phosphor of Example 1.

<Example 2 and 3>

Examples 2 and 3 were produced by the same method and conditions as in Example 1, except that the concentration of the calcium nitrate aqueous solution added to the phosphor suspension was changed to 0.3 mol % and 1 mol %, respectively.

＜Evaluation of Phosphor＞

Next, the obtained phosphors were evaluated by the following method.

First, for the phosphors of Comparative Example 1 and Examples 1 to 3, crystal phase, excitation spectrum/fluorescence spectrum, quantum efficiency, chromaticity coordinates, eluted F amount, and moisture resistance were evaluated. The evaluation results are shown in Table 1 and FIGS. 1-2.

[Table 1]

＜Crystal phase＞

The X-ray diffraction pattern of the phosphor was measured using an X-ray diffraction apparatus (Ultima IV manufactured by Rigaku Corporation). CuKα tubes were used for the measurement.

The phosphors of Comparative Example 1 and Examples 1-3 all have the same spectrum as the K ₂ SiF ₆ crystal and do not contain other crystal phases. The results of X-ray diffraction of the K ₂ SiF ₆ crystal, the phosphor of Example 1, and the phosphor of Comparative Example 1 are shown in FIG. 1 .

＜Excitation Spectrum/Fluorescence Spectrum＞

The excitation/fluorescence spectrum of the phosphor was measured with a spectrofluorophotometer (F-7000 manufactured by Hitachi High-Technologies Corporation). The excitation wavelength of the fluorescence spectrum in this measurement is 455 nm, and the monitoring fluorescence wavelength of the excitation spectrum is 632 nm.

The measurement results of the phosphor of Comparative Example 1 are shown in FIG. 2 . The phosphor of Comparative Example 1 has two excitation bands of ultraviolet light around a peak wavelength of 350 nm and blue light around a peak wavelength of 450 nm, and emits light in a plurality of narrow bands in the red region of 600 to 700 nm.

Regarding the phosphors of Examples 1 to 3, the excitation/fluorescence spectra measured by a spectrofluorophotometer had substantially the same shape as that of Comparative Example 1.

＜Quantum efficiency＞

The quantum efficiency of the phosphor was evaluated at normal temperature by the following method.

In integrating sphere side opening of A standard reflector (Spectralon manufactured by Labsphere) having a reflectance of 99% was installed. Monochromatic light at a wavelength of 455 nm was introduced into the integrating sphere through an optical fiber from an Xe lamp as a light source, and the spectrum of the reflected light was measured with a spectrophotometer (MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.). At this time, the number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm.

Next, a concave element filled with phosphor so that the surface becomes smooth was placed in the opening of the integrating sphere, irradiated with monochromatic light with a wavelength of 455 nm, and the spectra of the excited reflected light and fluorescent light were measured with a spectrophotometer. The photon number (Qref) of the excitation reflected light and the photon number (Qem) of the fluorescent light were calculated from the obtained spectral data.

The photon count of the excitation reflected light was calculated in the same wavelength range as the photon count of the excitation light, and the photon count of the fluorescent light was calculated in the range of 465 to 800 nm.

External quantum efficiency=Qem/Qex×100, absorptivity=(Qex−Qref)/Qex×100, and internal quantum efficiency=Qem/(Qex−Qref)×100 were obtained from the obtained three photon numbers.

＜Chromaticity coordinates＞

Chromaticity is calculated by using the algorithm in the XYZ chromaticity system specified in JIS Z 8701 and using the CIE1931 color matching function based on the method based on JIS Z 8724 (Measurement method of color - light source color -) for the spectrum measured with phosphors Coordinates (x, y). The wavelength range used for the calculation of the chromaticity coordinates was set to 465 to 780 nm.

＜Dissolved F amount＞

The content of fluorine in the supernatant obtained by dispersing the phosphor in a 100-fold methanol-water mixed solution (water content: 10% by mass) and leaving it to stand for 10 minutes was investigated. The measurement of this value was performed by ion chromatography-mass spectrometry using NIPPON DIONEX Corporation DX-320.

＜Moisture resistance evaluation＞

The moisture resistance evaluation of the phosphor was performed by the following method.

Put 3g phosphor into A culture dish made of PFA was placed in a tank of a constant temperature and humidity device (IW222 manufactured by YAMATO SCIENTIFIC CO., LTD.), and treated under high temperature and high humidity conditions with a temperature of 60°C and a relative humidity of 90%RH for 4 hours. The external quantum efficiency was measured by the above method, and compared with the external quantum efficiency before high temperature and high humidity treatment. That is, [external quantum efficiency after high-temperature and high-humidity treatment]/[external quantum efficiency before high-temperature and high-humidity treatment]×100 was calculated and evaluated as an index of moisture resistance.

In the case of Comparative Example 1, the absorptivity, internal quantum efficiency, external quantum efficiency, and chromaticity coordinates (x, y) of 455 nm excitation after the high-temperature and high-humidity treatment were 76%, 66%, 50%, (0.690, 0.307). The high-temperature and high-humidity treatment significantly lowered the internal quantum efficiency, and as a result, the external quantum efficiency was 79% of that before the high-temperature and high-humidity treatment, which was lower than the pass value of 85% for the humidity resistance evaluation.

On the other hand, in the case of Example 1, the external quantum efficiency of the phosphor after the high temperature and high humidity treatment was 62%, and the moisture resistance evaluation was 97%. In addition, the moisture resistance evaluations of the phosphors of Examples 2 and 3 were 94% and 98%, respectively.

As shown in Table 1, it was confirmed that the amount of eluted F in the supernatant obtained by dispersing and standing in a methanol-water mixed solution (water content: 10% by mass) with a mass ratio of 100 times was 2% by mass or less. In the case of , the moisture resistance is remarkably excellent.

<Example 4>

A light-emitting element comprising the phosphor of Example 1 and a cyan light-emitting LED as a light-emitting source was produced. This light-emitting element has excellent color rendering and color reproducibility because the phosphor of Example 1 with excellent moisture resistance is used, and also has less decrease in luminance over time than the light-emitting element using the phosphor of Comparative Example 1.

<Example 5>

Using the light-emitting element of Example 4, a lighting device as a light-emitting device was produced. Since this light-emitting device uses the phosphor of Example 1 having excellent moisture resistance, it has excellent color rendering and color reproducibility, and has less decrease in luminance over time than the light-emitting device using the phosphor of Comparative Example 1.

Claims (5)

1. A phosphor, which is represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , the element A is an alkali metal element containing at least K, and the element M is selected from Si, Ge, Sn, Ti, Zr and Hf more than one metal element, F is fluorine, and Mn is manganese, wherein the particle surface of the phosphor is modified so that the phosphor is dispersed in a methanol-water mixed solution ( The content of fluorine in the supernatant liquid obtained after standing still for 10 minutes in water content (10% by mass) was 2% by mass or less. 2. The phosphor according to claim 1, wherein the element A is K, and the element M is Si. 3. A light-emitting element comprising the phosphor according to claim 1 or 2 and a light-emitting light source. 4. A light-emitting device comprising the light-emitting element according to claim 3. 5. A method for evaluating the moisture resistance of phosphors, said phosphors are represented by the general formula: A ₂ MF ₆ : Mn ⁴⁺ , element A is an alkali metal element containing at least K, element M is selected from Si, Ge , Sn, Ti, Zr and more than one metal element in Hf, F is fluorine, and Mn is manganese, and the method comprises: measuring that the phosphor is dispersed in a methanol-water mixed solution ( The content of fluorine in the supernatant liquid obtained after standing still for 10 minutes in water content 10% by mass).