JP6435514B2 - Phosphor - Google Patents

Description

  The present disclosure relates to a light-emitting device used as a light source of an illumination device such as indoor lighting or a car headlight, a light source of a display such as a projector or a smartphone, and a phosphor that can be used in the light-emitting device.

  In recent years, a combination of a semiconductor light emitting device having a light emission wavelength of 380 nm to 480 nm (ultraviolet to blue) and a phosphor that absorbs a part of the emitted light and emits fluorescence having a longer wavelength than the emitted light is combined. Light emitting devices have been actively developed. For example, a cerium-activated yttrium aluminum garnet (YAG: Ce) phosphor absorbs blue light having a wavelength of 450 nm and emits light in yellow, which is a complementary color of blue. Since this phosphor has excellent temperature characteristics and conversion efficiency, it has already been put into practical use as a white light emitting diode equipped with the phosphor.

  Consider a display device in which a short wavelength light source is used as an excitation light source and visible light is converted by a phosphor. In order to realize this, a phosphor material that absorbs excitation light and can be converted into the three primary colors of red, green, and blue is required. In order to display a clear image as a projector, each primary color phosphor needs to emit light at an appropriate wavelength.

  Here, red is considered. Red is an important color for reproducing the texture of human skin color and the vividness of meat and flowers. Therefore, the red light emission peak wavelength must be around 620 nm. If the wavelength is shorter than that, the image becomes yellowish. On the other hand, when the wavelength becomes long, the visibility becomes low, so it looks dark. The half width of the emission spectrum is also an important factor, and the half width is preferably as narrow as possible. When the half width is wide, the yellow component is mixed on the short wavelength side. Since yellow has higher visibility than red, the mixing is at least yellowish as an image. On the other hand, if the spectrum extends in the infrared region, it is almost invisible to humans, so it is not recognized as red and is equivalent to a non-light emitting component. Therefore, the elements necessary for the red phosphor are two points, an appropriate emission peak wavelength and a narrow half-value width.

  In recent years, several red phosphors have been developed and put into practical use. For example, the alpha sialon-based phosphor is an aluminum and silicon oxynitride phosphor activated by divalent europium, and has a silicon nitride alpha structure. According to Non-Patent Document 1, the alpha sialon phosphor emits light at a central wavelength of about 600 nm and can be used for an image display device.

Fujikura Technical Review No. 108 (April 2005) Page 1 to Page 5

  However, in the light emitting device described above, the following problems are particularly raised with respect to the red phosphor. First, since the YAG: Ce-based phosphor has the emission wavelength center located in the yellow region as described above, the green purity is insufficient as a red phosphor for display. If it is used as a red phosphor, it is necessary to filter out all the light in the yellow region, resulting in a significant loss in efficiency.

  On the other hand, as described in Non-Patent Document 1, the alpha sialon-based phosphor needs to be fired under a nitrogen atmosphere at a high temperature (1700 ° C.) and under a pressurized condition. For this reason, the firing furnace is larger than a general electric furnace for ensuring pressure resistance, and as a result, the phosphor is more expensive than a general oxide phosphor. Most red phosphors have a full width at half maximum of about 100 nm. If the full width at half maximum is wide, it cannot be used effectively as pure red.

  As described above, the present invention is to provide a phosphor having a high red purity, a narrow half-value width, and a high effective conversion efficiency by a firing method using urea, which does not require high-pressure firing, as a nitriding agent. .

  In order to solve the above problems, the phosphor of the present invention comprises Eu as an activator, an alkaline earth element having at least one of Ca, Sr, and Ba, silicon, and nitrogen as main components, and light emission. The peak wavelength is 600 nm or more and 650 nm or less. With this configuration, a phosphor with high color rendering properties can be realized.

  The phosphor of the present invention further contains oxygen, and its molar amount is preferably smaller than that of nitrogen. According to this preferred configuration, oxygen having a large electronegativity is contained, so that the phosphor has a fluorescence peak at a short wavelength as compared with the case without oxygen. Then, by controlling the oxygen content within a range not exceeding the nitrogen content, a desired red phosphor having a high color rendering property can be realized.

  The phosphor of the present invention preferably further has a light emission half width of less than 100 nm. According to this preferable configuration, it is possible to suppress a cut amount of unnecessary wavelength components, so that a highly efficient phosphor can be realized.

  The phosphor of the present invention preferably further has a composition ratio of Sr: Si = 2: 1 and O: N = 1: 3. According to this preferred configuration, the red phosphor has a stoichiometrically stable composition. That is, the heat resistance is increased and the light deterioration is reduced, so that a phosphor with higher reliability can be realized.

  In the phosphor of the present invention, it is preferable that a mixture having a composition ratio of Sr: Si = 5: 1 and O: N = 9: 1 is further present. According to this preferred configuration, when the oxygen content is higher than that of nitrogen, light can be emitted in the vicinity of yellowish green. By partially mixing this, the color rendering property of red can be finely adjusted, and the phosphor can have the emission peak wavelength in the green region with good reproducibility.

  It is preferable that the phosphor of the present invention is further granular, has a planar defect at the center, and has a particle size of 2 μm or more. According to this preferred configuration, the phosphor has a planar defect at the center, and has a structure in which the single crystal phosphor crystal layer surrounds it. Further, since the external quantum efficiency of the phosphor is almost the same as the internal quantum efficiency, it means that the phosphor particles are sufficiently absorbed by the excitation light and can be fluorescent. In particular, due to the magnitude of absorption, the portion that functions as a phosphor is mostly outside the phosphor particles. Therefore, when the planar defect is sufficiently separated from the surface, that is, when the particle size is 2 μm or more, the excitation light hardly reaches the central portion, and is not deactivated by the planar defect, and is highly efficient. A phosphor can be realized.

  In the phosphor of the present invention, the nitrogen material is preferably urea. According to this preferable configuration, the phosphor can be realized at low cost.

  According to the present invention, a highly efficient red phosphor can be realized.

It is the graph showing the effective conversion efficiency with respect to the fluorescence peak wavelength and half value width of a fluorescent substance. (A) is a figure which shows the fluorescence spectrum concerning the fluorescent substance of this invention, (b) is a figure showing the position in the CIE1931 color coordinate concerning the fluorescent substance of this invention. It is a figure which shows the excitation and the fluorescence spectrum concerning the fluorescent substance of this invention. It is a figure which shows the relationship between the external appearance photograph of the fluorescent substance powder when changing the baking conditions concerning the fluorescent substance of this invention, baking temperature, and time. It is a figure which shows the elemental composition analysis result of the fluorescent substance of this invention. It is a figure which shows the fluorescence spectrum of the various mixed state concerning the fluorescent substance of this invention. (A) is the whole figure which shows the cross-sectional transmission electron microscope image of the fluorescent substance of this invention, (b) is the elements on larger scale of the cross-sectional transmission electron microscope image of the same fluorescent substance.

  Embodiments of the present invention will be described below with reference to the drawings.

(1) Regarding the relationship between the half-value width of the phosphor emission spectrum and the conversion efficiency of red light FIG. 1 assumes that the emission spectrum of the phosphor is Gaussian and changes the peak wavelength and half-value width. FIG. 6 is a contour plot of the ratio of components that can be recognized as red. In FIG. 1, SiAlON, SSN, SSE, and CASN represent phosphors. The contour lines in FIG. 1 represent the proportion of pure red light in the total emission spectrum, that is, the conversion efficiency as pure red. In FIG. 1, the contour lines of 25% and 40% indicate that the conversion efficiency as pure red is 25% and 40%, respectively. Moreover, the direction of the arrow in FIG. 1 represents the direction in which the conversion efficiency as pure red increases. The red region is defined as a wavelength range of 590 nm to 650 nm. When the full width at half maximum is very narrow, most light can be effectively used as pure red if the peak wavelength is in the red wavelength range. On the other hand, as the full width at half maximum increases, the proportion of effective use decreases exponentially. When the half width is 100 nm, only about 25% of the entire emission spectrum can be used as pure red. On the other hand, when the half width is 80 nm, about 40% of the component can be used as pure red. That is, reducing the half-value width by 20% has the same effect as improving the effective conversion efficiency by about 50%.

(2) Manufacturing method The manufacturing method of the phosphor of the present invention according to this embodiment will be described below.

First, strontium carbonate (chemical formula SrCO ₃ ), silica powder (chemical formula SiO ₂ ), and europium oxide (chemical formula Eu ₂ O ₃ ) are prepared as raw materials. They are all white powders. Strontium carbonate and silica are constituents of the mother crystal in the phosphor. Europium oxide is incorporated as a fluorescence activator in the mother crystal.

  For example, these raw materials are mixed at a ratio of 36 g of strontium carbonate and 0.8 g of europium oxide to 5 g of silica. After mixing, mix well to ensure even mixing.

  Next, the mixture is set in an electric furnace. The firing conditions are 1100 ° C. and 4 hours, and the atmosphere is atmospheric pressure. As a result, an oxide of strontium and silicon containing europium is obtained. Europium at this time is trivalent by oxidation firing.

Next, urea is added to the oxide. About 8 g of urea is added to 1 g of the oxide, and about 3 cm ³ of pure water is added for uniform stirring. This operation is for improving the reactivity by uniformly adhering once water-soluble urea around the calcined oxide.

  The obtained mixture is set in an electric furnace. The annealing conditions are 1500 ° C. for 2 hours, and the atmosphere in the furnace is normal pressure with nitrogen gas. Although it was white powder before annealing, it is formed as red phosphor powder under this condition after annealing.

In the present embodiment, the Eu source is europium oxide, but europium nitrate (chemical formula Eu (NO ₂ ) ₃ ) and hydrates thereof may be used. In this embodiment, urea is used as the nitriding agent. However, carbamide-based compounds (for example, chemical formula C (NH ₂ ) (NH) (OH)) and hydrazine-based compound hydrates (for example, chemical formula N _{2 H 2} · H ₂ O), also using the azide compound (e.g. formula NaN _3), the same effect can be obtained. In particular, since the carbamide compound has a molecular structure very close to that of urea, a preferable effect can be obtained similarly to urea. Further, in this manufacturing method, atmospheric firing is performed once. However, when a completely nitrided phosphor is obtained, the atmospheric firing step may be omitted. In this case, a red phosphor containing almost no oxygen is produced. On the other hand, when the temperature of atmospheric baking is further raised above 1100 ° C. or the time for nitriding baking is shortened or the temperature is lowered, a phosphor having a higher oxygen ratio than nitrogen is formed.

(3) Characteristics of the phosphor of the present invention Next, optical characteristics of the phosphor according to the present invention will be described.

  First, FIG. 2 shows the fluorescence spectrum of the phosphor according to the present invention (FIG. 2A) and its CIE1931 color coordinates (FIG. 2B). In FIG. 2A, the peak height at the peak wavelength is normalized as 1. In addition, in Fig.2 (a), the photograph of the fluorescent substance concerning this invention is attached together. As shown in FIG. 2A, the phosphor emits red light at a central peak wavelength of 622 nm. Further, the half-value width is as narrow as about 79 nm, and it is characterized in that there are few fluorescent components in adjacent wavelength regions (wavelengths less than 590 nm and 650 nm or more). This is because the raw material is effectively nitrided with urea. Considering the case where only the wavelength range from 590 nm to 650 nm is used as a red color with a filter or the like, it can be seen that about 40% cut (effective efficiency is about 60%) can be obtained from the actual spectrum shape shown in FIG.

  On the other hand, when the effective efficiency is obtained from FIG. 1 based on the obtained peak wavelength and half width, it is about 40%. The reason why the effective efficiency calculated from the actual spectrum is high is that the spectrum shape is not Gaussian and the peak portion is close to a broad trapezoid. That is, it turns out that this fluorescent substance has a more suitable spectrum shape as a red light source. As a result, it can function as a phosphor with high color rendering and high efficiency close to pure red.

  In addition, when viewing the CIE1931 color coordinates in FIG. 2B, it is located outside the triangle indicated by sRGB. This means that a higher-purity red color (color coordinates (x, y) = (0.620, 0.378)) than that required for sRGB can be realized by this phosphor. ing.

Next, the excitation / emission spectrum of the obtained phosphor is shown in FIG. In FIG. 3, IQE and EQE in particular on the left vertical axis mean internal and external quantum efficiencies, respectively. In FIG. Intensity indicates the emission spectrum intensity. The unit on the right vertical axis is an arbitrary unit. FIG. 3 shows that the excitation spectrum is very broad from the ultraviolet region to the yellow (wavelength of about 550 nm) region and is flat. This means that a wide range of excitation light sources from the ultraviolet region to the yellow region can be used, and it can be seen that the phosphor according to the present invention can be applied in a very wide range as a red luminescent material. Also, the difference between the external quantum efficiency and the internal quantum efficiency is only about 10%.

  Furthermore, changes in the fired product were confirmed by changing the firing temperature. The firing conditions were 4 conditions (samples A to D) in increments of 100 ° C. from 1300 ° C. to 1600 ° C., and the case where the firing time was very short (6 minutes, sample E) was also examined. Other conditions are as described above. The firing conditions for Samples A to E are summarized in Table 1.

  The difference between samples A to E is illustrated in FIG. From FIG. 4, it becomes a green fired product under low temperature conditions, and in particular, it is a green fired product at 1300 ° C. (sample A). At 1500 ° C., all were red phosphors (Sample C), and when the temperature was further increased, almost nothing remained (Sample D). This is probably because the fired product is thermally decomposed and disappears. As a result of the above firing temperature experiment, it was found that 1500 ° C. is the optimum temperature condition for obtaining a red phosphor in the present embodiment. Moreover, when baking time was shortened extremely (sample E), as shown in FIG. 4, the ratio containing a green baking thing became quite high. This indicates that sufficient firing time is required to sufficiently nitride the oxide with urea and obtain a desired oxynitride phosphor.

  Next, EDX (energy dispersive X-ray spectroscopy) analysis was performed on the green (sample A) and red (sample C) fired products. The results of elemental composition analysis are shown in Table 2. The investigated elements are strontium, silicon, oxygen, nitrogen, and europium, and the acceleration voltage of the electron beam is 5 kV. In addition, the value in Table 2 is the ratio of the number of atoms of each element, that is, the number of atoms, when the constituent element of the fired product is 100.

  From Table 2, it was found that both green and red contained all the examined elements, but the constituent ratio of each element was significantly different. First, in the green fired product (sample A), the ratio of strontium was very high compared to silicon, and the content ratio of oxygen was very high compared to nitrogen. The constituent ratio (composition ratio) of the elements was Sr: Si = 5: 1 and O: N = 9: 1, which was almost an integer ratio. On the other hand, in the elemental composition of the red phosphor (sample C), the nitrogen content is overwhelmingly higher than oxygen. The composition ratio (composition ratio) was Sr: Si = 2: 1 and O: N = 1: 3, and it was revealed that the ratio was almost an integer. Since both have an almost integer ratio, it can be seen that they are intrinsic crystal phases. Note that the composition ratio includes a manufacturing error.

  In FIG. 4, a green and red mixed fired product (sample B and sample E) is obtained at a firing temperature of 1400 ° C. When irradiated with excitation light, the green fired product becomes green and the red fired product becomes fluorescent in red. To do. In addition, in the middle of the green and red regions, it appears to be fluorescent in yellow. In order to examine this in detail, as shown in FIG. Note that the location a represents a green region, the location b represents a yellow-green region, the location c represents a yellow region, the location d represents a dark blue region, and the location e represents a red region. The result is shown in FIG. FIG. 6 shows that the green region (location a) itself has a peak wavelength of 540 nm. The red region (location e) is as described above. Further, the spectrum of the mixed region (location b, location c, location d) does not have a peak in the yellow region (wavelength near 560 nm), and the fluorescence emitted separately from the green phosphor and the red phosphor described above. It turns out that it is mixing. Thus, the fluorescent color of the present phosphor can be freely changed from green to red by well controlling the firing conditions.

  A cross-sectional transmission electron microscope image of the red phosphor obtained at a firing temperature of 1500 ° C. was observed. FIG. 7 shows the observation results. The left-hand photograph (FIG. 7A) is an overall image of the fluorescent particles, and the right-hand photograph (FIG. 7B) is a partially enlarged image thereof. The enlarged region is clearly indicated by a white frame in the left photograph (FIG. 7A). From FIG. 7, it can be seen that the present phosphor has a crystal structure, and the number of defects is extremely reduced particularly in the peripheral portion. On the other hand, many planar defects can be seen in the center. The reason why there are many defects in the center is derived from the formation mechanism of the phosphor. That is, when strontium silicon oxide doped with europium is nitrided and fired in the furnace, oxygen is desorbed from the oxide because of high reducibility. The remaining strontium and silicon are not kept solid at a firing temperature of 1500 ° C., and particularly strontium has a boiling point of 1382 ° C., and thus is a gas. Europium and silicon are in liquid form. When ammonia generated by the decomposition reaction of urea is supplied here, each element is nitrided and crystal growth occurs. If a seed crystal already exists, crystal growth occurs epitaxially on the surface. On the other hand, in the case of the initial stage of firing without a seed crystal, a seed crystal is accidentally formed. At this time, since the crystal plane orientation is not initially determined, many defects are included. Once the seed crystal is formed, a good quality crystal with few defects is obtained epitaxially. This can be said to be characterized in that the phosphor has a defect region as a growth starting point at the center.

As shown in the excitation / emission spectrum of FIG. 3, this phosphor is characterized by strong absorption. Europium divalent phosphors are coupled with the band structure of the europium divalent orbitals and the mother crystal, and thus have a wide excitation wavelength range, and as a result, have high absorption. When fluorescent conversion is performed with high efficiency using the present phosphor, the crystal grain size should be as large as possible, and the peripheral part with high crystallinity should be kept as far as possible from the center part with many defects. In particular, the particle size is desirably 2 μm or more. In order to obtain such a red phosphor, it is preferable to make the firing time as long as possible. Increasing the firing temperature is effective for improving crystallinity. However, since the raw material that cannot be reacted with ammonia and sublimates increases, the growth rate decreases, and as a result, the peripheral portion having high crystallinity is not so thick. Even if the crystallinity of the peripheral portion is improved, if the layer thickness is thin, it is not sufficiently absorbed and converted in the peripheral portion, and a lot of excitation light is absorbed in the high defect region in the central portion. The overall conversion efficiency will decrease.

  In summary, it was possible to obtain an oxynitride phosphor having the composition formula AE (l) Si (m) O (p) N (q): Z by firing with urea. Here, AE is an alkaline earth element that is at least one of calcium, strontium, and barium, Si is silicon, O is oxygen, N is nitrogen, and Z is a rare earth element. In addition, l, m, p, and q represent element amounts. This phosphor has an excitation spectrum in the wavelength region of 300 to 550 nm. Further, the fluorescent spectrum of the present phosphor has a center wavelength of about 620 nm and a half width of about 80 nm. That is, a phosphor that can be used as pure red can be obtained by firing with urea.

  Further, in obtaining phosphors from green to red, firing with urea as a raw material can narrow the half-value width of the fluorescence spectrum of the phosphor, thereby increasing the utilization efficiency of fluorescence generated from the phosphor. It can be done.

  According to the present invention, a highly efficient and excellent color rendering property light source can be realized by a highly efficient phosphor having a narrow half-value width and less light emission in a non-visibility region. Further, an inexpensive phosphor can be provided by a firing method using urea nitriding.

  ae place

Claims (7)

Eu as an activator,
It consists of an alkaline earth element having at least one of Ca, Sr, and Ba, silicon, nitrogen, and oxygen,
Above emission peak wavelength 600nm and Ri der below 650 nm, and the composition ratio of the alkaline earth elements: Si = 5: 1, O : N = 9: characterized in that it is a 1, the phosphor. Eu as an activator,
A phosphor composed of an alkaline earth element having at least one of Ca, Sr, and Ba, silicon, nitrogen, nitrogen, and oxygen, and having an emission peak wavelength of 600 nm or more and 650 nm or less ,
The phosphor is granular, has a planar defect at the center, and has a particle size of 2 μm or more . The phosphor according to claim 2 , wherein the phosphor has a smaller molar amount of oxygen than nitrogen. The phosphor according to claim 1 or 2 , wherein the phosphor has a light emission half width of less than 100 nm. The phosphor according to claim 2 , wherein the composition ratio of the phosphor is Sr: Si = 2: 1 and O: N = 1: 3. The phosphor according to claim 1 or 2 , characterized in that the nitrogen material of the phosphor is urea. The phosphor according to claim 1, wherein the alkaline earth element: Si = 5: 1 is Sr: Si = 5: 1 .