Patent Application
20130026414
The present invention relates to a silicate-based phosphor and a manufacturing method of the silicate-based phosphor and, more specifically, to a silicate-based phosphor using a gas phase reaction of SiOx (0.5≦x≦1.9) and a manufacturing method of the silicate-based phosphor.
At present, various illumination light sources such as an incandescent lamp, a fluorescent lamp and so on are used around us. Recently, a white LED, having a combination of characteristics such as low power consumption, long life, safety and so on, gets a lot of attention as an alternative illumination to the incandescent lamp or the fluorescent lamp. Further, a phosphor used in the white LED is also required to have higher performance regarding the emission efficiency and durability.
White LEDs are roughly classified into two types in terms of a method for producing a white color, and among them, the two-wavelength white LED that is the mainstream at present obtains a pseudo white color by using both an GaInN-based blue LED and a yellow phosphor YAG:Ce3+ (Y3Al5O12:Ce3+) but is not excellent in color rendering property, and thus cannot emit white light close to the natural light (see Non-Patent Document 1).
On the other hand, there exists a three-wavelength white LED excitable with near-ultraviolet light or blue light and emitting white light closer to the natural light. For example, many silicate-based phosphors excite with near-ultraviolet light or blue light and emit visible light and are thus regarded as promising three-wavelength white LED phosphors, but none of them has a high luminance at a practical level (see Non-Patent Documents 2, 3).
Hence, in consideration of the above-mentioned circumstances, an object of the present invention is to provide a silicate-based phosphor excellent in emission intensity and a manufacturing method of the silicate-based phosphor.
Conventionally, as a general manufacturing method of the silicate-based phosphor, a method for obtaining a phosphor by mixing predetermined amounts of a compound containing elements constituting the phosphor host and a compound containing an activator element, both compounds in a solid state such as powder or the like, and firing the mixture at a predetermined temperature is widely used (see Non-Patent Document 2). This synthesis method is realized by the solid-solid phase reaction and is thus called a solid phase method.
However, it is difficult for the solid-solid phase method to manufacture the phosphor purely having a composition according to stoichiometry and to obtain a highly-pure phosphor according to stoichiometry because excessive nonreactive impurities or complex oxide produced by the reaction remains as a result of the solid-solid phase reaction. Consequently, problems such as the aforementioned decrease in luminance of the phosphor and so on are pointed out.
The present inventors found that the phosphor may be synthesized using SiOx in the gas phase which is not usually used in the phosphor manufacturing field (a method for causing volatilized SiOx to react with other solid phase materials to synthesize the phosphor, also called a “gas-solid phase method”), and that the phosphor obtained using the gas-solid phase method may have better emission characteristics than those of the phosphor obtained by the conventional solid phase method, and reached completion of the present invention.
More specifically, the present invention includes the following compositions and characteristics.
[1] A manufacturing method of a silicate-based phosphor, including: introducing in a vessel raw material powders having a compound containing light-emitting ions selected from at least one of Eu, Ce, Mn, and Tb; and firing the raw material powders while supplying SiOx (0.5≦x≦1.9) in a gas phase.
[2] The manufacturing method of a silicate-based phosphor according to [1] wherein the raw material powders are a mixture further containing at least one of an alkali metal compound, an alkaline-earth metal compound, a magnesium compound, and a rare-earth compound.
[3] The manufacturing method of a silicate-based phosphor according to [2] wherein the silicate-based phosphor is M2SiO4:Eu2+ (wherein M is one or more selected from a group consisting of Ca, Sr and Ba).
[4] The manufacturing method of a silicate-based phosphor according to any one of [1] to [3] wherein the range for x of the SiOx is 0.8≦x≦1.2.
[5] The manufacturing method of a silicate-based phosphor according to any one of [1] to [4] wherein the firing is performed by supplying the SiOx to the raw material powders in a gas atmosphere at a temperature of 1200 to 1700° C. and subjecting the raw material powders to a gas-solid phase reaction at a temperature of 700 to 1700° C.
[6] The manufacturing method of a silicate-based phosphor according to [5] wherein the gas atmosphere is a reducing gas atmosphere.
[7] A silicate-based phosphor manufactured by the manufacturing method of a silicate-based phosphor according to any one of [1] to [6].
The present invention can provide a phosphor having better fluorescence characteristics than those of the phosphor obtained by the conventional solid phase method because of use of the gas phase synthesis at a part of the phosphor manufacturing processes. For example, in comparison between the example of Ba2SiO4:Eu2+ and the comparative example synthesized by the conventional method, the phosphor of the example exhibited the emission intensity of about 2.6 times higher than the emission intensity of the phosphor of the comparative example when they were excited at respective optimal excitation wavelengths and about 3.5 times higher when they were excited by a practical near-ultraviolet LED (405 nm), and therefore exhibited very high intensity as compared to the phosphor manufactured by the conventional method.
Hereinafter, the present invention will be described based on the following concrete embodiments referring to the accompanying drawings, but the present invention is not limited to the embodiments.
A manufacturing method of a silicate-based phosphor according to the present invention includes: introducing in a vessel raw material powders having a compound containing light-emitting ions selected from at least one of Eu, Ce, Mn, and Tb; and firing the raw material powders while supplying SiOx (0.5≦x≦1.9) in a gas phase. In addition, it is preferable that the raw material powders are a mixture further containing at least one of an alkali metal compound, an alkaline-earth metal compound, a magnesium compound, and a rare-earth compound.
Here, as the compound containing the light-emitting ions, though not particularly limited, a compound containing Eu such as Eu2O3, Eu2(CO3)3. 2H2O, Eu(NO3)3.6H2O, Eu2(C2O4)3.10H2O or the like, a compound containing Ce such as Ce2O3, Ce2(CO3)3.5H2O, Ce(NO3)3.5H2O, Ce2(C2O4)3.9H2O, Ce2(C2O4)3.10H2O or the like, a compound containing Mn such as MnO, MnCO3, Mn(NO3)2.6H2O, Mn(C2O4), Mn(C2O4)3.2H2O or the like, a compound containing Tb such as Tb2O3, Tb2(CO3).nH2O, Tb(NO3)3.6H2O, Tb(C2O4)3.10H2O or the like, and a combination thereof are preferably used. Further, though not included in the compound containing the light-emitting ions in a precise sense, CeO2 or Tb4O7 exhibiting the physical property similar to that of aforementioned Ce2O3 or Tb2O3 may be used.
Further, as the alkali metal compound, though not particularly limited, Li2O, Li2CO3, LiNO3, Li2C2O4, Na2O, Na2CO3, NaNO3, Na2C2O4, K2O, K2CO3, KNO3, Rb2O, Rb2CO3, RbNO3, Cs2O, Cs2CO3, CsNO3, Cs2C2O4, and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.
Further, as the alkaline-earth metal compound, though not particularly limited, CaO, CaCO3, Ca(NO3)2, Ca(NO3)2.4H2O, SrO, SrCO3, Sr(NO3)2, Sr(NO3)2.4H2O, BaO, BaCO3, Ba(NO3)2, BaC2O4, and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.
Further, a magnesium compound containing divalent Mg, that is equivalent to the alkaline-earth metal compound, can also be used in place of the alkaline-earth metal compound. Further, as the rare-earth compound, though not particularly limited, Sc2O3, Y2O3, La2O3, and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.
In the present invention, by maintaining a raw material mixture preferably containing at least one of the above-descried alkali metal compound, alkaline-earth metal compound, magnesium compound, and rare-earth compound, for example, in a temperature range of 700° C. to 1700° C. for 1 to 100 hours to fire the raw material mixture, and further supplying thereto SiOx, which has become gaseous in a gas atmosphere at a temperature of 1200° C. to 1700° C. to cause a gas-solid phase reaction of the raw material mixture, a phosphor very excellent in emission characteristics is obtained.
Note that when the above-described metal compound contains hydrate, hydroxide, carbonate, nitrate, oxalate which can be decomposed and/or oxidized into an oxide at a high temperature, it is also possible to make the raw material mixture into an oxide, for example, by previously calcining it at a temperature lower than the firing temperature, or make the raw material mixture into a precursor of the phosphor by removing crystallization water therefrom. Further, it is also possible to grind the raw material mixture after the pre-calcination.
A flowchart of a preferable manufacturing method among the methods for manufacturing a silicate-based phosphor of the present invention is illustrated in
One of important features of the present invention is that raw material powders (solid phase reaction raw materials) are fired while supplying SiOx (0.5≦x≦1.9) in a gas phase (namely, that a part of the starting materials (gas phase reaction raw material) is heated to cause a gas is phase reaction, and the solid phase reactant is fired while the gas phase reactant is reacted with the solid phase reactant, in other words, that a gas-solid phase reaction is caused), that is greatly different from a general solid phase synthesis (namely, all of the starting materials are solid-phase synthesized) used in conventional phosphor manufacturing methods.
Note that the conventional gas phase synthesis is a synthesis method applied to processes for producing a nanoparticle of about 1 to 100 nm. In contract, for manufacturing a phosphor for the white LED, it is required to obtain large particles grown to about 10 to 100 μm, and therefore the above-described solid phase method has been the suitable and time-proven method. Accordingly, researchers in a field for manufacturing the phosphors, in general, are less likely to understand or reach the way of thinking to employ the gas phase synthesis, suitable for the manufacture of nano-order particles, into the manufacture of phosphors. Furthermore, the gas phase raw material used in the conventional gas phase method is an expensive material such as an organic metal compound, and is not the kind handled in a reducing atmosphere gas in manufacturing phosphors, and therefore there is no example reporting practical characteristics for phosphors, obtained by applying the way of thinking of the gas phase synthesis to the manufacture of phosphor. On the other hand, the manufacturing method of the present invention is characterized by the gas-solid phase synthesis of causing SiOx in a gas phase to react with the other raw material in a solid phase.
In the manufacturing method of the present invention, SiOx (0.5≦x≦1.9) that is a raw material for synthesis in a gas phase is a material inexpensive and safe to handle. Note that the general manufacturing method of SiOx is performed by heating a mixture of a silicon-dioxide-based oxide powder and a substance reducing the powder, for example, silicon metal in an inert gas atmosphere or under a reduced pressure in a temperature range of 1100 to 1600° C., and cooling and collecting the generated SiOx gas. However, unreacted substance (Si, SiO2) or SiO2 generated by oxidization of SiO sometimes exist as impurities in the SiOx.
The verification by the inventors until now shows that since SiOx when it is closer to SiO more suitably acts, the range for x of SiOx preferably falls within 0.8≦x≦1.2, and more preferably, 0.95≦x≦1.1. Such a suitable high-purity SiO is commercially available from, for example, OSAKA Titanium technologies Co., Ltd. and Sanyo Trading Co., Ltd.
SiOx in the solid state can be volatile and be in the gas phase by being heated in a gas atmosphere at 1200 to 1700° C., preferably, at 1400 to 1700° C. into a gas phase. The SiOx in the gas phase is supplied to the raw material mixture and heated at a desired temperature in the temperature range of 700° C. to 1700° C. to cause gas-solid phase reaction.
Examples of the gas atmosphere include (1) an inert gas atmosphere composed of nitrogen, argon or the like, (2) an oxidized gas atmosphere composed of air, oxygen, oxygen-containing nitrogen, oxygen-containing argon or the like, and (3) a reducing gas atmosphere such as hydrogen-containing nitrogen containing 0.1 to 10 volume % hydrogen, hydrogen-containing argon containing 0.1 to 10 volume % hydrogen or the like. Note that to promote the gas-solid phase reaction of the present invention at a high yield, the carrier gas to supply SiOx and the atmosphere during firing is particularly preferably a reducing atmosphere such as hydrogen-containing nitrogen containing 0.1 to 10 volume % hydrogen, hydrogen-containing argon containing 0.1 to 10 volume % hydrogen or the like.
Though the silicate-based phosphor of the present invention manufactured as described above is not particularly limited as long as it is synthesized by the above-described manufacturing method, M2SiO4:Eu2+, Li2MSiO4:Eu2+, M3SiO5:Eu2+, M2(Mg, Zn)Si2O7:Eu2+, M3Si2O7:Eu2+, M3MgSi2O8:Eu2+, MAl2Si2O8:Eu2+, M3Sc2Si3O12:Ce3+, M9Sc2Si6O24:Eu2+, and a combination thereof are preferable. Here, M is one or more selected from a group consisting of Ca, Sr and Ba. Note that from the viewpoint of practical use of the phosphor based on various characteristics other than the emission characteristics, M2SiO4:Eu2+ is preferable as the silicate-based phosphor of the present invention, and (Ba1-ySry)2SiO4:Eu2+ (0≦y≦1) is more preferable.
Note that the starting materials for manufacturing (Ba1-ySry)2SiO4:Eu2+ (0≦y≦1) and the materials (the starting materials except SiOx, for example, BaCO3) undergoing a solid phase reaction are well solid-phase synthesized in the temperature range (1200 to 1700° C.) suitable for the gas phase synthesis of SiOx, so that by heating the phosphor manufacturing vessel in the aforementioned preferable temperature range, volatilization of SiOx and the solid phase synthesis (namely, firing) can be effectively performed at the same time.
Some examples of phosphor manufacturing apparatuses 1 realizing the manufacturing method of the silicate-based phosphor of the present invention are illustrated in
Further, as illustrated in
The silicate-based phosphor of Example 1 was manufactured by the gas-solid phase synthesis method of the present invention. Note that a flowchart of the manufacturing method of Example 1 is illustrated in
As a result, a solid phase reactant having (Ba0.99Eu0.01)7Sc6Al2O19 as a main phase was obtained by the solid phase reaction in the starting materials, and Ba2SiO4:Eu2+ was generated with a high yield on a surface of the solid phase reactant by the gas-solid phase reaction between SiOx supplied into the vessel and the starting materials.
(Identification of Sample)
For identification of the sample after the firing, a powder X-ray diffractometer (manufactured by Mac Science Ltd., MX-Labo) was used.
The XRD patterns at the lowermost stage and the upper stage thereof well coincided with and corresponded to the XRD patterns at the uppermost stage and the lower stage thereof, which were used as specimens. Therefore, it is endorsed that (Ba0.99Eu0.01)7Sc6Al2O19 has been the internal substrate and Ba2SiO4:Eu2+, or the objective substance, has been generated on the surface of the substrate.
As Comparative Example 1, Ba2SiO4:Eu2+ was synthesized by the conventional solid phase reaction. Note that a flowchart of the manufacturing method of Comparative Example 1 is illustrated in
(Evaluation of Fluorescence Characteristic)
Both the phosphors in Example 1 and Comparative Example 1 have excitation spectra in a very wide range of 300 nm to 450 nm. Note that the phosphor of Example 1 is strongly excited at a wavelength near 380 nm, whereas the phosphor of Comparative Example 1 is strongly excited at a wavelength near 360 nm. Here, the wavelength generally emitted from a near-ultraviolet LED ranges from 350 nm to 400 nm, and it is found that the phosphors in Example 1 and Comparative Example 1 are efficiently excited as the near-ultraviolet LEDs. Note that the reason why there was a difference in peak of the excitation spectra between Example 1 and Comparative Example 1 can be that a phosphor, having a higher concentration of Eu2+ being the light-emitting ion, was able to be synthesized by the procedure of Example 1.
Further, both phosphors of Example 1 and Comparative Example 1 have exhibited emission spectra, having a peak near 500 nm as illustrated in
Further, from the results of the excitation and emission spectra in
(Evaluation of Quantum Efficiency)
To discuss the reason why the large difference of the emission intensities was caused between the phosphor of Example 1 and the phosphor of Comparative Example 1, the quantum efficiency of each phosphor was measured using a fluorescence spectrophotometer (JASCO Corporation, FP-6500). These measurement results are shown in the following Table 1.
Here, the internal quantum efficiency means the release rate to the absorbed energy. On the other hand, the external quantum efficiency means the release efficiency to the radiated energy, which is calculated by multiplying the internal quantum efficiency by the sample absorption.
The results in Table 1 show that the external quantum efficiency in Example 1 is improved by about 20% as compared to the case of Comparative Example 1. Here, it can be said that because there is no large difference between the measurement results of their internal quantum efficiencies, the difference in the sample absorptions actually affect the improvement in the external quantum efficiency in Example 1. The conceivable reasons why the sample absorption of Example 1 was improved are that the activator amount of the light-emitting ion Eu2+ was increased, that the crystallization of the phosphor particle was improved and so on.
Though Ba2SiO4:Eu2+ was manufactured as the silicate-based phosphor and its emission characteristics were described in detail in the above Example 1, for example, SrCO3 or the like may be added to the starting materials to manufacture (Ba1-ySry)2SiO4:Eu2+ (0≦y≦1).
Further, though in Example 1, the method was employed that firstly producing the solid phase reactant having (Ba0.99Eu0.01)7Sc6Al2O19 as a main phase by the solid phase reaction between the starting materials in the synthesis process of the phosphor, and then, producing the phosphor on a surface of the reactant, the method of the present invention is not always limited to the above. Various solid phase reactants may be produced by combination of starting materials. Further, only the silicate-based phosphor may be synthesized by the gas-solid phase reaction without producing such a solid phase reactant as in the method described in
(Discussion of Firing Temperature)
Next, the condition of the firing temperature when manufacturing the silicate-based phosphor of Example 1 will be discussed. In addition of the above-described temperature condition at 1500° C., the silicate-based phosphors were manufactured also at the temperature conditions of 1400° C. and 1600° C., and their fluorescence characteristics were similarly evaluated. Note that in the cases of the firing temperatures of 1400° C. and 1600° C., the manufacturing conditions other than the firing temperature are the same as those in the case of 1500° C.
The emission intensity ratio for the sample fired at 1400° C. was 170% and therefore an improvement in its emission characteristics was confirmed from
In the above-described Example 1, simple silicate-based (Ba—Si—O based) phosphors containing only a Ba component were used. In the later-is described Example 2 or Example 3, it will be discussed whether or not silicate-based phosphors containing a Sc component or an Al component in addition to the Ba component, can be manufactured by the gas-solid phase method of the present invention and whether or not the products thereof exhibit suitable emission characteristics. Note that as the manufacturing methods of Example 2 and Example 3, the method illustrated in
As the solid phase reaction raw materials of the starting materials,
BaCO3 (Kanto Chemical Co., Ltd., 3N), Sc2O3 (Shin-Etsu Chemical Co., Ltd., 4N), and Eu2O3 (Shin-Etsu Chemical Co., Ltd., 4N) were used. The materials were each weighed out according to stoichiometry and pulvarized by acetone wet-mixing in an agate mortar and dried. The mixed and dried solid phase reaction sample was put on a first dish (an accommodating dish made of boron nitride (BN)), and SiO being the gas phase reaction raw material was put on a second dish. These dishes were introduced in a vessel placed under an inert gas atmosphere made of only argon, and subjected to the gas-solid phase reaction by firing for 12 hours at 1600° C. Note that the second dish, on which SiO was put, was placed on the upstream side in the flow direction of the inert gas from the first dish on which the solid phase reaction sample, was put so that volatilized SiO in the gas phase was appropriately supplied to the solid phase reaction sample.
(Identification of Sample)
Identification of the sample using a powder X-ray diffractometer (manufactured by Mac Science Ltd. MX-Labo) was performed as in Example 1.
The XRD pattern at the lower stage in
(Evaluation of Fluorescence Characteristics)
As the solid phase reaction raw materials of the starting materials, BaCO3 (Kanto Chemical Co., Ltd., 3N), Al2O3 (Kojundo Chemical Laboratory, 4N), and Eu2O3 (Shin-Etsu Chemical Co., Ltd., 4N) were used. The conditions of the mixing method, the firing method and so on are the same as those in Example 2 and therefore the description thereof are omitted here.
(Identification of Sample)
The XRD pattern at the lower stage in
(Evaluation of Fluorescence Characteristics)
From the above result of Example 3, it was found that BaAl2Si2O8:Eu2+ being the objective substance was able to be synthesized and caused to emit light by the gas-solid phase method of the present invention.
Further, the phosphors manufactured by the present invention are not always limited to those phosphors without departing from the spirit of the invention in the above-described novel synthesis method.
By using the silicate-based phosphor manufactured by the present invention, for example, as the phosphor of a three-wavelength white LED, a white LED can be provided which provides light closer to natural light and drastically improves in luminance.
Further, the silicate-based phosphor manufactured by the present invention is applicable not only to the white LED but also to wide range of usage such as display devices with a display panel such as a CRT, PDP, FED and the like, illumination apparatuses such as a fluorescent lamp and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-092592 | Apr 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/059090 | 4/12/2011 | WO | 00 | 10/10/2012 |
