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Sialon phosphor, process for producing the same, and illuminator and luminescent element employing the same

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Sialon phosphor, process for producing the same, and illuminator and luminescent element employing the same


Phosphor that can provide white LED that uses a blue LED or an ultraviolet LED as a light source and that has superior luminous efficiency. This phosphor includes, as a main component, α-type sialon represented by a general expression: (M1)x(M2)y(Si,Al)12(O,N)16 (where M1 is one or more types of elements selected from a group consisting of Li, Mg, Ca, Y, and lanthanide element (except for La and Ce) and M2 is one or more types of elements selected from a group consisting of Ce, Pr, Eu, Tb, Yb, and Er, and 0.3≦X+Y≦1.5 and 0<Y≦0.7 are established and the sialon phosphor consists of a powder having a specific surface area of 0.2 to 0.5 m2/g.


Browse recent Denki Kagaku Kogyo Kabushiki Kaisha patents - Tokyo, JP
Inventors: Hideyuki EMOTO, Masahiro IBUKIYAMA, Takashi KAWASAKI
USPTO Applicaton #: #20120270049 - Class: 428402 (USPTO) - 10/25/12 - Class 428 
Stock Material Or Miscellaneous Articles > Coated Or Structually Defined Flake, Particle, Cell, Strand, Strand Portion, Rod, Filament, Macroscopic Fiber Or Mass Thereof >Particulate Matter (e.g., Sphere, Flake, Etc.)

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The Patent Description & Claims data below is from USPTO Patent Application 20120270049, Sialon phosphor, process for producing the same, and illuminator and luminescent element employing the same.

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This application is a divisional of a pending application, U.S. Ser. No. 12/300,127 filed on Nov. 10, 2008, which is the National Stage Application of PCT International Application No. PCT/JP2007/059527, both of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to sialon phosphor excited by ultraviolet light or blue light to emit visible light and the manufacture method thereof as well as an illuminator and a luminescent element using the same. In particular, the present invention relates to phosphor that can be used for a blue light-emitting diode (blue LED) or an ultraviolet light-emitting diode (ultraviolet LED) and the manufacture method thereof as well as an illuminator and a luminescent element using the same, in particular, a white light-emitting diode (white LED).

TECHNICAL BACKGROUND

Phosphor is well-known that uses silicate, phosphate, aluminate, and sulfide as host material and that uses transition metal or rare-earth metal for the luminescent center.

On the other hand, such white LED has attracted attention that is excited by an excitation source having high energy (e.g., ultraviolet light or blue light) to emit visible light and has been developed. However, when the above-described conventional phosphor is used, the exposure to the excitation source disadvantageously causes a decreased phosphor luminance.

As phosphor having a small decrease in the luminance, nitride or oxynitride phosphor has attracted attention recently as material that has a stable crystal structure and that can shift the excitation light and the light emission toward the long wavelength.

As nitride and oxynitride phosphor, α-type sialon (Si—Al—O—N) for which a specific rare-earth element is activated has been known as having a useful fluorescence characteristic and has been examined for the use to white LED or the like (see Patent Documents 1 to 5 and Non-Patent Documents 1 and 2).

The α-type sialon has a structure in which the Si—N bonds of α-type silicon nitride crystal is partially substituted with Al—N bonds and Al—O bonds and electroneutrality is maintained by a specific element (Ca, Li, Mg, and Y or lanthanide metal except for La and Ce) interstitially solid-soluted to a crystal lattice. A part of the interstitially solid-soluted element is a rare-earth element functioning as the luminescent center to cause the fluorescence characteristic.

The α-type sialon is obtained by burning mixed powders consisting of silicon nitride, aluminum nitride, optionally aluminum oxide, and the oxide of an interstitially solid-soluted element or the like in nitrogen at a high temperature. The proportion between silicon nitride and aluminum compound, the type of an interstitially solid-soluted element, and the ratio of an element functioning as the luminescent center for example can provide various fluorescence characteristics. In particular, α-type sialon, which is obtained by solid-soluting Ca functioning as an interstitially solid-soluted element and Eu functioning as the luminescent center, is efficiently excited in a wide wavelength range from a ultraviolet region to a blue region and emits light in a range from yellow to orange. Thus, the development of a combination of this α-type sialon with an LED emitting blue light (which is a complementary color to yellow to orange) has been expected for white LED.

Ca2(Si, Al)5N8, CaSiAlN3 or β-type sialon obtained by activating a rare-earth element also has been found to have the similar fluorescence characteristic (see Patent Documents 6 and 7 and Non-Patent Documents 2 and 3).

In addition, nitrides (e.g., aluminum nitride, silicon nitride magnesium, silicon nitride calcium, silicon nitride barium, gallium nitride, silicon nitride zinc) and oxynitride phosphor (hereinafter also referred to as nitride phosphor and oxynitride phosphor in this order) have been suggested.

In the case of the α-type sialon powders for example, the reduction-nitridation method has been known as a synthesis method of these phosphors. According to the reduction-nitridation method, mixed powders of aluminum oxide (Al2O3), silicon oxide (SiO2), oxide of metal or element that can be solid-soluted into the lattice or the like is subjected to a heating processing in nitrogen atmosphere under the existence of carbon (see Non-Patent Documents 4 to 6).

Although the methods reported in Non-Patent Documents 4 to 6 are characterized in that raw material powders are low-cost and can be synthesized at a relatively low temperature of about 1500 degrees C., a plurality of intermediates are caused in the synthesis and gas components such as SiO and CO are generated to difficultly provide the single-phase one, causing a difficulty in the strict control of the composition and the control of the particle size.

Sialon powders are also obtained by burning the mixture of silicon nitride, aluminum nitride, and the oxide of metal or an element or the like solid-soluted into the lattice at a high temperature to grind the resultant sintered compact. However, this has caused a problem of a decreased light emission intensity of phosphor due to a grinding operation.

As described above, in the conventional technique, nitride including a constituting element and a compound including an activating element are merely mixed and heated or the mixture of oxides of the constituting elements is merely subjected to reduction-nitridation by carbon or the like. This conventional technique cannot provide nitride phosphor or oxynitride phosphor having a sufficient characteristic.

In the case of sialon phosphor in particular, when a manufacture method is used in which oxides including the constituting elements of solid-soluted elements (e.g., calcium or yttrium) or the activating element (e.g., cerium, europium) are used as raw material, a burning process causes a liquid-phase sintering to cause a stronger binding among particles. This has caused a case where a grind processing under severe conditions may be required in order to obtain powders having a target particle size. In this case, the grind processing under severe conditions cause an increase in the contamination and introduce defects into the surfaces of the respective particles, thereby disadvantageously causing a deteriorated light emission characteristic.

In order to solve this problem, the present inventors have suggested a manufacture method rarely requiring a grind processing by using raw material not including oxygen (e.g., raw material such as calcium fluoride or calcium cyanamide) and by devising a method for mixing raw materials for a burning process for example. Thus, the present inventors could improve the light emission intensity (see Patent Documents 8 and 9).

In order to realize white, a combination of a plurality of colors different from a monochromatic light is required. A general white LED is composed of a combination of ultraviolet LED or blue LED and phosphor that uses the light from the LED as an excitation source and that emits visible light (see Patent Documents 10 and 11 for example). Thus, in order to improve the white LED efficiency, it is required to improve the luminous efficiency of the ultraviolet LED or the blue LED itself and to improve the efficiency of phosphor in the LED. It is also required to improve an efficiency at which emitted light is taken out to the outside. In order to increase use of white LED including a general lighting use, all of these efficiencies must be improved. Patent Document 1: Japanese Patent No. 3668770 Patent Document 2: Japanese Patent No. 2003-336059 A Patent Document 3: Japanese Patent No. 2003-124527 A Patent Document 4: Japanese Patent No. 2003-206481 A Patent Document 5: Japanese Patent No. 2004-186278 A Patent Document 6: Japanese Patent No. 2004-244560 A Patent Document 7: Japanese Patent No. 2005-255895 A Patent Document 8: Japanese Patent No. 2008-45271 A Patent Document 9: Published Japanese translation of a PCT application No. 2005-123876 Patent Document 10: Japanese Patent No. H5-152609 A Patent Document 11: Japanese Patent No. H7-099345 A

Non-Patent Document 1: J. W. H van Krebel “On New Rare-Earth Doped M—Si—Al——O—N Materials”, T U Eindhoven, The Netherlands, 145-161 (1998)

Non-Patent Document 2: Dai 52 kai Ouyou Butsurigaku Kankei Rengou Kouenkai Kouen Yokousyu (March 2005, Saitama University) P. 1614-1615

Non-Patent Document 3: Dai 65 kai Ouyou Butsurigakkai Gakujyutsu Kouenkai Kouen Yokousyu (September 2004, TOHOKU GAKUIN UNIVERSITY) No. 3, p. 1282-1284

Non-Patent Document 4: M. Mitomo et al., “Preparation of α-SiAlON Powders by Carbothermal Reduction and Nitridation” (Ceram. Int., 14, 43-48 (1988))

Non-Patent Document 5: J. W. T. van Rutten et al., “Carbothermal Preparation and Characterization of Ca-α-SiAlON” (J. Eur. Ceram. Soc., 15, 599-604 (1995))

Non-Patent Document 6: K. Komeya et al., “Hollow Beads Composed of Nanosize Ca α-SiAlON Grains” (J. Am. Ceram. Soc., 83, 995-997(2000))

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

White LED phosphor is generally obtained by dispersing micron size particles in sealing material such as epoxy resin or silicone resin. In the case of α-type sialon phosphor, the particles are the secondary particles obtained by sintering a plurality of minute primary particles. Although the size and the distribution or the like have been examined, no attention has been paid on the surface texture of the secondary particles.

However, even the devising as disclosed in Patent Documents 8 and 9 only provides the resultant phosphor particles consisting of the secondary particles to which the primary particles having a diameter of about 0.2 to 5 μm are fixed in an irregular manner. This has caused a case where the secondary particles having a complicated surface due to significant concavities and convexes or the interface among the primary particles in the secondary particles has light scattering or absorption, causing the phosphor to have a decreased luminous efficiency.

Furthermore, general raw material powders such as silicon nitride or aluminum nitride have an average diameter of 1 μm or less. When these raw material powders are used as raw material for a conventional method to synthesize nitride or oxynitride phosphor, the resultant fine particles inevitably have a wide particle size distribution. Since the resultant fine particles particularly have a diameter of a few μm or less that strongly scatter the visible light, a problem of a decreased luminous efficiency has been caused.

On the other hand, white LED obtained so far has a lower luminous efficiency than a fluorescence lamp. Thus, LED having a superior luminous efficiency, especially white LED in particular, than a fluorescence lamp has been strongly demanded from the viewpoint of energy conservation in the industry field. Although white LED using oxynitride or nitride phosphor such as sialon phosphor has a higher efficiency than an incandescent lamp, increased applications of the LED including general lighting applications require a further improvement in the luminous efficiency. Thus, an improved luminous efficiency of phosphor has been an important task for the industry field.

In view of the above problems, through various examinations of α-type sialon phosphor, it is the first objective of the present invention to provide a white LED, in particular, a white LED using blue LED or ultraviolet LED as a light source having a superior luminous efficiency that has a peak in a wavelength range from 540 to 600 nm and that has a superior luminous efficiency.

It is the second objective of the present invention to solve the above problem of the conventional technique to provide an LED having a superior luminous efficiency (e.g., a white LED, in particular, a white LED using blue LED or ultraviolet LED as a light source) as well as phosphor having a superior fluorescence characteristic suitable for the LED to the industry field.

Means for Solving Problem

The inventors have examined the phosphor composed of α-type sialon as host material. The inventors have reached the present invention by finding that a specific interstitially solid-soluted element of the α-type sialon can be used to set the crystal lattice size within an appropriate range to provide the flat and smooth surface of the secondary particles. This provides phosphor having a peak in wavelengths in a range from 540 to 600 nm and having superior luminous efficiency. This can be used to provide an illuminator having a superior light emission characteristic.

Furthermore, the present inventors have reached the present invention by finding that the addition of a seed particle as a core of the grain growth into a raw material powder and the use of a dense boron nitride crucible in a synthesis process can improve the flat and smooth surface of the secondary particles.

In order to achieve the first objective, the sialon phosphor of the present invention is characterized in sialon phosphor that includes, as a main component, α-type sialon represented by a general expression: (M1)x(M2)y(Si,Al)12(O,N)16 [wherein M1 is one or more types of elements selected from a group consisting of Li, Mg, Ca, Y, and lanthanide element (whereas except for La and Ce) and M2 is one or more types of elements selected from a group consisting of Ce, Pr, Eu, Tb, Yb, and Er, and 0.3≦X+Y≦1.5 and 0<Y≦0.7 are established], and the sialon phosphor is a powder having a specific surface area of 0.2 to 0.5 m2/g. The above configuration is characterized in that the α-type sialon phosphor has a lattice constant a in a range from 0.780 to 0.788 nm and a lattice constant c in a range from 0.565 to 0.573 nm.

The above configuration is characterized in that, when powders consisting of the α-type sialon are evaluated based on an X-ray diffraction method, crystal phases other than that of the α-type sialon preferably have diffraction intensities that are all 10% or less to a diffraction line intensity of a face (102) of the α-type sialon.

The above configuration is characterized in that the M1 includes at least Ca, the M2 includes at least Eu and 0<Y≦0.1 is established and, when ultraviolet light or visible light having wavelengths in a range from 250 to 500 nm is emitted as an excitation source to the sialon phosphor, the sialon phosphor shows a light emission characteristic having a peak in a wavelength range from 540 to 600 nm.

The method of manufacturing α-type sialon phosphor of the present invention represented by the above general expression is characterized in that starting raw material includes α-type sialon in an amount of 5 to 30 mass %. In the above configuration, the starting raw material preferably includes the α-type sialon having a specific surface area in a range from 0.5 to 2 m2/g.

Another method of manufacturing the above-described sialon phosphor of the present invention is characterized in that the starting raw material is filled in a boron nitride-made crucible having a density of 1.75 g/cm3 or more and is burned in nitride atmosphere. The crucible preferably consists of pyrolytic boron nitride (P—BN).

An illuminator of the present invention is characterized in being composed of a light source and phosphor and uses sialon phosphor which is at least the above mentioned sialon phosphor or sialon phosphor obtained by the above-mentioned manufacture method.



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stats Patent Info
Application #
US 20120270049 A1
Publish Date
10/25/2012
Document #
13464855
File Date
05/04/2012
USPTO Class
428402
Other USPTO Classes
International Class
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