Oxynitride phosphor activated by a rare earth element, and...

Details Oxynitride phosphor activated by a rare earth element, and... Oxynitride phosphor activated by a rare earth element, and...

2003-04-08

2004-08-17

Kopec, Mark (Department: 1751)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C252S500000, C252S508000, C252S509000, C252S519100, C252S521300, C501S098100, C501S096500, C423S344000, C423S385000, C250S484400, C313S501000

Reexamination Certificate

active

06776927

ABSTRACT:

The present invention relates to an oxynitride phosphor activated by a rare earth element, which makes high luminance of a white light emitting diode (white LED) employing a blue light emitting diode (blue LED) as a light source possible. Further, the present invention relates to a sialon type phosphor optically activated by a rare earth element, which makes high luminance of white LED employing blue LED or an ultraviolet emitting diode (ultraviolet LED) as a light source possible.
Phosphors are widely known wherein a silicate, a phosphate (such as apatite) or an aluminate is used as a matrix material and such a matrix material is activated by a transition metal or a rare earth metal. On the other hand, phosphors wherein a nitride or an oxynitride is used as a matrix material and such a matrix material is activated by a transition metal or a rare earth metal, are not well known.
With respect to nitride phosphors, for example, German Patent 789,890 discloses aluminum nitride activated by manganese, and a literature “Izv. Akad. Nauk SSSR, Neorg. Master” 17(8), 1431-5 (1981) discloses magnesium silicon nitride (MgSiN
2
) activated by a rare earth element. Recently, only a red-emitting phosphor having ZnSiN
2
having a distorted wurtzite structure activated by Mn (T. Endo et al. “High pressure synthesis of “periodic compound” and its optical and electrical properties”, In T. Tsumura, M. Doyama and Seno (Editors), New Functionality Materials, Volume C, Elsevier, Amsterdam, The Netherlands, pp. 107-112(1993)), a red-emitting phosphor having CaSiN
2
activated by Eu (S. S. Lee et al. “Photoluminescence and Electroluminescence Characteristic of CaSiN
2
:Eu”, Proc. SPIE-Int. Soc. Opt. Eng., 3241, 75-83(1997)) and a phosphor having Ba
2
Si
5
N
8
activated by Eu, have been reported.
With respect to oxynitride phosphors, a phosphor using &bgr;-sialon as the matrix material (JP-A-60-206889), a phosphor having a silicate mineral or a Y—Si—O—N type composite silicon oxynitride having an apatite structure activated by Ce (J. W. H. van Krevel et al. “Long wavelength Ce
3+
emission in Y—Si—O—N materials”, J. Alloys and Compounds, 268, 272-277(1998)), a Ba
1−x
Eu
x
Al
11
O1
6
N phosphor having a &bgr;-alumina structure (H. Hintzen et al. “On the Existence of Europium Aluminum Oxynitrides with a Magnetoplumbite or &bgr;-Alumina-Type Structure”, J. Solid State Chem., 142, 48-50(1999), and S. R. Jansen et al. “Eu-Doped Barium Aluminum Oxynitride with &bgr;-Alumina-Type Structure as New Blue-Emitting Phosphor”, J. Electrochem. Soc., 146, 800-806(1999)) have been reported. Recently, only a phosphor using an oxynitride glass as a matrix material, has been proposed (JP-A-2001-214162).
Whereas, white LED has been used, for example, in the field where reliability is required for e.g. emergency illumination or signal light, in the field where miniaturization and weight reduction are desired, for example, for in-vehicle lightening or liquid crystal backlight, or in the field where visibility is required for e.g. guide plates at railway stations. The emitted color of such white LED, i.e. white light, is obtained by color mixing of lights and is one obtained by mixing of blue light emitted by blue LED of InGaN type with a wavelength of from 450 to 550 nm as a light source and yellow light emitted from the phosphor.
As a phosphor suitable for such white LED, a phosphor having Ce doped to a YAG type oxide represented by the composition formula (Y,Gd)
3
(Al,Ga)
5
O
12
, is most commonly employed. This phosphor is applied as a thin coating on the surface of the above-mentioned InGaN type blue LED as a light source.
However, an oxide type phosphor usually has a drawback that the emission intensity substantially decreases if the excitation wavelength exceeds 400 nm. Accordingly, white LED obtained by coating the surface of a blue LED chip with a phosphor made of a YAG type oxide, has been considered to have a difficulty such that the excitation energy of the YAG type oxide as the phosphor does not agree to the excitation energy of the blue LED as the light source, whereby the excitation energy can not efficiently be converted, and it is difficult to prepare white LED having high luminance.
In a first aspect, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an oxynitride phosphor activated by a rare earth element, which makes high luminance of a white light emitting diode (white LED) employing a blue light emitting diode (blue LED) as a light source possible.
The inventors of the present invention have found that the positions of excitation/emission peaks shown by a conventional oxide type phosphor shift towards a long wavelength side, when oxygen atoms surrounding the rare earth element as the emission center are substituted by nitrogen atoms to reduce the influence which electrons of the rare earth element receive from the surrounding atoms, and on the basis of this technical finding, they have proposed a phosphor which employs an oxynitride glass as the matrix material and which has an excitation spectrum extending to a visible region (≦500 &mgr;m).
On the basis of the above technical finding, the present inventors have further studied the presence of another oxynitride phosphor and as a result, have found that a crystalline oxynitride phosphor employing &agr;-sialon having a higher nitrogen content than the oxynitride glass, as the matrix material, wherein a part or all of metal Me (where Me is at least one metal selected from the group consisting of Ca, Mg, Y and lanthanide metals excluding La and Ce) in &agr;-sialon solid solution as the matrix material, is substituted by lanthanide metal Re1 (Re1 is at least one metal selected from the group consisting of Ce, Pr, Eu, Tb, Yb and Eu), or two lanthanide metals Re1 and a coactivator Re2 (where Re2 is Dy), to be an emission center, makes high luminance white LED possible. Thus, the first aspect of the present invention has been accomplished on the basis of this discovery.
Thus, according to the first aspect, the present invention provides:
1. An oxynitride phosphor activated by a rare earth element, represented by the formula Me
x
Si
12−(m+n)
Al
(m+n)
O
n
N
16−n
:Re1
y
Re2
z
, wherein a part or all of metal Me (where Me is at least one metal selected from the group consisting of Ca, Mg, Y and lanthanide metals excluding La and Ce) in &agr;-sialon solid solution, is substituted by lanthanide metal Re1 (where Re1 is at least one metal selected selected from the group consisting of Ce, Pr, Tb, Yb and Er), or two lanthanide metals of Re1 and a coactivator Re2 (where Re2 is Dy), to be an emission center.
2. The oxynitride phosphor activated by a rare earth element according to Item 1, wherein when metal Me is bivalent, 0.6<m<3.0 and 0≦n<1.5.
3. The oxynitride phosphor activated by a rare earth element according to Item 1, wherein when metal Me is trivalent, 0.9<m<4.5 and 0≦n<1.5.
4. The oxynitride phosphor activated by a rare earth element according to any one of Items 1 to 3, wherein m=1.5, n=0.75 and in the composition formula Me
x
Si
9.75
Al
2.25
O
0.75
N
15.25
:Re1
y
Re2
z
, 0.3<x+y<0.75 and 0.01<y+z<0.7 (where y>0.01 and 0.0≦z<0.1).
5. The oxynitride phosphor activated by a rare earth element according to Item 4, wherein 0.3<x+y+z<1.5, 0.01<y<0.7 and 0≦z<0.1.
6. The oxynitride phosphor activated by a rare earth element according to Item 2, 4 or 5, wherein metal Me is Ca.
The above oxynitride phosphor is composed of a single phase of &agr;-sialon, whereby it is required to incorporate a large amount of the rare earth metal, which limits reduction of costs.
In a second aspect, the present invention has been made under such circumstances, and it is another object of the present invention to provide a sialon type phosphor comprising &agr;-sialon dissolving a rare earth element in the structure, &agr;-sialon and unreacted silicon nitride, which makes high l

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