Pigment with day-light fluorescence

Details Pigment with day-light fluorescence Pigment with day-light fluorescence

2001-11-23

2004-01-27

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

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

C252S30140F, C106S461000, C106S482000, C423S351000

Reexamination Certificate

active

06682663

ABSTRACT:

TECHNICAL FIELD
This invention relates to a Pigment with day-light fluorescence and more particularly, but not exclusively to a pigment absorbing blue to green light and emitting fluorescence within the yellow to red spectral region under excitation by daylight or by an artificial light source. Further absorption in other spectral regions is possible, especially in the UV. More specifically, such a pigment can be used as a phosphor for light sources, especially for Light Emitting Diodes (LED) or electrical lamps. The pigment belongs to the class of rareearth activated silicon nitrides.
BACKGROUND ART
For Eu
2+
-doped material normally UV-blue emission is observed (Blasse and Grabmeier: Luminescent Materials, Springer Verlag, Heidelberg, 1994). Several studies show that also emission in the green and yellow part of the visible spectrum is possible (Blasse: Special Cases of divalent lanthanide emission, Eur. J. Solid State Inorg. Chem. 33 (1996), p. 175; Poort, Blokpoel and Blasse: Luminescence of Eu
2+
in Barium and Strontium Aluminate and Gallate, Chem. Mater. 7 (1995), p. 1547; Poort, Meijnhoudt, van der Kuip, and Blasse: Luminescence of Eu
2+
in Silicate host lattices with Alkaline earth ions in a row, J. Alloys and Comp. 241 (1996), p. 75). Hitherto, red Eu
2+
luminescence is observed only in some exceptional cases, such as in alkaline earth sulphides and related lattices of the rock-salt type (Nakao, Luminescence centers of MgS, CaS and CaSe Phosphors Activated with Eu
2+
Ion, J. Phys. Soc. Jpn. 48(1980), p. 534), in alkaline earth thiogallates (Davolos, Garcia, Fouassier, and Hagenmuller, Luminescence of Eu
2+
in Strontium and
Barium Thiogallates, J. Solid. State Chem. 83 (1989), p. 316) and in some borates (Diaz and Keszler; Red, Green, and Blue Eu
2+
luminescence in solid state Borates: a structure-property relationship, Mater. Res. Bull. 31 (1996), p. 147). Eu
2+
luminescence in alkaline-earth silicon nitrides has hitherto only been reported for MgSiN
2
:Eu (Gaido, Dubrovskii, and Zykov: Photoluminescence of MgSiN
2
Activated by Europium, lzv. Akad. Nauk SSSR, Neorg. Mater. 10 (1974), p. 564; Dubrovskii, Zykov and Chernovets: Luminescence of rare earth Activated MgSiN
2
, lzv. Akad. Nauk SSSR, Neorg. Mater. 17 (1981), p. 1421) and Mg
1-x
Zn
x
SiN
2
:Eu (Lim, Lee, Chang: Photoluminescence Characterization of Mg
1-x
Zn
x
SiN
2
:Tb for Thin Film Electroluminescent Devices Application, Inorganic and Organic Electroluminescence, Berlin, Wissenschaft und Technik Verlag, (1996), p. 363). For both Eu
2+
luminescence in the green and green/blue part of the spectrum was found.
New host lattices of the nitridosilicate type are based on a three dimensional network of cross-linked SiN
4
tetrahedra in which alkaline earth ions (M=Ca, Sr and Ba) are incorporated. Such lattices are for example Ca
2
Si
5
N
8
(Schlieper and Schlick: Nitridosilicate 1, Hochtemperatursynthese und Kristallstruktur von Ca
2
Si
5
N
8
, Z. anorg. alig. Chem. 621, (1995), p. 1037), Sr
2
Si
5
N
8
and Ba
2
Si
5
N
8
(Schlieper, Millus and Schlick: Nitridosilicate II, Hoch-temperatursynthesen und Kristallstrukturen von Sr
2
Si
5
N
8
and Ba
2
Si
5
N
8
, Z. anorg. alig. Chem. 621, (1995), p. 1380), and BaSi
7
N
10
(Huppertz and Schnick: Edge-Sharing SiN
4
tetrahedra in the highly condensed Nitridosilicate BaSi
7
N
10
, Chem. Eur. J. 3 (1997), p. 249). The lattice types are mentioned in Table 1.
Sulfide based phosphors (e.g. earth alkaline sulfides) are less desirable for lighting applications, especially for LED applications, because they interact with the encapsulating resin system, and partially suffer from hydrolytic attack. Red emitting Eu
2+
activated berates show already temperature quenching to a certain degree at the operating temperature of LEDs.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of this invention to obviate the disadvantages of the prior art. It is another object of the invention to provide a pigment for day-light fluorescence. It is a further abject to provide a yellow to red emitting luminescent material which is excitable at wavelengths around 200 to 500 nm, preferably 300 to 500 nm, together with high chemical and thermal stability.
Especially high stability up to at least 100° C. is highly desirable for LED applications. Their typical operation temperature is around 80° C.
These objects are accomplished by the characterising features of claim 1. Advantageous embodiments can be found in the dependant claims.
The new pigments show at least absorption within the blue-green spectral region. Furthermore they show fluorescent emission under absorption. Those Eu
2+
-doped luminescent materials show emission within the yellow to red spectral region, especially long wavelength red, orange or yellow emission. These pigments are based on alkaline-earth silicon nitride material as hostlattices. They are very promising, especially for LED applications, when used as phosphors. Hitherto white LEDs were realised by combining a blue emitting diode with a yellow emitting phosphor. Such a combination has only a poor colour rendition. A far better performance can be achieved by using a multicolour (for example red-green-blue) system. Typically the new material can be used together with a green-emitting (or yellow-emitting) phosphor, for example strontiumaluminate SrAl
2
O
4
:Eu
2+
, whose emission maximum is around 520 nm.
In detail, the new Pigment with day-light fluorescence uses a host lattice of the nitridosilicate type M
x
Si
y
N
z
:Eu, wherein M is at least one of an alkaline earth metal chosen from the group Ca, Sr, Ba and wherein z=⅔x+{fraction (4/3)}y. The incorporation of nitrogen increases the proportion of covalent bond and ligand-field splitting. As a consequence this leads to a pronounced shift of excitation and emission bands to longer wavelengths in comparison to oxide lattices.
Preferably, the pigment is of the type, wherein x=2, and y=5. In another preferred embodiment, the pigment is of the type, wherein x=1, and y=7.
Preferably, the metal M in the pigment is strontium because the resulting phosphor is emitting at relatively short yellow to red wavelengths. Thus the efficiency is rather high in comparison to most of the other elected metals M.
In a further embodiment the pigment uses a mixture of different metals, for example Ca (10 atom.-%) together with Ba (balance), as component M.
These materials show high absorption and good excitation in the UV and blue visible spectrum (up to more than 450 nm), high quantum efficiency and low temperature quenching up to 100° C.
It can be used as a pigment for coloring goods or as a phosphor for luminescence conversion LEDs, especially with a blue light emitting primary source together with one or more other phosphors (red and green).


REFERENCES:
patent: 6501102 (2002-12-01), Mueller-Mach et al.
patent: 2003/0006702 (2003-01-01), Mueller-Mach et al.
patent: 2003/0020101 (2003-01-01), Bogner et al.
Abstract for “Luminescence in Eu2+-doped Ba2Si5N8:Fluorescence, Thermoluminscence, and Upconversion”, Hoppe et l, Journ. Phys. Chem Solids, vol. 6 (12), Dec. 2000, pp. 2001-2006.*
Chem. Abstract citation 133:356760 Kotlyarchuk et al, “Plused Laser Deposition of Phosphor Nitride Thin Films”.*
Lee et al, “Photoluminescence and Electroluminscence Characteristics of CaSiN2:Eu Phosphor”, Proc. SPIE Int. Soc. Opt. Eng 3241, 1997, pp. 75-79.*
Lee et al, “Develpoment and Luminescent Characteristics of CaSiN2 Based Phosphors”.*
Lee, Lim: Development and Luminescent Characteristics of CaSiN2 Based Phosphors; Journal of the Institute of Electronic Engineering of Korea, Oct. 99 vol 36D, No. 10 pp. 31-36 ISSN 1226-5845.
Blasse and Grabmeier: Luminescent Materials, Springer Verlag, Heidelberg, 1994, p. 33-50.
Blasse: Special Cases of divalent lanthanide emission, Eur. J. Solid State Inorg. Chem. 33 (1996), p. 175.
Poort, Blokpoel and Blasse: Luminescence of Eu2+ in Barium and Strontium Aluminate and Gailate, Chem. Mater.

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