1. Field of the Invention
The present invention relates to a phosphor and an incandescent lamp color light emitting diode lamp using the same.
2. Description of the Related Art
In a technological field of illumination, a solid-state illumination, specifically, a white light illumination using a semiconductor light emitting diode has attracted a lot of attention and thus researches and developments have been widely and vigorously performed on the lighting apparatus.
A white light emitting diode lamp has attracted a lot of attention as a next generation illumination apparatus that replaces conventional incandescent lamps and fluorescent lamps and thus researches and developments have been carried out vigorously. The white light emitting diode lamp has already acquired a luminous efficacy comparable or superior to that of an incandescent lamp, even though the diode lamp is still in the process of development. In the near future, the white light emitting diode lamp is thought to become widely used as energy-saving illumination equipment.
On top of that, the white light emitting diode lamp has another advantage of being free of substances that impose a heavy burden on the environment such as mercury or the like. Moreover, the diode lamp has so small a size that it is quite often used as a backlight source of a liquid crystal display apparatus or the like and built-in in a cellular phone or the like.
The white light emitting diode utilized in the above white light emitting diode lamp is comprised of a light emitting diode chip that emits a short wavelength light such as blue or the like and a phosphor that is excited by absorbing part or all of the light emitted from the light emitting diode chip and emits a longer wavelength light such as yellow or the like. Thus, white light is obtained by mixing the blue light emitted from the blue light emitting diode as a light source and the yellow light emitted from the phosphor.
As an example of such a diode, there has been a white light emitting diode composed of a compound semiconductor blue light emitting diode chip and a cerium-activated Yttrium Aluminium Garnet (YAG) phosphor that absorbs blue light and emits yellow light, which is a complementary color of blue (See, for example, Japanese Patent Publications No. 2900928, 2927279, 3364229, U.S. Pat. Nos. 5,998,925, 6,069,440, 6,614,179, 6,592,780, S. Nakamura, “Present Performance of InGaN based blue/green/yellow LEDs,” Proc. SPIE 3002, pp. 26-35 (1997), and “Development of High-bright and Pure-white LED Lamps”, K. Bando, K. Sakano, Y. Noguchi and Y. Shimizu, J. Light & Vis. Env. Vol. 22, No. 1 (1998), pp. 2-5).
The white light emitting diode utilizing the YAG phosphor is disadvantageous in that it is difficult to improve color rendering thereof due to a deficiency of red component and to realize a low color temperature white light such as an incandescent lamp color light.
In order to eliminate such a disadvantage, there exists a technology that enables a white light emitting diode lamp by mixing two phosphors including a phosphor that emits red light (See, for example, Japanese Patent Application Laid-open Publications Nos. 2003-273409 and 2003-321675, U.S. Pat. No. 6,680,569, and R. Mueller-Mach, G. O. Mueller, M. R. Krames and T. Trottier, IEEE J. Selected Topics Quantum Electron., Vol. 8, No. 2, pp. 339-345 (2002), M. Yamada, T. Naitou, K. Izuno, H. Tamaki, Y. Murazaki, M. Kameshima and T. Mukai, Jpn. J. Appl. Phys., Vol. 42 (2003) pp. L20-L23.
In addition, in recent years, an oxynitride phosphor and a nitride phosphor are now paid attention to as a phosphor having higher reliabilities and a longer lifetime than a conventional sulfide phosphor and an oxide phosphor (See, for example, R. J. Xie, M. Mitomo, K. Uheda, F. F. Xu and Y. Akimune, J. Am. Ceram. Soc., 85[5] 1229-1234 (2002)).
Among them, an europium-activated Ca-α-SiAlON phosphor that has been originally developed as a high temperature and high strength material is promising as a phosphor for a white light emitting diode (See, for example, Japanese Patent Application Laid-open Publications No. 2002-363554, 2003-336059, 2003-124527, 2004-067837, U.S. Pat. No. 6,632,379, U.S. Patent Application Publication No. 2003/0168643, U.S. Pat. No. 6,657,379, R. J. Xie, M. Mitomo, K. Uheda, F. F. Xu and Y. Akimune, J. Am. Ceram. Soc., 85 [5] 1229-1234 (2002), J. W. H. van Krevel, J. W. T. van Rutten, H. Mandal, H. T. Hintzen, and R. Metselaar, J. Solid State Chem., 165, 19-24 (2002), G. Z. Cao and R. Metselaar, Chem. Mater., 1991, 3, 242-252, Z. J. Shen, M. Nygren, and U. Halenius, J. Mater. Sci. Lett., 16, pp. 263-266 (1997), Joost Willem Hendrik van Krevel, “On new rare-earth doped M-Si—Al—O—N materials: Luminescence Properties and oxidation resistance,”, Technische Universiteit Eindhoven, 2000, ISBN 90-386-2711-4, H. Mandal and M. J. Hoffmann, “Preparation of Multiple-Cation α-SiAlON Ceramics Containing Lanthanum,” J. Am. Ceram. Soc., 82 [1] 229-32 (1999)).
By the way, light color classification (chromaticity range) of fluorescent lamps is defined in Japanese Industrial Standard (JIS) Z 9112-1990, “Classification of Fluorescent Lamps by Chromaticity and Colour Rendering Property”. Incandescent lamp color is based on the classification defined therein.
In addition, chromaticity range of light from a 2700 K lamp as a light source having a low color temperature is defined in ANSI C78.376-2001, “Specifications for the Chromaticity of Fluorescent Lamps,” American National Standards Lighting Group—National Electrical Manufacturers Association.