A research group led by Professor Takumi Fujiwara at Graduate School of Engineering, Tohoku University and Assistant Professor Kazuhiro Masai at Institute for Chemical Research, Kyoto University successfully developed novel low-melting glasses containing no rare-earth elements with high photoluminescent efficiency in collaboration with Professor Toshinobu Yoko at Institute for Chemical Research, Kyoto University and Asahi Glass Co. Ltd.

 Low-melting glasses are generally processed at the working temperature of 500 degrees C or lower, and have been used as sealant materials for electronic components.  The glasses have recently been used as a complementary light source for application to white light emitting diodes (LED) in addition to sealing semiconductor materials.  As quantum efficiency of ultraviolet (UV)-excited photoluminescence in oxide glasses is generally low, a use of glasses for emitting materials needs methods to dope with ions such as rare-earth (RE) elements or to precipitate microcrystallines with luminescent property.

 In this study, the research group developed low-melting Sn-doped phosphate glasses with high quantum efficiency for photoluminescence as high as RE-doped glasses.  The newly developed glasses containing no RE elements showed blue light emission at a high efficiency of approximately 90% by UV light irradiation.  It was also demonstrated that the luminescent property did not significantly change when a temperature rose to the level at which glasses were able to be processed.

 The achievement will pave the way for application of new seal and emitting materials.  As energy-saving lighting in the promising field of LED, it is expected to be alternative materials for existing organic sealing materials that is deteriorated under strong UV light, to be economical and simple emitting materials by excluding RE elements in terms of energy saving, and to contribute to realizing white LEDs by the combination of UV LEDs and low-melting glasses.

 Transparent low-melting glass materials have high processability and are expected to innovatively spread effects as new, stable, reliable and nonorganic materials for white LEDs that have been developed with a limitation due to organic materials deterioration.

 A report on this research received the "28th Award for Distinguished Presentation” from the Japan Society of Applied Physics (JSAP) in spring meeting 2010.  The details were published in Applied Physics Express on August 6, 2010 (JSAP, Vol. 3, 214204).

[Contact]
Professor Takumi Fujiwara
Optical Materials and Science, Department of Applied Physics, Graduate
School of Engineering, Tohoku University
TEL/FAX: +81-22-795-7964
E-mail: fujiwara◎laser.apph.tohoku.ac.jp (Replace ◎ with @)
Website: http://www.apph.tohoku.ac.jp/fujiwara-lab/