SPring-8, the large synchrotron radiation facility

The research group at Koito Manufacturing Co., Ltd (president: Masahiro Ohtake) - in collaboration with a research group led by Prof. Hideo Hosono at Tokyo Institute of Technology (president: Yoshinao Mishima) and one led by Prof. Hiroshi Sawa at Nagoya University (president: Michinari Hamaguchi) - has developed a novel phosphor for LED named “Cl_MS phosphor^*1.”

Cl_MS phosphor is an oxide comprising elements that commonly occur in shells, bones, rocks, and salts, but its crystal structure is new.

In recent years, energy-efficient white LEDs have become increasingly popular in line with the shift toward realization of a low-carbon society, which is a global challenge.

The mainstream white LED of today is a combination of a blue-emitting chip and a yellow phosphor (YAG phosphor). This type of white LED, however, has inherent problems caused by its narrow light-emitting section: point-source lighting tends to provide an uncomfortable dazzling feeling, and the optimum illumination area is limited. Thus, it is a good device for partial illumination, but can not be the optimum main source for illuminating an entire room uniformly.

Cl_MS phosphor, the main achievement of this study, is capable of converting purple light into yellow with better than 90% efficiency, making it possible to constitute a white LED with very high luminous efficiency in combination with a blue phosphor and a purple-emitting chip^*2. The light emitting section of this white LED has a wide area (not a point source) and is capable of being configured into a variety of solid shapes. These features are instrumental for producing human-friendly main illumination with a drastic reduction of the uncomfortable dazzling feeling, and uniform wide-area illumination. In addition, it allows freedom to design a variety of configurations and shapes suitable for the intended use: a light bulb, line source, candle light, and others.

Additional features and advantages include the reduced color hue variations at production, and the promise of better yield.

Cl_MS phosphor, as described above, defies the conventional concept of white LEDs, and provides a promise to open up new possibilities. Above all, it is expected to spur the proliferation of white LEDs as the main in-house lighting source.

In this study, the group at Nagoya University carried out a detailed crystal-structure analysis of Cl_MS phosphor using the high intensity synchrotron radiation^*3 available at SPring-8, and the group at Tokyo Institute of Technology elucidated the light-emitting mechanism of Cl_MS phosphor.

These results appeared in the online version of Nature Communications (a UK science journal) on the 16th of October (BST) (17th Oct. JST).

Publication:
"A novel phosphor for glareless white light-emitting diodes"
Hisayoshi Daicho, Takeshi Iwasaki, Kiminori Enomoto，Yasutaka Sasaki, Yuzo Maeno, Yu Shinomiya,Shinobu Aoyagi, Eiji Nishibori, Makoto Sakata, Hiroshi Sawa, Satoru Matsuishi, Hideo Hosono
Nature Communications 3, Published 16 October 2012.