New Yellow Phosphor Realizes 10mm Diameter Semispherical White LED

Oct 18, 2012
Shinya Saeki, Nikkei Electronics
A white LED using a newly developed yellow phosphor (left) and an existing white LED (right)
A white LED using a newly developed yellow phosphor (left) and an existing white LED (right)
[Click to enlarge image]
The CL_MS phosphor
The CL_MS phosphor
[Click to enlarge image]
Prototypes of LED Lighting devices
Prototypes of LED Lighting devices
[Click to enlarge image]

A Japanese research team developed a new yellow phosphor, "CL_MS phosphor," for white LEDs used in lighting apparatuses.

The phosphor was co-developed by Koito Manufacturing Co Ltd, a research group led by Hideo Hosono (professor at the Tokyo Institute of Technology) and a group led by Hiroshi Sawa (professor at Nagoya University).

A white LED using the new phosphor emits a soft light suited for indoor use and has a low cost, compared with existing white LEDs, said Yuji Yokoya, executive vice president of Koito Manufacturing.

He did not disclose when Koito Manufacturing will start volume production of the phosphor but said that the company has already established a volume production technology for it and plans to have talks with LED and lighting apparatus makers.

94% quantum efficiency

The CL_MS phosphor is made by adding Eu (europium)2+ as an activator for light emission to a mother crystal whose chemical formula is (Ca1-x,Srx)7(SiO3)6,Cl2.

"It has a totally-new layered crystal structure," Koito Manufacturing said.

The CL_MS phosphor can convert purple light into yellow light with a quantum efficiency of 94%, absorbs a relatively small amount of blue light when being excited and realizes a high color reproducibility because it has a wide emission spectrum.

Koito Manufacturing developed a semispherical white LED whose diameter is 10mm by using the CL_MS phosphor, blue phosphor and purple LED chip.

"We thickly applied the CL_MS phosphor and blue phosphor particles with a low density," the company said.

Compared with an existing white LED structure that measures 2 x 2mm to 3 x 3mm and is about 0.5mm thick, the density of phosphor particles was reduced by 90-95%, it said.

5 advantages of new white LED

(Continue to the next page)