Red phosphor without colour drift, announces Koito

January 11, 2018 // By Julien Happich
Japanese news media Nikkei Technology Online reported that Koito Manufacturing Co Ltd together with the Tokyo Institute of Technology and Nagoya University, jointly developed a novel red phosphor for white LEDs, which does not cause colour shift.

Typically, the light spectrum of white LEDs is obtained through the conversion of a ultra-violet or violet/bluish light source through a mix of phosphors, that absorb the light and down convert it to different wavelengths.

But adjusting the white of such phosphor-based LEDs has proven difficult because until now, the red phosphors used tended to re-absorb some of the shorter wavelengths (blue, green, yellow) produced by other phosphors from the mix. This causes a red shift, altering the white and the colour rendering capability of the white LED.

Different light emission states of the FOLP:Eu2+ red phosphor.
(source: Koito Manufacturing)

According to the report, the joint research yielded a novel red phosphor, FOLP:Eu2+ (short for K2CaPO4F:Eu2+) called Fluorine Oxygen Ligand Phosphor with a crystal structure in which fluorine and oxygen ions are located around a light-emitting element.

The phosphor absorbs light within a wavelength range of 315-420nm, from ultraviolet to violet, to emit in the red with a high conversion efficiency while hardly absorbing visible light in the range from blue to yellow.

That means what once mixed with blue, green and yellow phosphors to obtain white light, no colour shift occurs.

Nikkei Technology Online -

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