Project EuroLED by Fraunhofer CAN New Technology for Warm White LEDs

At Fraunhofer CAN in Hamburg, researchers are developing light sources for more efficient, warmer white light LEDs.

Although LEDs are more energy-efficient than conventional light sources, they do not reproduce the full colour spectrum. Above all, they lack an efficient red phosphor for warmer white light. Scientists are now working on a nanoscale fluorescent system for white LEDs based on a new concept.

Similar to sunlight, the color temperature of light sources influences our well-being. The more red in the perceived spectrum, the warmer and more pleasant its effect is on us. 14 years ago it was possible for the first time to use LEDs to create a physiologically more pleasant working atmosphere, i.e. warm white light. The basis was the red phosphor CASN developed in Japan. Even today, white light LEDs are additionally coated with the red phosphor to produce warm white light. However, CASN is extremely inefficient because it emits a large part of the radiation in the infrared spectral range that is not visible to the human eye. The EuroLED partners are now developing a suitable alternative.

"At Fraunhofer IAP, we have already developed and patented a red-emitting nanoscale phosphor," explains Dr. Christoph Gimmler, who heads the EuroLED project at Fraunhofer CAN, a research unit of the Fraunhofer Institute for Applied Polymer Research IAP. "It is based on special nanoparticles modified with trivalent europium ions. This narrow-band emitter material can be applied as an additional layer to a conventional white LED. Trivalent europium ions have a very narrow emission band that is up to three times more visible to the human eye than the light emitted by the conventional red phosphor CASN. This makes Eu-doped material much more efficient than CASN," says Gimmler.

As part of the project, the Fraunhofer researchers will further optimize the phosphor. In particular, the luminous efficacy and the manufacturing costs are in focus. The project partners will then process the phosphor further for the development and production of prototypes of this new generation of LEDs. The technology is then to be advanced to series maturity and market launch.

"Originally, we produced the phosphor on a gram scale," explains Gimmler. "In the course of the project, we will produce the yield of up to 1 kg of material per batch in order to supply the project partners. In addition, in the pilot plant center for polymer synthesis and processing (PAZ) we have synthesis lines close to industry with which we could also make the material available on a tonne scale."