Nanoluminophores developed by CEA LITEN open the way to new applications for lighting and signage sectors.

CEA LITEN’s nanoluminophores*, developed for a variety of applications such as anti-counterfeit or photovoltaic systems, are once again breaking new ground. This time, they are converting primary light from the latest low-consumption LED developments for lighted sign and signalling applications. By lighting ceilings, entire walls or even windows, these applications offer greater energy efficiency and enhanced lighting quality. Another possibility is transparent indicator signs, cylindrical or spherical in shape, which display predetermined messages.

To obtain white light with good conversion efficiency, LITEN researchers use luminophores emitting at green and red wavelengths when excited by low-energy photons with blue wavelengths. While fluorescent nanometric semiconductor crystals known as quantum dots provide good efficiency and light quality, they remain relatively fragile.

Researchers are focusing on rare earths, which are more stable. Unlike many luminophores currently on the market that react to ultraviolet light (254 nm), rare earths can be used to produce materials activated by lower-energy blue light sources.“The energy difference between the photon consumed and the photon emitted is thus smaller and the conversion efficiency better,” explained Renard.

Direct applications in signage

So far, the scientists have developed a rare earth system embedded in a glass plate. The luminophores emit at green and red wavelengths and are excited by blue-green light at 490 nm. “To meet our ultimate objective of white light, we are adjusting the mixture and glass compositions to make the system excitable at 460 nm.”

At the same time, the scientists have deposited organic fluorescent ink (excitable at 460 nm) on plastic films. The first tests on luminophores emitting green light were conclusive. Now the scientists need to develop inks emitting in the red region and validate the mixtures for obtaining white light.

Custom signage applications are possible. “This nearly invisible ink makes it possible to create display areas on totally transparent objects,” noted Renard. CEA is also participating in the Luminosurf project, whose activities are part of the Axelera competitiveness cluster. Following the lead of Philips Eclairage, CEA plans to develop illuminated surfaces based mainly on luminophores excitable at 460 nm where efficiency is compatible with lighting standards. The first illuminated surface prototype should be ready in 2010.

*Substances emitting light when excited by photons, varying in size from 1 µm to a few nanometres.