Red Phosphor Heightens White LEDs

A new material could help LEDs produce more pleasing white light.

A team from Ludwig Maximilian University of Munich (LMU), in collaboration with Philips Technologie in Aachen, Germany, has developed a new red phosphor material based on the nitride Sr[LiAl₃N₄].

When doped with europium, it displays intense luminescence over a narrow range of frequencies in the red band. Peak emission occurs at wavelengths of around 650 nm, the researchers said, and peak width is 50 nm.

The new red phosphor material can improve the color rendering for white LEDs. Courtesy of Professor Wolfgang Schnick/Ludwig Maximilian University of Munich.

A single LED typically produces just one color tone (blue), but the researchers previously synthesized phosphor materials to allow that blue light to be converted into all the colors of the visible spectrum, reds in particular.

“The problem with commercially available white-light LEDs is that there is always a trade-off between optimal energy efficiency and acceptable color rendition,” said Dr. Wolfgang Schnick, a professor and chairman of inorganic solid-state chemistry at LMU.

Blue LEDs can be converted into white-light emitters by coating them with various luminescent ceramics, Schnick said. The researchers previously synthesized phosphor materials that allow this conversion by absorbing some of the blue light while re-emitting the energy at wavelengths corresponding to all the other colors of the visible spectrum, namely red.

Combining these colors, along with any unabsorbed blue light, results in pure white light.

In this recent study, the researchers found that the new red-emitting phosphor material has a significant influence on the color rendering index. Phosphors capable of emitting in the deep-red region enable the conflicting demands of optimal efficiency and color rendition to be reconciled, according to the researchers.

The research was published in Nature Materials (doi: 10.1038/nmat4012).

For more information, visit www.en.uni-muenchen.de.