Scientists at Leiden University have invented novel phosphor materials based on rare earth elements, which have excellent absorption properties in the near-ultraviolet (UV) range and show strong blue and/or green emission with high quantum efficiency. This invention is particularly suitable for white light-emitting diodes (LEDs) based on near-UV-LED chips.

Currently, there are two ways of producing white LEDs. One is to combine individual LEDs emitting in the blue, green, and red spectrum region, and then mix the three colors to produce white light. However, the low efficiency of the current green or yellow LEDs as well as the sophisticated control system limit this method.

The other way to produce a white LED is to use a phosphor material to convert monochromatic light from a blue- or UV-LED to broad-spectrum white light. The most commercially available white LEDs use a blue LED in combination with a yellow emitting phosphor, i.e. Y3Al5O12:Ce (YAG:Ce). Such a dichromatic approach allows only lamps with high color temperature, >5000K, to be obtained with a relatively poor color rendering index (CRI). These drawbacks can be overcome by using tricolor phosphors.

Blue emission component.
Green emission component.

Leiden University's invention provides phosphor material that has two emission centers, blue and green, thus emitting different colors. Since the relative concentrations of activators are adjustable at the atomic level, the desired color between blue and green can be adjusted much more easily than by mixing two separate phosphors. These materials exhibit high levels of absorption property when subject to near-UV-light, exceeding 95% at 380 nm. They show intense emission with high quantum efficiency. These novel phosphors, when combined with a suitable red emitting phosphor, are ideal candidates for near-UV-LED-based lighting devices.

For more information on this licensing opportunity, visit Leiden University.

Lighting Technology Magazine

This article first appeared in the November, 2010 issue of Lighting Technology Magazine.

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