All‐nitride monochromatic amber‐emitting phosphor‐converted light‐emitting diodes

Phosphor conversion of light-emitting diode (LED) radiation has been used in many configurations and combinations to generate white light. The concept of down conversion of, e.g., blue LED emission, offers also the possibility to provide efficient generation of monochromatic, high-color-purity light, especially in wavelength ranges in which direct radiation from non-converted LEDs is relatively inefficient, i.e., in the “yellow gap”. In the case described here, a blue-emitting LED is ‘fully’ converted to amber emission with a peak wavelength of 595 nm and a color purity of >96%, while demonstrating an external quantum efficiency exceeding that of direct AlGaInP LEDs of the same wavelength by a factor of almost two at room temperature, and the lumen output under equal drive conditions at 85 °C by more than a factor of four. An essential component in this high performance is, besides the choice of the right – nitride – phosphor, the use of this phosphor in a densely sintered ceramic form which has considerable optical advantages over powders. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)