Insulating host materials doped with trivalent cerium show quantum efficiencies of the Ce3+ emission ranging from zero to unity. Comparing optical and photoelectrical properties of a very efficient scintillator material (Lu2(SiO4)O:Ce) to those of cerium doped oxides with quenched emission, the radical differences for these materials are demonstrated to originate from the location of the cerium energy levels with respect to the host conduction band. Photoionization and subsequent nonradiative relaxation processes responsible for the luminescence quenching are discussed in a donor–acceptor model for the impurity ion and a rule for luminescence efficiency is derived, applicable to a variety of phosphor and scintillator materials.
In the present article we briefly review some materials research aspects related to ceramic phosphors and discuss both typical characteristics as well as unique features of such optical converters. Devices with more efficiency and/or higher luminous flux that are based on converting the pump light crucially enable the use of LEDs in white and single color illumination schemes for many applications. Advantages of generating white light with ceramics versus powder-in-silicone are discussed. High performance of single color conversion LEDs in terms of efficacy and external quantum efficiency for the visible region boost the output in data or home cinema projection and automotive signaling but more applications are appearing.
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