Short description
(English)
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After the ban of incandescent light bulbs, which consume about 90% of the incoming energy as heat, it is the future goal of mankind to produce artificial light with the impression of warm-white light, like day-light. Till now artificial white light is obtained by the combination of a GaN blue light-emitting diode (LED) with an inorganic yellow phosphor. A good phosphor should absorb the excitation energy and emit light afterwards as efficiently as possible.The elapsed time between excitation and emission should be very short to avoid afterglow. The quantum efficiency should be maximized as in the case of the so called quantum cutters. To achieve this goal, transitions with high transition probabilities and short lifetimes are needed. These criteria are best met by lanthanide ions showing 4f --> 5d transitions in various host lattices. A good yellow phosphor to obtain white light with a blue LED is for example yttrium alumnium garnet (Y3Al5O12) doped with Ce3+ [S. Nakamura, G. Fasol, The Blue Laser Diode, Springer, Berlin 1997]. This LED has been broadly used as long-life white-light sources in traffic lights, cycle lamps, car headlights, outdoor lighting, flashlights, or marking lamps in tunnels. The produced light looks, however, bluish cold. To obtain warm-white light a blue LED covered with two or three phosphors with lanthanide ions are needed, where at least one phoshor should emit red light leading to the warm impression. We propose to achieve this goal using modelling.
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