A red phosphor, ( Sr , Ca ) 2 P 2 O 7 : Eu 2 + , Mn 2 + , for UV light-emitting diodes (LEDs) was synthesized under a reducing atmosphere, and its luminescent properties were investigated. The phosphor absorbs UV light at around 400 nm and efficiently emits red light at approximately 610 nm through an energy transfer from Eu 2 + to Mn 2 + . The energy transfer occurs through dipole–quadrupole electric resonance as confirmed by the quantitative estimation of multipolar interactions. Using the varied input current test for the phosphor-loaded LED lamps, it was found that the luminescent efficiency of the phosphor decreased with increasing light flux. This might be due to an increased probability of excited-state absorption and the consequent nonradiative relaxation in Mn 2 + ions, as deduced from a simple analytical model.
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Kim et al. (2009) studied this question.
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