On The Validity of the Defect- Induced Negative Thermal Quenching of Eu2+-Doped Phosphors

In this paper, defect-induced negative thermal quenching (NTQ) of Eu2+-doped phosphors is overviewed. NTQ denotes that the integrated emission intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. The NTQ phenomenon of Eu2+ luminescence was reportedly observed in a broad variety of lattices. The NTQ of these Eu2+-doped phosphors was generally ascribed to thermally stimulated detrapping of the excitation light stored in defects (traps) and subsequent energy transfer from the defects to the Eu2+ 5d levels. Validity of defect- induced NTQ of Eu2+-doped phosphors is assessed and factors that may contribute to the measured emission intensity of a given phosphor at elevated temperatures are discussed. It is suggested that it is debatable whether NTQ could be an intrinsic property of the blue-emitting phosphor Na3Sc2(PO4)3: Eu2+, and whether the emission intensity enhancement with increasing temperature for Eu2+-doped phosphors could be related to energy transfer from defects. The temperature dependence of the measured emission intensity alone seems not to be a good measure for evaluating TQ property of a phosphor, since it is affected by not only the quantum efficiency of the phosphor but also some extrinsic factors at elevated temperatures.