Understanding the physical mechanisms behind thermal effects in phosphors is crucial for white light-emitting diodes (WLEDs) applications, as thermal quenching of their photoluminescence might render them useless. The two chemically close Eu-doped \Hosta and \Hostb crystals are typical phosphors studied for WLEDs. The first one sustains efficient light emission at 100∘C while the second one emits very little light at that temperature. Herein, we analyze from first principles their electronic structure and atomic geometry, before and after absorption/emission of light. Our results, in which the Eu-5d levels are obtained inside the band gap thanks to the removal of an electron from the 4f7 shell, attributes the above-mentioned experimental difference to an auto-ionization model of the thermal quenching, based on the energy difference between Eu5d and the conduction band minimum. For both Eu-doped phosphors, we identify the luminescent center, and we show that the atomic relaxation in their excited state is of crucial importance for a realistic description of the emission characteristics.
@article{arxiv.1508.06214,
title = {Understanding thermal quenching of photoluminescence from first principles},
author = {Samuel Ponce and Yongchao Jia and Matteo Giantomassi and Masayoshi Mikami and Xavier Gonze},
journal= {arXiv preprint arXiv:1508.06214},
year = {2015}
}