Microscopic Mechanism of the Heat-Induced Blueshift in Phosphors and a Logarithmic Energy Dependence on the Nearest Dopant-Vacancy Distance.

Heat-induced blueshift (HIB) observed in many luminescent materials is a puzzling phenomenon that has remained unexplained for decades. By using the high-throughput first-principles calculations and energy-screening techniques, we generated a number of model structures for five phosphors, RbLi[Li 3 SiO 4 ] 2 :Eu 2+ , Na[Li 3 SiO 4 ]:Eu 2+ , K[Li 3 SiO 4 ]:Eu 2+ , Sr[LiAl 3 N 4 ]:Eu 2+ , and Ca[LiAl 3 N 4 ]:Eu 2+ . Our analyses suggest, to a first approximation, a logarithmic energy dependence on the nearest distance between the dopant and the metal-cation vacancy. By identifying the 5 d → 4 f transition energies from the electronic structures calculated for the screened model structures, we show that the vibration of the Eu 2+ ion lying in an asymmetric and anharmonic potential well couples with the electronic states, leading to their HIB phenomena.