First-Principles Investigation of the Luminescence Mechanism of Eu2+ in M2SiO4:Eu2+ (M = Ba, Sr)

Abstract

Using first-principles band structure methods, we have investigated the nature of luminescence of Eu2+ ions in M2SiO4 (M = Ba, Sr). The calculated partial density of states indicates that in the α-structure, the longer wavelength emission from Eu2+ in these hosts originates from the activator ions occupying the ten coordinated M-site (M1) and is a typical 4f→5d transition. The emission from the Eu2+ ions occupying the nine coordinated site (M2) is blue- shifted and could be due to an anomalous transition. This conclusion is based on analyzes of the partial density of states of the 5d-like states of Eu and Ba or Sr ions. The lowest energy 5d-like states associated with Eu ions at M1 lie below the conduction band, while those for the M2 site move into the conduction band. Thus, the excited state of Eu at M2 will resonate with the Ba or Sr 5d-like states and could lead to anomalous transition.