Density functional calculations to understand Ba2-xEuxSiO4 photoluminescence thermal stability

Abstract

The green broad emission of Ba2-xEuxSiO4 can be deconvoluted into two peaks, which are related to Eu2+(I, 10-coordinated) and Eu2+(II, 9-coordinated) respectively. With Eu2+ concentration increasing (x = 0.01→0.05), the green emission become stronger, more thermally stable and red-shifted. The density functional theory (DFT) calculation was used to find the explanation for the phenomenon. The calculation results show that Eu2+ ions have site preference in Ba2SiO4 crystal, as more likely being Eu2+(I) than Eu2+(II). Compared Eu2+(II) with Eu2+(I), Edf (4f65d-4f7 electronic transition) is smaller but EdC (energy difference between 5d energy level and conductive bottom) is larger. It can be deduced that Eu2+ ion do-pant would start as Eu2+(I, shorter emission wavelength, less thermal stable), and then acts as Eu2+(II, longer emission wavelength, more thermal stable) when Eu2+ ions are more and more in the crystal. The calculation results provide a reasonable explanation for photoluminescence red-shift and thermal stability improvement with Eu2+ ion content increasing.