The enhanced bandgap and birefringence of rare-earth phosphates XPO4 (X = Sc, Y, La, and Lu): a first-principles investigation

Abstract

Rare-earth phosphates were thought to be good candidates as ultraviolet/deep ultraviolet optical materials due to their relatively large bandgap and optical properties. In this paper, the authors screened out a family of XPO₄ (X = Sc, Y, La, and Lu) compounds with an enhanced bandgap (HSE06 bandgap ≥ 7.61 eV) and birefringence (0.0934–0.2003@1064 nm) using first-principles calculations. The origin of enhanced optical properties was investigated using projected density of states, distortion indices, and Born effective charges. The results show that the PO₄ anionic groups and X–O polyhedra give the main contribution in determining the optical properties, and the PO₄ anionic groups give more contribution than other functional basic units. The spin–orbit interaction was also investigated. Similar band structures were found after spin–orbit coupling (SOC) was considered, and slightly enhanced birefringence was found when SOC was applied to these rare-earth phosphates.