The stability of coordination polyhedrons and distribution of europium ions in Ca6BaP4O17

Abstract

In this work, the coordination polyhedron stabilities and distributions of europium ions in Ca₆BaP₄O₁₇ (CBPO) luminescent materials are investigated. The density functional theory (DFT)-based first principles calculation results show that the PO₄ tetrahedrons can tilt in the structure, which leads to the atomic distortion of O13 and O12 in CBPO and the Eu²⁺/Eu³⁺-doped systems. The energy scale of about ∼0.1 eV suggests that stabilities of coordination polyhedrons are easily influenced by dynamic factors. The atomic distortion and vacancy of work as charge compensations in CBPO:Eu³⁺, and three lattice sites of europium are extracted and summarized. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) confirm that Eu³⁺ can occupy the Ca1, Ca2 and Ba sites of CBPO. The combination of first principles calculation and X-ray absorption fine structure (XAFS) provides more information about microstructures of luminescent materials.