Thermal stabilities, electronic structures and optical properties of intrinsic defects and dopant cerium in Ca4F2Si2O7

Abstract The thermal stabilities, electronic structures and optical properties of intrinsic defects and dopant Ce 3+ in Ca 4 F 2 Si 2 O 7 host are studied by using density functional theory (DFT) calculations (with PBE and hybrid PBE0 functionals) and wave function-based embedded cluster ab-initio calculations (at the CASSCF/CASPT2/RASSI−SO level). The calculated formation energies reveal that anion vacancies (V O and V F ) are always much more energetically favorable than cation vacancies (V Ca and V Si ) in Ca 4 F 2 Si 2 O 7 host, which is generally prepared under reducing atmospheres. According to the thermodynamic transition energy levels of intrinsic defects readily generated in undoped Ca 4 F 2 Si 2 O 7 (e.g. anion vacancies and antisite defects), we may identify the defect-induced host absorption and emission, whose exact origins are unclear previously. Moreover, on the basis of ab-initio calculated energies and relative oscillator strengths of the 4f→5d transitions of Ce 3+ at calcium sites with charge-compensating defect O F in their local environments, the excitation bands in the experimental spectra of Ce 3+ -doped Ca 4 F 2 Si 2 O 7 phosphors are also assigned. The main purpose of this work is to understand luminescence mechanisms of intrinsic defects and extrinsic dopants in the hosts for phosphors by using first-principles approaches.