First-principles study on site occupancies and excitation spectra of Na3LuSi2O7:Ce3+

Abstract

The observed strongly temperature-dependent luminescence of Ce3+-doped Na3LuSi2O7 indicates its potential applications in temperature sensing. The experimental assignments of excitation spectra to Ce3+ ions at two Lu sites are at odds with the empirical crystal-field analysis. Here, first-principles calculations were carried out to resolve the site occupancies of the Na3LuSi2O7:Ce3+ by considering the influence of the oxygen vacancy. The hybrid functional was utilized to overcome the well-known underestimation of the band gap so as to obtain energy levels of Ce3+ ions in the band gap more accurately. Based on our calculated results of defect formation energies and energy level structures, one set of the excitation spectra is assigned to Ce3+ ions at Lu(2) sites and the other to Ce3+ ions at Lu(2) sites with an adjacent O(3) vacancy. Furthermore, the thermal stabilities of these two luminescence centers are predicted, which is consistent with the previous reported experimental results. Our results exhibit the significance of intrinsic defects on the spectra and thermal quenching behavior of Ce3+-activated phosphors.