Roles of an oxygen Frenkel pair in the photoluminescence of Bi3+-doped Y2O3: computational predictions and experimental verifications

Abstract

Bi³⁺ as a dopant in wide-band-gap yttria (Y₂O₃) has been used as a green light emission center or a sensitizer of co-doped rare earth elements. Because the photoluminescence (PL) properties of Y₂O₃:Bi³⁺ vary remarkably according to heat treatment, the roles of point defects have been an open question. By using first-principles calculations and thermodynamic modeling, we have thoroughly investigated the formation of point defects in Y₂O₃:Bi³⁺ at varying oxygen partial pressures and temperatures, as well as their roles in PL. The photoabsorption energies of the Bi³⁺ dopant were predicted to be 3.1 eV and 3.4 eV for doping at the S₆ and the C₂ sites, respectively, values that are in good agreement with the experimental values. It was predicted that an oxygen interstitial (O_i) and an oxygen vacancy (V_O) are the dominant defects of Y₂O₃:Bi³⁺ at ambient pressure and an annealing temperature of 1300 K (3.19 × 10¹⁶ cm⁻³ for 1% Bi doping), and the concentrations of these defects in doped Y₂O₃ are approximately two orders of magnitude higher than those in undoped Y₂O₃. The defect in Y₂O₃:Bi³⁺ was predicted to reduce the intensity of PL from Bi³⁺ at both S₆ and C₂ sites. We verify our computational predictions from our experiments that the stronger PL of both 410 and 500 nm wavelengths was measured for the samples annealed at higher oxygen partial pressure.