Roles of an oxygen Frenkel pair in the photoluminescence of Bi ³⁺-doped Y₂O₃: Computational predictions and experimental verifications

Bi³⁺ as a dopant in wide-band-gap yttria (Y₂O ₃) 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 Y₂O ₃: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 Y ₂O₃: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. This journal is