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

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 rotes in PL. The photoabsorption energies of the Bi3+ dopant were predicted to be 3.1 eV and 3.4 eV for doping at the S-6 and the C-2 sites, respectively, values that are in good agreement with the experimental values. It was predicted that an oxygen interstitial (01) 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 x 10(16) 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 V-O(2+) in Y2O3:Bi3+ was predicted to reduce the intensity of PL from Bi3+ at both S-6 and C-2 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.