Excited state dynamics of Bi3+ centers in cubic Gd2O3

Abstract

Photoluminescence characteristics of Gd2O3:Bi are studied in the 4.2–800 K temperature range by the time-resolved spectroscopy methods. Purely cubic structure of Gd2O3:Bi is confirmed by XRD. The luminescence of Bi3+(S6) and Bi3+(C2) centers is found to arise from the electron transitions from the emitting level of the triplet excited state of Bi3+, corresponding to the 3P1 → 1S0 transitions of the free Bi3+ ion. Relaxation processes in the triplet excited state of Bi3+ ions do not result in the population of the lowest-energy metastable level. The absence of the radiative transitions, corresponding to the 3P0 → 1S0 transitions of the free Bi3+ ion, explains the short (0.3–2.0 μs) decay time of the triplet emission of Bi3+ even at 4.2 K. The conclusion is made that the fast luminescence decay cannot be caused by the mixing of the metastable and emitting levels of the triplet excited state of Bi3+ by the magnetic field created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. The electron transfer and recombination processes, resulting in the appearance of the photo- and thermally stimulated electron recombination luminescence of Bi3+(S6) and Bi3+(C2) centers under excitation in the Eexc > 4.3 eV energy region, are also discussed. The energy level positions of the Bi3+(S6) and Bi3+(C2) centers in the band gap of Gd2O3 are estimated.