Luminescence spectroscopy of the Bi3+ single and dimer centers in Y3Al5O12:Bi single crystalline films

Luminescence of the Bi3+ single and dimer centers in UV and visible ranges is studied in YAG:Bi (0.13 and 0.27 at% of Bi, respectively) single crystalline films (SCFs), grown by liquid phase epitaxy from a Bi2O3 flux. The cathodoluminescence spectra, photoluminescence decays, and time-resolved spectra are measured under the excitation by accelerated electrons and synchrotron radiation with energies of 3.7 and 12 eV, respectively. The energy level structure of the Bi3+ single and dimer centers was determined. The UV luminescence of YAG:Bi SCF in the bands that peaked at 4.045 and 3.995 eV at 300 K is caused by radiative transitions of Bi3+ single and dimer centers, respectively. The excitation spectra of UV luminescence of Bi3+ single and dimer centers consist of two dominant bands, peaked at 4.7/4.315 and 5.7/6.15 eV, related to the 1S0→3P1 (A band) and 1S0→ 1P1 (C-band) transitions of Bi3+ ions, respectively. The excitation bands that peaked at 7.0 and 7.09 eV are ascribed to excitons bound with the Bi3+ single and dimer centers, respectively. The visible luminescence of YAG:Bi SCF presents superposition of several wide emission bands peaking within the 3.125–2.57 eV range and is ascribed to different types of excitons localized around the Bi3+ single and dimer centers. Apart from the above mentioned A and C bands the excitation spectra of visible luminescence contain wide bands at 5.25, 5.93, and 6.85 eV ascribed to the O2−→Bi3+ and Bi3+→Bi4+ + e charge transfer transition (CTT) in Bi3+ single and dimer centers. The observed significant differences in the decay kinetics of visible luminescence under excitation in A and C bands of Bi3+ ions, CTT bands, and in the exciton and interband transitions confirm the radiative decay of different types of excitons localized around Bi3+ ions in the single and dimer centers.