On the excitation mechanism of the Bi3+ - Related localized exciton luminescence in Bi3+ - Doped aluminum garnets

Abstract

Microcrystalline powders of Bi3+-doped Y3Al5O12 and Lu3Al5O12 garnets have been studied by the X-ray diffraction, steady-state and time-resolved photoluminescence, and thermally stimulated luminescence methods. The conclusion is made that the excitation spectra of the Bi3+-related visible exciton-like emission of these compounds, which are located in the 4–6 eV energy range, cannot be explained by the charge-transfer transitions between the energy levels of Bi3+ and the conduction or valence band of the host, whose energies exceed 6 eV. To explain the features observed, this emission is suggested to appear due to the photostimulated electron transfer from the ground state of a Bi3+ ion to defect levels located in the band gap, resulting in the creation of temporary pairs of electron centers and hole Bi4+ centers. A hole delocalization from the Bi4+ ion to the neighboring oxygen O2− ion is also suggested, resulting in the creation of the {O− - Bi3+}-type hole center. As a result of the electron recombination with this hole center, the exciton localized around the Bi3+ ion is formed whose radiative decay is accompanied with the visible emission.