Photoluminescence origin in Bi3+-doped GdAlO3 perovskite

Abstract

Microcrystalline powders of GdAlO₃:Bi with different bismuth concentrations were synthesized by the modified sol-gel method. The pure orthorhombic perovskite structure of the investigated samples was confirmed by X-ray diffraction. Photoluminescence characteristics of GdAlO₃:Bi were investigated in the 4.2–500 K temperature range by the methods of steady-state and time-resolved luminescence spectroscopy. The ultraviolet emission spectrum of GdAlO₃:Bi is found to consist of two bands. The dominating 3.72 eV band is assigned to the electron transitions from the emitting and metastable levels of the triplet relaxed excited state of a single Bi³⁺ center, corresponding to the ³P_1,0 → ¹S₀ transitions of the free Bi³⁺ ion. A weak ≈3.65 eV band is attributed to the dimer {Bi³⁺ - Bi³⁺} center. The visible emission spectrum consists of two bands of an exciton origin centered at about 2.5 eV and 2.3 eV and assigned to the excitons localized around the single Bi³⁺ ions and dimer {Bi³⁺ - Bi³⁺} centers, respectively. The electron-transfer processes in the {Bi³⁺- Bi³⁺} pairs resulting in the appearance of the {Bi³⁺- Bi³⁺}-related UV and VIS luminescence are suggested. The influence of the magnetic field, created at the Bi³⁺ site by the magnetically ordered Gd³⁺ sublattice, on the decay kinetics of the triplet Bi³⁺ emission is found to be negligible. The effect of energy-transfer processes on the decay kinetics of this emission is discussed. The energies of the Bi³⁺ → Gd³⁺ and Bi³⁺ → Bi³⁺ electron-transfer transitions in GdAlO₃:Bi are estimated.