Photoluminescence and excited state structure of Bi3+-related centers in Lu2SiO5:Bi single crystalline films

Single crystalline films of Lu2SiO5:Bi, prepared by the liquid phase epitaxy method from the melt-solution based on Bi2O3 flux, are studied at 4.2–350 K by the time-resolved spectroscopy methods under excitation in the 2.4–6.2 eV energy range. An intense dominant ultraviolet (≈3.5 eV) luminescence of Lu2SiO5:Bi is shown to arise from the radiative decay of the metastable and radiative minima of the triplet relaxed excited state (RES) of Bi3+ centers which are related to the 3P0 and 3P1 levels of a free Bi3+ ion, respectively. At T<50 K, the radiative transitions from the metastable minima mainly take place. Thermally stimulated non-radiative transitions between the metastable and radiative minima of the triplet RES appear at T>50 K in the temperature evolution of the emission spectrum and decay kinetics. The excitation bands of the ultraviolet emission, located at 4.2 eV, 5.03 eV, and 5.95 eV, are assigned to the 1S0→3P1, 1S0→3P2, and 1S0→1P1 transitions of a free Bi3+ ion, respectively. The phenomenological model is proposed to describe the excited-state dynamics of Bi3+ centers in Lu2SiO5:Bi. Characteristic parameters of the triplet RES, in particular the energy separation between the excited states and the rates of the radiative and non-radiative transitions from these states, are determined. Much weaker ≈3.3 eV emission is ascribed to the Bi3+ ions located in the Lu2 lattice sites. Weak broad ≈2.2 eV and ≈2.3 eV emission bands are assumed to arise from the Bi3+-related localized excitons.