The post-annealing effects on the Stokes photoluminescence spectra of erbium-doped KNbO₃ polycrystalline

The annealing effect on Stokes photoluminescence (PL) spectroscopy of erbium-doped potassium niobate (KNbO₃) ceramics has been investigated by studying the relations between room-temperature PL spectra with the annealing conditions. The experiments showed that the shape and intensity of the PL spectra is a function of the annealing temperature; the relative intensity of ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and the ⁴S_3/2→⁴I_13/2 transitions increased where the annealing temperature was increased. After annealing, the relative intensity ratio of the 541 and 526nm peaks decreased gradually, indicating the decrease of the symmetry of ligand field and an increase of covalence. From the unusual phenomenon, in which the green and near-infrared transitions intensity change was different after annealing, the near-infrared emission may correspond to the ⁴I _9/2→⁴I_15/2 transition instead of ⁴S_3/2→⁴I_13/2 transition.