Polarization tuning the Stokes photoluminescence spectra of erbium doped KNbO3 ceramics

The poling effect in Stokes photoluminescence (PL) spectroscopy of erbium doped potassium niobate (KNbO3) ceramics has been investigated by studying the relations between PL spectra with the poling electric field, poling time, and annealing conditions, respectively. All the Stark splitting components of S3∕24→I13∕24 transition were evident after the poling process. The experiments also showed that the polarization enhances the fine structure and modifies the intensity ratio of the S3∕24→I15∕24, F9∕24→I15∕24, and S3∕24→I15∕24 transitions at different poling electric fields and poling times for the samples doped with 5% of erbium. Comparing the poling spectra with annealing spectra, we can see that both polarization and annealing can modify the intensity of PL. However, the mechanisms of the two effects are different. The frequency shift Δν of the peaks depended on the wavelength after poling demonstrates that the Stark splitting was produced by the dipole moment of erbium ions interacting with the internal local electric field due to polarization.