Polarization-induced enhancement of photoluminescence in Pr3+ doped ferroelectric diphase BaTiO3-CaTiO3 ceramics

Photoluminescence (PL) spectra impacted by electric polarization in Pr3+ doped diphase (1-x)BaTiO3-xCaTiO3 (x = 0.4–0.7) ceramics were studied systematically. The transparent electrode of indium tin oxide was deposited on both surfaces of ceramics to reduce experimental errors and then PL properties were characterized with and without polarization. An enhancement in PL intensity of ∼100% was obtained in the Ba1−xCaxTiO3 (x = 0.7) ceramics with polarization. It was found that the PL intensity increased the same level whether the poling direction was up or down. With the x increases, the enhanced factor decreased first and then increased, which ascribed to the ratio of the tetragonal Ba0.77Ca0.23TiO3 and orthorhombic Ba0.1Ca0.9TiO3 in the diphase ceramics. The investigation of UV-Vis reflective spectrum and X-ray Photoelectron Spectroscopy spectrum demonstrated that the polarization effect on the PL was attributed to the change of band gap of host by a local electric field around Pr3+ doped in Ba0.1Ca0.9TiO3. The local electric field was supposed to be produced by the remanent polarization from ferroelectric Ba0.77Ca0.23TiO3 matrix. The band gap of the host became smaller in the polarized sample, which suggests that an increase in the band gap excitation of the host, i.e., increasing the PL intensity.