The influence of defects formed by Ca excess and thermal post-treatments on the persistent luminescence of CaTiO_3:Pr

Red emitting CaTiO3:Pr phosphors with a nominal composition of Ca0.998+xPr0.002TiO3+δ (0.02≤x≤0.04) were prepared by solid state reactions with different thermal post treatments and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence. The Ca excess exhibited complete solubility up to 4% in the samples treated at 1400 °C but segregation in the form of Ruddlesden-Popper phases (Ca3Ti2O7 - Ca4Ti3O10) was observed in samples prepared at 1500 °C. The increase in temperature for stoichiometric samples showed a monotonic increase of decay time due to the reduction of non-radiative recombination defects. It was found that the Ca excess favored the formation of oxygen vacancies which are known to act as trap. In the samples treated at 1400 °C, 3% of Ca excess showed to be the best concentration to increase the decay time of persistent luminescence. For the samples treated at 1500 °C, the segregation of Ruddlesden-Popper phases left a constant amount of Ca soluble in all the CaTiO3 samples. This constant concentration of Ca caused the same density of defects and, consequently, the same decay time in all samples.