An approach to control of band-gap energy and photoluminescence upon band-gap excitation in perovskite-type La_1/3MO₃: Pr³⁺ (M = Nb, Ta)

Abstract

We synthesized polycrystalline Pr³⁺-doped perovskites La_1/3MO₃: Pr³⁺ (M = Nb, Ta), and investigated their crystal structure, optical absorption and luminescence properties. The optical band gap of La_1/3NbO₃ is smaller than that of La_1/3TaO₃, which is primarily due to the difference in electronegativity between Nb and Ta. In La_1/3NbO₃: Pr³⁺, the red emission assigned to the f-f transition of Pr³⁺ (¹D₂ to ³H₄ ) upon band gap photo-excitation was observed, whereas the f-f transition of Pr³⁺ with blue-green emission (³P₀ to ³H₄ ) was quenched. On the other hand, in La_1/3TaO₃: Pr³⁺, the blue-green emission upon band gap photo-excitation was observed. Their differences in emission behavior are attributed to the energy level of the ground and excited states of 4f² for Pr³⁺, relative to the energy levels of the conduction and valence bands, and the trapped electron state which mediates the relaxation of electron from the conduction band to the excited state of Pr³⁺.