An Approach to Control of Band Gap Energy and Photoluminescence upon Band Gap Excitation in Pr3+-Doped Perovskites La1/3MO3 (M = Nb, Ta):Pr3+

We synthesized polycrystalline pristine and Pr3+-doped perovslcites La1/3MO3 (M = Nb, Ta):Pr3+ and investigated their crystal structure, optical absorption, and luminescence properties. The optical band gap of La1/3NbO3 (3.2 eV) is smaller than that of La1/3TaO3 (3.9 eV), which is primarily due to the difference in electronegativity between Nb and Ta. In La1/3NbO3: Pr3+, the red emission assigned to the f-f transition of Pr3+ from the excited D-1(2) level to the ground H-3(4) state upon band gap photoexcitation (near-UV) was observed, whereas the f-f transition of Pr3+ with blue-green emission from the excited P-3(o) level to the ground H-3(4) state was quenched. On the other hand, in La1/3TaO3:Pr3+, the blue-green emission upon band gap photoexcitation was observed. Their differences in emission behavior are attributed to the energy level of the ground and excited states of 4f(2) 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+. La1/3NbO3:Pr3+ is a candidate red phosphor utilizing near-UV LED chips (e.g., lambda = 375 nin) as an excitation source.