An approach to control of band gap energy and photoluminescence upon band gap excitation in Pr(3+)-doped perovskites La(1/3)MO3 (M=Nb, Ta):Pr3+

We synthesized polycrystalline pristine and Pr(3+)-doped perovskites La(1/3)MO(3) (M = Nb, Ta):Pr(3+) and investigated their crystal structure, optical absorption, and luminescence properties. The optical band gap of La(1/3)NbO(3) (3.2 eV) is smaller than that of La(1/3)TaO(3) (3.9 eV), which is primarily due to the difference in electronegativity between Nb and Ta. In La(1/3)NbO(3):Pr(3+), the red emission assigned to the f-f transition of Pr(3+) from the excited (1)D(2) level to the ground (3)H(4) state upon band gap photoexcitation (near-UV) was observed, whereas the f-f transition of Pr(3+) with blue-green emission from the excited (3)P(0) level to the ground (3)H(4) state was quenched. On the other hand, in La(1/3)TaO(3):Pr(3+), 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 Pr(3+), 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 Pr(3+). La(1/3)NbO(3):Pr(3+) is a candidate red phosphor utilizing near-UV LED chips (e.g., λ = 375 nm) as an excitation source.