Systematic study of photoluminescence upon band gap excitation in perovskite-type titanates R 1/2Na1/2TiO3:Pr (R=La, Gd, Lu, and Y)

Pr3+-doped perovskites R 1/2Na1/2TiO3:Pr (R=La, Gd, Lu, and Y) were synthesized, and their structures, optical absorption and luminescent properties were investigated, and the relationship between structures and optical properties are discussed. Optical band gap of R 1/2Na1/2TiO3 increases in the order R=La, Gd, Y, and Lu, which is primarily due to a decrease in band width accompanied by a decrease in Ti-O-Ti bond angle. Intense red emission assigned to f-f transition of Pr3+ from the excited 1D2 level to the ground 3H4 state upon the band gap photo-excitation (UV) was observed for all compounds. The wavelength of emission peaks was red-shifted in the order R=La, Gd, Y, and Lu, which originates from the increase in crystal field splitting of Pr3+. This is attributed to the decrease in inter-atomic distances of Pr-O together with the inter-atomic distances (R, Na)-O, i.e., increase in covalency between Pr and O. The results indicate that the luminescent properties in R 1/2Na1/2TiO3:Pr are governed by the relative energy level between the ground and excited state of 4f 2 for Pr3+, and the conduction and valence band, which is primarily dependent on the structure, e.g., the tilt of TiO6 octahedra and the Pr-Ti inter-atomic distance and the site symmetry of Pr ion. - Graphical abstract: The red intense emission assigned to f-f transition of Pr3+ from the excited 1D2 level to the ground 3H4 state upon the band gap photo-excitation (UV) was observed upon the band gap photo-excitation in perovskites R 1/2Na1/2TiO3:Pr(R=La, Gd, Lu, and Y). It was found that the systematic changes in their luminescent properties are strongly dependent on the structure