Effect of electric field induced structural ordering on photo-luminescence and piezoelectric response of praseodymium doped (Na0.41K0.09Bi0.5)TiO3 ceramics

A correlation of the ferroelectric and photoluminescence response to the structural ordering of praseodymium doped (Na0.41K0.09Bi0.5)TiO3 has been investigated. It has been observed that the ferroelectric and photoluminescence response lacks one-to-one correlation. The ferroelectric response is generally driven by long-range polar ordering. On the contrary, photoluminescence response is concomitant to the local site symmetry around the praseodymium ion. The optimum ferroelectric response has been observed for 1.0 at. % praseodymium doped (Na0.41K0.09Bi0.5)TiO3, whereas for the sample with higher doping concentration, it diminishes gradually due to disruption of the long-range ordering. On the other hand, with the establishment of long-range ordering, no noticeable shift in the position and shape of the photoluminescence lines has been observed. However, a quenching in the photoluminescence intensity of the hypersensitive transitions (1D2 → 3H4) takes place, which has been associated with the modification in the local site symmetry. It has been argued that structural modification has an influence on the photoluminescence intensity but does not affect the energy levels of these transitions. The observed dielectric, piezoelectric, and photoluminescence response has been explained on the basis of the amphoteric nature of praseodymium in (Na0.41K0.09Bi0.5)TiO3.