A correlation of piezoelectricity and photoluminescence of europium doped (Na0.41K0.09Bi0.5)TiO3 with ferroelectric and structural ordering

A correlation between piezoelectricity and photoluminescence is investigated for europium doped (Na_0.41K_0.09Bi_0.5)TiO₃ ceramic. An optimum piezoelectric and dielectric response is observed for 1.0 at.% Eu doped (Na_0.41K_0.09Bi_0.5)TiO₃. For doping concentration higher than 1.0 at.% a gradual fall in the piezoelectric response is observed which is associated to the amphoteric nature of Eu³⁺ ion. On the contrary, the photoluminescence intensity increases monotonically with the increase in Eu concentration. On application of an electric field, although there is no noticeable shift in the position and shape of the photoluminescence line, a quenching of hypersensitive ⁵D₀ → ⁷F₂ transition is observed. The quenching effect is more evident for lower doping concentration (less than 2.0 at.%) of europium. The emergence of irreversible tetragonal phase, after application of the electric field, is attributed to the quenching of ⁵D₀ → ⁷F₂ transition. Based on these investigations it is concluded that the piezoelectric and photo-luminescence lack one-to-one correlation. The PL response is associated to the local site symmetry around Eu³⁺ and it is independent of the development of long-range ordering.