Correlations between mechanical and photoluminescence properties in Eu doped sodium bismuth titanate

• Eu doped Na0.5Bi0.5TiO3 shows a saturation of emission intensity beyond ~12% Bi substitution.
• Sharp recovery of elastic modulus and hardness is also observed at this doping level.
• The above mentioned concurrent phenomena are explained using a nano-phase segregation model.
• Model put forth is supported by nanoindentation, photoluminescence, XRD, and Raman results.

Nanoindentation technique is utilized to examine mechanical property variation in Eu doped Na0.5Bi0.5TiO3 (NBT). Doping levels of Eu in NBT is systematically varied. Dilute doping results in a linear reduction in both modulus and hardness. At higher concentrations, a recovery of the mechanical properties (to undoped NBT values) is observed. These experimental trends mirror variations in the optical emission intensities with Eu concentration. Observed trends are rationalized on the basis of a model, which hypothesizes phase segregation beyond a critical Eu doping level. Such segregation leads to the formation of pure NBT, nano-Eu saturated NBT, and nano-mixed Eu oxides in the microstructure. Pure NBT is optically inactive, while saturated Eu:NBT is a much better emitter when compared to europium oxide. Hence beyond the critical concentration, luminescence signal comes primarily from the saturated Eu:NBT phase. The model presented is supported by nanoindentation, and spectroscopic results.