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A-site off-stoichiometry has been an efficient method to enhance the electromechanical properties of lead-free Na0.5Bi0.5TiO3(NBT)-based piezoceramics. In this work, we have reported the effect of Na/Bi off-stoichiometry on the microstructural, structural, and electromechanical properties of the tetragonal 0.80Na0.5Bi0.5TiO3–0.20BaTiO3 (NBT–20BT) ceramic. The maximum piezoresponse ~ 115 pC/N is obtained for 4 mol% Na-deficient (20BT–Na46) and 2 mol% Bi-excess (20BT–Bi52) compositions. It is a 25% increment over the piezoresponse of the stoichiometric composition (20BT–Na50 ~ 90 pC/N). The enhancement in piezoresponse has been attributed to an optimized presence of polar-structural heterogeneity/disorder in the poled ceramic matrix and an optimized distortion of the long-range tetragonal ferroelectric phase. It is established that A-site off-stoichiometry is influencing the polar-structural heterogeneity/disorder and tetragonal lattice distortion via the grain size.

In the recent days, rare-earth doped phosphors have attracted an immense attraction in luminescence field for various solid-state lighting and electronic display device applications. However, need of efficient red phosphor is a prevalent challenge in this field. Herein, we report a bright red light emitting Na+ co-doped SrAl2O4:Eu3+ phosphor which is synthesized by modified sol–gel technique. These nanophosphors show excellent red emission due to characteristic 5D0 → 7Fj (j = 1, 2, 3, 4) transitions of the doped Eu3+ ions excited by 394 nm. Photoluminescence studies of both Eu3+ doped SrAl2O4 and Na+ co-doped SrAl2O4:Eu3+ has shown more than fourfold increase in the intensity for optimum Na+ addition. The improved decay time obtained from decay measurement has revealed that the co-doped Na+ has successfully reduced the nonradiative transitions. Thus, addition of monovalent Na+ to Eu3+ doped SrAl2O4 was found to be effective to address the charge imbalance problem along with significant enhancement in luminescence intensity and decay time. The results suggest that this nanophosphor could be a major candidate in the rapidly increasing field of solid-state lighting applications.