Luminescent–electrical–magnetic performances of sol–gel-derived Ni²⁺-modified Bi_0.5Na_0.5TiO₃

2.5 mol% Ni²⁺-modified Bi_0.5Na_0.5TiO₃ (BNT–Ni-0.025) ceramic has been fabricated based on the sol–gel method. The BNT–Ni-0.025 ceramic possesses a rhombohedral perovskite structure with denser microstructure than that of pure BNT ceramic. The introduction of certain amount of Ni²⁺ (e.g. 2.5 mol%) in BNT can reduce the sintering temperature (50 °C lower), effectively suppress the grain growth, greatly decrease the dielectric loss and then produce multifunctionality. The BNT–Ni-0.025 ceramic also exhibits good ferroelectric properties with a large remanent polarization of ~26 μC/cm². The observed weak ferromagnetism of the ceramic can be ascribed to the exchange interaction between free carriers (oxygen vacancy induced delocalized electrons) and the localized Ni²⁺ ions. Under the excitation of 370 nm, the BNT–Ni-0.025 ceramic shows broadband NIR luminescence centered at ~1480 nm from Ni²⁺ with long emission lifetime (28 µs), which can cover the optical communication window and be applied in broadband optical amplifiers. The multifunctional BNT–Ni-0.025 ceramic shows potentials in the application of optical–electrical–magnetic areas.