Improved piezoelectric and bright up-conversion photoluminescent properties in Ho-doped Bi0.5Na0.5TiO3–BaTiO3 lead-free ceramics

Lead-free ceramics of 0.94(Bi1−x Ho x Na)0.5TiO3–0.06BaTiO3 have been prepared by a conventional solid reaction method and their piezoelectric, ferroelectric and photoluminescent properties have been studied. After the partial substitution of Ho3+ for Bi3+, a new Bi0.5Na0.5TiO3-based solid solution with a pure perovskite structure is formed. The doping of Ho3+ has no obvious influence on the crystal structure of the ceramics. After the addition of a small amount of Ho3+ (x = 0.015), the piezoelectricity (d 33 = 187 pC/N, k p = 41.1 %, respectively) and ferroelectricity (P r = 25.2 μC/cm2) of ceramics are enhanced. The down-conversion and up-conversion photoluminescence of the ceramics are observed. A green down-conversion emission band at 548 nm is observed which is from the 5S2 → 5I8 transition of Ho3+; the main down-conversion excitation bands located at 410–500 nm is due to the 5I8 → 5G5, 6 transitions, and the maximum brightness of down-conversion photoluminescence are obtained at x = 0.015. The ceramic with x = 0.01 exhibits the maximum value of the up-conversion emission at 475 nm, which is attributed to the 5F3 → 5I8 transition. Our study shows that the ceramics with x = 0.01–0.02 exhibit simultaneously good piezoelectricity, strong ferroelectricity and excellent photoluminescence, suggesting a potential application in the electro-optic devices.