High electrical properties and good upconversion luminescence in SrBi1.94-xEr0.06YbxNb2O9 lead-free piezoelectric ceramics

Abstract

SrBi1.94-xEr0.06YbxNb2O9 (x = 0.000, 0.002, 0.004 and 0.006, noted as SBEN-xYb) composites were prepared using traditional solid-phase sintering technology. The influences of (Er, Yb)3+ co-doping on the electrical and luminous properties as well as energy band structure of SrBi2Nb2O9 (SBN) ceramics were systematically investigated. The outstanding comprehensive characteristics with low dielectric loss (tanδ ~ 0.073%), high remnant polarization (2Pr ~ 10.73 μC/cm2), large piezoelectric responses (d33 ~ 15 pC/N) and excellent upconversion photoluminescence (UC-PL) are simultaneously observed by Yb doping with a concentration of x = 0.004. The UC-PL spectrum excited by 980 nm laser shows double bands at 533 nm and 554 nm in the green region, and single band at 672 nm in the red region. A density functional theory (DFT) calculation was performed to reveal the physical origin of electrical conductivity and UC-PL. It is seen that the band gap consistently decreases, while the contribution from f state of (Er, Yb)3+ is intensified with increasing Yb3+, elaborating the variations of electrical conductivity and UC-PL intensity. Related mechanisms for the improvement of UC-PL and electrical properties were discussed.