Huge enhancement of upconversion photoluminescence in In3+ doped Ba0.85−xCa0.15TiO3:0.75%Er3+/xIn3+ lead-free ferroelectric ceramics

Enhanced green and red upconversion emissions under 980 nm excitation are observed in Ba0.85−xCa0.15TiO3:0.75%Er3+/xIn3+ lead-free ferroelectric ceramics which were synthesized by solid state reaction method. With increasing In3+ ions doping level from x = 0% mol the green and red emission intensities increase and reach the maximum at x = 1.75% mol. The maximum intensity of green emission at 550 nm is 20 times larger than In3+ ions undoped samples, which is unprecedented for Er3+-doped perovskite ferroelectric materials. Based on the ultraviolet-visible-near infrared absorption spectra, the enhancement of the luminescence intensity of the A-site In3+ doped Ba0.85−xCa0.15TiO3:0.75%Er/xIn ceramics is attributed to In3+-doping-induced relative increase in isolate Er3+ and decrease in the clustered-Er3+. The effects of In3+ doping on the crystal structure, dielectric, ferroelectric, piezoelectric properties of the ceramics were also studied and discussed.