Biaxial strain-induced strong enhancement of upconversion photoluminescence in lanthanide-doped ferroelectric thin films

The ability to manipulate and enhance the optical properties in luminescent materials is of great interest for both scientific research and practical applications. Here we present a systematic study of the effect of biaxial strain on the upconversion photoluminescence properties in lanthanide-doped ferroelectric thin films. Through control of the c/a ratios of BaTiO₃:Er films, the luminescent intensity of the films can be effectively increased by over seven times. The observed phenomenon can be understood in terms of the variation in crystal field around Er³⁺ ions induced by biaxial strain due to the lattice mismatch. Moreover, our results have bridged the identifications of lattice distortion and crystalline orientation through the light emission properties of lanthanide dopants. The intriguing interplay will aid further design of favorable lanthanide-doped phosphors via strain engineering.