Reversible modulation of photoenergy in Sm-doped (K0.5Na0.5)NbO3 transparent ceramics via photochromic behavior

Abstract

By simply doping with a certain amount of Sm³⁺, opaque lead-free (K_0.5Na_0.5)NbO₃ piezoelectric ceramics were fabricated into transparent/translucent ceramics. The photochromic (PC) behavior and associated reversible transmittance/luminescence modulation were realized via physical means. Upon illumination under a xenon lamp, the maximal decreased values of optical transmittance and luminescence intensity are 36.1% and 49%, respectively. Meanwhile, the colors of all the ceramics turn darker after illumination, and subsequently return to their initial states by thermal stimulus (200 °C for 5 minutes), exhibiting a typical PC phenomenon. Combining experimental and calculation results, it can be found that the PC mechanism is closely related to the vacancy defects induced by both high-temperature sintering and Sm³⁺-doping. Additionally, the Sm³⁺ effects on phase structures, microstructures, optical transmittance and photoluminescence properties of the ceramics were systematically studied. The substitution behavior of Sm³⁺ and vacancy defect concentrations on the energy band gap of the material were unraveled by the first principles calculations to further clarify the corresponding mechanism. The Sm³⁺-doped (K_0.5Na_0.5)NbO₃ transparent ceramics have potential for application in modulation and conversion of photoenergy, such as in optical memory and photo-switching devices. And the reversible tuning of transmittance in our material is especially attractive for exploring novel transparent PC materials.