Exploration about superior anti-counterfeiting ability of Sm³⁺ doped KSr₂Nb₅O₁₅ photochromic ceramics: Origin and atomic-scale mechanism

Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with great potential in anti-counterfeiting and data storage applications. Here, Sm³⁺-doped KSr₂Nb₅O₁₅ photochromic ceramics exhibit superior anti-counterfeiting ability: good covertness and considerable modulation ratio of luminescent emission intensity after photochromic reaction. The results show that the photochromism originated from oxygen and cation vacancies, which were directly identified by electron paramagnetic resonance and positron annihilation lifetime spectra. Unexpectedly, oxygen vacancies work more effectively than cation vacancies during photochromic reactions. Moreover, the extraordinary anti-counterfeiting ability was attributed to the high energy transfer rate, which was particularly caused by the short mean distance below 1 nm between the Sm³⁺ and vacancies. The work here has provided atomic-scale structural evidence and made a progress in understanding the photochromic origins and mechanism in color-center theory.