Self-Recoverable Mechanically Induced Instant Luminescence from Cr³⁺-Doped LiGa₅O₈

Currently, most of the mechanoluminescence (ML) phosphors strongly depend on postirradiation stimulation using ultraviolet light (denoted as “UV exposure” from hereon) to show the ML. However, only a few transition metal cations are proven to be effective luminescence centers, which hinder the development of more ML phosphors. This study reports a self-recoverable deep-red-to-near-infrared ML using Cr³⁺-doped LiGa₅O₈ phosphor with fully recoverable ML performance. The ML performance can be further optimized by tuning the trap redistributions by codoping the phosphor with Al³⁺ and Cr³⁺ cations. Theoretical calculations reveal the important role of Cr dopants in the modulation of local electronic environments for achieving the ML. Owing to the induced interelectronic levels and shallow electron trap distributions, the electron recombination efficiency is enhanced both through direct tunneling and energy transfer toward the dopant levels. Moreover, the ML of Cr³⁺-doped LiGa₅O₈ can penetrate a 2-mm-thick pork slice, showing that it can have wide-ranging in vivo applications, including the optical imaging of intracorporal stress/strain distribution and dynamics. Therefore, this work fabricates a novel ML material with self-recoverable luminescence in an extended wavelength range, increasing the number of potential ML candidates and promoting the fundamental understanding and practical applications of ML materials.