Realizing Near Infrared Mechanoluminescence Switch in LAGO:Cr Based on Oxygen Vacancy

Mechanoluminescence (ML) materials are featured with the characteristic of "force to light" in response to external stimuli, which have made great progress in artificial intelligence and optical sensing. However, how to effectively enable ML in the material is a daunting challenge. Here, a Lu₃Al₂Ga₃O₁₂:Cr³⁺ (LAGO: Cr³⁺) near infrared (NIR) ML material peaked at 706 nm is reported, which successfully realizes the key to unlock ML by the lattice-engineering strategy Ga³⁺ substitution for Al³⁺ to "grow" oxygen vacancy (O_v) defects. Combined with thermoluminescence measurements, the observed ML is due to the formation of defect levels and the ML intensity is proportional to it. It is confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance that such a process is dominated by O_v, which plays a crucial role in turning on ML in this compound. In addition, potential ML emissions from ⁴T₂ and ²E level transitions are discussed from both experimental and theoretical aspects. This study reveals the mechanism of the change in ML behavior after cation substitution, and it may have important implications for the practical application of O_v defect-regulated turn-on of ML.