Bright Chromium‐Sensitized Lanthanide NIR‐II Mechanoluminescence in a Piezoelectric Oxide

Abstract Near‐infrared (NIR) luminescent materials are critical components of high‐performance optical devices for frontier applications in anti‐counterfeiting, non‐destructive analysis, and deep‐tissue imaging. In this work, a bright Cr 3+ ‐sensitized lanthanide NIR‐II mechanoluminescence (ML) is developed in piezoelectric β‐Ga 2 O 3 . Specifically, a nearly complete energy transfer (ET) from highly doped Cr 3+ ions to Yb 3+ and Er 3+ acceptors is observed, resulting in pronounced ML at 1002 and 1542 nm. The NIR‐II luminescence intensity is further improved by cation alloying due to the promotion of octahedral distortion, culminating in 5.9‐ and 3.0‐fold stronger ML emissions compared to the well‐established CaZnOS:Yb 3+ and CaZnOS:Er 3+ , respectively. Furthermore, mechanistic investigations revealed that the ML behavior with high dopant concentration is enabled by strain‐induced piezoelectric potential without the involvement of trapping states, thus exhibiting exceptional cycling stability. Finally, an innovative multi‐level encryption framework is established for information protection with wavelength‐selective readout capabilities by optical or mechanical excitation.