Tunable self-recoverable near-infrared mechanoluminescence from platelike strontium-aluminate: SrAl<sub>12</sub>O<sub>19</sub>:Cr<sup>3+</sup>

The development of high-performance self-recoverable near-infrared (NIR) mechanoluminescent materials is crucial for advancing applications. In this work, we presented a self-recoverable NIR mechanoluminescent material, platelike SrAl₁₂O₁₉, through singly doped with Cr³⁺ and co-doped with lanthanide ions (Nd³⁺, Yb³⁺, Er³⁺) in one step. By modulating the Cr³⁺ doping concentration, we achieved precise control over the mechanoluminescence (ML) intensity as well as the spectral tunability between characteristic R-line emission (~ 690 nm) and the broadband emission (750-950 nm). Moreover, energy transfer from Cr³⁺ to lanthanide ions enables multispectral ML emission extending into the NIR-II window (1,000-1,700 nm). The resultant material exhibits excellent ML self-recoverability and high chemical stability. The co-doped system was demonstrated with great potential in dynamic stress visualization, naked-eye-invisible information encryption and special identification under challenging conditions (e.g., underwater). We further demonstrated practical applications by fabricating dual-mode flexible NIR mechanoluminescent paper sheets and sprayable coatings. This work contributes to the advancement of new NIR mechanoluminescent materials with unique morphological features for various scenarios, including the advancement of intelligent sensing and multi-level anti-counterfeiting technologies.