NIR Mechanoluminescence from Cr ³⁺ Activated Y ₃Al ₅O ₁₂ with Intense Zero Phonon line

Mechanoluminescence (ML) materials with long-wavelength emission bands are essential for future in vivo bioimaging, non-destructive testing of solids, etc. The lack of a defined mechanism, however, prevents the application of near infrared ML materials above 650 nm in several new fields. Here, the addition of Ga³⁺ ions to Y₃Al₅O₁₂: Cr³⁺ manipulates matrix microstructure evolution, boosting near-infrared (NIR) zero-phonon line (ZPL) stress optical output of the Cr³⁺ ion at 688 nm. The key factor changing the crystal field intensity D_q/B due to the addition of Ga³⁺ ions is what causes the luminescence amplification of ZPL. The ML fabricated by composite polydimethylsiloxane and Y₃Al₄GaO₁₂: Cr³⁺ (YAGG: Cr³⁺) may penetrate chicken feet epidermal tissue and 4 mm pork tissue thanks to the strong NIR ZPL emission of YAGG: Cr³⁺ phosphor. This discovery of enhancing near-infrared ZPL intensity by solid solution provides us with a new technique for optimizing NIR ML materials, as well as a new prospect for NIR ML materials in biological applications.