Multilevel Trap-Controlled Bright Mechanoluminescence of Sr/CaGa2S4: Eu2+ for Stress Sensing Applications

Abstract

Brighter, recoverable, and more practical green mechanoluminescence (ML) materials are urgently required in diverse fields such as visual stress sensing and advanced display lighting. Ce³⁺/Eu²⁺ doping, leveraging efficient f-d transition, remains one of the most promising approaches for achieving high-performance green ML. However, intense competition between afterglow and ML necessitates precise control of trap depths to develop high-brightness and recoverable ML materials in Ce³⁺/Eu²⁺ doped trap-controlled systems. In this work, the concept of multilevel trap control is introduced into Eu²⁺-doped MGa₂S₄ (M = Sr, Ca) materials and, for the first time, elucidate the mechanism underlying irradiation-induced ML recovery in powdered MGa₂S₄: Eu²⁺ (M = Sr, Ca) materials dominated by shallow-level traps. By optimizing activator doping concentration, depth and distribution of multilevel traps are effectively fine-tuned, achieving remarkable ML peak intensity compared with renowned SrAl₂O₄ materials (~57.3% for SrAl₂O₄: Eu²⁺, Dy³⁺, and ~84.3% for (Sr, Ca)Al₂O₄: Eu²⁺, Dy³⁺) while minimizing afterglow interference. Finally, the practical application potential of SrGa₂S₄:Eu²⁺ is demonstrated by employing fluorescent coatings to visualize crack propagation and stress distribution in construction materials. This study explores broader potential applications of SrGa₂S₄: Eu²⁺ in ML technologies and offers novel insights and strategies for developing high-performance ML materials.