应力保持时间对SrAl2O4∶Eu2+应力卸载发光行为的影响

Abstract： SrAl 2 O 4 ∶Eu 2+ is one of the most outstanding mechanoluminescent (ML) materials and has attracted consider• able interest for its applications in stress distribution sensing and structural health monitoring.A systematic investigation of its ML behavior and underlying mechanisms under different mechanical stimuli is essential for guiding practical application.In this study， SrAl 2 O 4 ∶Eu 2+ powders were embedded in an epoxy resin matrix to fabricate composite samples subjected to uniaxi• al compressive stress during compression-release cycles.The ML behavior during unloading after stress loading with different holding time was systematically investigated.The results show that no discernible ML is observed during unloading when the stress holding time is ≤2 s， whereas a pronounced ML peak appears during unloading when the holding time exceeds 2 s.This behavior can be attributed to a trap-mediated mechanism： during the stress-holding stage， the piezoelectric effect induc• es polarized charges on the grain surfaces， driving electrons to be captured by traps near the positively charged regions.With increasing holding time， these traps become progressively filled.Upon stress unloading， the rapid disappearance of the po• larized charges triggers the release of trapped electrons， which subsequently recombine with luminescent centers， giving rise to mechanoluminescence during unloading.In contrast， insufficient trap filling at short holding time prevents observable ML emission.These findings reveal the characteristic stress-unloading ML behavior of SrAl 2 O 4 ∶Eu 2+ and its strong dependence on the stress holding time， providing important insights into the ML mechanism and guidance for its practical applications.