Enhancement of impact-induced mechanoluminescence for structure health monitoring using swift heavy ion irradiation

Mechanoluminescence (ML) materials have recently attracted considerable attention due to their potential applications as an imaging sensor for detecting damages and measuring stress distributions in complex structures, which is difficult for conventional methods. SrAl ₂O ₄:Eu ²⁺ (SAOE) is a ML material with the best performance but it hydrolyzes rapidly under humid environment, which limits the scope of its applications especially in outdoor environments, e.g. structural health monitoring for buildings, bridges and tunnels. Thus ML materials with water resistance such as silicates and aluminosilicates have been developed, but the brightness of which is still much lower than SAOE. In this study, we report a novel method to improve the impact-induced ML in ML materials using the swift heavy ion (SHI) irradiation. The impact-induced ML intensity of CaSrAl ₂Si ₂O ₈:Eu ²⁺ was dramatically enhanced by about one order of magnitude using SHI irradiation. Furthermore, higher electronic stopping power and higher irradiation fluence were found to be more effective for improving the impact-induced ML. It is considered that the trap density suitable for the impactinduced ML was increased by the SHI irradiation, resulting in the impact-induced ML enhancement. The underlying mechanism was discussed, which is of great importance for developing new ML materials for structure health monitoring.