Recovery phenomenon of mechanoluminescence from Ca2Al2SiO7:Ce by irradiation with ultraviolet light

We have investigated the mechanoluminescence (ML) from ${\mathrm{Ca}}_{\mathrm{2}}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{SiO}}_{\mathrm{7}}:\mathrm{Ce}.$ The ML is clearly visible to the naked eye in the atmosphere. The luminescence integrated intensity is about 400 times as high as that of crystal sugar. The ML center has been identified as the ${\mathrm{Ce}}^{\mathrm{3+}}$ ion from spectra of the ML and also from the photoluminescence studies of ${\mathrm{Ca}}_{\mathrm{2}}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{SiO}}_{\mathrm{7}}:\mathrm{Ce}.$ The ML intensity decreases on repetitive application of stress but is completely recovered by irradiation with ultraviolet light. It is suggested that the ML mechanism arises from the movement of dislocations and recombination between electrodes and holes released from these traps which are associated with the ${\mathrm{Ce}}^{\mathrm{3+}}$ centers.