Mechanoluminescence of SrAl2O4:Eu(+), Dy(3+) under cyclic loading

The mechanoluminescence (ML) of SrAl2O4:Eu(+), Dy(3+) (SAO) has been of particular interest based on the possibility that these materials could be used as nondestructive, reproducible stress (or load) sensors. However, there has been no in-depth study of ML under a cyclic load. It was found that a cyclic load generated harmonics in the ML response. The second harmonic term exhibiting a doubled frequency was significant, but the others could be ignored. In addition, hysteresis behavior was observed in the ML and was examined by comparison with the hysteresis that is typical in piezoelectricity.