Strong mechanoluminescence from UV-Irradiated spinels of ZnGa2O4 : Mn and MgGa2O3 : Mn

The mechanoluminescence (ML) from spinels of MEAl2O4:Mn (MAO:Mn), MeGa2O4:M n (MGO:Mn) and ZnGa2O4:Mn (ZGD:Mn) has been investigated. It was found that the MGO:Mn and ZGO:Mn gave a strong ML response and a long-lasting phospho rescence (LLP). On the contrary, MAO:Mn exhibited very weak ML and no LLP. The high ML intensity of MGO:Mn and ZGO:Mn is attributed to a large number of trapped carriers which has been clarified by the measurement of thermolu minescence. The carrier traps in MGO:Mn and ZGO:Mn are assumed to be produc ed by the point defects due to the partially inverse spinel structure and t he oxygen vacancies generated by heat-treatment in a reducing atmosphere, I t is suggested that the trapped electrons in oxygen vacancies can be excite d by the application of friction, and the resultant recombination between t he excited electrons and the trapped holes in the point defects gives rise to an energy which can be transferred to Mn2+ centers to produce the green emission according to the transition T-4(1)((4)G) --> (6)A(1)(S-6).