Strong Mechanoluminescence from UV-Irradiated Spinels of ZnGa2O4:Mn and MgGa2O4:Mn

The mechanoluminescence (ML) from spinels of MgAl 2 O 4 :Mn (MAO:Mn), MgGa 2 O 4 :Mn (MGO:Mn) and ZnGa 2 O 4 :Mn (ZGO:Mn) has been investigated. It was found that the MGO:Mn and ZGO:Mn gave a strong ML response and a long-lasting phosphorescence (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 thermoluminescence. The carrier traps in MGO:Mn and ZGO:Mn are assumed to be produced by the point defects due to the partially inverse spinel structure and the oxygen vacancies generated by heat-treatment in a reducing atmosphere. It is suggested that the trapped electrons in oxygen vacancies can be excited by the application of friction, and the resultant recombination between the excited electrons and the trapped holes in the point defects gives rise to an energy which can be transferred to Mn 2+ centers to produce the green emission according to the transition 4 T 1 ( 4 G )→ 6 A 1 ( 6 S ).