Periodic triboluminescence of zinc sulphide

Powdered ZnS-Mn (Cu, Ag) was scattered in the form of a suspension in different solids. The mechanical excitation of triboluminescence was periodic with a frequency of 50 Hz. The resultant triboluminescence is also periodic if the exciting pressure does not exceed 700 kg/cm2. The creation of triboluminescence does not depend on the kind of surrounding medium.