Luminescence During Friction Between Diamond and Quartz in Low Vacuum (10-103 Pa)

We measured spectra of light-emissions during sliding friction between diamond and quartz in ambient gases of He, Ne, and Ar at 10-103 Pa. Two types of the light emission were observed; one has a band spectrum specific to each gas and the other has a continuous spectrum from 300 to 600 nm. The shape of the latter spectrum was almost the same for all the ambient gases while the pressure dependence of the intensity differed from gas to gas. The continuous spectrum is highly similar to that of photoluminescence caused by the oxygen vacancy in quartz. Microscopic spectroscopy revealed that the source of the continuous spectrum was on the friction track in the electric discharge region. Experimental results suggest that electrons or ions in the gas discharge stimulate the oxygen vacancy in quartz.