Characteristics of preflashover light emission from dielectric surfaces in vacuum

Luminescence from dielectric surfaces during preflashover in vacuum was observed under pulse excitation. By preflashover luminescence, we mean light emission under no flashover conditions. Study of light emission with respect to electrode configurations and spacing between the two electrodes shows that preflashover light emission is related to electron emission from the cathode and trapping/detrapping processes on the dielectric surface layer. Spectroscopic observations of the light emission indicate that the preflashover spectrum changes from one voltage shot to another voltage shot of the same amplitude and that the spectral distribution of the light emission depends on the dielectric material used. We believe that the light emission from preflashover is electroluminescence which may be attributed to de-excitation of excited species in the surface layers of the dielectric material