Optical quenching of photoconductivity in hexagonal selenium single crystals

The photoconductivity (PC) and the quenching of PC in hexagonal Se single crystals have been studied using símultaneously two radiations with different, wave lengths. Using primary radiation E_nu = 1.85 eV, secondary radiation in the quantum energy range 1.2 ... 1.6 eV at 80 ºK always quenched the PC, but that in the range 0.7 ... 1.2 eV either quenched or increased the PC depending on the type of crystal. When increasing the intensity of the quenching radiation the quenching saturated at about 30 % of PC. With constant weak quenching intensity the quenching in Omega^-1 was inversely proportional to the intensity of the primary radiation. Quenching only occurs at temperatures below ca. 200 ºK. At least two types of centers are effective in these excitations.