COMPARISON OF BISTABLE LIGHT-EMISSION OF A THIN CDS-CU FILM MEASURED IN REFLECTION AND TRANSMISSION GEOMETRY

All-optical photo-thermally induced bistabilities in luminescence of a thin (10 mu m) CdS:Cu film were studied at 170 K. The bistable effect was induced by the 514.5 nm line of an argon laser and measured by pu tting low-pass filters for yellow and red light in the reflected and t ransmitted beams. In the visible part of the spectrum, the loop contra sts measured in reflection geometry are considerably smaller than thos e achieved in transmission geometry. In the near infrared, however, th e loop contrasts do not depend on the geometry used. This is due to th e observation that visible emissions from the surface region depend le ss sensitively on temperature than do those from the bulk.