ESR on UV Irradiated Lead Halides at 80° K

Results are presented of electron spin resonance measurements on uv irradiated single crystals of PbCl2, PbBr2, and PbI2 at liquid nitrogen temperature. Both pure single crystals and PbBr2 crystals doped with Tl+, Ag+, Cu+, and Bi+++ ions are studied. The ESR spectra indicate that Pb+ ions occur as an initial step in the photochemical decomposition. These ions are probably present in clusters of two or three and coagulate to metallic lead particles. The ESR signals due to the conduction electrons of these small lead particles are studied. Some hole centres which are formed during the irradiation are also described. The experiments show that the ambient conditions of the crystals are much more important in the photolysis process than the presence of foreign ions.