The photodecomposition of lead iodide

A study of optical absorption, photoconductivity and photodecomposition in lead iodide has indicated that excitons are produced by the interaction of visible light with this material. These excitons are mobile and interact with lattice defects to produce chemical decomposition. The experiments on photodecomposition described in this paper are consistent with a mechanism in which two excitons react at a preferred site to give a molecule of iodine, two anion vacancies and a lead atom. The preferred sites are thought to be anion vacancies situated at surface imperfections. The factors influencing the growth of these centres of decomposition from atomic to microscopic dimensions are discussed. The exciton mechanism is consistent with observations on both the distribution of decomposition products and the kinetics of the decomposition process. A number of images, recorded on lead iodide, are reproduced in this paper to demonstrate the potential applications of the decomposition process in the fields of image recording and high resolution photography.