A PHOTOGRAPHIC STUDY OF THE HIGH-TEMPERATURE PHASE OF SILVER-IODIDE

Coatings of beta-phase silver iodide have poor photographic response, but when exposed at temperatures high enough to convert AgI to its alpha-phase, their photographic response is significantly improved. This increase in sensitivity is due not only to the longer wavelength of the absorption edge of the alpha-phase, but also to a change in quantum efficiency. The AgI of coatings that had been heated and rapidly cooled had changed from pure beta-phase into a mixture of 2H (beta-phase) and 7H polytypes. These coatings showed an enhanced room temperature response attributed to sulfur sensitization and electron-hole separation caused by the induced crystal defects, including mixed phases.