One-photon processes of latent image formation in silver halides

Abstract

A new one-photon process for latent image formation in silver halides is proposed. The model is an extension of the theoretical concepts of Gurney-Mott, Hamilton and Lowe. Hamilton proposed a four-photon mechanism for the photochemical formation of Ag₄ latent image centres. Subsequently, Lowe developed a two-photon mechanism, which includes hole trapping by Ag₂ reduction centres. Mitchell proposed a two-photon mechanism based on the presence of electron trapping Ag₂ centres that act as sublatent image centres. One-photon latent image formation was proposed which relied on gold-containing electron-trapping centres; however, these mechanisms were considered to be fogging mechanisms. From the concepts of the previous mechanisms, a one-photon latent image mechanism is proposed that does not result in fog. This one-photon process is based on the presence of both electron and hole-trapping Ag₂ centres on the same crystal before exposure. Both photoelectron and photohole, which arc formed by light absorption, participate in this mechanism. The required electron-hole energy separation is estimated to be about 1.4 eV and is thus well above the thermal energy at room temperature (about 0.03 eV). Experimental evidence for one-photon processes in silver halide systems supports the proposed one-photon mechanism for Ag₄ latent image formation.