Electron Spin Resonance and Optical Studies on Copper-Doped AgCl

Upon exposure at room temperature, large, strain-free AgCl crystals containing up to ${10}^{17}$ cuprous ions per ${\mathrm{cm}}^3$ show a stable darkening (print-out) and an electron spin resonance (ESR) absorption which is characteristic of cupric ions. The intensity of the print-out band and of the ESR signal are proportional. Essentially all the cuprous ions are converted to cupric ions by prolonged exposure. For well-annealed crystals, the cupric ESR signal is stable below 180°C in exposed samples and stable below 280°C in halogenated samples, showing that the cuprous ion is a deep hole-trap at room temperature. When the samples are deliberately strained, there are rapid decays in the ESR signal at room temperature. Evidence from ESR suggests that such decays are related to coagulation of cupric ions. Exposure at -180°C converts some cuprous to cupric ions without associated vacancies. Total conversion of cuprous to cupric ions by exposure at room temperature is not obtained in samples containing higher copper concentrations. It is suggested that, at sufficiently high concentrations, cupric ions can compete with intrinsic electron traps, thereby limiting the maximum ESR signal and darkening produced by exposure to smaller values than those expected on the basis of studies of samples with low copper concentration.