Diffusion of Pr³⁺ ions in silver halide crystals

The diffusion of Pr³⁺ ions in AgBr and AgCl_0.77Br_0.23 single crystals has been investigated by a method based on measuring the luminescence intensity distribution along the diffusion direction. The diffusion constants D₀ for these crystals were 3.8×10^-6 and 7.95 cm²/s; and the enthalpy of diffusion H values were 0.4 and 1.25 eV, respectively. A strong influence of the silver halide composition on Pr³⁺-ions diffusion parameters was observed. The low value of the diffusion enthalpy found for these ions is described in terms of an associated complex 3⁺-ion - cation vacancy motion by an exchange mechanism. The influence of the radius of the rare earth ions on the diffusion enthalpy is discussed.