Optical and Physical Properties of Silver Colour Centres in Microcrystals in Silver Bromide Films

Abstract

Results are presented of investigations of silver colour centres of molecular and colloidal types arising from the deep photolysis of AgBr microcrystals in ultra-fine-grain emulsions. Using experimental data connecting the position of the absorption maximum of first, secondary and “limited” colour centres, their dimensions and the sizes of the AgBr crystals, values of solubility, partial degree of solubility and surface tension ofAg in AgBr are calculated. Dependence of these values on the dimensions of the AgBr crystals are studied. It is shown that the surface tension increases ivilh the number of atoms in the colloidal particles. The solubility of Ag changes by 6 orders oj magnitude as the colloidal particles decrease from massive to atomic size. Good agreement is shown between the experimental results and the predictions of thermodynamic theory for the nucleation and growth of a new phase. The possibility of a photostimulated phase transition from molecular centres to colloidal ones is considered.