Caesium colloids in additively doped caesium halides: kinetics of precipitation and growth

The kinetics of the precipitation and size evolution of Cs colloids in additively coloured CsI, CsBr and CsCl have been studied. In the precipitation stage the dependence of the precipitated volume fraction on the annealing time has been fitted to the expression W=1-exp(-P(t/ tau ) a ). Values of a=1 for CsI and less than unity for CsBr and CsCl have been obtained. From the equilibrium between F centres and colloids, values for the enthalpy of evaporation of F centres from colloids of 0.45 eV for CsI, 0.46 eV for CsBr and 0.52 eV for CsCl have been found in the 430-610K temperature range. From optical absorption measurements, and taking into account different size distribution functions, values of the critical radius R c of the colloids during several sets of isothermal annealings have been obtained. A linear dependence of R c 4 on the annealing time has been observed. A mechanism limited by dislocations or grain boundary diffusion has been proposed both for the precipitation and ripening stages.