Study of the percolation effect in the luminescent structure of ZnS:Cu,Br phosphors on improving their radioluminescence

Solid-phase synthesis of ZnS-based luminescent material enclosing the associative luminescence centres formed by the dopant atoms of copper and bromine Cu’Zn-BrS● is discussed. Annealing the powder mix of ZnS, CuCl, and NH4Br in reducing atmosphere provides the diffusion and volume distribution of Cu+ and Br- ions in the two-phase ZnS matrix.
It was stated experimentally in five series of the synthesized phosphors that ZnS:Cu,Br forms the combined sphalerite--wurtzite crystal structure and the intensity of radioluminescence given by the Cu’Zn-BrS● associates sharply increases at a certain content of the wurtzite phase in ZnS structure 1.
A description of this phenomenon can be provided by the percolation theory instruments. The formation of the long interphase boundary between sphalerite and wurtzite phases in the phosphor grain of ZnS matrix as a percolation infinite cluster analogue results in the grain boundary diffusion rate increasing and an improvement in the luminescence centres' forming ability on the intercrystalline borders. Associated defects migrating through the volume of the crystal to its surface provide the surface luminescence centres and improve tritium radioluminescence.
Computer modelling of the diffusion process in the discussed system was conducted and a descriptive model of structure defect migration through the two-phase phosphor structure was developed. The application of this approach in solid-state physical chemistry provides an additional tool for controlling the structure and properties of functional materials.