Coverage ability of silver sulfide nanoparticles in sulfide composites

Sulfide composites ZnS/Ag$_2$S with various contents of silver sulfide have been synthesized by chemical co-deposition. The sizes of ZnS and Ag$_2$S nanoparticles in ZnS/Ag$_2$S composites containing less than $1.0$ mol % Ag$_2$S are $\sim4$ and $<3$ nm, respectively. The introduction of silver sulfide in ZnS/Ag$_2$S composites leads to the deposition of Ag$_2$S on the surface of ZnS nanoparticles. The doping of ZnS nanoparticles by only $1$ mol % Ag$_2$S nanoparticles is enough to form a covering silver sulfide shell on the surface of ZnS nanoparticles.