Room temperature visible photoluminescence from undoped ZnS nanoparticles embedded in SiO2 matrices

Thin films of ZnS nanoparticles embedded in SiO2 matrices were prepared by the pulsed laser deposition method using a rotating target. The as-prepared samples contained dispersed ZnS nanocrystallites mostly of less than 8 nm in diameter embedded in the SiO2 host. The nanoparticle size of the film increased with increasing sample annealing temperature and/or duration in the vacuum. Room temperature visible photoluminescence (PL) was found from the films without the need for any dopant. Contrary to the usual redshift following annealing, there was, instead, a blueshift of the PL which increased with increasing sample annealing. The mechanism of the PL and its blueshift is attributed to the S vacancies and the formation of ZnS(O2−) in the surface layers of the nanoparticles adjacent to the SiO2. The S vacancies arose partly from the laser ablation during the film preparation stage, and partly from the S-bond disruption at the surface of the ZnS particles during annealing. The ZnS(O2−) could be formed by the ...