Enhancement of photoluminescence in manganese-doped ZnS nanoparticles due to a silica shell

Zinc sulphide nanoparticles doped with manganese (ZnS:Mn) have been stabilized using thioglycerol $[{\mathrm{HSCH}}_{\mathrm{2}}{\mathrm{CH(OH)CH}}_{\mathrm{2}}\mathrm{OH]}$ molecules. The nanoparticles (∼1.7 nm) are highly stable and exhibit photoluminescence at ∼600 nm when excited with ultraviolet light. For increasing luminescence and stability the particles are further treated with tetraethylorthosilicate $(\mathrm{TEOS}\mathrm{)[}{\mathrm{Si(C}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{5}}{\mathrm{O)}}_{\mathrm{4}}]$ in an aqueous medium, yielding either a disordered silica matrix or spherical core-shell particles of up to ∼900 nm size with strongly enhanced luminescence under certain conditions. Photoluminescence, excitation spectroscopy, transmission electron microscopy, energy dispersive analysis of x-rays, x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy measurements have been performed for the characterization of the ZnS:Mn nanoparticles alone, in the silica matrix as well as in spherical silica shells. Among other things, the analysis indicates that the thioglycerol capping has been affected by the coating neither in the silica matrix nor in core-shell particles.