抄録
Copper-doped zinc sulfide nanoparticles (ZnS: Cu NPs) were synthesized in aqueous solution over specific ranges of feed concentrations. The primary objective of this study was to elucidate the effects of crystalline size and dopant density of the ZnS: Cu NPs, besides the state of surface defects, on their photoluminescence (PL) properties. The dopant density-an intrinsic content of the doped Cu per ZnS-was found to be 58% of the fed dopant ratio, irrespective of the latter value as well as the other feed ratio examined. The high intensity of PL observed for both undoped and Cu-doped ZnS-blue PL occurring near 420nm and green PL near 510nm, respectively-was only detected under large excess of the feed zinc content, indicating that the relevant PL occurs only in the prevalence of surface sulfur vacancy residing between ZnS band gap and acting as a donor to the ZnS valence band and Cu2+ level, respectively. With decreasing crystalline size of ZnS: Cu (as well as ZnS), the PL intensity tended to increase since the number of sulfur vacancies, in proportion to the surface area, available for a given particle mass was increased; a further decrease in the crystalline size below 2.5nm, however, resulted in an asymptotic value of PL intensity for a given dopant content, signifying the number of vacancies having reached a sufficient/required level. With increasing dopant density, more specifically, number of Cu2+ ions contained in one ZnS crystal, the PL intensity tended to increase, while an excess number of dopant ions tended to reduce the intensity due probably to a distortion in crystalline structure; an optimum number of copper ions was found to be at most unity in each ZnS crystal.
