Abstract
Enhanced photoluminescence (PL) is reported from Mn-doped ZnS nanocrystals (NCs) capped with ZnS (ZnS:Mn/ZnS core-shell NCs) and thioglycolic acid (TGA) (ZnS:Mn/ZnS core-shell NCs dispersed in an alkaline TGA solution). The NCs were prepared using a reverse micelle route. Comparing with initial ZnS:Mn core NCs, the ZnS:Mn/ZnS core-shell NCs exhibit much stronger orange PL (~580 nm). This is presumably the result of effective passivation of quenching ZnS:Mn NCs surface states by a pure ZnS shell. As for TGA-capped ZnS:Mn/ZnS core-shell NCs, the parallel decrease of a defect-related emission of ZnS is associated with the formation of a shell surface layer of TGA-Zn complexes. In summary, the combination of ZnS shells with TGA ligands was demonstrated to yield ZnS:Mn NCs with narrow size distribution and intense PL.
Highlights
Doped semiconductor nanocrystals (NCs) have been studied extensively in the past few decades since Bhargava [1] reported that ZnS:Mn2+ NCs exhibit high-luminescence quantum efficiency in 1994
Yang and Holloway reported on highly luminescent and photostable yellowemitting CdS:Mn/ZnS core-shell NCs [12]. They indicated that the intense PL of the NCs is based on the effective passivation of CdS:Mn core surface states by a ZnS shell
Because individual Mn impurities are most incorporated in NCs with zincblende structure by adsorbing on their (001) facet [4], ZnS NCs with zinc-blende structure are most desirable to enhance Mn2+ emission
Summary
Doped semiconductor nanocrystals (NCs) have been studied extensively in the past few decades since Bhargava [1] reported that ZnS:Mn2+ NCs exhibit high-luminescence quantum efficiency in 1994. Yang and Holloway reported on highly luminescent and photostable yellowemitting CdS:Mn/ZnS core-shell NCs [12] They indicated that the intense PL of the NCs is based on the effective passivation of CdS:Mn core surface states by a ZnS shell. Enhanced PL is observed when Mn-doped ZnS NCs are capped with an effective passivation layer, such as ZnO [14] or SiO2 [15]. These inorganic capping agents saturate the surface dangling bonds and substantially reduce the nonradiative centers of the NCs. When dispersed in liquids, solvent molecules can act as passivators as well. We investigated the effect of the concentration and pH of TGA solutions on the dispersion because TGA is stable in alkaline solution [22]
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