Influence of Organic Polymers as Capping Agent on Structural and Optical Properties of ZnS:Mn²⁺ and CdS Nanocrystals

We have synthesized the luminescent ZnS:Mn²⁺ and bare CdS nanocrystals by employing polyvinyl alcohol (PVA), citric acid (CA) and biotin as organic capping agents by chemical co-precipitation route. The synthesized materials were characterized by X-ray diffraction, small angle X-ray scattering and transmission electron microscopy for the structural analysis, while UV-Visible spectroscopy and photoluminescence (PL) for optical properties. The results show that all the three organic polymers have the same effect and are capable of controlling the growth of the nanoclusters. From UV-Visible absorption spectra, it was observed that different capping agents do not affect the band gap of ZnS:Mn²⁺ system as well, while capping effect clearly observed on PL properties of ZnS:Mn²⁺ system. We have observed a novel result that capping with biotin show excellent photo-luminescence as compared to capping of PVA and CA on ZnS:Mn²⁺-systems. On the other hand, the annealing of these systems leads to degradation of luminescence intensity.