Preparation of nanosheets embedded ZnSe/Bi2Se3 core/shell quantum dots for the study of optical properties and antibacterial activity

Cation exchange reaction is a well-known ion exchange method that is very much feasible for easy synthesis procedure and greater tunability in size and shape of nanomaterials. Here, we have synthesized different water dispersed ZnSe/Bi2Se3 core/shell quantum dots by using the cation exchange method with varying Bi content. The variation in Bi concentration allows the change in shell thickness which ultimately affects the structural and optical behaviors. The ZnSe/Bi2Se3 quantum dots exhibited type II band alignment. The as-prepared quantum dots embedded nanosheets exhibit broad, amorphous XRD pattern of the ZnSe phase. A shift in the peak position of the XRD pattern as well as Raman vibrational bands with varying Bi content suggests the formation of the Bi2Se3 shell. Also, the shifting among the XPS peaks confirms the change in the chemical environment of both Zn-Se and Bi-Se bonds in the hybrid system. This ensures the Se ions on the surface of ZnSe coordinated the bismuth complex. The increase in shell thickness enhances the band edge absorption and reduces the optical bandgap which is due to the increase in the particle size of the sample. A broad photoluminescence emission is observed for all the cases with 514 and 325 nm excitation. Each broad spectrum is comprised of different component peaks corresponding to excitonic and defects (vacancies and interstitials) related emission. The core/shell materials are most suitable for different biomedical applications. Hence, the ZnSe/Bi2Se3 quantum dots are analyzed for antibacterial activity, which showed a good antibacterial response against Staphylococcus aureus (ATCC 25,923).