Effect of synthesis temperature on the structure and optical properties of Zn-doped CdS nanoparticles

Zinc-doped CdS nanoparticles have gained significant attention due to their tunable optical properties. Substitution of CdS with higher band gap Cd_xZn_1-xS alloys has resulted in a reduction of the window absorption losses and an enhancement of the short circuit current. It is a potential material for solar cell applications surpassing the efficiency of pure CdS and ZnS. In our work, nanostructures of undoped and Zn-doped CdS were synthesized via the hydrothermal method with varying reaction temperatures. Structural properties were analysed using XRD patterns of the samples, which indicated the successful formation of hexagonal crystal structures of CdS nanoparticles. FESEM images further confirm these results and show the formation of CdS particles in the nano regime. Results of the optical characterization techniques, namely UV–Vis diffuse reflectance spectroscopy, suggest that in the case of Zn-doped CdS samples there is an increase in the band gap value due to the formation of Cd_xZn_1-xS. Photoluminescence studies of the doped and undoped samples indicate a blue shift of the band edge luminescence due to Zn doping, while variation in peak positions is observed with changes in the synthesis temperatures. The intensity ratio (i.e., ratio between band edge luminescence and defect luminescence) is enhanced with an increase in synthesis temperature; this defect luminescence is attributed to the formation of CdO acceptor levels. Raman spectra of the samples show vibrational modes of the doped and undoped samples. Here, the blue shift observed is attributed to the incorporation of zinc atoms in the CdS lattice.