Biphasic quantum dots of cubic and hexagonal Mn doped CdS; necessity of Rietveld analysis

Mn2+ doped CdS quantum dots (QDs) were prepared via a simple chemical synthesis method. Incorporation of Mn ions into CdS QDs was monitored by structural, magnetic and optical spectroscopy analysis. Although the diffraction patterns seemed to be single wurtzite hexagonal structure, analysis revealed biphasic composite of CdS QDs hexagonal wurtzite and cubic zinc blende. The band gap, crystal phase and the morphology of CdS QDs were found not to be greatly affected by Mn2+ doping, however there was an optimal Mn2+ doping content of 10% where the magnetism is maximum. The recorded photoluminescence (PL) emission spectra, excited at 370 nm, depict emission lines in the UV and blue-shift regions. The emission band reveals that the band gap of pure CdS QDs is around 3 eV which is greater than that of bulk CdS (2.42 eV). The band gap of Mn:CdS QDs is almost independent of Mn content (x) and the crystallite size remains almost the same for all values of x. The observed structural, magnetic and optical properties have been explained on the basis of formation of two phases of CdS doped with Mn. This work aims to highlight recent advances in the synthesis of Mn:CdS diluted magnetic semiconductor quantum dots and their wonderful performance.