Davydov Split PL Emission and EPR Correlation in β-MnS Layered CdS Nanorods

A comparison of manganese activated CdS nanorods with the nonactivated ones prepared by simple chemical methods in micellar medium reveals quantum confinement and blue shift in optical spectroscopy as a function of Mn2+. Powder XRD of all samples reveals orientation along the 002 plane, confirmed by HRTEM. Nonactivated CdS gives a blue band edge emission at 455 nm in the PL spectrum getting quenched on Mn2+ addition. The PL spectra of Mn2+ added CdS exhibit first an emission at 367.7 rim, which later gets subjected to Davydov splitting with a separation of similar to 0.045 eV, the singlet intensity decreasing and the doublet intensity increasing with Mn2+ input. This PL property is manifested in EPR as due to two different Mn2+ environments: (i) individual tetrahedrally coordinated uncoupled Mn2+ ions; (ii) Mn2+-Mn2+ physical dimer moieties. These are interpreted to arise from (i) the formation of a first layer of MnS on a CdS surface and (ii) the latter due to a second layer of MnS on top of the first to form MnS-MnS dimers. Mn2+ is present as metastable beta-MnS. The Davydov splitting is accompanied by a small energy shift. The double layer formation is confirmed by a bleaching experiment. Also noted is a low intensity band edge emission of CdS perturbed by Mn2+ blue-shifted from the quenched 455 nm emission. ICP and EDS confirm the purity of samples.