Davydov split PL emission and EPR correlation in β-MnS layered CdS nanorods

Abstract

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 nm, which later gets subjected to Davydov splitting with a separation of ∼ 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 β-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.