Influence of Co2+ on electrical and optical behavior of Mn2+-doped ZnS quantum dots

Publication date: July 2018
Source:Optics & Laser Technology, Volume 103
Author(s): P. Sakthivel, S. Muthukumaran
Co²⁺-doped Zn0.98Mn0.02S quantum dots with various concentrations of Co²⁺ from 0% to 4% have been successfully synthesized by a simple co-precipitation method. X-ray diffraction (XRD) pattern confirmed the acquirement of cubic structure and phase purity in all the samples. The average crystallite size of the particles was ∼3 nm observed from XRD result. Surface morphology of the samples was studied using scanning electron microscope (SEM). TEM study was also taken to know the structural parameters of the samples. Fourier transform infrared (FTIR) spectra proved the presence of Co²⁺ and Mn²⁺ in ZnS host lattice. Energy dispersive X-ray (EDX) analysis confirmed the elemental composition with their normal stoichiometric ratio. In the dielectric study, dielectric dispersion and dielectric loss were increased with Co²⁺ composition due to the increase of carrier concentration. From the AC conductivity measurement, the maximum conductivity was observed for Co²⁺ = 2% due to their higher charge carrier density and it was decreased for Co²⁺ = 4% due to the scattering of charge carriers. Because of the low dielectric constant at higher frequency, these materials can be used for high-frequency applications. The variation of peak intensity and wavelength shifting in UV-vis absorption and transmittance were discussed on the basis of formation of secondary phase and variation of charge carrier density. The continuous red shift of energy gap by Co²⁺-doping is attributed to the direct energy transfer between excited states and 3d levels of Co²⁺ ions. Photoluminescence spectra showed the strong and broad blue emission bands between 468 nm and 483 nm. Since higher transmittance was observed for Co²⁺ = 2% addition, this material can be selected for optimum applications of optoelectronic devices.



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