EDTA-assisted hydrothermal synthesis, characterization and photoluminescent properties of Mn2+-doped ZnS

Abstract

In this paper, undoped ZnS and Mn2+-doped ZnS nanocrystals were synthesized through a facile EDTA-assisted hydrothermal method. The as-synthesized powder samples were systematically characterized by employing the following characterization technique such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), UV–visible optical absorption and photoluminescence (PL) spectroscopy. X-ray diffraction pattern revealed the presence of material in single phase with average crystallite size of about 3nm and the material remained cubic over the whole Mn solid solution range. Formation of ultrafine, spherical and homogeneous dispersed nanoparticles with size 4nm was confirmed by HRTEM analysis. Absorption shoulders of the samples were blue-shifted as compared to bulk ZnS (3.6eV) with decrease in the energy band gap as the Mn concentration increases. The room temperature photoluminescence (PL) spectra of Mn2+-doped ZnS nanocrystalline showed extra peaks in yellow–orange and red region in comparison of pure ZnS. Mn induced PL was suggested with the significant enhancement of the PL intensity in ZnS:Mn nanocrystalline due to Mn incorporation. The red shift in the yellow–orange emission peak can be attributed to the change in band structure due to the formation of ZnS:Mn alloy with increase in Mn2+ concentration. The yellow–orange emission peak corresponds to the 4T1(excited)–6A1(ground) transition of Mn2+ ion in Td symmetry in the ZnS host lattice. The emission peak in the red region may be due to Mn2+ d–d transitions in (Zn Mn)S matrix as some of the nearest neighbors of Mn2+ are now predominantly S atoms due to their random positioning nature in the nanocrystallite and Mn–Mn interaction at high Mn2+ concentration. This type of doped semiconductors with multi-band emission can be made bioactive when they are linked with suitable biomolecules.