Synthesis of biotin caped Mn2+ activated ZnS quantum dots with their structural stability and modulation of opto-electronic properties

Mn 2+ activated ZnS (ZnS:Mn 2+ ) nanoparticles biotin matrix have been synthesized by chemical co-precipitation route. X-ray diffraction (XRD) results confirmed single phase zinc blend structure with crystallite sizes ranging from 1.5 to 1.9 nm. The small particle sizes are believed to have single domain crystallites because of quantum confinement of particles in the biotin matrix. Scanning electron microscopy (SEM) analysis shows smooth and polygon shape potato like morphology having cluster size varying from 77μm to 182μm. Optical measurement shows the band gap of 3.85 eV which has been blue shifted and is accredit to the quantum size effect. The particle size estimated for this gap is to be 2.03 nm and is good agreement with sizes obtained from XRD. The luminescence feature of the as synthesized sample was also reported. The photoluminescence (PL) spectra shows two wide peaks centred at 408 nm and 520 nm respectively. The first emission at 408 nm with short time is attributed to the defects of ZnS while another peak at 520 nm attributed in green emission due to the elemental sulphur species on the surface of zinc sulphide. The both emissions are blue shifted and are attributed to the small particle sizes. The well known manganese related orange-red emission peak cantered at 590 nm has not been observed and is completely quenched that confirmed that the Mn 2+ ions have been allocated outside the ZnS crystals. A new emission at 338 nm appears to have radiative transitions from the defect level to the acceptor levels. Thus, by using suitable activator and capping molecule, we are able to stabilize the growth of nanoparticles at room temperature, thereby enhance the structural and opto-electronic properties.