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Bindu K.R.,Sree Sankara Vidyapeetom College | Martinez A.I.,CINVESTAV | Vasudevan P.,Mahatma Gandhi University | Unnikrishnan N.V.,Mahatma Gandhi University | Anila E.I.,Union Christian College
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2012

We report the synthesis and characterization of nanostructured ZnS powders without using any capping agent. The synthesis was carried out by the wet chemical method. From X-ray diffraction analysis, it was found that nanostructured ZnS exhibited the cubic structure with an average size of 2.5 nm. High resolution transmission electron microscopy (HR-TEM) observations revealed the cubic structure with grain size of around 2.5 nm. In the UV-vis absorption spectrum, the absorption peak shows a blue shift with respect to bulk ZnS. The particle size estimated by considering the effective mass approximation is 2.1 nm. Photoluminescence spectrum exhibits two peaks at 360 nm and 450 nm. The emission color is blue for excitation at 245 nm with CIE coordinates x=0.14 and y=0.038 and it is bluish white when excited at 360 nm with CIE coordinates x=0.2 and y=0.36. It is demonstrated that quantum confinement effects are present in the nanostructured powders without the addition of any capping agent. © 2012 Elsevier B.V.


Bindu K.R.,Sree Sankara Vidyapeetom College | Sreenivasan P.V.,Union Christian College | Martinez A.I.,CINVESTAV | Anila E.I.,Optoelectronic and Nanomaterials Research Laboratory
Journal of Sol-Gel Science and Technology | Year: 2013

The structural, morphological, optical and electrical properties of α-axis oriented nanostructured ZnS thin film prepared by dip coating have been studied in this article. The X-ray diffraction studies of the film shows that the ZnS was crystallized with cubic structure of particle size 27 nm with a strong orientation along (200) plane which is advantageous for optoelectronic devices. The scanning electron microscopy and TEM micrograph reveals that the film consists of nano crystalline columnar particles. From the investigation of the absorption spectra of this ZnS film, the band-gap is found to be higher (4 eV) than bulk (3.7 eV) indicating a blue shift. It is found that the film is having a transparency of >90 % in the visible-near IR region from 400 to 800 nm. From the photoconductivity measurements, it is evident that the film is photosensitive in nature. From the electrical resistivity measurements the conductivity of the film was found to be 3.4 × 10-2 Ω-1 cm-1. Hot probe method indicates that the synthesized ZnS film is n-type. © 2013 Springer Science+Business Media New York.


Bindu K.R.,Sree Sankara Vidyapeetom College | Bindu K.R.,Union Christian College | Anila E.I.,Union Christian College
Journal of Fluorescence | Year: 2015

We report of the synthesis and characterisation of white emitting ZnS:Mn2+ nanoparticles. The spectroscopic properties and the crystal structure of Mn doped ZnS nanoparticles are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the synthesis temperature. The synthesis of the samples were carried out by the simple wet chemical precipitation method. The influence of synthesis temperature on structure and optical properties were studied at constant Mn concentration. The nanoparticles were structurally characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The XRD studies show the phase singularity of Mn doped ZnS particles having zinc-blende (cubic) structure at all temperatures. The band gap of the doped samples are red shifted with temperature. Electron Paramagnetic Resonance (EPR) spectra exhibited resonance signals, characteristic of Mn2+. Incorporation of Mn in the ZnS nanoparticles was confirmed by Inductively Coupled Plasma- Atomic Emission Spectroscopic studies (ICP-AES). The samples show an efficient emission of yellow-orange light centred at 590 nm which is characteristic of Mn2+ along with a blue emission at 435 nm due to sulfur vacancy. The overall emission is white at all temperatures with CIE co-ordinates in close agreement with achromatic white. © 2015 Springer Science+Business Media.

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