International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Volume 3 Issue 2, February 2014 www.ijsr.net Studies on the Synthesis and Characterization of Nano Phosphors for Field Emission Devices H. L. Vishwakarma 1 , Archana Sharan 2 , Anju Singh 3 1, 2, 3 Department of Applied Physics, Rungta College of Engg & Tech, Kohka Road, Kurud, Bhilai, Durg (C.G.)- 491024, India Abstract: Nano phosphors were synthesized by chemical precipitation method with mercaptoethanol as the capping agent. Manganese doped ZnS nano phosphors (ZnS: Mn) with varying concentration of capping agent as well as of Mn 2+ were synthesized at room tempera- ture. The optical absorption studies show that the absorption edge shifts towards blue region as the capping agent concentration is increased indicating that the effective band gap energy increase with decreasing particle size while with the change in doping concentration no varia- tion was observed in the absorption spectra. The nano phosphors obtained were characterized by XRD. It was found that as the capping agent concentration is increased, there is reduction in particle size. Keywords: Nano phosphors, characterization, Luminescence, Optical properties. 1. Introduction  ZnS is a direct transition semiconductor with the widest energy band gap among the group II- VI compound ma- terials. The most striking feature of ZnS nanocrystal- lites is that their chemical and physical properties differ dramatically from those of bulk solids. ZnS is a semi- conducting material, which has a wide band gap ma- terial of 3.70 eV [1], [2].  Among these, luminescent semiconducting nano phos- phors, also termed as nanophosphors, were paid much attention particularly for their life time shortening and enhanced emission efficiencies [3], [4]. Bhargava et al. first reported luminescent properties of Mn doped ZnS nano phosphors prepared by a chemical process at room temperature, which initiated investigation on this topic [5], [6]. Depending on the capping molecules present on the ZnS: Mn, particles passivate surfaces. ZnS doped with Mn 2+ nano phosphors are having high quantum ef- ficiency and luminescence intensity [7]. The band struc- ture of the semiconductor changes with decreasing in particle size.  Zinc sulphide doped with manganese (ZnS: Mn 2+ ) show interesting luminescence properties for application as phosphors [8]. In 1994 Bhargava et al. reported that the luminescence efficiency increases with decreasing par- ticle size and life time of Mn 2+ emission was shortened from milliseconds to nanoseconds due to quantum con- finement effect. This result has led to a new class of luminescent material finding applications in displays, sensors, lasers etc. As far as display is concerned the resolution depends greatly on the size of the pixel and improves with a reduction in the size of the pixel that is in turn determined by the size of the phosphor particles.  Zinc sulphide is an important semiconductor and has many optoelectronic applications including solar cells, photodiodes, light emitting diodes, nonlinear optics and heterogeneous photo catalysis. In the present study we have synthesized ZnS nano phosphors with varying concentration of capping agent using chemical precipi- tation technique. The particles are characterized using XRD. 2. Experimental Method  All the reactants and solvents used in this study were analytical grade and used without any further purifica- tion. The synthesis was carried out in water for its inhe- rent advantages of being simple and environment friendly. All steps of the synthesis were performed at room temperature and under ambient conditions.  In the present investigation chemical route synthesis technique has been adopted. Nano phosphors of ZnS are synthesized in aqueous medium through chemical precipitation technique starting from analar grade zinc salt and sodium sulphide, and using mercaptoethanol as capping agent. The nano phosphors are separated from the reaction medium by centrifugation at 3500 rpm and finally air dried. Different samples were prepared by changing the capping agent concentration. Special care has to be taken to maintain the same physical condition during the synthesis of the samples.  Absorption of the samples prepared with various con- centrations of capping agent and dopant were studied. Perkin Elmer λ-12 spectrometer was used to obtain the absorption peak of ZnS nano phosphors. The lambda- 12 UV/ VIS spectrometer features in all reflecting opti- cal system.  All the samples were characterized at IUC - Indore. The morphologies and sizes of the mercaptoethanol capped ZnS: Mn was determined by X- ray diffraction studies with CuK α radiation (λ = 1.5418 A 0 ). XRD data were collected over the range 5 0 - 75 0 at room temperature. X- ray diffraction patterns have been obtained by Bruk- er D8 Advance X- Ray diffractometer. The particle size was calculated using Debye- Scherrer Formula.  The finite three- dimension crystal lattice diffracts X- rays in manner analogous to the reflection of visible Paper ID: 02013895 219