IJSTE - International Journal of Science Technology & Engineering Volume 2 Issue 11 May 2016 ISSN (online): 2349-784X Synthesis and Luminescence Properties of Ni Doped ZnS Nanoparticles B. Hariprasad Reddy G. S. Harish Research Scholar Research Scholar Sri Venkateswara University, Tirupati, 517502, India. Sri Venkateswara University, Tirupati, 517502, India. P. Sreedhara Reddy Professor Sri Venkateswara University, Tirupati, 517502, India. Abstract In this paper we discussed cost effective chemical co-precipitation method for preparing water soluble Ni doped ZnS nanoparticles and studied the effect of dopant concentration on the structural, morphological, compositional and photo luminescence properties using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX) and photo luminescence studies. Broadened XRD peaks confirmed the formation of nano-sized ZnS: Ni nanoparticles with cubic structure at different capping agent concentrations. SEM and EDAX analysis showed surface morphology and effective elemental composition of prepared nanoparticles. The Raman peak observed at 344 cm-1 can be assigned as the LO mode of cubic ZnS. Ni doped ZnS nanoparticles and showed broad emission ranging from 440-520 nm. The Photo Luminescence intensity of ZnS: Ni Nanoparticles is enhanced by the incorporation of Ni ions. Keywords: chemical co-precipitation, nanoparticles, photoluminescence, scanning electron microscopy, X-ray diffraction I. INTRODUCTION The nano-sized materials have found many novel applications and are attracted great interest due to enhanced mechanical, optical, opto-electronic and magnetic properties of nanocomposite. II VI semiconducting nanoparticles have attracted great interest due to their unique structural, optical and electronic properties which arise due to their large surface to volume ratio [1-5]. ZnS nanoparticles doped with Ni2+ have been obtained by chemical co-precipitation from homogeneous solutions of zinc and nickel salt compounds with S2- as precipitating anion formed by decomposition of sodium sulfide. Average particle size and structural analysis of the doped and pure ZnS nanoparticles were observed by X-ray diffraction analysis. Enhanced luminescence properties were observed in photoluminescence spectra of ZnS nanoparticles doped with Ni2+. Composition analysis and surface morphology information were obtained from EDS and SEM analysis respectively. Raman studies showed the absence of impurities and effective doping of Ni2+ ions into ZnS. II. EXPERIMENTAL AND CHARACTERIZATION TECHNIQUES All the chemicals were of analytical reagent grade and were used without any further purification. The samples were prepared by chemical co-precipitation method using pure zinc acetate, nickel chloride and sodium sulfide. Appropriate amounts of Zn(ac)2 and NiCl2. 6H2O were dissolved in 50ml distilled water. To this solution, 50ml of sodium sulfide solution is added drop wise under constant stirring until to get fine precipitate of Ni doped ZnS nanoparticles. After the completion of the reaction, products were collected and thoroughly washed for several times with distilled water and ethanol, Ni doped ZnS nanoparticles were subjected to various characterization studies. The X-ray diffraction patterns of the samples were collected on a Seifert 3003 TT X- Ray diffractometer with the Cu Kα radiation (λ=1.5405a ). Elemental composition of the prepared samples were analyzed through EDS using Oxford Inca Penta FeTX3 EDS instrument attached to Carl Zeiss EVO MA 15 Scanning Electron Microscope. Photoluminescence spectra of the present Nano powders have been recorded using a Horiba-Fluorolog-3 (Model FL3-22) spectrofluorometric at room temperature (300 K). Raman Spectroscopic studies of the as prepared samples were carried out using LabRam HR800 Raman Spectrometer. All rights reserved by www.ijste.org 216
III. RESULTS AND DISCUSSION Elemental Analysis: Chemical composition analysis of all samples was done by EDS technique. In order to analyze the amount of Ni content and distribution in doped ZnS this technique is much useful. Fig.1 (a), (b), (c) and (d) shows EDS spectra of Pure ZnS, Zn 1-xNi xs (x=0.02,0.04, 0.06) nanoparticles respectively. EDS spectra of the samples confirmed that the amount of Zn, S and Ni were close to the nominal (target) values. (a) (b ) (c) (d ) Fig. 1: EDS spectra of (a) Pure ZnS nanoparticles, (b) Zn1-xNixS, x= 0.02, (c) Zn1-xNixS, x= 0.04 and (d) Zn1-xNixS, x= 0.06 nanoparticles Morphological Studies: The surface morphology is studied by Scanning Electron Microscope (SEM), by observing the top and cross-sectional views of the sample. The surface morphologies of the Pure ZnS, Zn 1-xNi xs (x=0.02, 0.04, 0.06), nanoparticles were shown in fig. 2 (a), (b), (c) and (d) respectively. It is noticed that in the doped samples the agglomerated particles appear to be nearly spherical with the distribution becoming nearly homogeneous. All rights reserved by www.ijste.org 217
Fig. 2: SEM image of (a) Pure ZnS nanoparticles, (b) Zn1-xNixS, x= 0.02, (c) Zn1-xNixS, x= 0.04 and (d) Zn1-xNixS, x= 0.06 nanoparticles Structural Analysis: According to Fig. 3 shows the XRD patterns of pure ZnS, Zn 1-xS: Ni x (x=0.02, 0.04, 0.06). The three diffraction peaks in the XRD patterns for all four products (Figure 3) were indexed as the (1 1 1), (2 2 0) and (3 1 1) crystal planes of cubic ZnS, although the three diffraction peaks were slightly shifted to higher angles with increasing Ni concentration. This indicated that Zn 1 xni xs nanoparticles were successfully synthesized. The average particle size calculated by Debye Scherrer s equation [a] for ZnS: Ni nanoparticles lie in the range of 8-10 nm. -------------------[a] Where, D is the average particle size and β hkl is full width at half maximum of XRD peak expressed in radians and θ is the position of the diffraction peak Photoluminescence Studies: Fig. 3: XRD patterns of Pure ZnS, Zn1-xNixS, x= 0.02, 0.04 and 0.06 The room temperature PL spectra of pure ZnS, Zn 1-xS: Ni x (x=0.02,0.04, 0.06) nanoparticles are shown in fig. 3.4. The excitation wavelength is 320nm. For pure ZnS nanoparticles a broad emission peak is observed at around 450nm [6]. Ni doped ZnS nanoparticles showed broad emission ranging from 440-520nm. P.Yang, et.al observed emission peaks of ZnS: Ni nanocrystals at 520nm [7] and R. Mohan et al.[8] reported emission peak centered at 425 nm. Ni doped ZnS nanoparticles showed broad emission peak at around 440 nm, which may be due radiative recombination of sulfur vacancies and ZnS host lattice. In this study with incorporation of Ni 2+ ions a broad emission ranging from blue region to green region is observed. The Photo Luminescence intensity of ZnS: Ni Nanoparticles is enhanced by the incorporation of Ni 2+ ions as in fig. 4. All rights reserved by www.ijste.org 218
Raman Spectroscopy: Fig. 4: PL spectra of Pure ZnS, Zn1-xNixS, x= 0.02, 0.04 and 0.06 Fig.5 shows the typical Raman scattering data to the pure ZnS and at different concentration of Ni (2, 4 and 6 at.%). For bulk cubic ZnS, the Raman peaks were observed near 271 and 352 cm -1 corresponding to transverse optical (TO) and longitudinal optical (LO) modes respectively [11]. S. Kumar et al.,[12] reported broadening of the Raman peaks and their shifting towards lower energy as compared to the bulk values. As the carrier concentration in the semiconductor increases, the frequency of L+ mode increases from bulk LO mode frequency and the frequency of L- mode increases from zero to TO mode frequency. Hence the peak at 258 cm-1 observed in the present sample can be attributed to the TO mode. The Raman peak observed at 344 cm-1 can be assigned as the LO mode of cubic ZnS. The shifting of Raman peaks towards lower energy may due to quantum confinement effect. No other impurity peaks were observed which supports the effective doping of Ni into ZnS. Fig. 5: Raman spectra of Pure ZnS, Zn1-xNixS, x= 0.02, 0.04 and 0.06 IV. CONCLUSION Undoped and Ni doped ZnS nanoparticles were successfully synthesized through facile chemical co-precipitation method. The assynthesized nanoparticles were subjected to chemical analysis (EDAX) and the estimated compositions were compliance with that of the starting compositions. XRD studies demonstrated that Ni doped ZnS nanoparticles were in cubic zincblende crystal structure with an average particle size of the order of 8-10 nm. No other impurity peaks were observed in Raman spectroscopic studies which supports the effective doping of Ni into ZnS. Photoluminescence measurements revealed that Ni doped ZnS nanoparticles All rights reserved by www.ijste.org 219
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