, Czech Republic, EU , Brno th 7 – th Nov 5 STRUCTURAL, MORPHOLOGICAL AND OPTICAL CHARACTERIZATIONS OF ANNEALED EDTA CAPPED ZNS NANOCRYSTALS PREPARED BY CHEMICAL PRECIPITATION METHOD M. A. Osman 1 , A. A. Othman 1 , Waleed A. El-Said 2 , A. A. Abu-sehly 1 , A. G. Abed-Elrahim 1 1 Physics and 2 Chemistry departments, Faculty of Science, Assiut University Abstract ZnS nanocrystals were prepared by the chemical co-precipitation method. The effect of annealing temperature (Ta) on the morphological, structural and optical absorption behavior was investigated using x-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), UV-vis spectroscopy, selected area electron diffraction (SAED) and Fourier transform infrared (FTIR) spectroscopy. Analysis of XRD patterns for as prepared and annealed samples showed that, increasing Ta leads to an increase in the crystallite size (D) from 2.67 to 19.6 nm. It is noticed that the obtained values of lattice parameters from HRTEM Images and SAED patterns are in good agreement with that deduced from XRD analysis. Furthermore, annealing process at 600 o C and 700 o C results, in complete phase transformation from as prepared ZnS cubic structure to ZnO hexagonal structure. Analysis of the XRD patterns, SAED, HRTEM and FTIR confirm this phase transition. Analysis of the optical absorption spectra indicates noticeable decrease in the direct band gap from 4.70 to 3.22 eV with increasing Ta. This behavior is attributed to the enhancement in crystallinity and the increase in particle size of ZnS nanoparticles. Moreover, UV photo-induced effect on the optical absorption edge was studied. Keywords: annealing and UV induced effects, morphology, nanostructure, ZnS phase transition, optical absorption behavior 1. INTRODUCTION In recent years, studies on semiconductor nanocrystals such as ZnS and CdS have drawn significant attention due to their unique structural, electronic and optical properties originating from their large surface to volume ratio and quantum confinement effect [1]. Usually the absence of appropriate stabilizer results in the reactivity and agglomeration of semiconductor nanoparticles [2]. ZnS is a promising material for various device applications such as electroluminescence devices [3], field emission displays [4] and sensors [5,6], light emitting diodes in the near UV region [7]. Considerable effort has been paid to tune properties of ZnS nanoparticles such as optical band gap, electronic structure and luminescence properties by changing their particle size. The thermal annealing process results in remarkable changes in the structure, absorption edges due to the movement of dislocations, native defects and adsorption / decomposition on the surface. In this study nanoparticles of ZnS capped with EDTA were prepared by the chemical co-precipitation method. Thermal annealing effects on morphological, structural and optical properties have been studied. In addition UV induced effect on optical absorption edge was investigated. 2. EXPERIMENTAL DETAILS 2.1. Sample preparation ZnS nanoparticles were synthesized at room temperature using the chemical precipitation method. Zinc acetate (Zn(CH3COO)2) and sodium sulfide (Na2S) were used as source materials and EDTA (C10H16N2O8) as a capping agent. All chemicals used were of AR grade. 0.8 M Zn(CH3COO)2.2H2o was dissolved in 75 ml double distilled water, 0.08 M EDTA was added to solution of Zn +2 ions as capping agent and 0.8 M of Na2S was dissolved in