Electrical and optical studies of pure and Ni-doped CdS quantum dots

Arfat Firdous,D. Singh,M. M. Ahmad

doi:10.1007/s13204-012-0065-0

Abstract

Quantum dots of CdS and Ni-doped CdS were synthesized through chemical precipitation method using a high-boiling solvent. Nanocrystallinity of the as prepared nanostructure is confirmed using X-ray diffraction (XRD). The mean crystal size obtained by full-width half maxima (FWHM) analysis is 3.33 nm for CdS, 3.37 nm for CdS:Ni (2 mM) and 3.39 nm for CdS:Ni (4 mM). The electrical conductivity data reveal semiconducting behaviour of both pure CdS and Ni-doped CdS nano-crystals. The optical absorption analysis conducted in UV–vis range 200–900 nm reveals the transparency of these nanocrystals in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 2.65 eV for CdS, 2.59 eV for CdS:Ni (2 mM) and 2.53 eV for CdS:Ni (4 mM) nanoparticles. This implies that pure CdS and Ni doped CdS are blue shifted with respect to the bulk CdS (2.42 eV); however, Nickel doped CdS nanocrystals are red shifted with respect to pure CdS nanocrystals.

Highlights

Pure and doped semiconductor nanocrystals are extensively investigated to obtain basic information on impurity states in quantum dots and to examine their potential applications in novel light-emitting devices
There is a small shift in broad peaks of Ni-doped CdS with respect to the pure CdS nanocrystals; this small shift in intensity may be assigned to the presence of dopant(Ni) in doped nanocrystals
The aim of the present work was to investigate the effect of Ni doping on the structural, electrical and optical properties of CdS quantum dots for its possible use as tunable lightemitting devices and low-voltage display, because of observed shift in energy band gap

Summary

Introduction

Pure and doped semiconductor nanocrystals are extensively investigated to obtain basic information on impurity states in quantum dots and to examine their potential applications in novel light-emitting devices. The synthesis and characterization of nanostructured materials especially II–VI group semiconductors is very important in the field of optics due to their strongly size dependent optical properties(Awschalom and Kikkawa 1999; Geng et al 2004; Jayanthi et al 2007; Hebalkar et al 2001). CdS has been used widely as an important phosphor for photoluminescence (PL), electroluminescence (EL) and cathodoluminescence (CL) devices due to its better chemical stability, favourable electronic and optical properties for optoelectronic applications compared with other chalcogenides such as CdSe. Doping of CdS nanoparticles by transition metal ions and rare earth ions (Li and Wang 2003; Firdous 2010; Colvin et al 1994; Yang et al 2001; Liu et al 2000; Papakonstantinou et al 1998; Xu et al 1998; Trindade and Brien 1996a) have been

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