Spectral investigations on undoped and Cu2+ doped ZnO-CdS composite nanopowders

Undoped and Cu2+ doped ZnO-CdS composite nanopowders were synthesized by simple chemical precipitation method. Structural and spectroscopic properties of the prepared samples have been characterized by XRD, SEM with EDS, TEM, FT-IR, UV-Vis, EPR and Photoluminescence studies. X-ray diffraction pattern contains a series of peaks corresponds to hexagonal phase of ZnO and CdS. The average crystallite sizes of undoped and Cu2+ doped samples are determined and are in the range of 25-30 nm. SEM and TEM micrographs reveal that the samples show spherical like structures with little agglomeration. FT-IR spectra show the fundamental mode of vibrations of Zn-O at 515 cm(-1), Cd-S at 621 cm(-1) and other functional groups. Optical absorption spectrum of Cu2+ doped sample consists of three bands at 665, 823 and 1192 nm attributed to the transitions B-2(1g) --> E-2(g), B-2(2g) and (2)A(1g) respectively. Crystal field and tetragonal field parameters are evaluated as Dq = 1214, Ds = 1610 and Dt = 389 cm(-1). From EPR, spin-Hamiltonian and hyperfine splitting parameters are evaluated for Cu2+ doped sample as g(parallel to) = 2.3391, g(perpendicular to) = 2.0550 and A(parallel to) = 130 x 10(-4) cm(-1), A(perpendicular to) = 36 x 10(-4) cm(-1). The optical and EPR data suggests that Cu2+ entered into host lattice as tetragonally distorted octahedral site symmetry. PL spectra consists two emission bands at 367, 380 nm in UV region. A sharp blue emission peak at 425 nm and a broad green emission peak in the range of 450-570 nm are observed. The enhanced visible emission is observed after doping. (C) 2014 Elsevier B.V. All rights reserved.