Comparative investigation on the Di-/ferro-electric and optical properties of Ce/Nd dual doped ZnO nanostructures prepared in different reaction mechanisms

Abstract

Pristine and Ce 3+ /Nd 3+ co-doped ZnO nanoparticles were synthesized using wet chemical co-precipitation and hydrothermal techniques. Pure, Ce/Nd di-doped and CTAB assisted Ce/Nd di-doped ZnO samples prepared by co-precipitation method were given names as C1, C2 and C3, respectively. Pure, Ce/Nd di-doped and CTAB assisted Ce/Nd di-doped ZnO samples prepared by hydrothermal method were given names as H1, H2 and H3, respectively. The hexagonal wurtzite phase of the six prepared powders was confirmed using Powder X-ray diffraction. Size analysis has shown an increment in crystallite size after doping particularly the sizes were 33.75, 34.97 and 84.18 nm of C1, C2, and C3, respectively and 27.74, 53.23 and 73.13 nm of H1, H2 and H3, respectively. FT-IR and Raman spectroscopy were used to farther confirm the single-phase structure of ZnO samples without any particularities due to doping ZnO with cerium and neodymium atoms. A very strong band in FT-IR spectra which corresponds to Zn–O stretching bonds of pure and doped ZnO nanostructures occurs at very low wavenumbers (356 and 359 cm −1 ). SEM technique was used to probe the morphologies of ZnO and Ce/Nd-ZnO which revealed collective nanostructured shapes of the as-synthesized nanoparticles. Cerium and neodymium doping into the ZnO structure was examined and confirmed using Energy Dispersive X-ray (EDX) spectroscopy. The UV-Vis absorption spectra showed remarkable reduction in the optical band gap energies of the samples namely they were 3.157, 3.102 and 2.701 nm for C1, C2 and C3, respectively and 3.170, 3.018 and 2.819 nm for H1, H2 and H3, respectively. The photoluminescence properties of the pure and Ce/Nd co-doped ZnO nanoparticles revealed less emissions of the defects where the green emission peaks were low intense and sharp. The dielectric phase transition was found at high curie temperature (170 °C) in pure ZnO nanoparticles and it was enhanced up to (243 °C) upon doping. Ferroelectric loops of all pelletized samples were studied. Due to the dual doping of cerium and neodymium elements into ZnO the remnant polarization (P r ) was increased and coercive field (E c ) was decreased. The remnant polarization (P r ) and coercive field (E c ) were (0.076 μC/cm 2 , 7.351 kV/cm), (0.160 μC/cm 2 , 6.110 kV/cm) and (0.338 μC/cm 2 , 5.002 kV/cm) of C1, C2 and C3, respectively. Those of H1, H2 and H3 were (0.060 μC/cm 2 , 6.584 kV/cm), (0.177 μC/cm 2 , 5.809 kV/cm) and (0.319 μC/cm 2 , 4.674 kV/cm), respectively. Based on the above-mentioned achievements, the as-synthesized Ce/Nd co-doped ZnO is a promising optoelectronic lead-free high T c ferroelectric material for designing photoelectric nanodevices , photodetectors and memory devices. • Pure and Ce/Nd co-doped ZnO nanostructures were synthesized by two different techniques. • Ferroelectric phase transition for pure ZnO appeared at high temperature value which got increased in the doped C3 and H3 samples. • Due to dual doping of cerium and neodymium elements into ZnO the remnant polarization (P r ) was increased and coercive field (E c ) was decreased. • Remarkable shrinkage in the band gap was observed for doped ZnO nanostructures. • Sharp green emission peaks are obtained with slight increment in their intensity after doping.