Development and study of the structural and optical properties of hexagonal ZnO nanocrystals

Abstract

ZnO is a promising member of the semiconducting materials of II-VI group. ZnO nanocrystals have shown potential applications in various novel technologies. In the present investigation of ZnO nanocrystals, a novel chemical route using Zinc acetate as organic precursor is being reported. ZnO nanocrystals were characterized using X-ray diffraction, scanning electron microscopy UV-visible (UV-vis) spectroscopy, and photoluminescence measurements. The X-ray diffraction studies reveal the typical hexagonal structure of ZnO nanocrystals along the preferred orientation of (101) and (100) planes. The optical bandgap of ZnO nanocrystals was found to be 3.50 eV from the absorbance spectrum, which is higher than that of the bulk ZnO material. A blueshift of 21 nm is observed in the excitonic transitions, which clearly indicates the formation of ZnO nanocrystals. Photoluminescence spectroscopy of the ZnO nanocrystals showed a strong emission peak at 365 nm near the band edge along with a weak green-yellow emission peak spanning the range of 450 to 600 nm. The blueshifting was also observed in the photoluminescence spectrum, in accordance with the UV-vis spectroscopy in contrast to the bulk ZnO material.

Origin and role of elasticity in the enhanced DMMP detection by ZnO/SAW sensor

“…It indicates the growth of oriented ZnO thin films having its c-axis normal to the surface of substrate. The growth of preferred c-axis orientation is attributed to the minimum surface free energy of (0 0 2) plane in wurtzite ZnO structure [19,20]. The (0 0 2) XRD peak for all ZnO thin films was observed at Bragg's angle (2Â) lower than the reported value (34.42 • ) for bulk ZnO [19,20].…”

“…The growth of preferred c-axis orientation is attributed to the minimum surface free energy of (0 0 2) plane in wurtzite ZnO structure [19,20]. The (0 0 2) XRD peak for all ZnO thin films was observed at Bragg's angle (2Â) lower than the reported value (34.42 • ) for bulk ZnO [19,20]. The deviation of 2Â (from bulk ZnO) is associated with the presence of stress which might be attributed to the presence of native defects [18].…”

Synthesis and optical study of heat-treated ZnO nanopowder for optoelectronic applications

“…In general, ZnO shows four PL emissions; (a) a nearband edge (NBE) emission at 380 nm called UV emission, attributed to free-excitons recombination, (b) a blue emission at 460 nm because of intrinsic defects such as oxygen and zinc interstitials (c) a green emission (GL) at 540 nm, known as deeplevel emission and is caused by impurities such as oxygen vacancies, zinc interstitials and (d) a red emission at 630 nm attributed to radiative recombination of a delocalized electron close to the conduction band with deeply trapped hole in the oxygen interstitials (Oi− centres) or may be due to oxygen and zinc anti-sites etc. [27][28][29][30] In our case the samples showed a prominent UV emission at 358 nm called nearband edge emission (NBE) and a deep-level green emission (DGE) at 525 nm; however after heat treatment intensity of the DGE decreased while that of the UV emission increased. This may be due to the effect of heat treatment on the intrinsic defects in the as-prepared ZnO nanopowders.…”

Investigation on room temperature photoluminescence of pure and aluminum doped zinc oxide nanoparticles

“…This decrease in particle size originated from the quantum confinement effect [26] and the blue shift observed in the absorbance spectra of nanoparticles was due to the quantum confinement effect [27].…”