Photoluminescence Of ZnO Nanowires Research Articles

Photoluminescence of ZnO Nanowires: A Review.

One-dimensional ZnO nanostructures (nanowires/nanorods) are attractive materials for applications such as gas sensors, biosensors, solar cells, and photocatalysts. This is due to the relatively easy production process of these kinds of nanostructures with excellent charge carrier transport properties and high crystalline quality. In this work, we review the photoluminescence (PL) properties of single and collective ZnO nanowires and nanorods. As different growth techniques were obtained for the presented samples, a brief review of two popular growth methods, vapor-liquid-solid (VLS) and hydrothermal, is shown. Then, a discussion of the emission process and characteristics of the near-band edge excitonic emission (NBE) and deep-level emission (DLE) bands is presented. Their respective contribution to the total emission of the nanostructure is discussed using the spatial information distribution obtained by scanning transmission electron microscopy−cathodoluminescence (STEM-CL) measurements. Also, the influence of surface effects on the photoluminescence of ZnO nanowires, as well as the temperature dependence, is briefly discussed for both ultraviolet and visible emissions. Finally, we present a discussion of the size reduction effects of the two main photoluminescent bands of ZnO. For a wide emission (near ultra-violet and visible), which has sometimes been attributed to different origins, we present a summary of the different native point defects or trap centers in ZnO as a cause for the different deep-level emission bands.

Piezophototronic effect enhanced luminescence of zinc oxide nanowires

Experimental findings on electroluminescence or photoluminescence of ZnO nanowires have been drawn much attention due to their promising applications in many areas. One of the current challenges on this technology is a deeper understanding of this phenomenon in order to adopt it into practical device designs. In this work, a theoretical analysis of the stimulated emission of ZnO nanowires taking into consideration of the piezotronics effect has been conducted using the quantum mechanics theory. It is revealed that extra piezoelectric charges induced by applied mechanical forces increase the overall charge density of the nanowire, subsequently enhancing the emission intensity. Electronic bandgap varying with the diameter of the nanowire determines the peak value in the electromagnetic spectrum. Both wavelength and intensity of the stimulated emission can be tuned by controlling the dimension of the nanowires and external applied mechanical forces.

Enhancement of the near-band-edge photoluminescence of ZnO nanowires: Important role of hydrogen incorporation versus plasmon resonances

We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nanoparticles deposited by dc sputtering. A strong enhancement of the near-band-edge emission was observed in all metal-coated samples but also if the samples were treated with Ar plasma without any nanoparticle deposition. High-resolution photoluminescence spectroscopy revealed hydrogen-donor-bound-exciton emission in all samples indicating unintentional hydrogen incorporation. A shorter decay time of the near-band-edge emission was observed in all cases. The results indicate that unintentional hydrogen incorporation plays a dominant role when metal deposition is performed by sputtering.

Enhanced near-band-edge emission and field emission properties from plasma treated ZnO nanowires

Near-band-edge emission in photoluminescence of ZnO nanowires was found to be significantly improved after plasma treatment. The ratio of ultraviolet emission peak intensity before and after plasma treatment is as high as 3.5. Field emission properties were considerably enhanced after plasma treatment as well. Current emission density has been increased two orders of magnitude under the same electric field. Passivation of surface states and surface morphology change were found to be responsible for such an effective improvement. Our results suggest that the plasma treatment method is effective in enhancing both the near-band-edge emission in photoluminescence and field electron emission performance from ZnO nanowires.

Photoluminescence study of ZnO nanowires grown by thermal evaporation on pulsed laser deposited ZnO buffer layer

The ZnO nanowires are grown by thermal evaporation on pulsed laser deposited ZnO buffer layer on silicon. Photoluminescence of ZnO nanowires is studied at various temperatures in the range from 6 K to room temperature and varying excitation intensities. At 6 K, the photoluminescence profile of ZnO nanowires shows bound exciton, free excitons (FXAn=1,FXAn=2), longitudinal optical phonon replicas (FXAn=1-mLO, m=1, 2, 3) of free exciton (FXAn=1), and donor acceptor pairs. The first longitudinal optical phonon replica (FXAn=1-1LO) dominates at room temperature. Photoluminescence peak shifts by 47 meV from free exciton energy with the increase in temperature to room temperature.