We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

ZnO nanoparticles were prepared by coprecipitation method at 450C. X-ray diffraction result indicates that the sample is having a crystalline wurtzite phase. Transmission electron microscopy (TEM) result reveals that the ZnO sample is spherical in shape with an average grain size of about 50nm. X-ray peak broadening analysis was used to evaluate the crystalline sizes and lattice strain by the Williamson-Hall (W-H) analysis. All other relevant physical parameters such as strain, stress, and energy density values were also calculated using W-H analysis with different models, viz, uniform deformation model, uniform deformation stress model and uniform deformation energy density model. The root mean square strain was determined from the interplanar spacing and strain estimated from the three models. The three models yield different strain values; it may be due to the anisotropic nature of the material. The mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherrers formula and W-H analysis is highly intercorrelated.

/pdf/williamson-hall-analysis-in-estimation-of-lattice-strain-in-1epz6r1apj.pdf

Williamson-Hall analysis in estimation of lattice strain in nanometer-sized ZnO particles

https://www.tandfonline.com/doi/pdf/10.1088/1468-6996/9/3/035004

Enhanced bioactivity of ZnO nanoparticles?an antimicrobial study

Photoluminescence and cathodoluminescence (CL) spectra of stoichiometric and oxygen-deficient ZnO films grown on sapphire were examined. It was found that the intensities of the green and yellow emissions depend on the width of the free-carrier depletion region at the particle surface; the thinner the width, the larger the intensity. Experimental results and spectral analyses suggest that the mechanism responsible for the green (yellow) emission is the recombination of a delocalized electron close to the conduction band with a deeply trapped hole in the single ionized oxygen vacancy Vo+ (the single negatively charged interstitial oxygen ion Oi−) center in the particle.

Photoluminescence and cathodoluminescence studies of stoichiometric and oxygen-deficient ZnO films

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

https://www.mdpi.com/1996-1944/3/4/2260/pdf

Quantum Dots and Their Multimodal Applications: A Review

Identification of the transition responsible for the visible emission in ZnO using quantum size effects

The luminescence of nanocrystalline ZnO particles: the mechanism of the ultraviolet and visible emission

The influence of particle size on the luminescence quantum efficiency of nanocrystalline ZnO particles

An overview is presented of size-selective photoetching experiments on nanocrystalline semiconductor particles. Four different compounds (CdS, ZnS, PbS, and ZnO) have been prepared by standard colloid−chemical synthetic methods. For CdS, the initial mean radius of 35 A could be gradually decreased to 7.5 A by size-selective photoetching. The adjustment of the particle size can be controlled to a high degree by varying the wavelength of the light that is used. It is also shown that the particle size distribution narrows during the photoetching process from about 40% to 10−15%. For ZnS and ZnO, only the feasibility of the technique could be demonstrated. This is due to the fact that these compounds have very large band gaps which limit the range for photoetching experiments. The initial radius of the ZnO particles was approximately 30−35 A and could be decreased to about 15 A, again accompanied by a narrowing of the particle size distribution. For PbS, no concrete evidence was obtained for the feasibility o...

Size-Selective Photoetching of Nanocrystalline Semiconductor Particles

Summary
Fructan (polyfructosylsucrose) is an important storage carbohydrate in many plant families. fructan:fructan 6G-fructosyltransferase (6G-FFT) is a key enzyme in the formation of the inulin neoseries, a type of fructan accumulated by members of the Liliales. We have cloned the 6G-FFT from onion by screening a cDNA library using barley sucrose:fructan 6-fructosyltransferase (6-SFT) as a probe. The deduced amino acid sequence showed a high homology with plant invertases and 6-SFT. Incubation of protein extracts from transgenic tobacco plants with the trisaccharide 1-kestose and sucrose resulted in the formation of neokestose and fructans of the inulin neoseries with a degree of polymerization up to six. Introduction of the onion 6G-FFT into chicory resulted in the synthesis of fructan of the inulin neoseries, in addition to the synthesis of linear inulin.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313X.1997.11030387.x

Fructan of the inulin neoseries is synthesized in transgenic chicory plants (Cichorium intybus L.) harbouring onion (Allium cepa L.) fructan:fructan 6G-fructosyltransferase

A. van Dijken

Papers

Identification of the transition responsible for the visible emission in ZnO using quantum size effects

The luminescence of nanocrystalline ZnO particles: the mechanism of the ultraviolet and visible emission

The influence of particle size on the luminescence quantum efficiency of nanocrystalline ZnO particles

Size-Selective Photoetching of Nanocrystalline Semiconductor Particles

Fructan of the inulin neoseries is synthesized in transgenic chicory plants (Cichorium intybus L.) harbouring onion (Allium cepa L.) fructan:fructan 6G-fructosyltransferase