A.N. Mallika

Synthesis and optical characterization of porous ZnO

In this paper, a simple and cheap method to prepare porous ZnO by using zinc nitrate, ethanol and triethanolamine (TEA) is reported. The as-prepared sample consisted of nano and micro pores. The sample was calcined at 300 °C, 400 °C and 500 °C with different heating rates. At 500 °C, the nano pores disappeared but the sample maintained its micro porosity. Field emission scanning electron microscopy (FE-SEM) pictures confirmed that the size and growth of ZnO nanoparticles depended on the heating conditions. The infrared (IR) absorption peak of Zn-O stretching vibration positioned at 457 cm−1 was split into two peaks centered at 518 cm−1 and 682 cm−1 with the change of morphology. These results confirmed that Fourier transform infrared (FT-IR) spectrum was sensitive to variations in particle size, shape and morphology. The photoluminescence (PL) spectrum of porous ZnO contained five emission peaks at 397 nm, 437 nm, 466 nm, 492 nm and 527 nm. Emission intensity enhanced monotonously with increase of temperature and the change was rapid between temperatures of 300 °C and 500 °C. This was due to the elimination of organic species and improvement in the crystallanity of the sample at 500 °C.

Annealing effects on the structural and optical properties of ZnO nanoparticles with PVA and CA as chelating agents

The effects of annealing temperatures and chelating agents on the structural and optical properties of ZnO nanoparticles were investigated. The average particle size of ZnO nanoparticles increased with increase of annealing temperatures. The decrease of the full width at half maximum (FWHM) with increasing annealing temperatures inferred increase of particle/grain growth. The grain sizes were also observed to be increased with increase of annealing temperatures. From the absorption spectra of the samples, the absorption was red-shifted and the energy band gap was blue-shifted with increase of annealing temperatures. A sharp UV emission peak was observed and the intensity of this peak increased with annealing temperatures corresponding to the high crystallinity in the samples. At high annealing temperature of 700°C, ZnO exhibited a less intense deep level emission. This negligible deep level emission was attributed to the oxygen vacancies created at higher annealing temperatures.

Optimizing the Optical Properties of ZnO Nanoparticles with Al Doping

This paper reports on the structural and optical properties of Al with different doping concentrations on ZnO nanoparticles prepared through Sol–Gel method. The XRD results revealed the wurtzite structure of ZnO without any secondary phase related to Al. The absorption spectrum of the sample exhibited an absorption in UV region and the Photoluminescence properties of Al doped ZnO were studied.

Effect of Mg substitution on the structural and optical properties of ZnO by sol-gel method

This paper reports on the structural and optical properties of Mg doped ZnO nanoparticles through sol-gel method using polyvinyl alcohol as chelating agent. For studying the effect of Mg doping on particle size and morphology, the prepared samples were characterized by using X-ray diffractometer, and Field Emission Scanning Electron Microscope (FE-SEM). The optical properties of the samples were investigated by UV-Vis spectroscopy (UV-Vis), and Fourier Transform Infrared Spectroscopy (FTIR). The particles size was evaluated using Scherrers formula from XRD patterns. It was observed from XRD studies that the particles size decreased with increasing Mg concentrations. It is observed from FE-SEM microstructure that the grain size of the samples decreased with increasing Mg doping. The samples exhibited a blue shift in absorption in UV spectra indicating good optical properties.