K. Venugopal Reddy

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.

Structural and magnetic properties of Ni 0.5−X mg x cu 0.05 Zn 0.45 Fe 2 O 4 ferrites for multilayer chip inductor applications

Ni0.5−xMgxCu0.05Zn0.45Fe2O4 (x=0.0, 0.4 and 0.5) ferrites were prepared through sol-gel method and investigated their electromagnetic properties suitable for Multi layer chip inductor (MLCI) applications. Initial permeability and AC electrical resistivity are found to increase with increase in Mg substitutions. It is also observed that initial permeability is constant up to 10MHz frequency range showing high operating frequency of the material. The parameters like resonance field and spin-spin relaxation time obtained from Electron spin resonance spectra (ESR) increased with increasing Mg concentration, whereas peak - to - peak line width decreased. The observed variations have been analyzed and discussed in detail.

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.

RETRACTED CHAPTER: An Intense Green Emission From ZnO Nanoparticles Coated with MgO

This paper addresses the effects of annealing temperature on photoluminescence of ZnO nanoparticles coated with MgO. ZnO nanoparticles as well as ZnO coated with MgO showed only a sharp UV emission peak positioned at 396 nm at an annealing temperature of 600 °C. As the annealing temperature increased from 600 to 900 °C, the intensity of green emission enhanced monotonously. The green emission intensity at 900 °C is 18 times higher than its value at 700 °C. But at 1,000 °C, green emission intensity decreased. FT-IR spectra of ZnO@MgO showed that MgO evaporation took place with increase of temperature from 700 to 1,000 °C. These results indicates that intensity of green emission depends on thickness of MgO shell coated over the ZnO nanoparticles.

Effect of temperature on Photoluminescence properties of ZnO/mesoporus silica nanocomposite

This paper reports on Photoluminescence (PL) properties of ZnO nanoparticles incorporated in mesoporous silica matrix (MPS). The effect of temperature and annealing times on photoluminescence properties of ZnO/ MPS nanocomposite were studied. The strong UV emission at 363 nm from the sample annealed in oxygen atmosphere at 550°C indicates the formation of very small ZnO nanoparticles. The sample shows blue-green emission band when annealed at 300°C for three hours. The increase in annealing time to 5h turns the blue-green PL band to blue band and further increase in annealing time causes the increase in intensity without any shift. Quenching of blue emission at high temperatures is observed.