Ch. Sujatha

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.

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.

Photoluminescence of ZnO−SiO2 nanocomposite and its excitation wavelength dependence

The influence of SiO2 capping and excitation wavelength on photoluminescence (PL) of ZnO nanoparticles was studied. XRD and FE-SEM analysis of the samples showed that the particles size reduced from 54 nm to 10 nm with SiO2 capping. The PL spectra of ZnO−SiO2 nanocomposites were acquired with 320 and 353 nm excitation wavelengths. A sharp UV emission positioned at 398 nm was obtained with 353 nm excitation wavelength and its intensity is five times greater than the one achieved with 320 nm excitation wavelength. It was also found that with SiO2 capping, intensities of the 418 nm and 587 nm emission peaks increased.

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.

Observation of excitation wavelength dependent photoluminescence from ZnO nanoparticles embedded in mesoporous silica

This manuscript reports on the excitation wavelength dependent photoluminescence (PL) of ZnO nanoparticles embedded in mesoporous silica (MS) matrix. FT-IR spectra of MS and ZnO/MS nanocomposite confirmed the unaltered structure of MS with ZnO loading. The successful encapsulation of ZnO nanoparticles in MS matrix was evidenced by HR-TEM. The PL of ZnO/MS was red shifted from 395 nm to 504 nm only by changing the excitation wavelength. This kind of unusual behavior is termed as red edge effect (REE).

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.