Abstract: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 ℃, 400 ℃ and 500 ℃ with different heating rates. At 500 ℃, 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 ℃ and 500 ℃. This was due to the elimination of organic species and improvement in the crystallanity of the sample at 500 ℃.

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Abstract: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 ℃, ZnO exhibited a less intense deep level emission. This negligible deep level emission was attributed to the oxygen vacancies created at higher annealing temperatures.

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In the present paper, Mg and Cu co-doped ZnO nanoparticles (Zn 0.95-x Mg 0.05 Cu x O) synthesized using SolGel method and their structural, optical properties were studied. Hexagonal wurtzite structure of ZnO was confirmed from XRD results. With Cu doping CuO related phase was formed without altering the crystal structure. The average crystallite size of ZnO decreased with increase of Mg and Cu co-doping. TEM results confirmed the nano size crystalline nature of ZnO nanoparticles. From FE-SEM micrographs, the particle sizes decreased and the morphology became less hexagonal with increase of Cu concentrations along with Mg in ZnO. The weaker and broadened E 2 (high) mode in Raman with increase of Cu doping concentrations may be attributed to wurtzite crystalline structure of ZnO is weakened. Thus, resulting to reduction of the growth induced strains which in good agreement with XRD results. From UV-Vis analysis, fundamental exciton absorption is observed at 377 nm for undoped ZnO. With addition of the dopants (Mg, Cu) the peak got blue shifted from 377 to 355 nm. The blueshift was attributed to the strains produced with dopants but not due to quantum confinement effect due to the sizes of the particles are not comparable of the Bohr atomic radius.