S. Pal; A. Sarkar; D. Sanyal; T. Rakshit; D. Kanjilal; P. Kumar; S. K. Ray; D. Jana
Abstract
1.2 MeV Argon (Ar) ion irradiation turns white coloured ZnO to yellowish (fluence 1 × 10 14 ions/cm 2 ) and then reddish brown (1 × 10 14 ions/cm 2 ). At the same time the material becomes much more conducting and purely blue luminescent for the highest fluence of irradiation. To get ...
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1.2 MeV Argon (Ar) ion irradiation turns white coloured ZnO to yellowish (fluence 1 × 10 14 ions/cm 2 ) and then reddish brown (1 × 10 14 ions/cm 2 ). At the same time the material becomes much more conducting and purely blue luminescent for the highest fluence of irradiation. To get insight on the defects in the irradiated samples Ultraviolet-visible (UV-vis) absorption, Raman, and photoluminescence (PL) spectroscopy and Glancing Angle X-Ray Diffraction (GAXRD) measurements have been carried out. Enhancement of overall disorder in the irradiated samples is reflected from the GAXRD peak broadening. UV-vis absorption spectra of the samples shows new absorption bands due to irradiation. Complete absorption in the blue region of the spectrum and partial absorption in the green and red region changes the sample colour from white to reddish brown. The Raman peak representing wurtzite structure of the ZnO material (~ 437 cm -1 ) has decreased monotonically with the increase of irradiation fluence. At the same time, evolution of the 575 cm -1 Raman mode in the irradiated samples shows the increase of oxygen deficient disorder like zinc interstitials (IZn) and/or oxygen vacancies (VO) in ZnO. PL spectrum of the yellow coloured sample shows large reduction of overall luminescence compared to the unirradiated one. Further increase of fluence causes an increase of luminescence in the blue region of the spectrum. The blue-violet emission can be associated with the interstitial Zn (IZn) related optical transition. The results altogether indicates IZn type defects in the highest fluence irradiated sample. Large changes in the electrical resistance and luminescent features of ZnO using Ar ion beam provides a purposeful way to tune the optoelectronic properties of ZnO based devices.
Anand Kumar Tripathi; Mohan Chandra Mathpal; Promod Kumar; Vivek Agrahari; Manish Kumar Singh; Sheo Kumar Mishra; M. M. Ahmad; Arvind Agarwal
Abstract
The Ni doped titania nanostructures were synthesized by sol-gel method followed by calcination at 400°C for one hour. The optical band gap for these nanostructures indicates the red shift. The doped TiO2 nanostructures are spherical in shape. The pure TiO2 exhibits all the possible emission bands ...
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The Ni doped titania nanostructures were synthesized by sol-gel method followed by calcination at 400°C for one hour. The optical band gap for these nanostructures indicates the red shift. The doped TiO2 nanostructures are spherical in shape. The pure TiO2 exhibits all the possible emission bands while Ni-doped TiO2 nanoparticles show blue-green emission bands. The results suggest that Ni2+ replace some Ti 4+ in TiO2 lattice with tensile strain while TiO2 remained in the form of anatase phase, reduces its band gap energy. The synthesized TiO2 exhibits enhanced photoconducting properties. The work suggest that the titania based materials can have potential applications in photovoltaics, optoelectronic devices and photoconductors in replacement of expansive materials by controlling the compositions and morphology of the nanostructures.
Vikash Kumar; Swati Kumari; Pawan Kumar; Manoranjan Kar; Lawrence Kumar
Abstract
The correlation between structural and optical properties of nanocrystalline ZnO synthesized by the citrate precursor method has been investigated. The Rietveld refinement of X-ray diffraction pattern confirms the P63mc space group and formation of single phase hexagonal wurtzite structure with presence ...
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The correlation between structural and optical properties of nanocrystalline ZnO synthesized by the citrate precursor method has been investigated. The Rietveld refinement of X-ray diffraction pattern confirms the P63mc space group and formation of single phase hexagonal wurtzite structure with presence of tensile strain at the lattice site. The presence of Raman active optical phonon mode at 436 cm -1 which is a significant character of ZnO with hexagonal wurtzite structure supports the XRD result. FE-SEM result shows that the size of the particle is about 20 nm with nearly spherical shapes. The optical band gap energy at room temperature has been calculated as 3.28 eV using the Tauc plot technique. The UV-Vis sub-gap absorption curve supports the presence of strain inside the crystal. The photoluminescence spectrum indicates the dominancy of the defect related deep level or trap state emissions over the near band edge UV emissions using an excitation wavelength of 320 nm.
