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Gautam, Sanjeev,Chae, Keun Hwa,Llanos, Jaime,Peñ,a, Octavio,Asokan, K. Elsevier 2018 Vacuum Vol.158 No.-
<P><B>Abstract</B></P> <P>The oxytellurides are layered structure material which shows low lattice thermal conductivity and hence making them suitable for high temperature thermoelectric applications. We report the electronic structural properties of rare-earth doped oxytellurides [Ln<SUB>2</SUB>O<SUB>2</SUB>Te (Ln = La, Sm and Gd)] prepared by solid state reaction method. This research is focused on the suitability of rare-earth oxychalcogenide as a thermoelectric material using the electronic structure investigations. The X-ray absorption spectra at O K-edge show the O 2<I>p</I> bonding with Ln 5<I>d</I> and 4<I>f</I> and Te 5s states and the Ln M-edges show that the valences of Ln are to be trivalent or mixed states. The Ln M-edges are also simulated with Cowan code, and electronic structures of these oxytellurides are discussed. The substitution of different rare earth metals at the Ln-site, may enhance the thermoelectric property and stability of the material.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oxytellurides Ln<SUB>2</SUB>O<SUB>2</SUB>Te (Ln = La, Sm and Gd) synthesized by the solid state reaction. </LI> <LI> NEXAFS shows the O 2<I>p</I> bonding with Ln 5d and, 4f and Te 5s states. </LI> <LI> Ln M-edge NEXAFS confirm the valences of Ln are to be trivalent and mixed. </LI> <LI> Cowan code and Thole et al. hypothesis are used to discuss the electronic structure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Electronic structure studies of Fe-doped ZnO nanorods by x-ray absorption fine structure
Gautam, Sanjeev,Kumar, Shalendra,Thakur, P,Chae, K H,Ravi Kumar,Koo, B H,Lee, C G Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.17
<P>We report the electronic structure studies of well-characterized polycrystalline Zn<SUB>1−<I>x</I></SUB>Fe<SUB><I>x</I></SUB>O(<I>x</I> = 0.0, 0.01, 0.03 and 0.05) nanorods synthesized by a co-precipitation method using x-ray absorption fine structure (XAFS). X-ray diffraction (XRD) reveals that Fe-doped ZnO crystallizes in a single phase wurtzite structure without any secondary phase. From the XRD pattern, it is observed that peak positions shift towards lower 2&thetas; value with Fe doping. The change in the peak positions with increase in Fe contents clearly indicates that Fe ions replace Zn ions in the ZnO matrix. Linear combination fittings at Fe <I>K</I>-edge demonstrate that Fe is in a mixed-valent state (Fe<SUP>3+</SUP>/Fe<SUP>2+</SUP>) with a ratio of ∼7 : 3 (Fe<SUP>3+</SUP> : Fe<SUP>2+</SUP>). XAFS data are successfully fitted to wurtzite structure using IFEFFIT and Artemis. The results indicate that Fe substitutes Zn site in the ZnO matrix in tetrahedral symmetry.</P>
Gautam Alok Sagar,Sanjeev Kumar,Sneha Gautam,Aryan Anand,Ranjit Kumar,Abhishek Joshi,Kuldeep Bauddh,Karan Singh 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.4
The present paper designed to understand the variations in the atmospheric pollutants viz. PM10, PM2.5, SO2, NO2, and CO during the COVID-19 pandemic over eight most polluted Indian cities (Mumbai, Delhi, Bangalore, Hyderabad, Lucknow, Chandigarh, Kolkata, and Ahmedabad). A significant reduction in the PM2.5 (63%), PM10 (56%), NO2 (50%), SO2 (9%), and CO (59%) were observed over Major Dhyan Chand Stadium. At Chhatrapati Shivaji International Airport, a decline of 44% in PM2.5 and 50% in PM10 was seen just a week during the initial phase of the lockdown. Gaseous pollutants (NO2, SO2 & CO) dropped up-to 36, 16, and 41%, respectively. The Air Quality Index (AQI) shows a dramatic change from 7% to 67% during observation at Chandigarh and Ballygunge during the inspection. Whereas, Ahmedabad, Worli, Income Tax Office, Talkatora, Lalbagh, and Ballygaunge have showed a significant change in AQI from 25.76% to 68.55%. However, Zoo Park, CST, Central School, and Victoria show relatively low variation in AQI in the range of 3.0% to 14.50% as compare to 2019 after lockdown. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) analysis suggested that long range transportation of pollutants were also a part and parcel contributing to changes in AQI which were majorly coming from the regions of Iran, Afghanistan, Saudi Arabia, as well as a regional grant from Indian Gangatic plains and Delhi Non-capital region.
Study of the Electronic Structure and Luminescence of Mn-doped SrS Phosphors
Ankush Vij,Sanjeev Gautam,채근화,R. Brajpuriya,S.P. Lochab 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.10
In this paper, the electronic structure and the luminescence properties of Mn (1 mole%)-doped SrS phosphors synthesized by using the solid state diffusion method are reported. The X-ray diffraction pattern reveals a single-phase rocksalt structure, and the average crystallite size calculated using a Williamson-Hall plot is 72 nm. The near-edge X-ray absorption fine structure (NEXAFS) collected at Mn L<sub>3,2</sub>-edges confirms the presence of divalent Mn in SrS. A bright green photoluminescence (PL) at 547 nm is observed at an excitation wavelength of 355 nm, which may be attributed to the <sup>4</sup><i>T</i><sub>1</sub>−<sup>6</sup><i>A</i><sub>1</sub> inner atomic transition of the 3<i>d</i> electrons in the Mn<sup>2+</sup> ion under the cubic crystal field of SrS. We have also studied the thermoluminescence (TL) of UV (254 nm)-irradiated Mn-doped SrS phosphors. The TL glow curve has a well-resolved single peak around 360 K, which shifts slightly to lower temperatures with increasing UV exposure time, confirming second-order kinetics. A kinetic analysis of the experimental TL glow curve has been carried out using Chen’s peak shape method to determine the trapping parameters.