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71.
A Sarkar M Chakrabarti D Sanyal D Bhowmick S Dechoudhury A Chakrabarti T Rakshit SK Ray 《J Phys Condens Matter》2012,24(32):325503, 1-325503, 9
Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6?MeV H(+) ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378?eV (10?K). The irradiation creates an intense and narrow emission at 3.368?eV (10?K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368?eV emission indicate its origin as a 'hydrogen at oxygen vacancy' type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164?±?1?ps) and irradiated crystal (175?±?1?ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ~4?×?10(17)?cm(-3) (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ~175?ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed. 相似文献
72.
S. Chattopadhyay S.K. Neogi P. Pandit S. Dutta Tamita Rakshit D. Jana S. Chattopadhyay A. Sarkar S.K. Ray 《Journal of luminescence》2012,132(1):6-11
A systematic study on the modification of optical properties in mechanically milled ZnO powder has been reported here. The average grain size of the powder becomes ~20 nm within 4 h of milling. Fluctuations of average grain size have been noticed at the initial stage of milling (within 15 min). Changes in grain morphology with milling have also been noticed in scanning electron micrographs of the samples. Room temperature optical absorption data shows a systematic red shift of absorption band edge (~3.25 eV). The band tail parameter (extracted from the optical absorption just below the band edge) follows a simple exponential relation with the inverse of the average grain size. Significant increase of the band tail parameter has been noticed at low grain size regime. It has been analyzed that high values of band tail parameter is a representative of VZn–VO type divacancy clusters. Room temperature photoluminescence spectra show decrease (except for 120 min milling) of band edge emission intensity with increase of milling time. Subsequent decrease of sub-band edge emission is, however, less prominent. The variation of PL intensity ratio (intensity at band edge peak with that at 2.3 eV) follows simple exponential decrease with the increase of band tail parameter. This indeed shows that band edge emission in ZnO is related with the overall disorder in the system, not grain size induced only. 相似文献
73.
Electro-optic material has several applications in optical communication, integrated optics and in data processing. The modulator is generally used for the purpose of amplitude and phase modulation of optical wave by the electrical message signal. Again the Vπ voltage of an electro-optic modulator is an important parameter for the modulator. For the application of the Vπ amount of electrical signal in the modulator the phase difference between two specific orthogonally polarized light waves changes from 0 to π. Thus the increase of Vπ relates with the increase of electrical power requirement for modulation. Here in this paper the authors propose a new and novel concept for reduction of Vπ voltage for the modulator. To reduce the value of the Vπ voltage the multi passing technique of the beam through the modulator is used. If Vπ is reduced the power requirement as well as the modulation cost will be greatly reduced to achieve a faithful and a meaningful optical communication. This paper describes also the necessary optical systems required for the multi passing technique. 相似文献
74.
We report on previously unobserved intersystem degeneracies in two-component equal-mass Fermi gases with interspecies zero-range interactions under isotropic harmonic confinement. Over the past 10 years, two-component Fermi gases consisting of n_{1} spin-up and n_{2} spin-down atoms with interspecies zero-range interactions have become a paradigm for modeling condensed matter systems, nuclear matter, and neutron matter. We show that the eigenenergies of the (n_{1}+1,n_{2}-1) system are degenerate with the eigenenergies of the (n_{1},n_{2}) system for any s-wave scattering length a_{s}, including infinitely large, positive, and negative a_{s}. The existence of the intersystem degeneracies is demonstrated explicitly for few-body systems with n_{1}+n_{2}=4, 5, and 6. The degeneracies and associated symmetries are explained within a group theoretical framework. 相似文献
75.
S.C. Parida S.K. Rakshit S. Dash Ziley Singh B.K. Sen V. Venugopal 《Journal of solid state chemistry》2006,179(7):2212-2230
The thermodynamic properties of three different types of ternary oxides RFeO3(s), R3Fe5O12(s) and RFe2O4(s) (where R=Ho and Er) have been determined by calorimetric and solid-state galvanic cell methods. Heat capacities of RFeO3(s) and R3Fe5O12(s) have been determined by differential scanning calorimetry from 130 to 860 K. Heat capacity measurements from 130 to 860 K revealed λ-type anomalies for RFeO3(s) and R3Fe5O12(s) compounds which are assigned due to magnetic order-disorder transitions. The oxygen chemical potentials corresponding to the three-phase equilibria involving these ternary oxides have been determined by using solid-state electrochemical cells. The standard molar Gibbs energies of formation of RFeO3(s), R3Fe5O12(s) and RFe2O4(s) have been computed from the oxygen potential data. Based on the thermodynamic information, oxygen potential diagrams have been computed for the systems R-Fe-O (R=Ho and Er) at two different temperatures: T=1250 and 1450 K. Thermodynamic functions like , , Ho, Go, , , , , and have been generated for the compounds RFeO3(s) and R3Fe5O12(s) based on the experimental data obtained in this study and the available data in the literature. 相似文献
76.
Rupali Mishra Raghvendra S. Yadav Avinash C. Pandey Sharda. S. Sanjay 《Journal of luminescence》2010,130(3):365-198
We report the formation of highly stable and luminescent ZnO@Cd(OH)2 core-shell nanoparticles by simple introduction of cadmium salt in the initial precursor solution, used to synthesize ZnO nanoparticles by sol-gel route. The cadmium to zinc salt concentration ratio has been also varied to control the growth of ZnO nanoparticles at the smaller particle size. Formation of ZnO@Cd(OH)2 core-shell nanostructure has been confirmed by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). UV-vis absorption spectroscopy exhibits blue-shift in absorption edge on increasing cadmium concentrations. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO@Cd(OH)2 nanoparticles in comparison to bare ZnO nanoparticles. It is postulated that Cd(OH)2 layer at the surface of ZnO nanoparticles prevents the agglomeration of nanoparticles and efficiently assists the trapping of hole at the surface site, a first step necessary for visible emission. The Fourier transform infrared spectroscopy (FTIR) also supports our assumption about surface chemistry. 相似文献
77.
P. MAITI P.RAKSHIT S. BANERJEA 《应用数学和力学(英文版)》2011,32(5):635-644
The present paper is concerned with scattering of water waves from a vertical plate, modeled as an elastic plate, submerged
in deep water covered with a thin uniform sheet of ice. The problem is formulated in terms of a hypersingular integral equation
by a suitable application of Green's integral theorem in terms of difference of potential functions across the barrier. This
integral equation is solved by a collocation method using a finite series involving Chebyshev polynomials. Reflection and
transmission coefficients are obtained numerically and presented graphically for various values of the wave number and ice-cover
parameter. 相似文献
78.
Rupali Rastogi Nazia Tarannum Ranu Agarwal R. J. Butcher 《Phosphorus, sulfur, and silicon and the related elements》2017,192(3):300-306
The synthesis of novel dithiophosphate derivatives has been achieved. Two O,O′-alkanediyl S-(N-phthalimidomethyl) dithiophosphates and two Zinc bis(O,O′-alkanediyl) dithiophosphates are synthesized by an easy and facile chemical synthetic route. Zinc bis[O,O′-(2-methylpentane-2,4-diyl) dithiophosphate] L1, Zinc bis[O,O′-(2-ethylhexane-1,3-diyl) dithiophosphate] L2, O,O′-(2-methylpentane-2,4-diyl) S-(N-phthalimidomethyl) dithiophosphate L3 and O,O′-(2-ethylhexane-1,3-diyl) S-(N-phthalimidomethyl) dithiophosphate L4 are synthesized from the respective ammonium salts. Compounds L1, L2, L3, and L4 are characterized by (CHN) elemental analysis, ESI mass, FT-IR, 1H, 13C, and 31P NMR techniques. The crystal structure of ammonium O,O′-(2-methylpentane-2,4-diyl) dithiophosphate is discussed. L1, L2, L3, and L4 were evaluated for antimicrobial activity. It was found that the phthalimide derivatives L3 and L4 showed much better antifungal potential against some species of fungus. The Zinc dithiophosphates L1 and L2 showed good antibacterial activity against Bacillus cereus and Escherichia coli. 相似文献
79.
Excited state proton transfer (ESPT) in biologically relevant organic molecules in aqueous environments following photoexcitation is very crucial as the reorganization of polar solvents (solvation) in the locally excited (LE) state of the organic molecule plays an important role in the overall rate of the ESPT process. A clear evolution of the two photoinduced dynamics in a model ESPT probe 1-naphthol (NpOH) upon ultrafast photoexcitation is the motive of the present study. Herein, the detailed kinetics of the ESPT reaction of NpOH in water clusters formed in hydrophobic solvent are investigated. Distinct values of time constants associated with proton transfer and solvent relaxation have been achieved through picosecond-resolved fluorescence measurements. We have also used a model solvation probe Coumarin 500 (C500) to investigate the dynamics of solvation in the same environmental condition. The temperature dependent picosecond-resolved measurement of ESPT of NpOH and the dynamics of solvation from C500 identify the magnitude of intermolecular hydrogen bonding energy in the water cluster associated with the ultrafast ESPT process. 相似文献
80.