Vol. 8 & Issue 3 ; Section C : Physical Sciences

Date : May 2018 to July 2018

 

A theoretical study of optical properties of CdS quantum dots and evaluation of optical band gap of CdS nanoparticles, particle size and temperature dependent intensity of PL-spectra as a function of photon energy

Chandni Verma, Hari Sumiran Singh and L. K. Mishra

[DOI: 10.24214/jcbps.C.8.3.20114]

  • Abstract

    Using the theoretical formalism of N. Soltani etal [Chalcogenide Lett. 9, 321(2012)], N. Q. S. Sabir [Int. J. Nanosci. Nanotechnol. 8, 111 (2012)], P. Ghosh et al.. [arXiv:1606.06711v][cond-mat.mtrl-Sci] 21 June 2016 and Silan Baturang [J. BAUN Inst. Sci. Technol. 19, 264 (2017)], we have theoretically studied CdS nanoparticle and CdS QDs. We have evaluated energy band gap and particle size of fcc and hcp structure nanoparticle. Our theoretically obtained results show that particle size increases with increase of the irradiation times whereas energy band gap decreases with increase of irradiation times. The particle size obtained for hcp structure is large compared to fcc structure. We have evaluated time dependent PL-intensity as a function of photon energy for different temperature and Full width at half maximum (FWHM) broadening as a function of temperature. Our evaluated results show that temperature dependent PL-intensity increase, attain maximum value and then decrease as a function of photon energy for each temperature. However the maximum value of peak enhances as one increase the temperature. Our results of FWHM broadening as a function of temperature increase with temperature. The results show that the large no of relaxation processes are involved in this broadening.The dominant contribution comes from exciton-phonon coupling and ionized impurity scattering. Our theoretically evaluated results are in good agreement with those of the other theoretical workers.The entire evaluation in this paper is based on time independent Schrodinger equation with Density Functional method (DST), Brus equation and empirically established Varshni relation. These studies will be quite helpful in order to understand the different relaxations processes involved in light emission from CdS nanoparticle and CdS QDs. These are very important for future applications in photonic and optoelectronic devices.

A theoretical study of electronic, thermal and surface properties of CdS/Cd1-xZnxS quantum dot and evaluation of exciton binding energy, exciton oscillator strength and radiative life time of the confined exciton as a function of dot radius

Chandani Verma, Hari Sumiran Singh and L. K. Mishra

[DOI: 10.24214/jcbps.C.8.3.21532]

  • Abstract

    Using the theoretical formalism of A. John Peter etal.[Chin Phys B21, 087302 (2012)], J. Hu etal.[Science 292, 2060 (2001)], W. Su etal.[J. Am. Chem. Soc. 124, 12944 (2002)] and A. Franceschetti etal.[Phys. Rev B60, 1819 (1999)], we have theoretically studied the electronic and optical properties of CdS/Cd1-xZnxS quantum dot. We have also performed a comparative study of electronic and optical properties of CdS and CdSe quantum dots. The entire evaluation is based on the Variatioal technique within the single band effective mass approximation. Our theoretically evaluated results show that the exciton binding energy increases with increase of dot radius for each value of the concentration x from 0.2 to 0.6. The optical band gap decreases with increase of dot radius and also with increase of Cd content. Exciton oscillator strength increases with dot radius but radiative life time of the confined exciton decreases with increase of dot radius. Our comparative theoretical study of CdS and CdSe dot show that VBM (Valence band maximum) to CBM (Conduction band maximum) interband transitionincreases with size. For the same size of the dot, it is observed that e-h Coulomb binding energy is stronger in CdS than in CdSe dot.These theoretical results will be quite useful for further research in device appliacation for CdS and CdSe band material.

A theoretical study of Dynamic Structure factor and evaluation of impurity scattering rate, dispersion relation of collective mode and Spectral density of a Fermi super fluid along the BCS-BEC crossover region

Shipra Kumari, Pradhan Durga Shankar Prasad  and L. K. Mishra

[DOI: 10.24214/jcbps.C.8.3.23355]

  • Abstract

    Using the theoretical formalism of T. H. Johnson etal.[PRL, 116,240403 (2016)], Y. Nishida [PRL 114, 115302 (2015)], W. Yi and X. Chi[Phys. Rev. A92, 013623 (2015)] and A. Sindona etal. [PRL 111, 165303 (2013)], we have theoretically evaluated the dynamic structure factor (DSF) and spectral density of Fermi super fluid along BCS-BEC crossover regime. The evaluation is based on a model in which an impurity atom is trapped by an anharmonic potential with...........................

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Spectroscopic Studies on the Mechanism of Interaction between Vitamin B12 and Vitamin C with Bovine Serum Albumin

Husain Alsamamra, Ibrahim Hawwarin, Musa Abutier

[DOI: 10.24214/jcbps.B.8.3.25672]

  • Abstract

    The interaction between vitamin C and vitamin B12 with bovine serum albumin has been investigated. The binding mechanism was studied by UV-absorption and fluorescence spectroscopy. From spectral analysis both vitamins showed strong ability to quench the intrinsic fluorescence of BSA through a static quenching procedure. The binding constants are estimated to be 1.39 x 104 M-1 for vitamin C and 1.61 x 104 M-1 for vitamin B12. FT-IR spectroscopy was used to determine the protein secondary structure. The observed spectral changes indicates an increase of intensity for HSA-vitamin C interaction and a reduction of intensity for HSA-vitamin B12 interaction. While in the difference spectra of vitamin B12-BSA complexes, intensity decreases as the concentration of vitamin B12 increases for amide I. This variation of intensity is related indirectly to the formation of H-bonding in the complex molecules.

A theoretical study of quantum critical behavior and evaluation of Spin-lattice relaxation rate, magnetic entropy, pressure dependent Neel temperature and Knight shift of some heavy-electron materials

Madhavi Kumari, Satish Chandra Prasad and L. K. Mishra,

[DOI: 10.24214/jcbps.C.8.3.27390]

  • Abstract

    Using the theoretical formalism of Y-F Yang and D. Pines [Proc Natl Acad Sci USA 109, E3060-E3066 (2012) and Y-F Yang etal [ PRL, 103, 199004 (2009)], we have theoretically studied the quantum critical behavior of some heavy-electron materials. We have evaluated NMR/NQR spin-lattice relaxation rate as a function of temperature for some fixed values of pressure, magnetic entropies at Neel temperature as a function of pressure, Kondo liquid temperature as a function of pressure, specific heat coefficient and NMR Knight shift as a function of magnetic field and Hall coefficient RH as a function of temperature for some heavy-electron materials. Our evaluated results show that spin-lattice relaxation rate increases with increase of temperature for all the values of pressure taken. The values are large for low pressure but small for large pressure. Our evaluated values of Kondo liquid temperature as a function of pressure increase with increase of pressure. Our evaluated values of magnetic entropies at Neel temperature as a function of pressure decrease with increase of pressure. Our evaluated results of specific heat coefficient and NMR Knight shift decrease with increase of magnetic field. Our evaluated values of Neel temperature TN and delocalization temperature TL as a function of magnetic field show that TN decrease with magnetic field but TL increase with magnetic field. Our evaluated results of Neel temperature as a function of pressure indicate that the value increase with pressure. Our evaluated values of Hall Coefficient RH as a function of temperature show that RH decrease with increaseof temperature. Our all evaluated results are in good agreement with the experimental data and also with other theoretical workers. The entire evaluation in this paper is based on phenomenological two-fluid model. Here, there are two very independent liquids Spin liquid (SL) and Kondo liquid (KL) with two very characteristic temperatures. These liquids play very important role in explain the quantum critical behavior of heavyelectron materials.

Estimate the types and the natural radioactivity element contents and the radiological hazard values of some
sediment samples at Benghazi coast–Libya

Jemila Mussa Ali,Hamad. M. Adress.Hasan and Adel .A.Al-Majbari

[DOI: 10.24214/jcbps.C.8.3.29195.]

  • Abstract

    The natural radioactivity element types and their concentrations of some sediment samples collected from Benghazi coast (Libya) were determined by used high pure germanium (HPGe) gamma-ray spectroscopy. The radio activity contents of the radionuclides were used to calculate the radiological hazard values. The results showed that the average activity concentrations of 238U , 232Th and 40K were 11.03, 4.185 and 27.94 Bq/kg respectively. The external radiation hazard values were ranged between (0.039 - 0.137 Bq/kg). The recorded values which obtained in the this study for the sediment samples under investigation were less than the recommended of safe values
    and permissible limits which given by UNSCEAR.

The Existence of Anharmonic Effect due to Phonon-Phonon Interactions and its Contribution to Specific Heat of Materials.

P. Poddar, A.K. Sah& D.P. Singh

[DOI: 10.24214/jcbps.C.8.3.29606]

  • Abstract

    Previous researchers have revealed the anharmonicity of the lattice waves to cause deviation in specific heat from Debye T3 law. The energy spectrum of phonons can not be fully described by the Debye law. For anharmonicity of lattice waves, this contribution must be expected for metals and insulators also. Specific heat of metals, viz, Al, Cu, Ag, Ni, Fe, Pd and Pt was identified with the electronic contribution. Later experiment revealed the linear term in specific heat of almost all metals, at low temperatures. But intensive study of the transport properties namely thermoelectric properties, thermal and electrical conductivities of metals at low temperatures finds deviation of the electrons from the free electron model. The light of the recent development in this regard the earlier notion of linear temperature dependent term of specific heat appears to be doubtful, because electrons may not. Debye did not take into account the anharmonicity of the lattice wave in his theory of specific heat of solids at low temperatures.