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Indian Journal of Pure and Applied Physics

 

 

 

ISSN: 0019-5596

CODEN: IJOPAU 42 (11) 787-866

Volume 42

Number 11

NOVEMBER  2004

 

 

CONTENTS

 

Review Paper

 

Blue electroluminescence in organic semiconductors

Aparna Misra, Lokendra Kumar, Pankaj Kumar, S K Dhawan, M N Kamalasanan* & Subhas Chandra

793

 
Nuclear Physics

 

Cluster radioactivity in barium isotopes

K P Santhosh* & Antony Joseph

806

 

Atomic and Molecular Physics

 

Spectroscopic studies of molluscan shells

R Konwar, R Changmai & G D Baruah*

 

812

Three electron bonding in thiazyl halides-NSZ [Z= F, Cl, Br]

S Mayilavelan*, S Ramadasse & R Balakrishnan

857

 
Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics and Fluid Dynamics
 

Interferometry based security hologram readable with an encoded key hologram

A K Aggarwal*, Sushil K Kaura, Amit K Sharma, Raj Kumar & D P Chhachhia

816

 

Excess volumes, deviation in viscosities and compressibilities of binary mixtures consisting of morpholine, piperidine with methanol and pyridine at different temperatures

G V Rama Rao, A Viswanatha Sarma & C Rambabu*

820

 

Effect of mixed electrolytes on the temperature of sound velocity maximum of water

G Venkata Ramana, E Rajagopal & N Manohara Murthy*

827

 

Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties

 

Application of pseudopotential to III-V semiconductor compounds

A R Jivani, P N Gajjar & A R Jani*

833

 

13C NMR and dielectric relaxation studies of methanol + nitrile systems

V Madhurima, J Sobhanadri & V R K Murthy*

837

 

Short circuit current variation of CIGS solar cells with grain boundaries recombination velocity

Lakshman Singh, Manish Saxena* & P K Bhatnagar

841

 

Effect of Sn impurity on the photoconductivity in a - Se85 Te15 thin films

Vineet Sharma, Anup Thakur, Pradeep S Chandel, G Madhok, N Goyal & S K Tripathi*

845

 

Microwave dielectric relaxation study of binary mixtures of cyclohexylamine with acetophenone and p-chloroacetophenone in dilute solutions of benzene

K K Gupta, A K Bansal, P J Singh* & K S Sharma

849

 

Interdisciplinary Physics and Related Areas of Science and Technology

 

Simple first-order multifunction filter

N A Shah*, S Z Iqbal & B Parveen

854

 

*The corresponding author has been indicated by (*) mark in case of papers with more than one author.

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, November 2004, pp. 793-805

 

 Blue electroluminescence in organic semiconductors

Aparna Misra, Lokendra Kumar*, Pankaj Kumar, S K Dhawan, M N Kamalasanan & Subhas Chandra

 

Light emitting diodes based on organic materials are of considerable interest owing to their attractive characteristics and potential applications in flat panel displays. This paper focuses on some important blue light emitting organic materials. Particularly the attention has been paid to the absorption, photoluminescence (PL), electroluminescence (EL) spectra, current-voltage (I-V) and luminescence-voltage (L-V) characteristics of blue light emitting organic semiconductors, as well as those of the para-hexaphenyl (PHP). Syntheses of some important blue light emitting materials have also been discussed. Para hexaphenyl (PHP), which was synthesized by the conventional Kovacic method, is one of the important blue light emitting p-conjugated oligomers. OLEDs fabricated, using PHP as an emitter, TPD and PBD as the hole transport layer and electron transport layer respectively, gave efficient blue electroluminescence. The photoluminescence (PL) and electroluminescence (EL) of PHP occur at 423 nm, indicating PHP as an excellent blue emitter. This oligomer showed strong absorption peaks at 297 and 318 nm. The devices showed non-linear electrical properties and bright electroluminescence with low turn on voltages (9V). Some of our most recent work in the development of a variety of blue light emitting devices has been included and discussed in detail.

 

[Keyword: Blue light emitters, Electroluminescence, OLEDs, Para hexaphenyl, Photoluminescence, Small molecules]

IPC Code: G 01 J 3 /00; H 01 L 51/00

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp 806-811

 

Cluster radioactivity in barium isotopes

K P Santhosh* & Antony Joseph

 

The half life time and other characteristics for the emission of clusters like 8Be, 16O, 20Ne, 24Mg, 28Si and 32S have been computed within the Coulomb and proximity potential model and the predicted half life time values have been compared with other models. It is found that 8Be emission from 112Ba is most favourable for measurements with the lowest half life time value [log10 (T1/2) = 7.23s]. Geiger-Nuttall (GN) plots for all clusters have been studied and are found to be linear. It is found that the inclusion of proximity potential will not produce any deviation from the linear nature of GN plots. The nuclear structure and shell effects are evident from the observed variation in slope and intercept of GN plots.

 

[Key words: Cluster radioactivity, Cluster model, Fission model]

IPC Code: G 01 T 1/00

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, November 2004, pp 812-815

 

Spectroscopic studies of molluscan shells

R Konwar*, R Changmai & G D Baruah

 

The spectral characteristics of few naturally occurring molluscan shells have been investigated with the help of laser induced fluorescence, X-Rays, absorption and FTIR spectroscopic techniques. The laser induced fluorescence (LIF) or the stimulated laser induced fluorescence from molluscan shells exhibits diffuse bands in the region 5860-6350 Å and some discrete bands in the region 5000-5400Å. The fluorescence spectra of different shells are found to be different. The FTIR spectra show predominantly the vibrational bands of CaCO3. But there are additional bands, which are not characteristic of CaCO3. The X-ray photograph and iridescence pattern of few shells are presented.

 

[Keywords: Laser induced fluorescence, Molluscan shells]

IPC Code: G 01 J 3/42

 

   

 

Indian Journal of Pure & Applied Physics

 Vol. 42, November 2004, pp. 816-819

 

 

Interferometry based security hologram readable with an encoded key hologram

A K Aggarwal, Sushil K Kaura, Amit K Sharma, Raj Kumar & D P Chhachhia

 

A simple and cost-effective method for making security holograms has been presented, which incorporates holographic interferometry as verification feature in addition to spatially separated sharp focus spots. When the security hologram is illuminated with decoding reconstructing beam generated from an encoded key hologram, two spatially separated sharp focus spots emerge at the predefined positions and can be read through a photoelectric detector array. In addition, these focused spots upon divergence in longitudinal direction further generate specific kind of interferometric fringe patterns of random profile contained in them, which are suitable for further visual inspection. These machine-readable and visual verifiable features can be used for better counterfeit-resistant security codes in embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presented.

 

[Keywords: Security holograms, Holograms, Optical security]

IPC Code: G 02B 5/32

 

 

 

Indian Journal of Pure & Applied Physics 

Vol. 42, November 2004, pp. 820-826

 

Excess volumes, deviation in viscosities and compressibilities of binary mixtures consisting of morpholine, piperidine with methanol and pyridine at different temperatures

 G V Rama Rao, A Viswanatha Sarma & C Rambabu*

 

The density, viscosity and ultrasonic velocity in binary liquid mixtures of morpholin, piperidine with methanol and pyridine have been determined at different temperatures from 303.15 to 318.15K over the whole composition range. These data have been utilized to estimate the excess volumes VE, deviation in viscosity (Dh), deviation in adiabatic compressibility (Dbad) and excess intermolecular free length (LfE) at the above temperatures. The excess values have been found to be useful in estimating the strength of the interactions in the liquid mixtures. Analysis of these parameters indicates that there are intermolecular interactions among components of the binary mixtures that lead to the possible hydrogen bond formation (of the type N H-O and NH-N) between unlike molecules.

 

[Key words: Binary mixtures, Density, Ultrasonic velocity, Viscosity]

IPC Code: B 01 J 19/10

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 827-832

  

Effect of mixed electrolytes on the temperature of sound velocity maximum of water

G Venkata Ramana*, E Rajagopal & N Manohara Murthy*

 

Effect of mixed electrolytes (KCl + KBr), (KCl + KI) and (KBr + KI) on the temperature of sound velocity maximum (TSVM) of water, Tw, has been studied by determining the ultrasonic velocity with an accuracy of ± 0.003% using single crystal variable path interferometer working at 3 MHz. The velocity measurements were carried out at ; 2°C intervals over a range of 5°C on either side of TSVM of the solution. The accuracy in fixing TSVM is ± 0.2°C. The structural contribution to the shift in Tw of pure water due to the addition of mixed electrolytes, DTstr, has been found to be negative and increasing with concentration of mixed electrolytes. At any given concentration DTstr of (KCl + KBr) > (KCl + KI) > (KBr + KI). DTstr is also found to vary linearly with ionic strength of the mixed electrolyte solutions, and at any given ionic strength DTstr of (KCl + KBr) > (KCl + KI) > (KBr + KI). The results are explained in terms of enhancement in the structure breaking nature of Cl-, Br- and I- due to K+ and is found to be in the order of I- > Br- > Cl-.

 

[Keywords: Electrolytes, Sound velocity, Water]

IPC code: G 01 N

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 833-836

 

Application of pseudopotential to III-V semiconductor compounds

A R Jivani, P N Gajjar & A R Jani

 

The recently proposed model potential which includes covalent correction terms, is employed to calculate total energy, energy band gap at Jones-zone face and bulk modulus of GaP, GaAs, GaSb, InP, InAs and InSb. The ratio of the covalent bonding term Ecov to the second order term E2 confirms the essentiality of higher order correction for zinc blende-type crystals. The calculated numerical results for the total energy, energy band gap at Jones-zone face and bulk modulus of these compounds are in good agreement with the experimental data than other such theoretical findings.

 

[Keywords: Pseudopotential, Perturbation theory, Semiconductor, Energy band gap]

IPC Code: B 28 D 5/00

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 837-840

 

 13C NMR and dielectric relaxation studies of methanol+nitrile systems

V Madhurima, J Sobhanadri & V R K Murthy

 

13C NMR studies for both spin-lattice relaxation time (T1) and chemical shifts were obtained for two systems namely methanol+acetonitrile and methanol+acrylonitrile. The dielectric dispersion data was also obtained for these systems. The 13C NMR and dielectric dispersion data with a view to understand the conformation of these systems and also to understand the basic mechanisms of relaxation in the same have been presented. A correlation between the rotational correlation time from NMR and the dielectric relaxation time for the two systems have been reported. The confirmation of the ring-like conformer for methanol+acetonitrile system using 13C NMR chemical shift data.

 

[Keywords: Dielectric dispersion, 13C NMR, Methanol, Acetonitrile, Acrylonitrile, ab-initio]

IPC Code: R 01 R 27/26

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, November 2004, pp. 841-844

 

Short circuit current variation of CIGS solar cells with grain boundaries recombination velocity

 Lakshman Singh, Manish Saxena & P K Bhatnagar*

 

The material CuInxGa1-xSe2 (CIGS with 0<x<0.3) has attracted much attention, recently, all over the world as a prospective material for photovoltaic application. The addition of gallium in CIS (CuInSe2) considerably improves not only the performance but the stability and efficiency of the device also. A theoretical analysis of variation of short circuit current density (JSC) of polycrystalline solar cell has been reported. As the grain size (dG) and grain boundary recombination velocity (SGB) play an important role in deciding device characteristics, the calculations of the dependence of short-circuits photocurrent density (JSC) have been done on these parameters. The results show a good agreement with the experimental results. A small discrepancy may be attributed to the fact that the typical shape of the grains was assumed to be square-face columnar shaped.

 

[Keyword: Grain boundaries, Recombination velocity, Grain size, Short circuit current density, CIGS solar cells]

IPC Code: H 01 L 31/0272

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, November 2004, pp. 845-848

 

Effect of Sn impurity on the photoconductivity of a- Se85Te15 thin films

 Vineet Sharma, Anup Thakur, Pradeep S Chandel, G Madhok, N Goyal & S K Tripathi

 

Temperature and intensity dependence of photoconductivity (sph) is studied in vacuum evaporated thin films of Se85Te15 and Se83Te15Sn2 with a view to see the effect of Sn impurity on the photoconductive behaviour of binary a-Se85Te15 alloy. Dark conductivity (sd) is also measured as a function of temperature. The dark conductivity, sd increases and activation energy (DE) decreases after the addition of Sn impurity. sph decreases upon Sn incorporation. Rise of photocurrent shows a maximum before attaining the steady state value and this behaviour decreases after the addition of Sn impurity. Photosensitivity (sph/sd) also decreases. The results are explained in terms of the increase in the density of defect states on Sn incorporation in the Se85Te15 binary alloy.

 

[Keywords: Chalcogenide glasses, Photoconductivity, Defects, Hopping]

IPC Code: G 01 R

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 849-853

  

Microwave dielectric relaxation study of binary mixtures of cyclohexylamine with acetophenone and p-chloroacetophenone in dilute solutions of benzene

K K Gupta, A K Bansal, P J Singh & K S Sharma*

 

Static permittivity at 100 kHz, complex permittivity at 8.93 GHz and high frequency permittivity at frequency of the D-lines of sodium of cyclohexylamine (CHA), acetophenone (ACT), p-chloroacetophenone (PCLA) and for the binary mixtures of CHA+ACT and CHA+PCLA have been measured in dilute solutions of benzene at different temperatures. The measured values of permittivity and dielectric loss have been used to evaluate relaxation times [t0, t(1) and t(2)], dipole moment (m), distribution parameter (a) and thermodynamical parameters like molar free energy of activation (DFÎ), molar enthalpy of activation (DHÎ) and molar entropy of activation (DSÎ). The relaxation times of binary mixture compositions are consistent with the computed values obtained from various theoretical methods. Present study suggests the existence of both the intramolecular and overall orientation in both the binary mixtures. Formation of complexes is noticed in 1:1 binary mixture of CHA+PCLA.

 

[Keywords: Microwave dielectric relaxation, Binary mixtures]

IPC Code: G 01 R 27/26

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 854-856

 

 Simple first-order multifunction filter

 N A Shah, S Z Iqbal & B Parveen

 

A new first-order configuration simultaneously implementing LP, HP, and AP filtering functions is presented. The circuit is based on and employs two CCIIs, two floating, two grounded resistors, and one grounded capacitor. The topology of the circuit is amenable for construction using translinear conveyors (CCCII) also. This version of the circuit facilitates electronic control of cutoff frequency besides offering saving in components as it employs only one capacitor and two resistors instead of five passives. The realizability condition for allpass response is simple and temperature independent. The circuit enjoys low sensitivity figures. The, PS (PSPICE) PICE simulation is obtained confirming the theoretical analysis.

 

[Keywords: Voltage mode, Current conveyor, Current controlled conveyor, First order filter]

IPC Code: H 03 K 3/00

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, November 2004, pp. 857-862

 

Three electron bonding in thiazyl halides - NSZ [Z = F, Cl, Br]

S Mayilavelan, S Ramadasse and R Balakrishnan

 

Force fields of NSF, NSCl and NSBr have been studied employing the iterative force field refinement technique proposed by the authors in an earlier paper. While the force field of NSF is in conformity with the structure obtained through the simple electron pairing approach, those of NSCl and NSBr show deviation. Further, the discrepancy in the calculated centrifugal distortion constants of NSCl suggests a different structure. Three-electron bonding seems to be a better proposal for NSCl and NSBr. A detailed force field-structure analysis is presented on the basis of three-electron bonding model.

 

[Keywords: Three electron bonding, Thiazyl halides]

IPC Code: G 09B 23/00