R. Ramakrishna Reddy

Spectroscopic studies of Nd3+-doped alkali fluoroborophosphate glasses

A new family of three optical glasses of the following chemical composition with 1 mol% of Nd3+ were prepared to examine the effects of alkali fluorides in unmixed form: 40(NaPO3)6+10BaF2+9ZnF2+20B2O3+20RF+1NdF3, where RF=LiF, NaF and KF. On the basis of the measured values of densities and refractive indices, the dielectric constant, reflection losses, molar refraction, Nd3+ ion concentration in glasses and several other physical properties were determined. Absorption spectra of these glasses were recorded and Judd–Ofelt intensity parameters (Ωλ) have been calculated. Radiative lifetimes (τR) and branching ratios (βR) for the fluorescent levels have been determined. To understand the laser efficiency of these materials, the values of the spectroscopic quality factor (Ω4/Ω6) has been evaluated and it is found that glass C could be suggested as a suitable lasing material.

Wintertime spatial characteristics of boundary layer aerosols over peninsular India

During an intense field campaign for generating a spatial composite of aerosol characteristics over peninsular India, collocated measurements of the mass concentration and size distribution of near-surface aerosols were made onboard instrumented vehicles along the road network during the dry, winter season (February-March) of 2004. The study regions covered coastal, industrial, urban, village, remote, semiarid, and vegetated forestlands. The results showed (1) comparatively high aerosol (mass) concentrations (exceeding 50 μ g m(-3)), in general, along the coastal regions (east and west) and adjacent to urban locations, and (2) reduced mass concentration ( 50% of the total) of coarse-mode aerosols (>1 μ m). The spatial composite of accumulation-mode share to the total aerosol mass concentration agreed very well with the monthly mean spatial composite of aerosol fine-mode fraction for February 2004, deduced from Moderate-Resolution Imaging Spectroradiometer data for the study region, while a point by point comparison yielded a linear association with a slope of 1.09 and correlation coefficient of 0.79 for 76 independent data pairs. Pockets of enhanced aerosol concentration were observed around the industrialized and urban centers along the coast as well as inland. Aerosol size distributions were parameterized using a power law. Spatial variation of the retrieved aerosol size index shows relatively high values (>4) along the coast compared to interior continental regions except at a few locations. Urban locations showed steeper size spectra than the remote locations.

Electronic polarizability and optical basicity properties of oxide glasses through average electronegativity

Abstract The average electronic oxide polarizability ( α o 2− ) and optical basicity ( Λ ) of numerous simple oxides have been estimated on the basis of different properties of oxides: average electronegativity ( χ av ) and energy gap ( E g ). The estimated values are in good agreement with the literature values. Similarly the optical basicity and average electronic polarizability of binary oxides glasses (phosphate, borate, silicate, germanate, tellurite and titanate) have been evaluated on the basis of average electronegativity ( χ av ) only. The performance of the present method is compared with Dimitrov and Komatsu relationships. A good agreement is observed between the computed and literature values.

Potential energy curves and dissociation energies of NbO, SiC, CP, PH+, SiF+, and NH+

The potential energy curves for the electronic ground states of astrophysically important NbO, SiC, CP, PH+, SiF+, and NH+ molecules are constructed by the RKRV method. The dissociation energies are determined by curve-fitting techniques using the five-parameter Hulburt-Hirschfelder function. The estimated dissociation energies are 7.86±0.16, 3.66±0.09, 5.12±0.12, 3.08±0.09, 6.46±0.14, and 3.02±0.09 eV for NbO, SiC, CP, PH+, SiF+, and NH+, respectively. The estimatedD0 values are in reasonably good agreement with literature values. If we utilizeD0 values of PH+, SiF+, and NH+, ionization potentials for PH, SiF, and NH are derived. The ionization potentials are 10.12, 7.13, and 13.66 eV, respectively, for PH, SiF, and NH. Dissociation energies for the above molecules are also estimated by use of the Birge-Sponer extrapolation and Hildenbrand and Murad methods.

Optical electronegativity, bulk modulus and electronic polarizability of materials

Correlations between the energy gap, optical electronegativity and bulk modulus are given for compound and ternary chalcopyrite semiconductors. Bulk modulus and electronic polarizability values have been evaluated from the optical electronegativity. The estimated values of these parameters are in good agreement with the available experimental data.

Relationship between energy gap, refractive index, bond energy and the szigeti charge in polyatomic binary compounds and semiconductors

Abstract An empirical relation Egen = 36.3 between the energy gap and refractive index is proposed. The applicability of the proposed relation is tested for 60 different polyatomic binary compounds. Our estimated refractive indices are in good agreement with the experimental values. The Szigeti charge variation with respect to single bond energy and refractive index is investigated for II–VI and III–V semiconductors. Relationships between formula weight and refractive index and bond energy and refractive index are also proposed.

Correlation between optical basicity, electronegativity and electronic polarizability for some oxides and oxysalts

A new method for calculating the optical basicity, electronic polarizability and oxygen electronegativity of oxides and oxysalts has been evaluated based on the concept of average electronegativity given by Asokamani and Manjula. The estimated parameters are in good agreement with the Duffy values. The results are also discussed in relation to the nature of bonding. It is suggested that the impurity of average electronegativity in predicting different parameters is well emphasised.

Electron Paramagnetic Resonance and optical absorption spectra of Cr(III) ions in alkali cadmium borosulphate glasses

The Electron Paramagnetic Resonance (EPR) spectrum at 9.205 GHz and at 300 K has been examined for a series of Cr3+ ions doped alkali cadmium borosulphate [R2SO4-CdSO4-B2O3 (RLi,Na,K or Cs)] glasses. The low field EPR spectral resonance lines are attributed to isolated Cr3+ ions where as the high field spectral resonance lines are attributed to exchange coupled pairs of Cr3+ ions. The absorption spectra of Cr3+ ions ions in these glasses show two broad bands characteristic of Cr3+ ions in octahedral symmetry. The bands are slightly shifted to higher wavelength side from Li glass to Cs glass. From the optical spectra the crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C are evaluated. From the EPR and optical data, it is concluded that, the site symmetry around the Cr3+ ions is octahedral and the nature of bonding is predominantly covalent in nature.

Studies on aerosol optical properties over urban and semi-urban environments of Hyderabad and Anantapur

Aerosols in the troposphere exert an important influence on global climate and the environment through scattering, transmission and absorption of radiation as well as acting as nuclei for cloud formation. Atmospheric aerosol particles influence the earths radiation balance directly by scattering of infrared energy and indirectly by modifying the properties of clouds through microphysical processes. The present study addresses visibility, radiative forcing, size distribution and attenuation of aerosols over the period from January to May, 2001 for urban and semi-urban regions of Hyderabad and Anantapur. High aerosol loading has been observed over urban environment compared to semi-urban environment. Aerosol optical depth values increased from January to April and then decreased during May over both urban and semi-urban regions. Over urban region, visibility decreased from January to April and increased during May. Similar trend has been observed over semi-urban region with relatively higher values of visibility. Radiative forcing estimated using aerosol optical depth values increased from January to April and then decreased during the month of May over urban and semi-urban areas. High visibility and low radiative forcing has been noticed over semi-urban area due to less aerosol loading. Wavelength exponent and turbidity coefficient registered high values over urban environment compared to semi-urban environment. Attenuation coefficient showed high values over urban region compared to semi-urban region. It reveals that semi-urban environment receives high solar flux than urban environment. Using 10 channel quartz crystal microbalance, measurements of total mass concentration and mass size distribution of near surface aerosols has been made over semi-urban environment and compared with size distribution derived from inversion methods based on aerosol optical depth variation with wavelength. The sensitivity of constrained linear inversions for inferring columnar aerosol size distributions has been discussed in detail in the paper.

Relationships between lattice energy, interionic distance and plasma energy in II–VI group semiconductors

Abstract Lattice energies have been evaluated from the interionic distances for II–VI group semiconducting compounds based on the assumption that a linear relation exists between lattice energies and interionic distances within a molecular group of compounds. A new linear relation has also been proposed for the evaluation of plasma energy directly from the lattice energy values. The calculated plasma energy values are used in the estimation of electronic polarizability in II–VI group semiconducting compounds. Good agreement is observed between computed and literature values of electronic polarizability.