T.V.R. Rao

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.

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.

Absorption and emission spectral studies of Sm3+ and Dy3+ doped alkali fluoroborate glasses

Absorption and photoluminescence spectra of Sm 3 + and Dy 3 + doped alkali fluoroborate glasses of the composition 90.5 B 2 O 3 + 4 AlF + 5 RF + 0.5 LnF 3 (R= Li, Na, K and Ln = Sm, Dy) are reported. On excitation, with 402 nm, the Sm 3 + glasses were found to be orange fluorescent in colour and richness of that colour was high in the Na + glass, compared to Li + and K + glasses. Similarly, on excitation with 398 nm, the Dy 3 + glasses were fluorescent yellow and that colour was richer in the K + glass.

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.

Luminescence properties of Nd3+: TeO2–B2O3–P2O5–Li2O glass

Abstract An IR transmitting circular glass window of Nd 3+ -doped borophosphate–tellurite system in the following chemical composition (mol%) was prepared: 65TeO 2 +12B 2 O 3 +12P 2 O 5 +10Li 2 O+1Nd 2 O 3 . For this Nd 3+ -doped (heavy metal glass) optical material, besides the determination of density and refractive indices, an absorption spectrum (350–3200 nm) at 300 K was obtained. Based on the estimated refractive indices ( n F , n d and n C ) at three different wavelengths (486.1, 589.1 and 656.3 nm), the glass dispersive power ( v d ) and non-linearity characteristic factors ( n 2 , γ ) were examined. Parameterization of the elastic constants of this glass was done from the measurement of longitudinal and shear velocities. From the measured absorption band positions, energy level structure ( E k ,F k ,ξ 4 f ,α,β,γ, β and δ %) parameters and from the recorded spectral profiles, oscillator strengths were computed. Both the measured and computed band energies are correlated satisfactorily with an rms deviation of ±89 cm −1 . By applying the Judd–Ofelt parameterization, the radiative ( A , A T , T R ) factors of the luminescent transitions ( 4 F 3/2 → 4 I 13/2,11/2,9/2 ) of the glass were evaluated. Temperature dependent luminescence spectral analyses were carried out in the temperature range of 10–300 K to understand the fluorescence efficiency of a prominent lasing transition ( 4 F 3/2 → 4 I 11/2 ) at 1.06 μm and for the other two transitions ( 4 F 3/2 → 4 I 9/2 , I 13/2 ) at 0.89 and 1.33 μm as well.

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.

Potential energy curves, dissociation energies and Franck–Condon factors of NI and ScI molecules

Abstract The potential energy curves for the electronic ground states of NI and ScI molecules are constructed by using the RKRV method. The ground state dissociation energies of NI and ScI are determined by curve fitting techniques using the five parameters Hulburt–Hirschfelder function. The estimated dissociation energies are 1.64 and 2.85 eV for NI and ScI, respectively. The estimated dissociation energy values are in good agreement with the literature values. The Franck–Condon factors for the bands b1Σ+–X3Σ− system of NI and B1Π–X1Σ+ system of ScI molecules have been determined using an approximate analytical method of Fraser and Jarmain. The absence of the bands in these systems is explained.

Bulk modulus and electronic polarizability of compound and ternary chalcopyrite semiconductors

Simple correlations between the bulk modulus (B), effective nuclear charge (Z) and refrative index are given for compound and ternary chalcopyrite semiconductors. Bulk modulus and electronic polarizabilities are evaluated. Results are in good agreement (±15%) with experimental values.

Diurnal and seasonal variabilities in surface ozone and its precursor gases at a semi-arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

Measurements of surface ozone and its precursor gases (NOx and CO) have been made at a semi‐arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in tropical Indian region for the period, 2001–2003. NOx and CO levels were the highest during morning and late night hours at this site. Diurnal variations of ozone concentrations varied from 25 ppbv to 50 ppbv and were observed to increase gradually after sunrise, attaining a maximum value by the evening and decreasing gradually thereafter. During monsoon months, the diurnal amplitude of ozone was found to be small (20–25 ppbv). Seasonal variation in ozone showed a pronounced maximum (40–50 ppbv) in the winter and summer. Local pollutants were major contributors to the ozone levels during this period. Ozone shows a yearly mean mixing ratio of about 35.9 ± 8.8 ppbv. The daytime concentration of CO and NOx varied between 200 to 1200 ppbv and 3 to 20 ppbv respectively for the period studied. Annual average mixing ratios of oxides of nitrogen (NOx) and CO were observed to be 3.9±0.6 ppbv and 436±64 ppbv, respectively.