V. Chandra Mouli

Raman spectroscopy, thermal and optical properties of TeO2-ZnO-Nb2O5-Nd2O3 glasses.

The glasses with composition 75TeO2-10ZnO-(15-x)Nb2O5-xNd2O3 (0≤x≤9 mol%) were prepared using melt quenching method and their physical properties such as density (ρ), molar volume (VM), average crosslink density (nc¯), oxygen packing density (OPD) and number of bonds per unit volume (nb) were determined. Raman spectroscopic studies showed that the glass network consists of TeO4, TeO3+1, TeO3 and NbO6 units as basic structural units. The glass transition temperature (Tg), crystallization onset (To) and thermal stability (ΔT) were determined from DSC thermograms. The Raman and DSC results were found to be correlated with the physical properties. In the optical absorption spectra six absorption bands were observed with different relative intensities at around 464, 522, 576, 742, 801 and 871 nm which are assigned to the transition of electrons from (ground state) 4I9/2→G11/2; 4I9/2→2K3/2, 2G7/2; 4I9/2→4G5/2, 4G7/2; 4I9/2→4S3/2; 4F7/2→2H9/2, 4F5/2 and 4I9/2→2F3/2 respectively. From optical absorption data the energy band gap (Eopt) and Urbach energy (ΔE) were calculated.

Structural, thermal and optical properties of TeO2–ZnO–CdO–BaO glasses doped with VO2+

The glasses with composition 64TeO2-15ZnO-(20-x)CdO-xBaO-1V2O5 (0⩽x⩽20 mol%) were prepared by conventional melt quenching technique. X-ray diffraction analysis was used to confirm the amorphous nature of the glasses. The optical absorption studies revealed that the cut-off wavelength (λα) decreases while optical band gap energy (Eopt) and Urbach energy (ΔE) values increase with an increase of BaO content. Refractive index (n) evaluated from Eopt was found to decrease with an increase of BaO content. The physical parameters such as density (ρ), molar volume (Vm), oxygen packing density (OPD), optical basicity (Λ), molar refraction (Rm), and metallization criterion (M) evaluated and discussed. FTIR and Raman spectroscopic studies showed that the glass network consists of TeO4, TeO3+1/TeO3 and ZnO4 units as basic structural units. The glass transition temperature (Tg) of glass sample, onset crystallization temperature (To) and thermal stability ΔT were determined from Differential Scanning Calorimetry (DSC). Using electron paramagnetic resonance (EPR) spectra of vanadium glasses the spin Hamiltonian parameters and dipolar hyperfine coupling parameters of VO(2+) ions were calculated. It was found that V(4+) ions in these glasses exist as VO(2+) in octahedral coordination with a tetragonal distortion and have C4V symmetry with ground state dxy. Tetragonality (Δg∥/Δg⊥) of vanadium ion sites exhibited non-linear variation with BaO content.

Structure, glass transition temperature and spectroscopic properties of 10Li2O-xP2O5-(89-x)TeO2-1CuO (5≤x≤25 mol%) glass system.

X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), infrared (IR), Raman, electron paramagnetic resonance (EPR) and optical absorption studies on 10Li2O-xP2O5-(89-x)TeO2-1CuO glasses (where x=5, 10, 15, 20 and 25 mol%) have been carried out. The amorphous nature of the glasses was confirmed using XRD and FESEM measurements. The glass transition temperature (Tg) of glass samples have been estimated from DSC traces and found that the Tg increases with increasing P2O5 content. Both the IR and Raman studies have been showed that the present glass system consists of [TeO3], [TeO4], [PO3] and [PO4] units. The spin-Hamiltonian parameters such as g∥, g⊥, and A∥ have been determined from EPR spectra and it was found that the Cu2+ ion is present in tetragonal distorted octahedral site with [Formula: see text] as the ground state. Bonding parameters and bonding symmetry of Cu2+ ions have been calculated by correlating EPR and optical data and were found to be composition dependent.

Electron spin resonance studies of Cu2+ doped in cadmium maleate dihydrate single crystals

Electron spin resonance studies have been carried out on Cu2+ ion doped in single crystals of cadmium maleate dihydrate at 303 and 77K. It has been found that Cu2+ enters this lattice interstitially. The spin Hamiltonian parameters have been evaluated and the ground state wave function is found to be predominantly |X2 −Y2〉 with a slight admixture of |3Z2 −r2〉.

Electron spin resonance and optical absorption studies of Cu2+ doped in potassium hydrogen maleate single crystals

Abstract The results of electron spin resonance studies on Cu2+ doped in potassium hydrogen maleate single crystals at 300 K are presented. The spin Hamiltonian parameters evaluated indicate a square planar environment for Cu2+ ion in this lattice. From the crystal structure data and the direction cosines of the principal axes of the g tensor, it is concluded that the Cu2+ ion enters the lattice in an interstitial position. Charge compensation is achieved by the release of protons. Using the optical absorption and ESR data, bonding parameters and orbital reduction factors are also evaluated.

ESR and optical absorption studies on copper doped (NH4)2Cd2(SO4)3 single crystals

Abstract ESR and optical studies have been carried out on Cu 2+ doped (NH 4 ) 2 Cd 2 (SO 4 ) 3 single crystals, which belong to the Langbeinite series, at room temperature and 77 K. The spin Hamiltonian parameters at 77 K were determined as g| = 2.027, g ⊥ = 2.283 and A | = 95 × 10 −4 cm −1 , A ⊥ = 31 × 10 −4 cm −1 . These parameters suggest that Cu 2+ is in a compressed octahedral position. From the nature of the spectra it is deduced that the Cu 2+ ion is entering the lattice interstitially, the charge compensation being achieved by the release of a pair of protons. The ground state wave function was found to be predominantly |3 Z 2 − r 2 〈 with a slight admixture from | X 2 − Y 2 〈 orbitals. The bonding parameters were also evaluated.

EPR study of Cu2+ in Na2O-NaF-B2O3-Bi2O3 glasses

Electron paramagnetic resonance (EPR) studies have been performed on the glass system (30−x) NaF-xNa2O-50B2O3-20Bi2O3 doped with CuO as a paramagnetic probe. The calculated g values indicate that Cu2+ is in a tetragonally elongated octahedral co-ordination, and the Jahn-Teller character gives rise to anisotropic hyperfine structure. The spin-Hamiltonian parameters and Σ-bonding parameter, α2, are calculated. Varying the fluoride ion concentration and its effect on these parameters is also discussed.

Electron spin resonance and optical absorption studies on copper-doped lithium hydrazinium sulphate single crystals

ESR and optical absorption studies have been carried out on Cu2+-doped lithium hydrazinium sulphate single crystals at 303 K. The spin-Hamiltonian parameters evaluated indicate a N2O2 square planar environment for Cu2+ ion in this lattice. The correlation ofESR and crystal structure data leads us to conclude that Cu2+ ion enters the lattice interstitially. Charge compensation is achieved by the release of protons. Using the optical absorption andESR data, bonding parameters and orbital reduction factors are also evaluated.

Thermal stability and transport studies of (100 - 2x)TeO{sub 2}-xAg{sub 2}O-xWO{sub 3} (7.5 {<=} x {<=} 30) glass system

Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO2–xAg2O–xWO3 (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO4], [TeO3]/[TeO3+1], [WO4] units. Thermal properties such as the glass transition (Tg), onset crystallization (To), thermal stability (ΔT), glass transition width (ΔTg), heat capacities in the glassy and liquid state (Cpg and Cpl), heat capacity change (ΔCp) and ratios Cpl/Cpg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO2–22.5Ag2O–22.5WO3 glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27–260 °C, the activation energy (Eact) values varied from 1.393 to 0.272 eV and for the temperature interval 170–260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10−9 to 1.47 × 10−6 S cm−1.

ESR studies of Cu2+ doped in triglycine calcium bromide single crystals

Electron spin resonance studies were carried out on Cu2+ doped triglycine calcium bromide. The spectra recorded at room temperature revealed well-resolved hyperfine spectra of63Cu superposed with super-hyperfine lines due to14N nuclei. The spin Hamiltonian parameters are evaluated. It was concluded that the Cu2+ enters the lattice interstitially.