A. Edukondalu

Optical properties of amorphous Li2O–WO3–B2O3 thin films deposited by electron beam evaporation

Abstract Thickness dependencies of the optical properties of as-deposited amorphous 30Li2O–10WO3–60B2O3 thin films prepared by electron beam evaporation on glass substrates at a base pressure of 9 × 10−7 Torr were studied. Glancing angle X-ray diffraction studies were performed to confirm the amorphous nature of the prepared films. The absorption coefficient α (and therefore the extinction coefficient k) was determined from the reflectance and transmission spectra in the strong absorption region. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. The optical constants, such as optical band gap, Urbach energy, the average excitation energy Eo and the dispersion energy Ed, of the thin films were determined. The optical data revealed the existence of allowed indirect transitions.

MIXED ALKALI EFFECT IN (40-x)K2O–xLi2O-10Na2O–50B2O3 GLASSES—PHYSICAL AND OPTICAL ABSORPTION STUDIES

So far only a handful of publications have been concerned with the study of the mixed alkali effect in borate glasses containing three types of alkali ions. In the present work, the mixed alkali effect (MAE) has been investigated in the glass system (40–x) K2O–x Li2O –10Na2O–50B2O3.(0≤x≤40 mol%) through density and modulated DSC studies. The density and glass transition temperature of the present glasses varies non-linearly exhibiting mixed alkali effect. We report the mixed alkali effect in the present glasses through optical properties. From the absorption edge studies, the various values of optical band gap (Eo) and Urbach energy (ΔE) have been evaluated. The values of Eo and ΔE show non-linear behavior with compositional parameter showing the mixed alkali effect. The band gap energy based average electronic polarizability of oxide ions αO2–(Eo), optical basicity A(Eo), and Yamashita–Kurosawa’s interaction parameter A(Eo) have been examined to check the correlations among them and bonding character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and interaction parameter, the present K2O– Li2O–Na2O–B2O3 glasses are classified as normal ionic (basic) oxides.

FTIR and Raman studies on 25Bi2O3-(75-x)B2O3-xBaO glasses

Raman and Infrared spectroscopies have been employed to investigate the 25Bi2O3-(75-x)B2O3-xBaO glasses in order to obtain information about the competitive role of Bi2O3 and B2O3 in the formation of glass network. FTIR and Raman spectra show that these glasses are made up of [BO3], [BO4], [BiO3] pyramidal and [BiO6] octahedral units.

Spectroscopic studies of xLi2O-(40-x)Bi2O3-20CdO-40B2O3 Glasses

Glasses with composition xLi2O-(40- x)Bi2O3-20CdO-40B2O3 where (0 ≤ x ≤ 40) have been prepared using melt quench technique. Optical absorption spectra of the pure glasses reveled that the cutoff wave length decreases and optical band gap (Eopt) and Urbach energy (ΔE) increases with increase in Li2O content. The Eopt values of these glasses are found to be in the range 2.818-3.258 eV where as the values of ΔE are in the range 0.21-0.33 eV. Raman and infrared spectroscopies have been employed to investigate these glasses in order to obtain information about the competitive role of Bi2O3 and B2O3 in the formation of glass network. IR and Raman spectra show that these glasses are made up of [BO3], [BO4], [BiO3] and [BiO6] units. The formation of Cd in tetrahedral co-ordination was not observed.

Physical and optical studies on Li2O-Na2O-WO3-B2O3 glasses

Glasses with composition xLi2O-(30-x)Na2O-10WO3-60B2O3 (where x=0, 5, 10, 15, 20, 25 and 30 mol%) have been prepared using the melt quenching technique. In the present work, the mixed alkali effect (MAE) has been investigated in the above glass system through density and optical studies. The density of the present gasses varies non-linearly, the exhibiting the mixed alkali effect. From the optical absorption studies, the values of direct optical band gap, indirect optical band gap energy (Eo) and Urbach energy(ΔE) have been evaluated. The values of E0 and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect.

Physical, Optical absorption and EPR studies on fluoro- bismuthate glasses

Glasses of the xLiF-(50-x)Li2O-20SrO-30Bi2O3 system, with 0 ≤ x ≤ 20 mole % were studied by EPR and Optical measurements. The changes in both density and molar volume indicate structural modifications occur due to addition of LiF. The glass transition temperatures are observed to decrease with an increase in LiF content in the compositions. The local structure around Cu2+ ions has been examined by means of electron paramagnetic resonance and optical absorption measurements. It is observed that the spin-Hamiltonian parameters calculated from the EPR spectra are influenced by the glass composition. The Cu2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu2+ is and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d-d transition bands of Cu2+ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated.

Raman spectroscopic studies on mixed alkali borotungsten glasses

Mixed alkali borate glasses of composition xLi2O-(30−x)K2O-10WO3-60B2O3 (0 ≤ x ≤ 30 mol%) were prepared by melt quench technique. The structure of present glass system was investigated by Raman spectroscopy. The characteristic bands of these glasses due to the stretching and bending vibrations were identified and analyzed by the increasing of alkali content. This fact allowed us to identify the specific structural units which appear in these glasses and thus to point out the network modifier role of alkali oxide for low concentrations and its former role at high concentrations.

OPTICAL PROPERTIES ON Li2O-K2O-WO3-B2O3 GLASS SYSTEM

Mixed alkali tungsten borate glasses xLi2O–(30–x) K2O–10WO3–60B2O3 (0 < x < 30) were prepared from the melts. These glasses were characterized using X-ray diffraction, differential scanning calorimetry and density measurements. Optical absorption studies were carried out as a function of alkali content to look for mixed alkali effect (MAE) on the spectral properties of these glasses. From the study of ultraviolet absorption edge, the optical band gap energies and Urbach energies were evaluated. The average electronic polarizability of the oxide ion, optical basicity and the interaction parameters were also evaluated for all the glasses. Many of these parameters vary non-linearly exhibiting a minima or maxima with increasing alkali concentration, indicating the mixed alkali effect. An attempt is made to interpret MAE in this glass system in terms of its glass structure.

SYNTHESIS AND SPECTROSCOPY OF SOME QUATERNARY OXYFLUORIDE GLASSES DOPPED WITH COPPER

Electron paramagnetic resonance (EPR) and optical absorption spectra of copper ions in xLiF-(50-x)Li2O-20SrO-30Bi2O3 glass system have been studied. MDSC studies showed that the glass transition temperature decreases with LiF content. Optical absorption spectra of the pure glasses reveled that the cut off wave length increased and optical band gap energy decreased with increase in LiF content. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu2+ ions. The Cu2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu2+ is d x2 y2 and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d-d transition bands of Cu2+ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated from various techniques.