Narrow Results

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 (E_o) and Urbach energy (ΔE) have been evaluated. The values of E_o 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 α_O2–(E_o), optical basicity A(E_o), and Yamashita–Kurosawa’s interaction parameter A(E_o) 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.

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.

Glasses having composition 20CdOxBi₂O₃(79.5-x)B₂O₃0.5Pr₆O₁₁ with x varying from 15 to 35 mol% have been synthesized. Optical absorption and fluorescence spectra were measured at ambient temperature. A close correlation is observed between the Bi₂O₃ content and the spectroscopic properties such as Judd-Ofelt intensity parameters Ω_λ = (λ = 2, 4, 6), radiative and structural properties of prepared glasses doped with Pr³⁺ ion. The variation of Ω₂ with Bi₂O₃ content has been attributed to changes in the asymmetry of the ligand field at the rare earth (RE) ion site (due to structural change) and to changes in RE-O covalency, whereas the variation of Ω₆ has been related to the variation in RE-O covalency. Following the luminescence spectra, various radiative properties like transition probability (A_rad), radiative lifetime (τ_r), branching ratio (β_r) and stimulated emission cross section (σ) have been calculated. The branching ratio for ³P₀ → ³F₂ transition of Pr³⁺ glass system arrive at 41 to 40%, respectively, and the predicted spontaneous radiative transition probability rates are high and varies from 14032 to 14864 s⁻¹. In addition, the glass stability is improved in which the substitution of B₂O₃ for Bi₂O₃ strengthens the glass network structure. The bismuth based glass as a host for Pr³⁺ ion doped suggesting their suitability for laser applications.