الفهرس 
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Abstract
In the present work, glasses with composition:[XBi2O3–24Na2O–(75-X) B2O3–1Er2O3]with X=0, 5, 10, 15, 25, 33, 40 mol.% were investigated aiming to study the effect of Bi2O3 addition on the physical behavior of the prepared samples. The samples were prepared using conventional melt-quenching technique. The amorphous nature of the prepared samples was confirmed by X-ray diffraction (XRD). The density (ρ) was measured by applying conventional Archimedes method with carbon tetrachloride as the immersion liquid (ρ0 = 1.592 g/cm3). It is observed that the density increases with increasing Bi2O3 content. This increasing in density is mainly due to the difference in the atomic masses and atomic radii of Bi and B ions. Also the molar volume (VM) increases with increasing Bi2O3 content. Such unexpected results can be attributed to the formation of non-bridging oxygen (NBO) and expands (opens up) the structure of the prepared samples. Rare earth ion parameters such as rare earth ion concentration (N), average ion separation (rp) and field strength (F) have been calculated and studied. The oxygen packing density (O) which is a measure of the tightness of packing of the oxide network was calculated. It is found that its values decreases with increasing Bi2O3 content, which indicates that the glass network becomes less tightly packed and degree of disorder increases with increasing Bi2O3 content. The electronic polarizability and the optical basicity have been estimated on the basis of the electronegativities of the consist elements. The effect of Bi2O3 on the structure of the glass was investigated by IR spectroscopy indicating that the presence of [BO3], [BO4] and [BiO6] structural units. Deconvolutions of IR spectra were used to calculate the ratio N4 .It was found that its values depend on composition. Absorption spectra of the samples were obtained and analyzed. The spectra consist of eleven absorption bands corresponding to the transition between 4I15/2 ground state and excited states of erbium ions. The oscillator strengths have been estimated, where Judd- Ofelt approach has been applied to evaluate the intensity parameters Ωλ (λ=2, 4, 6). The variation of Ω2 with composition has been attributed to the change in the asymmetry of the ligand field at rare earth site. The variations of Ω4, Ω6 are related to the rigidity of the host matrix. The optical band gap energy (Eg) and the width of the tail, urbach energy, (ΔEe) of the localized states in the band gap have been estimated. The refractive index was calculated using approximate equation.