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Multi component PbO–Al2O3–TeO2–GeO2–SiO2 glasses doped with different concentrations of V2O5 ranging between 0 and 1.0 mol % were prepared by melt quenching technique. XRD and SEM techniques have been employed for the confirmation of glass ceramic nature of the samples. Optical absorption spectra of these samples exhibited two broad bands at about 626 and 831 nm corresponding to ²B2g→²B1g and ²B2g→²Eg transitions, respectively. The optical band gap has shown the maximal value, 3.16 eV for 0.4 mol % of nucleating agent V2O5 beyond this concentration it is observed to decrease. The EPR spectra of the doped glass ceramics have exhibited a well resolved hyperfine pattern consists of eight parallel and eight perpendicular lines which are the characteristics of VO2+ ions. The increase in the intensity of the resonance signal beyond 0.4 mol % of V2O5 has been attributed to the increase in the concentration of paramagnetic vanadyl ions. The analysis of these spectroscopic investigations reveals that the glass ceramics doped with 1.0 mol % of V2O5 are suitable for semiconducting devices. [ABSTRACT FROM AUTHOR]

P2O5─PbO─ Ga2O3─Dy2O3 glasses doped with different concentrations of Bi2O3were prepared by conventional melt quenching technique. The prepared glasses were characterized by optical absorption and luminescence studies. The observed decreasing trend in energy band gap values of the titled glasses indicates the increasing degree of depolymerization in the network with increase in Bi2O3 content. The sample doped with 3 mol % of Bi2O3 exhibits higher luminescence at all excited wavelengths rather than other samples. Significant energy transfer parameters viz., the luminescence quantum efficiency (ηQ), energy transfer efficiency (ηET), energy transfer parameter (Q), energy transfer probability (PDA) and critical transfer parameter (R0) were evaluated for all the titled glasses by using the lifetime values. The evaluated color coordinates values at different excitation wavelengths have revealed that in general these glasses emit bright white light. But in particular the glass sample doped with 3 mol % of Bi2O3 is more suitable for the fabrication of white light emitting diodes (W-LEDs). The correlated color temperature (CCT) values for the prepared glasses are observed in the range 3300 – 4050K which are nearer to commercial and day W-LED sources. From all these investigations it can be seen that the glass doped with 3 mol % Bi2O3 is a potential candidate for the development of W-LEDs. [ABSTRACT FROM AUTHOR]

Glass ceramics with composition 10Na2O− 30PbO−10Bi2O3−(50-x)SiO2: xV2O5 (0 ≤ x ≤ 5) were synthesized by melt quenching and heat treatment method. XRD and SEM studies have indicated that the samples contain well defined and randomly distributed grains of different crystalline phases. Optical absorption spectra of these samples exhibited two absorption bands at 629 and 835 nm which are the characteristics of V4+ ions. The EPR spectra of these samples have exhibited well resolved hyperfine structure consisting of sixteen-eight parallel and eight perpendicular lines with a raise in their intensity with an increase in the content of V2O5 up to 3 mol% indicates the increase of redox ratio V4+/V5+ in the glass ceramic matrix. [ABSTRACT FROM AUTHOR]

Glass ceramics with the composition 10CaF2−20ZnO–(15-x)Bi2O3−55P2O5:x Fe2O3(0≤x≤2.5) were synthesized by melt-quenching technique and heat treatment. These glass ceramics were characterized by XRD and SEM. Spectroscopic studies such as optical absorption, EPR were also carried out on these glass ceramics. From the absorption spectra the observed bands around 438 and 660nm are the octahedral transitions of Fe3+ (d5) ions and another band at about 536 nm is the tetrahedral transition of Fe3+ (d5) ions. The absorption spectrum also consist of a band around 991 nm and is attributed to the octahedral transition of Fe2+ ions. The EPR spectra of the prepared glass ceramics have exhibited two resonance signals one at g1=4.32 and another signal at g2=2.008. The observed decrease in band gap energy up to 2 mol% Fe2O3 doped glass ceramics is an evidence for the change of environment around iron ions and ligands from more covalent to less covalent (ionic) and induces higher concentration of NBOs which causes the depolymerization of the glass ceramic network. [ABSTRACT FROM AUTHOR]