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Glasses of composition PbO–Nb 2 O 5 –GeO 2 –SiO 2 doped with different concentrations of Cr 2 O 3 (ranging from 0 to 0.5 mol%) were prepared by conventional melt quenching technique. The prepared glasses were characterized by X-ray diffraction (XRD). Spectroscopic studies viz., optical absorption, EPR, FTIR, Raman and photoluminescence were carried out on these glasses. The optical absorption spectra exhibited three bands at about 646, 674 and 711 nm which are the characteristic bands of octahedral Cr 3+ ions. From the analysis of the absorption spectra the crystal field splitting parameters D q , B and nephelauxetic parameters (β and h ) were evaluated. The EPR spectra exhibited two resonance signals at g≈1.97 and g≈4.84. FTIR and Raman spectra have revealed the increasing presence of GeO 6 and NbO 6 structural units in the glass network with increasing the concentration of Cr 2 O 3 in the glass network. Photoluminescence spectra exhibited a broad emission band in the wavelength region 600 to 850 nm with a meta center at about 680 nm which is also a characteristic of Cr 3+ ions. Correlating optical and EPR data the molecular bonding coefficient parameter (α) has been evaluated. The quantitave correlation and analysis of all the results indicated that the glasses doped with higher content of Cr 2 O 3 are efficient luminescence materials. [ABSTRACT FROM AUTHOR]

Multi-component glass ceramics with composition 29PbO–5Al 2 O 3 –1TeO 2 –10GeO 2 – (55–x) SiO 2 doped with different concentrations of CuO (0 ≤ x ≤ 1.0 mol %) were synthesized by melt quenching technique and subsequent heat treatment. These glass ceramics were characterized by X–ray diffraction, scanning electron microscope, differential thermal analysis, optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman studies. The absorption spectra of these glass ceramics exhibited a broad absorption band in the range 650–950 nm which is ascribed to 2 B 1g → 2 B 2g octahedral transition of Cu 2+ ions. A feeble band around 364 nm is also identified in the samples doped with CuO up to 0.6 mol% as being due to charge transfer between the two oxidation states Cu 2+ and Cu + of copper ions. The EPR spectrum recorded at room temperature exhibited a strong resonance signal at g ⊥ = 2.072 and a shallow quadruplet at about g ǁ = 2.401. FTIR and Raman spectra of the titled samples provide significant information about various structural units viz ., silicate, germanate, PbO 4 , PbO 6 , AlO 6 , TeO 4 and TeO 3 that are present in these ceramic matrix. Analysis of the spectroscopic investigations reveals that with an increase in the concentration of CuO up to 0.6 mol% copper ions do exist in Cu 2+ and Cu + states and they act as modifiers and net work formers respectively. Therefore, glass ceramic sample contains 0.6 mol% of CuO is favorable for memory switching action. [ABSTRACT FROM AUTHOR]

Multi-component CaF 2 −ZnO–Bi 2 O 3 −P 2 O 5 glasses doped with different concentrations of CoO (ranging from 0 to 1.0 mol %) were crystallized by heat treatment. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and differential thermal analysis (DTA) techniques. The XRD patterns have indicated the presence of various phases viz., Ca 3 (PO 4 ) 2 , Bi 3 PO 7 , CaZn 2 (PO 4 ) 2 , Bi(PO 4 ), Zn 3 (PO 4 ) 2 , ZnCo(P 2 O 7 ), CaCoP 2 O 7 , ZnCo 2 O 4 , CoF 2 , Co 3 O 4 and CoF 3 . Conventional spectroscopic studies such as optical absorption, FTIR and Raman were also carried out on these glass ceramic samples. The analysis of these results has indicated that cobalt ions exist in both Co 2+ and Co 3+ states in the glass ceramic network. These studies have further revealed that the rigidity of the glass ceramic network decreases up to 0.6 mol% of CoO. Beyond this concentration the insulating strength of the prepared samples is found to increase. [ABSTRACT FROM AUTHOR]