Spectroscopic and structural properties of Cr³⁺ ions in lead niobium germanosilicate glasses

Glasses of composition PbO–Nb₂O₅–GeO₂–SiO₂ doped with different concentrations of Cr₂O₃ (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 Cr³⁺ 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 GeO₆ and NbO₆ structural units in the glass network with increasing the concentration of Cr₂O₃ 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 Cr³⁺ 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 Cr₂O₃ are efficient luminescence materials.