Structural investigations of some bismuth–borate–vanadate glasses doped with gadolinium ions

X-ray diffraction (XRD), Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopies have been employed to investigate the xGd₂O₃ · (95 − x)[2Bi₂O₃ · B₂O₃] · 5V₂O₅ glass system, with 0 ≤ x ≤ 25 mol%. The glass samples have been prepared by melting at 1,100 °C for 10 min followed by rapid cooling at room temperature. The structure of samples was analyzed by means of XRD. The pattern obtained did not reveal any crystalline phase in the samples up to 25 mol%. FTIR spectroscopy data suggest that the gadolinium ions play the network modifier role in the studied glasses. These data show that the glass network consists of BiO₃, BiO₆, BO₃, BO₄, and VO₄ structural units. The FTIR data show that a conversion among these units takes place and this process mainly depends on the Gd₂O₃ content. The EPR spectra of the studied glasses exhibit three important features with effective g-values of ≈5.9, 2.85, 2.0 and a weaker feature at g _eff ≈ 4.8. For low Gd₂O₃ contents (x ≤ 10 mol%), the EPR spectra have the typical ‘‘U’’-type shape. For higher contents of Gd₂O₃ (x > 10 mol%), the spectral features are broadened and finally are dominated by a single broad absorption line located at g _eff ≈ 2.0. This broad EPR line is associated to the Gd³⁺ ions present predominantly as clustered species.