Magnetic and IR spectroscopic behavior of some glasses containing gadolinium and neodymium ions

Glasses containing rare-earth ions have attracted a great deal of interest due to their important applications for optical telecommunication, laser technology and immobilization of radioactive materials. Spectroscopic and magnetic susceptibility measurements performed on such glasses reveal interesting aspects concerning the basic structural units of the host glass matrix, distribution of the rare earth ions in the glass matrix and the nature of magnetic interactions between these ions. In order to extend the available information concerning bismuthate glasses containing gadolinium and neodymium we performed the investigation of the xR2O3·(1-x)(3Bi2O3·PbO) system (denoted xRBP) with R=Nd and Gd and 0 ≤ x ≤ 0.25 using magnetic susceptibility and IR spectroscopic measurements. IR spectra were recorded in the 400-2000 cm-1 range with a Bruker IFS 66-1 spectrophotometer using the KBr pellet technique. Magnetic susceptibility measurements were performed on a Faraday type balance in the temperature range 80 to 300 K. The IR spectra of the xRBP glasses show the features characteristic of the base glass matrix, 3Bi2O3·PbO. No dramatic changes occur with increasing the R2O3 content, x, of the samples. Some of the IR spectral features are associated to the structural units involving the Bi3+ heavy cation ( at 460, 600 and 855 cm-1 ). The absorption band from 855 cm-1 represents the convolution of the absorption bands reported for different bismuthate glasses at 847 and 860 cm-1, assigned to the total symmetric stretching vibrations of the [BiO3] and [BiO6] polyhedra, respectively. The increase of the R2O3 content, x, of the xRBP samples determines the increase of the absorption band at 855 cm-1 and its slow shift to 850 cm-1 for x=0.30 suggesting the increase of the number of [BiO3] structural units. The structural changes observed by varying the R2O3 content of xRBP glasses and put in evidence by the IR investigation suggests that the R ions play a network modifier role in these glasses. The magnetic behaviour of xRBP glasses is due to the presence of R3+ ions since the Bi2O3·PbO host glass matrix was found to be diamagnetic. The dependence of the inverse magnetic susceptibility as a function of temperature for the xRBP glasses shows a Curie-Weiss type behaviour. The paramagnetic Curie temperature θp is a rough indicator of magnetic interaction between R3+ ions. The θp values were zero for the samples with x≤0.05 and small and negative (|θp|≤ 9 K) for those with x>0.05 suggesting that in the samples with x≤0.05 the R3+ ions are present only as isolated species, while in those with x>0.05 as both isolated and coupled (by weak antiferromagnetic interactions). (author)