GADOLINIUM DOPED BISMUTH GERMANATE GLASSES AND VITROCERAMICS 

D. Udvar, S. Simon.

Faculty of Physics, Babes-Bolyai University, M. Kogalniceanu no 1, 400084 Cluj-Napoca, Romania
udvar@phys.ubbcluj.ro

Glasses based on the heavy metal oxide have the capacity to accept rare earth ions in a relatively high amount [1].
The local structure of the glasses belonging to the 0.5Gd2O3·99.5[xBi2O3(1-x)GeO2] system, with  0.12 < x < 0.875 were studied by Electron Paramagnetic Resonance (EPR). Differential Thermal Analysis (DTA) was used in order to investigate the thermal behavior of the vitreous samples and to establish the heat treatment temperature for crystallization of the samples. Vitroceramic samples were obtained by heat treatment of the glass samples at 600°C for 24 hours. The crystalline phases induced in the glass matrix by heat treatment were identified by X-Ray diffraction. For different concentration of the bismuth oxide in the samples the following crystalline phases: 1:2, 1:1, 4:3, 2:1 and 12:1 phases were observed.
The spectra for the gadolinium doped bismuth germanate glasses are typically “U“ spectrum with the resonance lines at g = 2; 2.85; 4.8 and 5.9, specific for non-crystalline systems. The results suggest that the Gd3+ ions are homogeneously distributed in the host glass and play both the network former and network modifier role in the studied glasses. 
After heat treatment the intensity of the resonance line at g = 4.8 is decreasing by increasing the concentration of the Bi2O3 content evolution accompanied by the developing of the new line with g = 4.3 associated with Gd3+ ions in a cubic environment. The EPR spectra for crystalline samples are a superposition of spectra belonging to gadolinium ions dispoded in the component crystalline phases.

1. S. Simon, R. Pop, V. Simon, M. Coldea, J. Non-Cryst. Solids, 331, 1-3, 1 (2003)