Spectroscopic investigation of AgI-doped borate glasses

AgI-doped superionic borate glasses xAgI–(1−x)[Ag2O–nB2O3] (n=2, 0.5) in bulk and thin film forms were studied by infrared specular reflectance and transmission spectroscopy. The short-range order structure of the network was found to be directly affected by AgI, and this was accounted for by isomerization and disproportionation reactions between triangular and tetrahedral borate species for the diborate (n=2) and pyroborate (n=0.5) families, respectively. This effect is reflected in the decrease of the glass transition and fictive temperature upon AgI addition. Analysis of the transmission spectra of thin films for diborate glasses showed that optical and thermal history effects lead to spectral differences between thin films and bulk samples. Far-infrared analysis for pyroborate glasses revealed two distinct environments for silver ions formed by oxygen atoms and iodide anions. At high AgI contents the silver-iodide sites are probably growing into AgI-like clusters. In the diborate family the presence of a range of oxide, iodide and mixed O/I environments for silver ions is supported by the far-infrared data. Thus, the nature of sites exploited by silver ions in AgI-containing borate glasses depends on both Ag2O and AgI content.