Local Structure around Er3+ Ions in Sol-Gel Derived GeO2 Glasses Studied by Vibrational and XAFS Spectroscopy

Vibrational, Er LIII-edge X-ray absorption fine structure (XAFS), and upconversion fluorescence spectra have been measured for sol-gel derived xEr2O3•(100-x)GeO2 (x=1-10) glasses. Raman spectra indicated that with increasing the Er2O3 content, the bridging angle of the Ge-O-Ge linkage was distorted and non-bridging oxygen atoms (NBOs) were generated. Infrared absorption spectra of the glasses showed that the amount of the residual OH group increased with increasing the Er2O3 content. XAFS analysis showed the argumentation of both the coordination number (NEr-O) and the Debye-Waller factor (σEr-O) with increasing the Er2O3 content. This argumentation is probably due to the coordination of NBOs, OH group, and bridging oxygen atoms (BOs) to the Er3+ ion. XAFS analysis for the glasses gives no evidence of clustering of Er3+ ions as reported previously. Quenching of Er3+ upconversion fluorescence in the glasses with high Er2O3 content is considered to be caused mainly by the coordinated OH group.