A pulsed EPR study of clustering of Yb3+ ions incorporated in GeO2 glass

The structural aspects of clustering of Yb3+ ions and the paramagnetic behavior of these clusters have been investigated in GeO2 glasses doped with 140-1100 ppm by weight of Yb2O3 using time-domain EPR spectroscopic techniques. The echo-detected EPR (EDEPR) spectra of Yb3+ ions and their unusual dependencies on microwave power and magnetic field have been found to be indicative of the formation of clusters of these rare earth ions in GeO2 glass that behave as non-Kramers type spin systems. The magnetic field and concentration dependence of phase relaxation rates of Yb3+ in these glasses further substantiate such a scenario and indicate the formation of clusters of Yb3+ ions. A comparison of the EDEPR spectra with calculated cw-EPR line shapes yields a semi-quantitative measure of the typical cluster size of greater than or equal 3 Yb atoms and intra-cluster Yb-Yb distances of 3.5-4.0 angstroms in these glasses at doping levels of greater than or equal 350 ppm of Yb2O3. 21 refs.