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 GeO ₂ glasses doped with 140-1100 ppm by weight of Yb₂O ₃ using time-domain electron paramagnetic resonance (EPR) spectroscopic techniques. The echo-detected EPR (EDEPR) spectra of Yb ³⁺ 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 ≥3 Yb atoms and intra-cluster Yb-Yb distances of 3.5-4.0 Å in these glasses at doping levels of ≥350 ppm of Yb₂O₃.