High field electron paramagnetic resonance of Gd3+-doped glasses: Line shapes and average ion distances in silicates

Abstract

The average distances between ${\mathrm{Gd}}^{\mathrm{3+}}$ ions in multicomponent silicate glasses doped with 0.058 to up to 4.64 wt % ${\mathrm{Gd}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ are characterized by electron paramagnetic resonance (EPR) line broadening effects at high-field (95 GHz, $W$ band). Increase in the EPR resonant field/frequency above that of the conventional $X$ band (9.5 GHz) simplifies the ${\mathrm{Gd}}^{\mathrm{3+}}$ EPR spectra and increases the sensitivity of the EPR linewidth to concentration induced broadening effects. Least squares line shape simulations show that the broadening can be described by a Lorentzian function with a width proportional to the average ${\mathrm{Gd}}^{\mathrm{3+}}$ concentration which is in good agreement with the existing theories. Analyses of the concentration dependence of Lorentzian line broadening indicate an onset of clustering of ${\mathrm{Gd}}^{\mathrm{3+}}$ ions at $\text{>\hspace{0.05em}1}\mathrm{wt}\mathrm{ \%}$ doping levels.