Fracton contribution to the temperature dependence of the homogeneous linewidth of theD05−7F0transition inEu3+-doped glasses

Laser-induced fluorescence line-narrowing techniques were used to measure the homogeneous linewidth of the ${}_{}{}^5{}_{}{}^{}\mathrm{D}_0^{}{}_{}{}^{}$ ${\mathrm{-}}^7$ ${\mathrm{F}}_0$ transition in ${\mathrm{Eu}}^{3+}$-doped glass hosts after resonant excitation. The homogeneous linewidths were measured as a function of temperature between 10 and 300 K and as a function of excitation wavelength across the inhomogeneous bands in two types of silicate and one germanate glass. The residual inhomogeneous linewidth at 10 K increases linearly with energy across the band and the homogeneous width at both high- and low-energy sides of the inhomogeneous band exhibits a $T^2$ temperature dependence over the entire range investigated. A model based on the fracton concept for the anomalous vibrational degrees of freedom of the glass hosts is developed to explain the observed behavior of the temperature-dependent line broadening.