Physical Review Letters
Optical Homogeneous Linewidths of Pr+ in Be F2 and Ge O2 Glasses
John Hegarty, William M. Yen
Abstract
Optical homogeneous linewidths of the $^{3}P_{0}\ensuremath{-}^{3}H_{4}(1)$ transition of ${\mathrm{Pr}}^{3+}$ in Be${\mathrm{F}}_{2}$ and Ge${\mathrm{O}}_{2}$ glasses reveal an anomalously smooth quadratic dependence on temperature from 8 to 300 K. The low-temperature behavior is consistent with a recent model of Lyo and Orbach involving an interaction with a single two-level system but the smooth quadratic behavior at all temperatures has deep consequences for the relative roles played by the ordinary phonons and the two-level system in line broadening.