Fluorescence line narrowing was used to measure the homogeneous broadening of the ${}_{}{}^2{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$${\mathrm{A}}_2$ transition of ${\mathrm{Cr}}^{3+}$ ions in Al(1) sites, within the spinel blocks, of crystalline silver β-alumina. The homogeneous linewidth increases as $T^{1.74}$ in the temperature range 7–200 K. This temperature evolution is interpreted as being caused by the interaction between impurity ions and two-level systems, as usually observed in glasses. The glasslike behavior of β-alumina is related to disorder which is present in the conduction planes and which is the origin of the superionic conductivity of this compound.

• Received 8 February 1988

DOI:https://doi.org/10.1103/PhysRevB.38.1072