Fluorescence of ${\mathrm{Cr}}^{3+}$ ions in the two different octahedral sites of the spinel block of β- and β’’-alumina have been measured by time-resolved fluorescence line-narrowing spectroscopy. For the excitation either a pulsed or a chopped cw-dye laser was used. Lifetimes and splittings of the ground state ${(}^4$${\mathit{A}}_2$) and of the ${}_{}{}^2{}_{}{}^{}$E state have been measured by tuning the excitation energy within the inhomogeneous profile of the ${\mathit{R}}_1$ and ${\mathit{R}}_2$ lines of the split ${}_{}{}^2{}_{}{}^{}$E${\mathrm{-}}^4$${\mathit{A}}_2$ transition. In sodium β’’-alumina, we have isolated several inequivalent emitting centers, which are related to different configurations of the stabilizing ${\mathrm{Mg}}^{2+}$ ions.

• Received 17 May 1993

DOI:https://doi.org/10.1103/PhysRevB.49.6501