Luminescence of the Cr3+ ion in sodium B- and B''-alumina: Site selection by time-resolved fluorescence line narrowing

Fluorescence of Cr3+ ions in the two different octahedral sites of the spinel block of ?- and ?''-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 (4A2) and of the 2E state have been measured by tuning the excitation energy within the inhomogeneous profile of the R1 and R2 lines of the split 2E-4A2 transition. In sodium ?''-alumina, we have isolated several inequivalent emitting centers, which are related to different configurations of the stabilizing Mg2+ ions