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

Abstract

Fluorescence of ${\mathrm{Cr}}^{3+}$ ions in the two different octahedral sites of the spinel block of \ensuremath{\beta}- and \ensuremath{\beta}''-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}$${\mathit{A}}_{2}$) and of the $^{2}$E state have been measured by tuning the excitation energy within the inhomogeneous profile of the ${\mathit{R}}_{1}$ and ${\mathit{R}}_{2}$ lines of the split $^{2}$E${\mathrm{\ensuremath{-}}}^{4}$${\mathit{A}}_{2}$ transition. In sodium \ensuremath{\beta}''-alumina, we have isolated several inequivalent emitting centers, which are related to different configurations of the stabilizing ${\mathrm{Mg}}^{2+}$ ions.