Two-photon absorption spectroscopy of Eu2+ ions in KCl and KI.

Abstract

Two-photon absorption (TPA) spectroscopy is used to study f\ensuremath{\rightarrow}f transitions in europium as an impurity in KCl and KI. The spectrum of the transition from the ground state ${(\mathrm{}}^{8}$${S}_{7/2}$) to the excited ${(\mathrm{}}^{6}$${P}_{7/2}$) state consists of four sharp absorptions as predicted by group theory for a J=(7/2) level with ${C}_{2v}$ local symmetry. The transition to the $^{6}\mathrm{P}_{5/2}$ state is not present in both samples, in spite of the excellent signal-to-noise ratio of the data. We do not understand this point. We also show in this paper that TPA spectroscopy of the f\ensuremath{\rightarrow}f transitions of ${\mathrm{Eu}}^{2+}$ is an excellent way to study the aggregated phases of divalent ions in alkali halides. The spectra show very distinct absorptions due to each of the three aggregated phases of ${\mathrm{Eu}}^{2+}$ in KCl as opposed to the one-photon absorption and fluorescence of the 4${f}^{6}$5d transition where the broad bands make the analysis of the aggregated phases difficult.