Zero‐Phonon Transitions of Eu⁺⁺ ‐ and Sm⁺⁺ ‐Doped Alkali Halides

Abstract

The theory of the electron-phonon coupling for impurity centres in ionic crystals is reviewed in order to point out the most significant parameters involved in the optical properties of the zero-phonon lines. The absorption and emission spectra of alkali halides doped with Eu++ and Sm++ have been measured for temperatures ranging from 15 up to 175 O K . In general the analysis of the experimental data agrees fairly well with the theory. The Huang-Rhys factor has been determined and also the effective frequencies which are responsible for the thermal behaviour of the spectra. However the electron-phonon interaction alone has been found not to be sufficient in order to explain the thermal dependence of the zero-phonon line strength and an additional mechanism for its thermal de-excitation has been proposed.Nous avons reexamine la theorie du couplage electron-phonon pour les centres localishs dans les cristaux ioniques pour mettre en evidence les parametres impliques dans les proprietes optiques des raies sans phonons. On a mesure les spectres d'absorption et d'emission des ions Eu++ et Sm++ dans les halogenures alcalins t i des temperatures comprises entre 15 et 175 OK. En general les resultata experimentaux sont en bon accord avec la thhorie. Nous avons determine le facteur de Huang et Rhys et les frequences effectives qui sont responsables de la variation des spectres avec la temperature. Le couplage electron-phonon n'est pas suffisant pour expliquer la variation avec la temperature de l'intensite de la raie sans phonons; nous avons propose un mecanisme additionnel pour la deexcitation thermique de la raie sans phonons.

Phonon Structure in the Luminescence of Sm++ Doped KClxBr1–x and KxRb1–x alloys

“…the structure in the line and the large increase of its half-width have been detected because the line in the ordered systems (KCl:Sm, KBr:Sm, etc.) is very sharp [9]. We then suggest that the effect of disorder on the zero-phonon line can be seen as a superposition of emissions coming from Sm++ ions in different configurations.…”

Zero‐Phonon Transitions in the Optical Spectra of Impurity Molecular Crystals

“…The main subject of the investigation until recently have been only inorganic crystals. We list here some first experimental papers which have been made to check the theoretical conclusions on the temperature broadening and shift of the zerophonon lines: [29], 1731, and 1741 (Cr3+ and V2+ ions in A1,0, and MgO), [75] (uranium ion in CaF, and SrF,), [76] (Eu2+ and Sm2+ ions in alkali halides), [77] (Sd ion in yttrium-aluminium garnet), [78] (Mn4+ ion in Mg titanates).…”

Zero‐Phonon Lines in the Luminescence Spectra of Impurity Organic Crystals and Electron–Phonon Interaction

“…I n the last years a great number of papers were published in which the zerophonon lines in the spectra of various defect and impurity inorganic crystals were studied. (See, for example, [I, 21 (colour centres in alkali halides), 13 to 51 ( C F , Vz+ ions in A1,0, and MgO), 161 (uranium ion in CaF, and SrF,), [7] (Eu2+ and Sm2+ ions in alkali halides). [S~l (Nd ion in yttrium-aluminium garnet), 191 (Mn4+ ion in Mg titanates).…”