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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 1399-1421 
    ISSN: 0392-6737
    Keywords: Impurity and defect absorption in solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The controversial far-infrared optical absorption in Li-doped alkali halides is now attributed to transitions between the low-lying energy levels of an anharmonic oscillator composed of three halogen-ion pairs centred at the cation site which vibrate in theT 1u ungerade mode. This oscillator is electronically coupled to the impurity dragging it into rotation over 〈111〉 sites. Several experimental features derive simply from our model such as the absence of any clear-cut lithium-isotope effect and the low-frequency range. The capital effect of an F centre at a 〈001〉 nearest-neighbour (nn) site is to reduce the dimensionality of vibration forcing the impurity to rotate in the perpendicular (001)-plane. This upgrades the optical frequency in proportion to (3/2)1/2 and shrinks the off-centre displacement. We finally show that recent computer-simulation data on Li-doped alkali halides provide a solid ground for regarding the Li off-centredness as a pseudo-Jahn-Teller phenomenon.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 117-130 
    ISSN: 0392-6737
    Keywords: Magneto-optical effects ; Solid alkali halides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Gli effetti di dicroismo magnetico circolare hanno costituito in passato un ottimo mezzo per chiarire il ciclo ottico dei centriF in alogenuri alcalini e la natura dello stato eccitato rilassato. Abbiamo usato tale tecnica per studiare la debole doppia emissioneF trovata recentemente in NaI e la luminescenza dei centriF edF A (di tipo I e II) in KCl. Si è trovato che l'emissioneF a minore energia in NaI e l'emissioneF A (I) in KCl∶Na+ si comportano come la ben nota emissione dei centriF, il che conferma l'attribuzione di tale luminescenza in NaI allo stato eccitato rilassato normale. L'emissioneF a energia maggiore in NaI e l'emissioneF A (II) in KCl∶Li+ mostrano un comportamento completamente diverso. I dati sperimentali sono stati confrontati con la teoria vibronica di Ham e Grevsmuhl dello stato eccitato rilassato.
    Abstract: Резюме Магнитный круговой дихроизм ранее применялся как инструмент для выяснения оптического циклаF центров в щелочных галогенидах и природы релаксирующего возбужденного состояния. В этой работе мы используем эту технику для исследования слабого двойного F излучения, обнаруженного недавно в NaI и при люминесценцииF иF A центров (типа I и типа II) в KCl. Мы обнаружили, что длинноволновоеF излучения в NaI иF A (I) излучение в KCl∶Na+ ведет себя как хорошо известное излучениеF центров, что подтверждает приписывание вышеуказанной люминесценции в NaI нормальному релаксирующему возбужденному состоянию. Полностью отличное поведение обнаруживает коротковолновоеF излучение в NaI иF A (II) излучение в KCl∶Li+. Полученные экспериментальные данные сравниваются с вибрационной теорией Гама и Гревсмула для релаксирующего возбужденного состояния.
    Notes: Summary The magnetic circular dichroism has been in the past an excellent tool to clarify the optical cycle of theF centres in alkali halides and the nature of the relaxed excited state. We have used such technique to study the weak doubleF emission found recently in NaI and the luminescence ofF andF A centres (of both type I and II) in KCl. We have found that the long-wavelengthF emission in NaI and theF A (I) emission in KCl∶Na+ behave like the well-known emission of theF centres, confirming the attribution of the above luminescence in NaI to the normal relaxed excited state. A completely different behaviour is displayed by the short-wavelengthF emission in NaI and by theF A (II) emission in KCl∶Li+. The experimental data have been compared with the Ham and Grevsmuhl vibronic theory of the relaxed excited state.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0392-6737
    Keywords: Solid alkali halides ; Optical rotatory power ; Impurity and defect absorption in solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A theory which explains self-consistently the emission and the polarization rotation of transmitted light has been developed forF A centres in crystals with cubic symmetry. Azimuthal dependences ofF A luminescence in alkali halides are very informative for determining the electron-phonon interaction as well as the parameters related to the structural and optical quality for coulour centre lasers crystals. The theoretical results are applied to the interpretation of the luminescence properties ofF A (Li) centres in KCl, RbCl and KF.
    Type of Medium: Electronic Resource
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