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  • 1
    Electronic Resource
    Electronic Resource
    Absorption lineshape ofF A centres in alkali halides (1988)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 10 (1988), S. 693-708 
    Details
    ISSN: 0392-6737
    Keywords: Impurity and defect absorption in solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Sono state studiate per la prima volta le forme di riga delle bande di assorbimento dei centriF A in alogenuri alcalini. Il nuovo metodo usato per questa indagine è basato sulla determinazione attraverso misure di luminescenza della sovrapposizione fra le bandeF A1 eF A2 . I risultati sperimentali sono stati confrontati con i valori dedotti da bandeF A teoriche di diverse forme. La forma di riga dell'assorbimento a bassa temperatura, sia per i centriF A (I) in KCl: Na+ sia per i centriF A (II) in KCl: Li+ e RbCl: Li+, è approssimata molto meglio da una somma di due curve Lorentziane che da quella di due bande Gaussiane o Poissoniane. Questo risultato rivela una differenza imprevista rispetto ai centriF, il cui assorbimento ha una forma di riga Poissoniana alle stesse temperature.
    Abstract: Резюме Впервые исследуются формы линий зон поглощения дляF A центров в щелочно-галоидных соединениях. Предлагается новый метод исследования. Этот метод основан на определении перекрытия междуF A иF A2 зонами из измерений люминесценции. Экспериментальные результаты сравниваются с вычисленными величинами, полученными из теоретическихF A зон различной формы. ДляF A (I) центров в KCl: Na+ иF A (II) центров в KCl: Li+ и RbCl: Li+ форма линии поглощения при низких температурах оказывается ближе к сумме двух Лоренцевых кривых, а не двух Гауссовых или Пуассоновых зон. Этот результат обнаруживает неожиданное отличие отF центров, форма линии поглощения которых, как известно, представляет Пуассонову кривую при тех же температурах.
    Notes: Summary The lineshapes of the absorption bands ofF A centres in alkali halides have been studied for the first time. The new method used for this investigation is based on the determination of the overlap between theF A1 andF A2 bands from luminescence measurements. The experimental results have been compared with calculated values deduced from the theoreticalF A bands of different shapes. For bothF A (I) centres in KCl: Na+ andF A (II) centres in KCl: Li+ and RbCl: Li+ the absorption lineshape at low temperature is much closer to a sum of two Lorentzian curves than that of two Gaussian or Poissonian bands. This result shows an unexpected difference with theF centres, whose absorption lineshape is known to be Poissonian at the same temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02451107
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  • 2
    Electronic Resource
    Electronic Resource
    Spin-orbit coupling, spin-lattice relaxation, and spin-memory studies ofF-center-molecular-ion pairs in alkali halides (1993)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 15 (1993), S. 207-228 
    Details
    ISSN: 0392-6737
    Keywords: Magnetooptical effects ; Insulators
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The spin-orbit parameter Δ, spin-lattice relaxation timeT 1, and spin-mixing parameter ɛ ofF H(OH−) andF H(CN−) centers in several alkali halides have been studied with magnetic circular dichroism at ∼2 K. A close comparison of the experimental results before and after optically induced association of theF center with the molecular ion has been made. In crystals of NaCl structure the negative spin-orbit parameter Δ changes little betweenF andF H centers in the same host. For CsCl and CsBr two values of Δ have been derived forF H(CN−) centers with axis parallel or perpendicular to the magnetic field. In all studied systems, the spin-lattice relaxation timeT 1 is already shorter before aggregation compared toF formation. The spin-mixing parameter ɛ decreases slightly forF H(OH−) compared toF centers, while it increases drastically forF H(CN−) defects and reaches its maximum possible value ɛ=0.5 in cesium halides. First attempts to interpret these magneto-optical results will be presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456904
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  • 3
    Electronic Resource
    Electronic Resource
    Revisited vibronic model for Li+ ion and F A (Li) centre in alkali halides (1991)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 1399-1421 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02457128
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic circular dichroism in the luminescence ofF andF A centres in alkali halides (1990)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 117-130 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02453031
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  • 5
    Electronic Resource
    Electronic Resource
    Lifetime measurements of colour centres by a multifrequency phase fluorometer (1986)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 7 (1986), S. 379-388 
    Details
    ISSN: 0392-6737
    Keywords: Defects in crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si riportano le prime misure di tempi di vita dell'emissione dei centri di colore usando uno spettrofluorometro a correlazione di fase e di modulazione in funzione presso il laboratorio del Programma per l'Utilizzazione della Luce di Sincrotrone (PULS, Frascati). Si discutono i risultati relativi ai centri F ed agli aggregati di centri F nel fluoruro di sodio.
    Notes: Summary The first measurements of emission lifetimes in colour centres using a cross correlation phase and modulation fluorometer operating at the synchrotron radiation facility PULS (Frascati) are reported. Preliminary results on the F and F-aggregate centres in NaF are briefly summarized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02453239
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  • 6
    Electronic Resource
    Electronic Resource
    Detailed model of the photostimulated realignment ofF FA centres in KCl:Li+ (1987)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 9 (1987), S. 1105-1114 
    Details
    ISSN: 0392-6737
    Keywords: Impurity and defect absorption in solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto La riorientazione fotostimolata dei centriF A in KCl:Li+ è descritta con un modello semplice che tiene conto dell’angolo di disallineamento e della sovrapposizione delle code delle due bande di assorbimento. Con questo modello abbiamo interpretato la dipendenza dell’intensità di luminescenza dalla polarizzazione della luce di eccitazione. Il fitting dei dati sperimentali dà un angolo di off-axis di circa 5° ed una sovrapposizione delle bande maggiore di quella prevista per curve di tipo gaussiano.
    Abstract: Резюме С помощью простой модели описывается фотостимулированная переориентацияF A центров в KCl:Li+. Эта модель учитывает угловое удаление центров от оси и перекрытие хвостов двух зон поглощения. С помощью этой модели мы интерпретируем зависимость интенсивности люминесценции от поляризации возбуждающего пучка. Подгонка экспериментальных данных дает угловое удаление от оси порядка 5° и большее перекрытие зон, чем было предсказано для гауссовых форм линий.
    Notes: Summary The photostimulated reorientation of theF A centres in KCl:Li+ is described by a simple model that takes into account the off-axis angle of the centres and the overlapping of the tails of the two absorption bands. With this model we have interpreted the dependence of the luminescence intensity on the polarization of the exciting beam. The fitting of the experimental data gives an off-axis angle of approximately 5° and an overlapping of the bands larger than that predicted for Gaussian line shapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02451095
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic circular dichroism in the absorption of theF A centre in KCl doped with Li and Na (1990)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 995-1003 
    Details
    ISSN: 0392-6737
    Keywords: Magneto-optical effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The spin-orbit structure ofF A centres in KCl:Li and KCl:Na have been studied by means of the magnetic circular dichroism. Due to theirC 4V symmetry theF A centres have two different spin-orbit parameters, Δ‖ and Δ⊥, which only in the KCl:Li case follow the relation: Δ‖ 〈 ΔF 〈 Δ⊥ as expected from the theory. For a close comparison we have also reported our measurement of the spin-orbit coupling ofF centre in KCl. The spin-orbit parameters of theF andF A centres have been determined using the method of moment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02453045
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  • 8
    Electronic Resource
    Electronic Resource
    Self-consistent analysis of absorption and emission data forF A centres in alkali halides (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 127-139 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02451694
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  • 9
    Electronic Resource
    Electronic Resource
    Broadening of Er3+ electronic states in phosphate glasses (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7975-7984 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absorption and emission spectra of Er3+-doped and Er3+–Yb3+-codoped phosphate glasses have been studied within the temperature interval from 10 to 300 K. The analysis of Er3+ Stark splitting for the excited state 4I13/2 and the ground-state 4I15/2 multiplets is performed. Simulation of inhomogeneous broadening of Stark levels has shown that all (2J+1) components of both multiplets are split by random distortions of the initial symmetric polyhedron, consisting of the neighboring oxygen ions in phosphate glasses. Inhomogeneous broadening of Stark levels is different for each energy level and reflects the sensitivity of a particular energy level to the variation of crystal field. At least three energy levels participate in shaping the low-energy side of the emission spectra, caused by the 4I13/2→4I15/2 transition. The emission linewidth corresponding to the transition to the highest by energy Stark component is assumed to derive from comparable contributions of inhomogeneous and homogeneous broadening, the latter caused by intra-multiplet transitions. The presence of the highest Stark level in the crystal-field splitting of the ground-state 4I15/2 manifold with a high rate of nonradiative relaxation is essential for writing the rate equations which describe the laser operation of erbium glass lasers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408916
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  • 10
    Electronic Resource
    Electronic Resource
    Anisotropy of two-photon excited f–f transitions of Eu2+ in KMgF3 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 457-464 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polarization dependence of sharp intraconfigurational 4f7 transitions of Eu2+ in KMgF3 have been studied by means of two-photon excitation spectroscopy. A new puzzle appears connected with the site-symmetry distortion at the Eu2+ ions and the weakness of third-order spin-orbit corrections, suggesting a mechanism for intraconfigurational interaction independent from crystal-field strength and from the site symmetry on the rare-earth ion. Intensity and polarization dependencies of the 8S7/2→6P7/2,6P5/2,6D9/2 transitions have been satisfactorily interpreted in terms of second-order perturbation theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478106
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