Radiative and nonradiative processes of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>F</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>F</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>centers in NaBr and NaI

Baldacchini, G.; Pan, David S.; Lüty, Fritz

doi:10.1103/physrevb.24.2174

Cited by 38 publications

(5 citation statements)

References 17 publications

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“…not available. However, there is strong experimental evidence [26] that the ground state of the F' centre becomes more and more deeply bound from NaCl to NaI. This trend is indeed shown in the results of our calculation, table 1.…”

Section: Optical Binding Energysupporting

confidence: 83%

Two-electron defect systems in ionic crystals: application to F' centres in alkali halides

Zhang

Song

1994

J. Phys.: Condens. Matter

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The extended-ion method for the study of excited states in ionic crystals is modified for such two-electron defect systems as the F' centre and positronium in alkali halides. Exclusive use of 1s floating Gaussian functions as the basis is the main feature of the method. Some degree of electron correlation is built-in in this method. Applied to F' centres, it is found that in NaI the spin-singlet ground state is deeply bound, and there is also a bound triplet state. Comparison with experimental data regarding the optical and thermal dissociation energies in several alkali halides gives reasonable agreement.

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Section: Optical Binding Energysupporting

confidence: 83%

Two-electron defect systems in ionic crystals: application to F' centres in alkali halides

Zhang

Song

1994

J. Phys.: Condens. Matter

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“…In particular, to search for efficient laser materials, radiationless processes that affect the luminescence efficiency have to be clarified. 1 Since Dexter et al 2 proposed a criterion for quenching of the emission using a configuration coordinate model, several experimental [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and theoretical [22][23][24][25][26][27][28] investigations of the radiationless processes in F center 29,30 ͑point defect that consists of an electron trapped at an anion vacancy͒ in alkali halide crystals were performed. In order to explain the radiationless process, we sketch an optical cycle in F centers using a 1s-2p ͑two-level͒ model, as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…31 ͑3͒ Thermally activated ionization process. 3,7 Ionization occurs from the lowest RES to the conduction band, which is active at higher temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…Most studies on radiationless processes in F centers have been conducted within the framework of the 1s-2p model. 2,[4][5][6][7][8][9][10][11][12][13][14][22][23][24][25][26] However, in a recent development, the role of the 2s state in the ES has been recognized and a 1s-2p-2s ͑three-level͒ model, as illustrated in Fig. 2, has been proposed.…”

Section: Introductionmentioning

confidence: 99%

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Luminescence efficiency ofFcenters in KI studied by lifetime measurements

2009

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The luminescence efficiency of isolated F centers in KI was studied as a function of the excitation energy by measuring the lifetime for ordinary luminescence. The emission intensity measured under a pulse excitation was found to obey nonexponential decay. The luminescence efficiency decreases to below unity when the excitation energy exceeds 1.96 eV, which corresponds to the slope position at the higher energy side of an F absorption band. The threshold value for the luminescence efficiency is lower than that previously obtained from cw measurements but close to that predicted theoretically by Leung and Song. We have traced the origin of this difference by performing experiments based on the cw method and found out the reason. It is shown that there is a relationship between quantities obtained by the cw method and those obtained by our lifetime measurement. Our experimental data are thoroughly analyzed using a model for the radiationless process of Leung and Song, which is based on a 1s-2p model. A 1s-2p-2s model is also discussed.We have obtained excitation spectra for fast and slow components from the results of A f and A s shown in Fig. 7͑b͒ by using Eqs. ͑A4͒ and ͑A5͒ in Appendix, in which the number of irradiation times n is 87 and the duration time t p is 4.6 s. They are denoted by I cw,f cal and I cw,s cal respectively, and presented in Fig. 8 as a function of the excitation energy, together with the absorption curve of the F band. We see that I cw,s cal well coincides with the F absorption band except for the high-energy side near the K band. This fact means that I cw,s cal is just the excitation spectrum of slow component and the emission of slow component occurs under thermal equilibrium. The other important fact is that I cw,f cal spectrum with the peak of 2.06 eV is not related to the F absorption band. This result suggests that fast and slow components arise from different sources. The deviation of I cw,s cal from the F band in the high-energy side reflects the decrease in s due to radiationless processes.In Sec. IV E, we will show that I cw,s cal agrees with the excitation spectrum obtained by the cw method. C. Dependence of the fast component's lifetime on F center concentrations and temperatures

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“…The dynamical nonradiative transition has been studied theoretically[105] and experimentally[106,107]. On the other hand, there is another interpretation that the small efficiency of luminescence at the F center in NaBr, NaI is attributed to an ionization to form the F center (an anion vacancy with two trapped electrons) with full efficiency[108].…”

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confidence: 99%

Dynamics of nuclear wave packets at theFcenter in alkali halides

Koyama

Suemoto

2011

Rep. Prog. Phys.

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The F center in alkali halides is a well-known prototype of a strongly coupled localized electron-phonon system. This colour center is one of the long studied targets in the field of photophysics because it is simple but rich in variety. Steady-state spectroscopy, such as modulation spectroscopy and Raman scattering spectroscopy, has elucidated the strength of the electron-phonon coupling in the (meta-)stable state, i.e. the ground state and the relaxed excited state. Picosecond spectroscopy has improved understanding of the state mixing in the transient state. Owing to recent developments of ultrafast lasers with pulse widths shorter than oscillation periods of phonons, it has been possible to perform real-time observation of lattice vibration, and the understanding of the transient state has been remarkably expanded. In this paper, we review early and present studies on dynamics of electron-phonon coupling at the F center, especially recent real-time observations on the dynamics of nuclear wave packets in the excited state of the F center in KI, KBr, KCl and RbCl. These real-time observations reveal (i) spatial extension of the electronic wave function of a trapped electron, (ii) the difference between the coupled phonons in the ground state and the excited state, (iii) diabatic transition between the adiabatic potential energy surfaces and (iv) anharmonicity of the potential energy surface.

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Radiative and nonradiative processes ofFandF′centers in NaBr and NaI

Cited by 38 publications

References 17 publications

Two-electron defect systems in ionic crystals: application to F' centres in alkali halides

Two-electron defect systems in ionic crystals: application to F' centres in alkali halides

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Dynamics of nuclear wave packets at theFcenter in alkali halides

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