Vibrational relaxation of the<i>F</i>center in NaI and NaBr

F, De Matteis; Leblans, M.; Schoemaker, D.

doi:10.1103/physrevb.49.9357

Cited by 8 publications

(9 citation statements)

References 20 publications

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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%

“…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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

2009

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“…Such a simultaneous observation of a crossover process and a transition from the the RES was, e.g., proposed for the intrinsic nonradiative relaxation of the F center in NaI. 35 However, since both the intermediate and slow component have a negative sign somewhere in the wavelength range between 595 and 620 nm, they are probably not related to electronic relaxation: It was argued in Sec. III that excited-state absorption, associated with the negative sign of electronic relaxation, is not likely to be observed so close to the F H -band maximum.…”

Section: B Elimination Of Slow Electronic Contributionsmentioning

confidence: 71%

“…6 A 10-ps relaxation component observed in the inducedtransparency measurements on the F center in NaI was interpreted as a contribution due to this crossover process. 35 For the isolated F center in KBr this process cannot occur, since the crossing point lies above the energy reached after optical excitation. When energy transfer to the stretching mode of OH Ϫ or OD Ϫ occurs, additional potential energy curves have to be considered, which are shifted upwards by a multiple of the vibrational frequency ͑Fig.…”

Section: B Crossover Relaxation and E-v Transfermentioning

confidence: 99%

Electronic, vibrational, and configurational relaxation of theFH(OH−
Gustin
¹
,
Leblans
²
,
Bouwen
³

et al. 1996
Phys. Rev. B
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The relaxation after optical excitation of the F H (OH Ϫ ) center in KBr is studied with a picosecond pumpprobe technique for induced transparency. Three different relaxation components can be distinguished: ͑i͒ a nearly temperature-independent component decaying in a few ps; ͑ii͒ a component which decays slower than 10 ns at all temperatures; and ͑iii͒ a strongly temperature-dependent component with a time constant of the order of 100 ps at 50 K and at least 10 ns below 20 K. We observe essentially no effect on the relaxation time of the components under OH Ϫ →OD Ϫ substitution. Because of its picosecond time scale, its temperature independence, and the Raman measurements presented in an earlier paper, we identify the first component as a radiationless electronic transition during lattice relaxation, which occurs mainly near the first crossing point reached. This corresponds to the excitation of one quantum of the stretch vibration. Because the other components change from induced transparency to induced absorption under probe-wavelength variation, they are very probably not related to electronic relaxation processes. The nanosecond component is interpreted as vibrational relaxation. It appears in the relaxation scans as a result of the influence of the stretch vibration on the electronic absorption. Effects of the probe power on the relaxation measurements below 30 K, show that also optical conversion between the two KBr:F H (OH Ϫ ) configurations is involved in the relaxation process. These configurations possess different electronic absorption bands and are essentially different orientations of OH Ϫ with respect to the F center. The third, strongly temperature-dependent component is associated with the recovery of the thermal equilibrium between these configurations. ͓S0163-1829͑96͒03434-0͔

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“…The crystal structure of superconducting LuNi2B2C has been determined to be body-centred tetragonal, with NaC1-type LuC layers alternating with Ni2B2 blocks [4]. Band structure calculations of both the RE = Y and Lu materials predict that, despite an initial resemblance to the cuprate high-Tc superconductors, the electronic structure of RENi2B2C is in fact three-dimensional, with significant contributions from all of the constituent atoms to the metallic character of the material [5,6]. The question then arises as to whether these intermetallic materials are a new class of unconventional superconductors, or whether they represent a particular optimisation of the conditions favouring BCS superconductivity.…”

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confidence: 99%

A Resonant-Photoemission Study of YNi ₂ B ₂ C

Golden¹,

Knupfer²,

Kielwein³

et al. 1994

Europhys. Lett.

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Valence level photoemission measurements of the normal-state electronic structure of the new boro-carbide intermetallic superconductor YNi2B2C are presented. The behaviour of the Ni-dominated valence band peak at 1.4 eV binding energy and the states at EF across the Ni 3p absorption threshold clearly indicate significant Ni3d contributions at these energies. In addition, the transfer of spectral weight from the main Ni3d valence band to a two-hole bound-state satellite at ∼ 8 eV signals the role played by electron correlation in these materials. The peak in the DOS predicted to lie at EF in band structure calculations is not observed in the experiment, possibly also due to the effects of electron correlation.

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Vibrational relaxation of theFcenter in NaI and NaBr

Cited by 8 publications

References 20 publications

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Electronic, vibrational, and configurational relaxation of theFH(OH−
Gustin
¹
,
Leblans
²
,
Bouwen
³

et al. 1996
Phys. Rev. B
Self Cite
10
0
1
0
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A Resonant-Photoemission Study of YNi ₂ B ₂ C

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Vibrational relaxation of theFcenter in NaI and NaBr

Cited by 8 publications

References 20 publications

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Electronic, vibrational, and configurational relaxation of theFH(OH−Gustin1, Leblans2, Bouwen3 et al. 1996Phys. Rev. BSelf Cite10010View full textAdd to dashboardCite

A Resonant-Photoemission Study of YNi 2 B 2 C

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Electronic, vibrational, and configurational relaxation of theFH(OH−
Gustin
¹
,
Leblans
²
,
Bouwen
³

et al. 1996
Phys. Rev. B
Self Cite
10
0
1
0
View full text Add to dashboard Cite

A Resonant-Photoemission Study of YNi ₂ B ₂ C