摘要:

A new method is presented to observe radiofrequency transitions between ligand hyperfinestructure levels. Contrary to conventional Endor no microwave field is required, the role of the microwave transition being taken over by cross relaxation processes. Mechanism and results of this “Endor without microwaves” are discussed in detail for the system CaF2:Tm2+. The analysis of the signals reveals details of the dynamics of the spin system.

ISSN:0033-7579    

DOI:10.1080/00337578308220646

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Two-photon excitation spectrum of the luminescence emitted in the AT-band has been observed in KBr:In+and NaBr:Tl+. The nonlinear excitation follows the A-band lineshape but reveals a feature, not present in one-photon spectrum, that may be interpreted as due to the forbidden1AIg→3AIutransition. The cross section of the process indicates that the two-photon transitions are indirect ones, allowed by phonons. The dependence of the emitted light intensity upon the direction of polarization of the exciting photons, makes it possible to identify the symmetry of the transitions.

ISSN:0033-7579    

DOI:10.1080/00337578308220647

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

We report both experimental and theoretical studies of the Tl0(l) center in KC1, a center consisting of a neutral Tl atom perturbed by the field of an adjacent anion vacancy. Absorption bands peaking at 1040, 720, 550, and 340 nm are all shown to belong to the Tl0(l) center. Measured band strengths, polarizations, energy splittings (including the Stokes shift between absorption and emission of the fundamental) and relative band widths make very good fit to prediction based on the Tl0(l) model.

ISSN:0033-7579    

DOI:10.1080/00337578308220648

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Recently Lüty and coworkers1achieved efficient laser action from a colour centre in Tl doped alkali halides, which they described as FA(T1) centres. Also recently Goovaertset al.2identified by ESR a T10atom next to an anion vacancy, which was called Tl0(l) centre. We proved with ODMR experiments unambiguously the identity of both centres. An “optical excitation” spectrum of the ODMR lines reveals several absorption bands of this centre peaking at 1040, 725, 550, 405, 335, 290 and 254 nm. The magnetic circular dichroism of the two low energy bands can be quantitatively explained with the wave functions of a Tl0atom in the axial field produced by the anion vacancy.

ISSN:0033-7579    

DOI:10.1080/00337578308220649

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Low-temperature (≲25 K) photoluminescence spectra of Ir3+-doped AgBr single crystals were obtained. These spectra are highly structured and show a progression in a low-frequency (∼38 cm−1) resonance vibrational mode and the participation of other localized vibrations. A sharp zero-phonon (ZP) line was observed at 15622.9 cm−1. The temperature dependence of the luminescence intensity was determined. The emission is rapidly quenched with temperature so that above 25 K no emission bands are observed.

ISSN:0033-7579    

DOI:10.1080/00337578308220650

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

We have measured the paraelectric resonance (PER) absorption for RbCl: Ag+ under hydrostatic pressure and observed a transition near 1.4 kbar in agreement with earlier work. The intensity of the PER signal drops drastically at 1.4 kbar and then decreases more slowly at higher pressures. However, the dipole moment changes little throughout this transition. We interpret these results as arising from two distinct single Ag+centers; one with a single on-center potential well, and the other with 12 off-center wells. The transition is assumed to occur when the two potentials become energetically equivalent.

ISSN:0033-7579    

DOI:10.1080/00337578308220651

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Nuclear spin relaxation measurements can be successfully used to determine the correlation tims τ of the localized motion of dilute centers in alkali halides up to about 10−11s, as we have demonstrated in previous work. Now, a detailed analysis of the nuclear spin relaxation process is presented, which leads to a BPP type relation between the correlation time T and the motion-induced part of the nuclear spin relaxation rate. Nuclear spin relaxation measurements were carried out on RbCl:Ag+as a function of a static electric field E applied to different crystallographic directions of the crystal between 1.4 K and 4.2 K. Generally, the interaction of a paraelectric defect with the electric field leads to an increase of the correlation time when increasing the field. An evaluation of the data gives τ = τ (E,T). The results are discussed in terms of phonon-assisted tunneling.

ISSN:0033-7579    

DOI:10.1080/00337578308220652

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The influence of the impurity aggregation state on the absorption and luminescence spectra of KCl:Cu irradiated at room temperature has been studied. Unirradiated samples excited with UV light show two main emission bands at 400 and 420 nm, ascribed to isolated Cu+ions and copper aggregates respectively. The same emission bands appear in the thermoluminescence spectra. The F and M bands show annealing steps simultaneous with the glow peaks. It is shown that the radiation induced Cu−and Cu0centers can be electrically compensated by anion vacancies. It is suggested that radiation induces impurity aggregation as well as anion interstitial aggregation. Thermal release of interstitials may excite isolated Cu+ions and copper aggregates, either through energy transfer from F + H recombination or byH+α→Vk,Vk+ Cu0reactions.

ISSN:0033-7579    

DOI:10.1080/00337578308220653

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The stability of the europium second phase precipitates in NaCl, NaBr, KC1, and KBr under room temperature X-irradiation has been analyzed using the photoluminescence technique. The irradiation tends to destroy the pre-existing metastable precipitates creating complexes of a much simpler nature. In parallel with this destruction an enhanced europium precipitation into the stable dihalide phase EuX2(X=Cl, Br) was found to occur.

ISSN:0033-7579    

DOI:10.1080/00337578308220654

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Recently Badalyan and Baranov reported an ESR spectrum of atomic hydrogen on anion sites in RbCl with partly resolved Rb superhyperfine (shf) interaction and concluded from it that the hydrogen atoms are off-centre along [111]. We have performed an ENDOR investigation of these centres and found that the hydrogen atoms down to approx. 15 K are on-centre. The shf and quadrupole interactions with 1st and 5th shell Rb and 2nd and 4th shell CI neighbours were determined as well as the activation energy for the hydrogen vibrations. The shf interactions are quantitatively interpreted with a charge transfer model applied earlier to KC1. The results are compared with those in KCl.

ISSN:0033-7579    

DOI:10.1080/00337578308220655

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor