摘要:

The resonance Raman scattering (RRS) of F centers, particularly the photon-energy dependence of linear polarization of the RRS, has been studied on the basis of a vibronic viewpoint. With combinination of previous results that have explained magnetic circular dichroism (MCD) spectra, a vibronic scheme of the Franck-Condon state of F centers for KCl, KBr and KI crystals is established.

ISSN:1042-0150    

DOI:10.1080/10420159508227265

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Luminescence in Hg2Cl2, crystals excited with UV light is investigated in the spectral region 0.8–2.25 eV. Measurements are performed on as-grown samples and on samples previously exposed to UV light at RT. Six emission bands are found which depend on the concentration of the photochemical entities produced by irradiation of the crystals at RT. It is concluded that infra-red (IR) luminescence of Hg2Cl2originates from crystal defects. The observed emission bands are tentatively attributed to the emission of (HgCIxBr3−x)−and (HgClxBr4−x)2−complexes formed with residual Br impurities. Centres responsible for IR Hg2Cl2emissions are excited: (i) via excitons of Hg2Cl2, (ii) via excited states of isolated Hg2Br2molecules, and (iii) resonantly through the excitation bands of defect centres.

ISSN:1042-0150    

DOI:10.1080/10420159508227266

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Autler-Townes interactions are observed in the time domain by performing a modified echo experiment. Constructive and destructive interferences characteristic of the Autler-Tomes components in electron spin triplet states are observed for two different color centers in calcium oxide and diamond crystals, respectively.

ISSN:1042-0150    

DOI:10.1080/10420159508227267

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionicRbAg4I5crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystalsRbAg4I5due to additive coloring in iodine vapours, ionic implantation and γ-ray irradiation are considered.

ISSN:1042-0150    

DOI:10.1080/10420159508227268

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Emission and excitation spectra were accurately detected as a function of the temperature (in the range 18-300 K) in NaF and LiF samples containing unperturbed M-centres: different coloration techniques and ageing effects were tested in order to obtain the pure M-emission band. On the basis of collected data new trends and correlations are proposed between the halfwidth of the emission bands (H), the effective modes (ω), and the Huang-Rhys factors (S) for M and F centres: the H(M) values are roughly half the H(F) ones, M-emission S values are very similar in different crystals, ω and H values for the M- and F-emissions are proportional to the transverse optical frequency ωTvalues.

ISSN:1042-0150    

DOI:10.1080/10420159508227269

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The temperature dependence of the electron nuclear double resonance (ENDOR) spectra of FH(CN−) centres in KCl was investigated in the temperature range between 10–220 K. At the lowest temperature of 10 K only one CN−orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than the carbon. With the very small thermal activation energy of 2.9 meV the opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN−and of the13C interaction of the CN−molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy of 4.2 meV. It is assumed that a soft local mode involving those two nearest K nuclei and the CN−is causing the strong temperature dependence. The shf interactions of14N nuclei have not been seen, probably because of the dynamical effects.

ISSN:1042-0150    

DOI:10.1080/10420159508227270

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The results of measurements of the magnetic circular dichroism of the optical absorption (MCDA) and optically detected electron paramagnetic resonance (ODEPR) of X-irradiated KBr:In crystals are presented. The MCDA bands and ODEPR parameters of In°(1) centers and In2+centres have been measured. The mechanism of the energy storage in KBr:In crystals is found not to be simply the formation of correlated F centre-In2+centre pairs as was assumed previously. Considerable similarities to the storage phosphor BaFBr:Eu2+were found for the photostimulated emission and read-out properties.

ISSN:1042-0150    

DOI:10.1080/10420159508227271

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Recombination luminescence emission spectra, TSL and trap spectra estimated by fractional glow technique (FGT), in nominally pure and Li-, Bi- and Ho-doped CdWO4, crystals are reported. According to the investigations by FGT heterovalent impurities Li, Bi and Ho causes localized electronic states which act as traps for charge carriers. It is shown that TSL results in emission of known blue-green luminescence band by emptying of the Li+-related traps in CdWO4-Li and yellow luminescence band by emptying of the Bi3+-related traps in CdWO4-Bi. It is proposed that blue-green and yellow luminescence occur by recombination correspondingly of free holes and free electrons at different intrinsic tungstate group related luminescence centers.

ISSN:1042-0150    

DOI:10.1080/10420159508227272

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Thermo- and photostimulated processes are studied in reduced hydrogen containing α-Al2O3excited by UV light. It is found that UV excitation in F absorption band at 90 K results in a ionization of the F-centers and capture of released electrons at defects thus producing an anisotropy absorption band at 4.2 eV and the dominant thermoluminescence (TL) peak at 260 K. The 260 K TSL peak is accompanied by complete bleaching of the 4.2 eV absorption band andvice versa—by light stimulation in the region of the 4.2 eV band the 260 K TSL peak disappear and released electrons recombine with F+-centers. Both the effect of the preliminary high-temperature thermal treatment of samples on formation of 4.2 eV-centers and the observed dichroism characteristics allows to conclude that corresponding complex defect contains hydrogen and can involve vacancy pair.

ISSN:1042-0150    

DOI:10.1080/10420159508227273

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Direct quantitative correlations have been recently observed between the T-centre EPR signal and an optical absorption band at 370 nm, in X-irradiated YSZ, suggesting that the colour centre and the paramagnetic centre might be the same entity. In order to confirm this hypothesis, theoretical modeling was undertaken, where by appropriate refinement the known electronic structure of the T-centre is shown to be compatible with an optical transition, having an oscillator strength of the correct magnitude.

ISSN:1042-0150    

DOI:10.1080/10420159508227274

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor