摘要:

Absorption and emission spectra of impurity clusters and precipitates in NaCl:Pb have been measured. The results from emission kinetics measurements reveal a complicated behaviour in the 330 nm band usually ascribed to PbCl2—like phase. The band with a maximum at 380 nm appears in the emission spectrum of this crystal after fast quenching from 500[ddot]C to RT. The corresponding lifetime is close to the value of isolated lead centres. We suggest that it belongs to small lead clusters with NaCl structure.

ISSN:1042-0150    

DOI:10.1080/10420159508222693

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Thin crystals of Na1−xKxI:Tl+solid solutions with thicknesses of 0.1 ∼ 10 μm have been produced and their phase separation has been observed in both regions of the exciton band and Tl+impurity band. An intermediate band of Tl+was recognized in the absorption spectrum of Na0.5K0.5I:Tl+. A precursor phenomenon was found as a temporal change of the intensity ratio of two Tl+emission bands.

ISSN:1042-0150    

DOI:10.1080/10420159508222694

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Metallic Na was formed on crystal surfaces of NaCl with irradiation by electron beams of low energy (10–30 KeV) or photon fluxes in the VUV region and was evaluated with AES and UPS. The states of Na formed in or on NaCl crystals with irradiation of high (21 MeV) and low energy electrons and VUV photons are discussed comparing the results from different analysis methods.

ISSN:1042-0150    

DOI:10.1080/10420159508222695

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Sodium particles in heavily irradiated synthetic doped NaCl and natural rocksalt have been studied by electron spin resonance (ESR), differential scanning colorimetry (DSC) and dielectric loss measurements. For the first time we have studied quantum size effects of Na colloids in irradiated NaCl at different temperatures between 140 K and 30 K. A weak temperature dependence of the electronic susceptibility of these particles is observed, that deviates from the simple metallic behaviour and may be due to interactions in the system. The magnetic properties of sodium particles in heavily damaged NaCl (3–15 mole % metallic Na) measured by ESR below 160 K might be associated with antiferromagnetic interactions between the extremely small colloids, which suggests a transition to a spin density or charge density wave ground state; this is in agreement with the observation of an anomalous peak in the AC conductivity at about 150 K.

ISSN:1042-0150    

DOI:10.1080/10420159508222696

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The visible emission and excitation spectra of AgBr microcrystals containing single and parallel double twin planes has been obtained. A band at 462.28 nm (2.6813 eV) is observed in the excitation spectrum. This feature is about 2.5 meV below the indirect exciton band edge. Coincident emission features are observed. The band in the excitation spectrum of microcrystals with two parallel twin planes is often split into a doublet with splittings between 1 and 2 meV. The new band is assigned to an exciton created at a stacking fault and the splittings are thought to be due to tunnelling of the exciton between proximate twin planes.

ISSN:1042-0150    

DOI:10.1080/10420159508222697

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The optical functions of metallic particles, resulting from the precipitation of alkali ions implanted in LiF crystals, have been calculated from optical absorption and reflectivity measurements in the photon energy range 0.4–6 eV. Optical data are analyzed in terms of local electrical field effects. The real part of the dielectric function remains positive in the whole energy spectrum, in opposition to the one calculated in the Maxwell-garnett approximation where enhanced reflection should correspond to negative values of the dielectric function. Additional resonances shown by the enery loss function are responsible for this discrepancy. An absorption peak associated to Li precipitates and a secondary peak of the plasma resonance are revealed, so as a loss structure at 5 eV due to F centres also detected in electron energy loss spectrometry (REELS). Implications for non linear optical properties are addressed.

ISSN:1042-0150    

DOI:10.1080/10420159508222698

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Low Energy Cluster Beam Deposition (LECBD) has been used to synthesize cermets with controlled size nanoparticle. In the Bi-SiOxsystem, this technique allows the formation of Bi nanograins uniformaly distributed in the SiOxinsulating matrix. The size of the Bi nanograins (mean diameter about 4 nm) may be responsible of a surprising optical property of the LECBD Bi-SiOxcermets. The difference between theoretical and experimental optical behavior of LECBD cermets is assumed to be a clue of size effects inducing a metal-semiconductor transition.

ISSN:1042-0150    

DOI:10.1080/10420159508222699

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The article deals with the investigation of concentration dependences of absorption, luminescence and photosensitivity impurity bands, caused by the introduction of overstoichiometric cadmium atoms (Cdi) into the lattice of strongly anisotropic CdI2layered crystal. The model, explaining concentration dependences of CdI2-Cdispectra, suggests localization of Cdiatoms in Van-der-Waals gaps of layered crystals and their interaction with themselves and with lattice iodine atoms. The character of these interactions strongly depends on Cdi, concentration (i.e. on the distance between Cdiatoms) and changes froms-Cdi-p-I (at NCdi< 10<sp>18 cm−3) tos-Cdi-s-Cdiinteraction at higher concentration. The quantum-chemical simulations were carried out to confirm the proposed model.

ISSN:1042-0150    

DOI:10.1080/10420159508222700

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We present Raman scattering spectra of CaF2samples with Ca colloids and MgO:Li with Li precipitates. The samples have been prepared by different thermal and irradiation treatment in order to achieve different colloid sizes. Exciting in the colloid surface-plasmon band we observe SERS of the whole density of states of CaF2or MgO phonons, the intensity being enhanced when the excitation approaches the colloid band maximum. In order to explain the appearance of the one phonon density of states and the resonant behaviour we propose a mechanism consisting of surface plasmon and charge transfer excitation, superposed to the electromagnetic process.

ISSN:1042-0150    

DOI:10.1080/10420159508222701

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The structure of the complex Fe-Co mixed oxides system, prepared as an industrial ammonia catalyst, is studied by TEM (transmission electron microscopy). The introduction of Co in the system create a high density of structural extended defects. Concentration of Co bigger than 10 a. % lead to the formation of a high density of precipitates which were identified as Co3O4in the magnetite matrix. The data in this phase identification was obtained by moiré fringe analysis.

ISSN:1042-0150    

DOI:10.1080/10420159508222702

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor