摘要:

The distortion undergone by BaF2: Mn2+below 50 K is examined here through the analysis of the experimental isotropic (As) and anisotropic (Ap) superhyperfne constants. This quantitative analysis support that the “short” Mn2+-F−distance experiences a decrement of 8(4) pm with respect to the distance R= 232(2) existing in the OhMnF86-complex in BaF2at room temperature. By contrast the “long” Mn2+-F−distance becomes 250(3) pm.

ISSN:1042-0150    

DOI:10.1080/10420159108224874

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The interaction of excitons with lattice defects - Tl ions in the activated KJ crystal is studied at low temperatures. Luminescence of Tl under the excitation in the 1s exciton absorption band (5.85 eV) is examined. The participation of the localized excitons created and trapped near Tl ions during that process is shown. Those localized excitons decay into lattice defect pairs which take part directly in the excitation and luminescence of Tl and cause a broadening of Tl luminescence bands.

ISSN:1042-0150    

DOI:10.1080/10420159108224875

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Synchrotron Radiation is extensively used in defect research to study the electronic properties of defects and impurities. After a rapid survey of the principles and characteristics of the source, are shown some techniques recently used in this field: excitation of luminescence of ion impurities and excitions, time decay investigation, Augee-free luminescence, two-phot on spectroscopy and defect creations processes.

ISSN:1042-0150    

DOI:10.1080/10420159108224876

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effects of disorder on optical lineshapes and luminescence decay in potential tunable laser materials are discussed. The particular examples considered include transition metal (TM) ions in insulators, colour centres in NaCl and recombining excitons in II-VI superlattices.

ISSN:1042-0150    

DOI:10.1080/10420159108224877

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420159108224878

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420159108224879

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Solid solutions Ca1x-yLuxGdyF2+x+yfor 10−4≤ x ≤ 2 × 10−2and y=0.0001 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). It has been found that the ITC spectrum from 77 to 420 K is very weak and the main peak is attributed to the relaxation of both Lu3+-F−xand Gd3+F−inn dipoles. No polarizable clusters are present in the temperature range explored here. The EPR spectra show the presence of Gd3+tetragonal and cubic centers due to the local and non local compensation, respectively. The continuous decrease in the molar fraction of Gd3+tetragonal centers together with the low concentration of Lu nn dipoles is an evidence of the existence at these low and intermediate concentrations of large clusters such as the cubo-octahedral hexamer which has been proposed for CaF2crystals very highly doped with small trivalent cations.

ISSN:1042-0150    

DOI:10.1080/10420159108224880

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Site selective laser methods are uniquely suited for studying systems where multiple defect centers are present. The development of kinetic methods has provided dramatic new insights into the defect structures present in fluorites.

ISSN:1042-0150    

DOI:10.1080/10420159108224881

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Using Brillouin scattering techniques, the acoustic mode frequencies associated with the set of elastic constants in NdF3have been measured as a function of temperature from 300 to 1325 K. Significant deviations from linear behaviour for certain elastic constants were observed above about 1050 K and attributed to a diffuse phase transition into a superionic state. Similar studies on a series of compounds CaF2(10 mold% ReF3) where Re represents La, Nd, Tb and Tm demonstrate a marked reduction in the superionic transition temperature, Tc, compared with pure CaF2. In the doped crystals significant differences in Tcand the subsequent development of disorder are dismissed in relation to the presence of extrinsic defect clusters.

ISSN:1042-0150    

DOI:10.1080/10420159108224882

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this paper we present an study on the EPR and photoluminiscence spectra of Gd3+in the mixed crystals Ca0.998-xRxGd0.002F0.002+x(x≤0.35, R=La or Y). For x <0.1 the EPR spectrum shows a main signal due to cubic Gd3+that is broadened as x increases. Different broadenings are found for La and Y samples For high x values the EPR spectrum is similar to that in glass matrices. The results are explained taking to account a random second rank crystal field due to the extra charges associated with R3+and fluorine intersitials. The6P→6S emission of Gd3+also has been measured. The influence of R concentration on this luminiscence has been studied.

ISSN:1042-0150    

DOI:10.1080/10420159108224883

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor