摘要:

With increasing X on Ca1-xSrxF2mixed crystals doped with Eu2+(4f65d) ions, the absorption peak shifted linearly to that of SrF2:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF2in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength.

ISSN:1042-0150    

DOI:10.1080/10420159108224904

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Eu2+complex centre in Ca1-xBaxF2crystals was studied with different values of x. And a new kind of ESR centre attributed to Eu2+-Ba2+complex was found at room temperature. The determined spin Hamiltonain parameters are g=1.995+-0.001, B02= 117.6(G), B22= 16.1(G), B04= 0.24(G), B24= 4.63(G), and B44= -3.47(G). Approximate hfs constants are |A151| = 37(G) and |A153| = 16.4(G), respectively. The ESR signals grew with x, but the fine structure spectra were broadened and finally disappeared as well as usual cubic Eu2+ones.

ISSN:1042-0150    

DOI:10.1080/10420159108224905

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Solid solutions Ca1-xGdxF2+xfor 3 × 10−7≤ x ≤10−1have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). The EPR experiments show the presence of two single-ion sites a cubic and a tetragonal Gd3+center which co-exist with comparable abundances for intermediate impurity concentrations. The cubic center predominates at very low and high concentrations. Seven different relaxation processes have been identified from the ITC spectra and the variation of their intensity vs. x was measured. The absolute concentrations of the cubic and nn Gd3+dipoles were calculated. The scavenging of interstitial fluorines by the neutral clusters explains both the abundance of cubic sites at high concentration and the variety of orientable clusters detected by ITC.

ISSN:1042-0150    

DOI:10.1080/10420159108224906

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Calcium fluoride solutions with Al3+, Yb3+and La3+fluorides were studied using the ITC technique. The observed relaxations at 130K and 210K were assigned to dipoles nnRs3+-F−i(Rs= La or Yb) and to the L-shape clusters respectively. A band at 360K, due to big clusters of dipoles, was found in the Yb3+doped samples and in the matrices with Al3+together with La3+. Only the presence of Al3+in the calcium fluoride is not sufficient to produce dipoles, but association with La3+or Yb3+aids the aggregation of dipoles forming big clusters. A Maxwell-Wagner-Sillars relaxation originates a peak at 290K, which is observed in almost all samples, including the pure one.

ISSN:1042-0150    

DOI:10.1080/10420159108224907

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We present the results of a molecular dynamics study of CaF2(10 mol % LaF3). No diffusion of fluorine ions is observed in pure CaF2below the transition temperature (TC≈ 1460K) to the fast-ion phase. However, doping with La3+ions promotes fluorine ion diffusion in this temperature range, and tends to suppress it above TC. Various ion migration mechanisms are discussed.

ISSN:1042-0150    

DOI:10.1080/10420159108224908

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Magnetic circular dichroism in the 4431 Å absorption line of the oxygen compensated CaF2:Dy3+crystal has been used to measure transient phenomena in the Kramers doublet ground level6H15/2of the Dy3+ion during magnetic field reversal. After inverting the field with a rate 10 T·s−1<dB/dt < 400 T·s−1a considerable spin inversion with the final electron spin polarization PFwas achieved while PF=-0.86±0.03 relaxed to less than 0.05 when dB/dT < 10−2T·s−1.

ISSN:1042-0150    

DOI:10.1080/10420159108224909

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We study efficiency of autoionization and recombination transitions for europium in CaxCd1-xF2host lattice depending on the energy level position of Eu2+4f65d1(e) excited states in respect to the conduction band (CB) states. From photoluminescence (PL) and absorption measurements we conclude that for x in the range of 1 - 0.65 thermalization within the 4f65d1(e) multiplet is faster than the appropriate autoionization transition.For x > 0.65, when all the excited 4f65d1states are degenerate with the CB autoionization is immediate, Eu2+intra-ion emission is quenched and a new Eu-related emission appears, which we tentatively assign to a radiative capture emission of hot nonequilibrium electrons.

ISSN:1042-0150    

DOI:10.1080/10420159108224910

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The spectroscopy of Sr1-xBaxF2:Eu2+mixed crystals is reported and explained by using an impurity-trapped exciton model. The broadening of the absorption and emission structures are interpreted as a Fano effect.

ISSN:1042-0150    

DOI:10.1080/10420159108224911

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The determination of the static dielectric constant ϵsat low frequencies of the mixed lead halides PbCl2xBr2(1-x)vs. the composition x shows the existence of a discontinuity for the equimolar composition. A discontinuity is also observed for the same composition for the shift of the energetic position of the first excitonic reflectivity peak.This discontinuity is interpreted in terms of the anionic substitution.

ISSN:1042-0150    

DOI:10.1080/10420159108224912

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Measurements of the19F nuclear relaxation times are reported for the fluorite-structured Pb0.84Bi0.16F2.16single crystal. The formation of clusters by thermal treatment, as revealed by changes in the fluorineT2during temperature cycling, is discussed.

ISSN:1042-0150    

DOI:10.1080/10420159108224913

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor