Copper and silver, respectively, were introduced into single crystals of CsCdF3. Our detailed electron paramagnetic resonance (EPR) study showed that both elements enter the Cd lattice site—copper as Cu2+, silver as Ag+, which then was converted into Ag2+ by x raying the corresponding samples. Cu2+ and Ag2+ were shown to present in their ground state a pseudostatic Jahn–Teller effect. Motional effects were observed in the respective EPR spectra and studied in some detail for Cu2+ as they are seen over a wide temperature range. Predictions of a stochastic Kubo model [J. Phys. Soc. Jpn. 9, 935 (1954)] were compared with the temperature dependent linewidths of the motionally averaged EPR spectrum. A power law (Tn with n≂1.9) was determined for the temperature dependence of the reorientation frequency between 30 and 90 K.

A combination of sub-nanosecond photoexcitation and femtosecond supercontinuum probing is used to extend femtosecond transient absorption spectroscopy into the nanosecond to microsecond time domain. Employing a passively Q-switched frequency tripled Nd:YAG laser and determining the jitter of the time delay between excitation and probe pulses with a high resolution time delay counter on a single-shot basis leads to a time resolution of 350 ps in picosecond excitation mode. The time overlap of almost an order of magnitude between fs and sub-ns excitation mode permits to extend ultrafast transient absorption (TA) experiments seamlessly into time ranges traditionally covered by laser flash photolysis. The broadband detection scheme eases the identification of intermediate reaction products which may remain undetected in single-wavelength detection flash photolysis arrangements. Single-shot referencing of the supercontinuum probe with two identical spectrometer/CCD arrangements yields an excellent signal-to-noise ratio for the so far investigated chromophores in short to moderate accumulation times.

The persistent phosphorescence and thermoluminescence of SrAl 2 O 4 :Eu 2+ :Dy 3+ is reported for a variety of different excitation wavelengths and excitation temperatures, to provide new insights in the mechanism of the trapping and detrapping. These measurements reveal that the trapping is strongly dependent on the wavelength and temperature. First, with increasing loading temperature, the thermoluminescence peak shifts to lower temperatures which corresponds to a change of trap population. Secondly, the integrated thermoluminescent intensity increases with increasing loading temperature. All wavelength and temperature dependent experiments indicate that the loading of the traps is a thermally activated processes. Utilizing different wavelengths for loading, this effect can be enhanced or reduced. Furthermore excitation with UV-B-light reveals a tendency for detrapping the phosphor, reducing the resulting thermoluminescent intensity and changing the population of the traps.

21Eu was introduced into pure and oxygen codoped BaMgF single crystals. A detailed EPR study of this ion (S57 / 2) was realized on 4 both types of systems. The result is that only one spectrum was observed involving a strong crystal field. The associated site symmetry of the impurity is C . It occupies very closely a Barium lattice site as was established by correlating the EPR results with those of a refined Eu EPR spectrum (the only one). Optical emission and excitation experiments were performed between 13 000 and 53 000 cm . The 21 7 6 1 results due to the Eu impurity are given and discussed qualitatively within the 4f ⇔4f 5d scheme.

Electron paramagnetic resonance, electron-nuclear double resonance, and optical spectroscopy of the tetragonal Yb 3ϩ center in KMgF 3 are reported here. The results of these experiments allow us to conclude that a previously given structural model as well as the interpretation of the optical spectrum of this center are incorrect. A model is presented and experimentally and theoretically justified. In particular, the values of the hyperfine and transferred hyperfine interaction parameters were determined as well as an experiment-based energy-level scheme. Its parametrization is performed by including simultaneously the crystal field and the spin-orbit interaction within the 7 F term. Furthermore, a theoretical analysis of the transferred hyperfine interaction ͑THFl͒ parameters is presented. It is further shown from optics and from microscopic calculations of the THFI parameters that g ʈ and g Ќ have opposite signs and that the rule of correspondence between the cubic g factor and g ϭ 1 3 (g x ϩg y ϩg z) does not depend on the relative magnitude of the cubic and lowsymmetry crystal field acting on the rare-earth ion.

The Yb 3+ paramagnetic center of the trigonal symmetry (''oxygen'' paramagnetic center T 2 ) in CaF 2 and SrF 2 single crystals is studied by EPR and optical spectroscopy. The Stark level energies of the Yb 3+ multiplets are established from absorption, luminescence and excitation luminescence spectra and the crystal field parameters are calculated. r

BaFCl single crystals doped with Sm 3+ ions were studied by using the EPR method. Several types of paramagnetic Sm 3+ centres were found. The parameters of the corresponding spin Hamiltonians were determined. Structural models and ground states of the observed centres are proposed.

A recent investigation of the (BaF -MgF ) phase diagram produced several new compounds which are suitable hosts for Rare Earth of each of them to a specific barium lattice site. The luminescence emission of both the 4f -4f 5d and the 4f -4f transitions is observed.6 8The relative importance of the two emissions is strongly temperature dependent. The emission intensities of the intra f-shell P → S 7 / 2 7 / 2 6 transitions increase strongly on going from 295 K to 77 K. Thus, the lowest levels of the 4f 5d configuration are approximately 6 degenerate with the P manifold. © 1998 Elsevier Science S.A. / 2