Recently, we have discovered a fascinating photophysical effect in spin crossover complexes of iron(II) : Light-Induced Excited Spin State Trapping (LIESST). At sufficiently low temperatures, the low spin state (1A1) can be converted quantitatively to the high spin state (5T2) by irradiating the sample into the 1A1 → 1T1 d-d absorption band (—540 nm). The resulting metastable HS state has a very long lifetime at low temperatures, in some cases it does not decay noticeably over a period of several days at 10 K. Only at temperature above some critical temperature does thermal relaxation back to the LS state set in. The sample can also be reconverted to the LS state by irradiating into the 5T2 → 5E absorption band (∞50 nm). The system thus behaves like an optical switch. The relative positioning - horizontally and vertically - of the potential wells of the two spin states is crucial for the lifetime of the metastable HS state.

Polarized Raman measurements on single crystals of CuO yield the symmetry assignments of the three predicted Raman active lattice modes : 297cm⁻¹ (A_g, 344cm⁻¹ (B_g) and 629cm⁻¹ (B_g). These results are compared to literature data, including IR spectra. Our measurements confirm at low temperature the appearance of an additional Raman band around 240 cm⁻¹. The temperature dependence of the linewidth of the A_g mode presents an anomalous behavior near the magnetic phase transition, suggesting the possible presence of magnon-phonon couplings in the antiferromagnetic phase.

We report on the growth of Nd_2-xCe_xCuO_4-δ single crystals (0<x<0.2) from Cu₂O flux. Free separated crystals with maximum size of 5x8x0.15 nm³ have been obtained. Magnetic AC susceptibility measurements show a sharp superconducting transition at temperatures up to 23 K. The temperature dependence of the lattice parameters has been measured by means of X-ray powder diffraction between 10 K (a=3.9413(3) Å, c=12.0290(18) Å) and 290 K (a=3.9482(3) Å, c=12.0590(18) Å). Room temperature Raman spectra reveal a new band at 320 cm^-1 which is not observed in Nd₂CuO₄. Raman spectra of crystals withT_c ranging from 7 to 22 K show a systematic intensity change of the broad band at 590 cm^-1.

The polarized Raman spectra of four different beryl crystals were studied at room temperature in the range from 30 to 4000 cm^-1. The spectra show significant differences between the samples studied, and corrections are proposed for the reference Raman spectra of beryl previously reported by Adams and Gardner (1974). Type II water is observed in two crystals; the corresponding symmetric Raman stretching band at 3595 cm^-1 is extremely strong for an impurity (about 20% of the strongest beryl lattice mode). Another, sharper, band of similar intensity at 3605 cm^-1 could possibly originate from a hydroxyl stretching mode. Additional weaker bands are observed around 1600 cm^-1 and 3600–3750 cm^-1. The first polarized Raman spectra of bazzite are presented and discussed.

A study of viscosity and temperature effects on the rate of back electron transfer (BET) within an exciplex (9,10-dicyanoanthracene/N,N-dimethylaniline) with a strong charge transfer character in six non-polar solvents is reported. The extent of charge transfer has been estimated from the solvatochromic and thermochromic shifts of the fluorescence. Conformational changes are a prerequisite to the BET. In non-viscous solvents, where they are much faster than the ET step itself, the observed rate can be explained within the theory of non-adiabatic ET reactions, while in more viscous solvents, a time-dependent electronic coupling constant V has been introduced. In decalin and butylbenzene, a transition from a "solvent independent" to a "solvent controlled" non-adiabatic regime is observed.

The construction of a new high-resolution multichannel low-cost pulse generator is reported. It is fully computer controlled through a simple RS232 serial interface. Its features are 1 ns resolution within any time, pulse delays up to 16 ms and pulse lengths up to 65 mu s, and pulse sequence repetition rate from 66 Hz up to 250 kHz. It has fully programmable sequencing, including step increments for any pulse delay or length. It governs a pulsed ESR spectrometer, which is also described, but it could be used in a very wide range of experimental set-ups. A few examples of spin-echo detected ESR and ESEEM of some paramagnetic centres are shown.