Level crossing experiments cross-relaxation measurement

Level Anticrossing and Cross-Relaxation Effects A. The Level Anticrossing Experiment Cross-Relaxation Effects Microwave Studies Radiofrequency Studies Lifetime Measurements VI. Coherence Experiments A. The Rotating Frame Free Precession Spin Echoes... 

Two ongoing experiments are described. In both experiments optical pumping is employed as a means of creating non-equilibrium spin distributions. In both cases the spins couple with one another via either nuclear or electron spin-spin interaction. The first experiment is to measure spatial transport of spin orientation in order to determine the mean spin-spin cross-relaxation rate between Tm" ions in SrF2. In the second experiment transient changes in spin population are observed as Pr" "3 spin levels come into resonance with neighboring F spin levels. This monitors the cross-relaxation rate between Pr" "3 and F and provides a means for verifying the spectroscopy of the Pr" "3 ions. 

The most important implication of these data, however, is the statement they make about the nonradiative relaxation from the levels below 2500 A. If the chemical activity in the thermally equilibrated experiments is limited to the high levels reached by thermal activation, then nonradiative relaxation from the levels below about 2500 cm is a single process— intersystem crossing to the triplet state. Measurement of nonradiative decay rates from those levels could then provide an explicit picture of the dependence of intersystem crossing on the initial vibrational modes and energies. Unfortunately, proof of this proposition cannot be derived from the available data. 

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