F-type Defects Research Articles

Energy transfer between F-type defects in CaO studied by optical-microwave double-resonance spectroscopy

Cascade energy transfer between photo-excited F+, F+A, F and FA point defects in CaO is reported utilizing highly selective optical-microwave double-resonance methods. Time-resolved MIDP experiments show a shortening of the lifetime of the Tx, y spin sublevels in the photo-excited triplet state of F defects in CaO: Mg. The lifetime shortening is attributed to the effect of energy transfer to the FA centers in this host crystal. A rate constant of 53 s−1 characterizes the transfer process at T = 1.2 K.

Thermal change of magnetic loss in preilluminated yttrium-iron-garnet single crystal

A photoinduced decrease in permeability μ′ is observed over 90% in a highly pure single crystal of yttrium-iron-garnet (YIG) grown by a floating zone method. Even after the illumination is removed, the influence remains up to 230 K. By annealing under oxygen atmosphere in the preparation stage, the magnitude of the effect is reduced to 40%. On warming after the sample is illuminated by a flash lamp at 77 K, the imaginary part of permeability μ″ below 10 kHz is found to show the double peaks, activation energies of which are 0.1 and 0.3 eV, respectively. Besides, it has been observed that the dependence of magnitude of each peak on the strength of illumination is different. These features are discussed in terms of one or two electron F-type defects (oxygen vacancy) and photoexcited two levels.