No abstract

With electron nuclear double resonance (ENDOR) the superhyperfine interactions of Fe3+ impurities with five shells of Li neighbours were measured in a congruent LiTaO3 crystal. From the analysis of the ENDOR spectra it is found that Fe3+ is on a substitutional Li+ site on the threefold symmetry axis of the crystal. From the shape of the ENDOR spectrum it is concluded that most Fe3+ impurities are on very perturbed sites.

EPR studies on ultraviolet-irradiated crystals of AgC1:Pd have confirmed earlier results on AgCl:Cu for the existence of an energy barrier in the self-trapping of the photohole. The height of this barrier is near 1.8 meV. Migration of the self-trapped hole was found to be athermal for temperatures below 30 K; above 35 K the self-trapped hole hops, with a diffusivity given by D =7&(10 exp( -. 61 meV/kT) cm /sec. This suggests that the value of the electron transfer integral is about 1% of the energy of the phonons involved, that the bandwidth for the self-trapped hole is of the order of 2 meV, and that the binding energy of the hole is approximately 0.1 eV. The dependence on temperature of the efficiency of photoproduction of various trapped-carrier palladium centers was determined, and was correlated with the migration of the self-trapped hole. The presence of a small amount of Fe + "tracer" served to indicate those decay processes that were due to thermal release of trapped holes.

Investigation of polycrystalline diamond films by electron paramagnetic resonance at 9.5 and 35 GHZ has revealed the presence of forbidden transitions resulting from a simultaneous microwave induced flipping of unpaired electron spins and environmental nuclear spins. The spacing of the resonance lines identifies hydrogen as the atom neighboring the paramagnetic active site.

Hole trapping at cation vacancies in doped, irradiated silver halides is studied by means of electron paramagnetic resonance (EPR). From detailed studies of the behavior of the EPR spectra upon thermal annealing and of the effects of the concentrations of various divalent cations, it is demonstrated that in AgCl the positive hole can indeed be bound to the negative cation vacancy.The resulting two types of paramagnetic centers, which survive up to 70 and 110 K, respectively, are identified as perturbed self-trapped hole centers with a cation vacancy in either the nextnearest-neighbor or nearest-neighbor position in the equatorial plane, respectively. In addition, the perturbing cation vacancy is determined to be an isolated vacancy, free from any nearby divalent cation. In AgBr, however, no corresponding EPR effects due to the interaction between the hole and the cation vacancy have been observed.