MAGNETIC-FIELD AND FREQUENCY-DEPENDENCE OF ELECTRON-SPIN RELAXATION-TIMES OF THE E' CENTER IN IRRADIATED VITREOUS SILICA

The electron spin relaxation time, T-1, of the E' defect in gamma-irra diated vitreous silica, was measured by time-domain EPR and found to b e approximately independent of microwave frequency between 1 and 9 GHz and to increase by about 50% at 19.4 GHz. Preliminary results indicat e a further increase in T-1 at 95 GHz. At each microwave frequency, T- 1 varies monotonically with position in the EPR line. T-1 is longer ne ar the parallel axis and shorter in the perpendicular plane of the g-a xis system. T-1 is interpreted in terms of coupling to local vibration al modes of the defect center. The electron-spin-echo phase-memory tim e, T-m, extrapolated to small B-1, is independent of microwave frequen cy. It is equal to the electron spin T-2 determined by electron-electr on dipole interaction. (C) 1995 Academic Press, Inc.