MAGNETO-OPTICAL STRUCTURE OF MGO F-BAND

The paramagnetic Faraday-rotation pattern of the MgO F center has been investigated, using the ESR-optical double-resonance method, at 12 kG and 1.8°K. The rotation is centered precisely upon the familiar 4.95-eV absorption band, in agreement with the extrapolated position predicted from a previous observation on the extreme low-energy tail of the band. The p-state spin-orbit parameter is given as - (123) cm-1. The pattern is highly symmetrical, consistent with a very nearly Gaussian absorption band. The width of the pattern is about 30% less than the width which would correspond to a Gaussian absorption band with rigid magneto-optic shift, if the F band is assumed to be Gaussian with the accepted half-width of 0.48 eV. This implies that noncubic electron-lattice interaction is present: The third moment of the circular dichroism (computed from the observed rotation) in fact has a value such as to indicate that noncubic modes are strongly dominant. The same rotation spectrum is observed in samples of both neutron-irradiated and additively colored MgO. However, in the latter there are curious discrepancies between the apparent F-center densities as gauged by the absorption band intensity, the ESR signal strength, and the Faraday rotation amplitude. This is discussed in terms of a postulated near coincidence of the F and F bands, and the occurrence of F-F conversion during the measuring operation; the connection with other observations on the F-F relationship in MgO is indicated. © 1969 The American Physical Society.