关键词: ESR, anisotropy, MgF$_{2 }$crystal, multinuclear free radicals

Abstract: In this work, more than 130 line peaks in electron spin resonance (ESR) spectra have been discovered of the laser material MgF$_{2}$ crystal in room-temperature experiments. A sample is cut from the shoulder part of the MgF$_{2 }$ crystal, and another is from the MgF$_{2}$:Co crystal. The samples were not treated by any irradiation. The same anisotropic ESR spectra of the two samples indicate that the dopant Co$^{2+}$ introduces defects which induce the same multinuclear free radicals as in dislocations in the sample of MgF$_{2}$. These paramagnetic solid multinuclear free radicals show good stability, and their ESR spectra are found to be anisotropic. ESR signals are derived from three different types of multinuclear free radicals from a tentative simulation analysis.When the direction of the applied magnetic field is along the [100] or [010] orientation of the crystal, the magnetic field at which the ESR signals are detected ranges from 0.2294T to 0.4654T and the width of this range is 0.2362T (corresponding to an energy band of 0.233eV); the most narrow peak in the ESR spectra has a width $\Delta H$ about 1.28$\times $10$^{-3}$T. This width $\Delta H$, equivalent to the energy difference of two neighbouring levels, is very small, only 1.85$\times $10$^{-7}$eV (or 1.46$\times $10$^{- 3}$cm$^{-1}$).This fact indicates that the ground state is highly degenerate, and splits into nearly quasi-continuous energy levels like an energy band in an applied magnetic field. It may be served as a new starting point of solid laser exciter frequency modulation.

Key words: ESR, anisotropy, MgF$_{2 }$crystal, multinuclear free radicals