Electric broadening of the electron paramagnetic resonance lines of Cr3+ in zinc tungstate

The parameters describing the linear effect of an electric field on the X-band electron paramagnetic resonance frequency of the impurity Cr 3+ , charge compensated by Li + , in zinc tungstate have been measured. This allows an explanation of the anomalous behaviour of the resonance linewidth when the magnetic field is rotated in the magnetic zx plane. The linewidth in specimens of high Cr 3+ concentration is almost entirely due to the internal electric fields arising from the charged impurities Cr 3+ and Li + acting via the linear electric field effect. The resulting linewidth arises from the equal and opposite shifts in the resonance frequency for the two non-equivalent sites for Cr 3+ in the zinc tungstate lattice. The root-mean-square internal field has been measured and agreement found with the value calculated by assuming the Li + and Cr 3+ ions to be randomly distributed throughout the lattice. A specimen of lower Cr 3+ concentration has been investigated, and an explanation of the complete behaviour of the linewidth in terms of a simple model is presented.