EPR investigation of paramagnetic centres in β‐rhombohedral boron

Abstract

AbstractA symmetrical EPR line with a g‐factor of 2.0028 is observed in β‐rhombohedral boron at temperatures above 300 °K. The spin density is measured in the range 300 to 1000 °K. It increases exponentially with the temperature and an activation energy of about 0.40 eV is obtained. The line width exhibits a minimum in the neighbourhood of 450 °K. These results suggest a carrier model with localized wave functions. The number of corresponding electronic states is very large. In the neighbourhood of 300 °K, the line width, line shape, and g‐value are within experimental errors the same as those reported for the EPR line observed under illumination with a radiation of about 0.8 μm. The two EPR spectra may thus be attributed to the same electronic states being occupied either by optical or by thermal excitation. Measurements of line width and spin density for the photo‐induced EPR line between 77 and 300 °K are reported and support this hypothesis.