Emission and absorption x-ray edges of Li

The $K$ x-ray emission edge of Li is measured between 85 and 490 K and analyzed to obtain the temperature dependences of the edge position and of a Gaussian edge-broadening function. Full width at half-maximum edge widths range from 0.22 ± 0.05 eV at 85 K to 0.38 ± 0.05 eV at 440 K. Edge positions shift from 54.81 ± 0.02 eV at 85 K to 54.86 ± 0.02 eV at 440 K and to 54.91 ± 0.02 eV after melting. Emission and absorption spectra measured with the same spectrometer establish a 0.10 ± 0.02 eV separation between the emission and absorption edges. These results are compared with recent theories describing incomplete lattice relaxation about the core hole. We conclude that for a core-hole lifetime of 0.016 to 0.030 eV the theories give a satisfactory explanation of the premature peak in the emission spectra. We suggest also that phonon—core-hole interactions provide the dominant edge-broadening mechanism, and that many-body effects are small.