Exciton Screening in Amorphous Mg-Bi and Mg-Sb Alloys

The Mg $L_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ absorption edge ($h\nu =50\mathrm{}$ eV) has been studied as a function of composition in amorphous Mg-Bi and Mg-Sb alloys using a synchrotron source and a high-resolution grazing-incidence spectrometer. Exciton lines occur and are most prominent for low-conductivity material, e.g., corresponding to ${\mathrm{Mg}}_3$ ${\mathrm{Bi}}_2$. Screening of the electron-hole interaction takes place as the conductivity increases, but a remnant enhancement remains at threshold even in pure Mg metal.