Spectroscopic techniques for studying bandstructure

Since the valence electron falling can originate from any of the occupied levels in the band, the corresponding x-ray emissions cover a range of frequencies. Where there are many states in the valence band with similar energies you get higher emission intensities, and vice-versa.

Therefore, the x-ray emission band gives an indication of the variation of the density of states across the band. It is not an exact match though, because you must make allowances for the ease with which the incoming photon may eject an electron from different types of orbital.

X-ray emission gives information about the densities of states of the occupied areas of the band and x-ray absorption information about the unoccupied areas.