Energy-Dependent Photoemission Intensities of "f" States in EuS, GdS, and US

Photoemission measurements of $f$ states and valence-band energies of EuS, GdS, and US for photon energies from 5 to 41 eV show characteristic energy-dependent emission strengths of "$p$," "$d$," and "$f$" states. These energy dependences permit the "$l$" character of various levels to be identified in many cases. For example, the emission strength of the $4f^7$ level in EuS increases about 100-fold relative to the 3-eV wide valence "$p$" band which lies just below the $4f^7$ level. GdS shows a deep $4f^7$ level at about 9 eV below the Fermi level $E_{\mathrm{F}}$, and US shows an "$f-d$" band at $E_{\mathrm{F}}$.