$M_{4,5}$ emission spectra from ${\mathrm{Gd}}_2$${\mathrm{O}}_3$ and ${\mathrm{Yb}}_2$${\mathrm{O}}_3$

The $M_{4,5}$ emission spectra from ${\mathrm{Gd}}_2$ ${\mathrm{O}}_3$ and ${\mathrm{Yb}}_2$ ${\mathrm{O}}_3$ have been obtained in fluorescence on a double-crystal spectrometer. The profiles differ from the $M_{4,5}$ emission spectra excited by electron impact. These differences are due to resonance radiation and substantiate the interpretation given by Bonnelle and Karnatak. The $M\alpha$ emission line was found to lie above (in energy) the $M_5$-absorption resonance line in ${\mathrm{Yb}}_2$ ${\mathrm{O}}_3$, which is in contrast to ${\mathrm{Gd}}_2$ ${\mathrm{O}}_3$ and general experience. It is suggested that this observation is a result of the discrete nature of the absorption lines. With the help of estimated binding energies for the final configurations $5p_{\frac{1}{2},\frac{3}{2}}^{5}4f^7$, the photoelectron spectrum of ${\mathrm{Gd}}_2$ ${\mathrm{O}}_3$ is discussed.