Hole-induced shakedown process in the $M_4$,5 fluorescent emission spectrum of lanthanum

The hole-induced shakedown process is observed in the x-ray $M_4$,5 fluorescent emission spectrum of lanthanum. Comparison of the $M_4$,5 fluorescent emission spectrum of lanthanum (the 4f level is empty in the ground state) with the electron-excited spectra shows that x-ray emission, which is caused by transitions from occupied 4f states to empty 3d states, appears even in the fluorescent spectrum of lanthanum. This result indicates that the shakedown transition from the conduction-band states to the empty 4f level occurs in the presence of a 3d core hole. Also, a satellite was observed on the low-energy side of the $M_5$$O_3$ diagram line and attributed to the transition 3${\mathit{d}}_{5/2}^{\mathrm{-}1}$4${\mathit{f}}^1$→5${\mathit{p}}_{3/2}^{\mathrm{-}1}$4${\mathit{f}}^1$. This gives further evidence of the hole-induced shakedown transition.