The N4,5 emission spectra were measured in order to investigate the radiative decay of the 4d94fn+1 excited states, where n was the number of 4f electrons in the ground state. These spectra exhibited an intense and broad emission peak above the N4,5 threshold in addition to sharp peaks below the threshold. The energy positions of these emission peaks were compared with those of the peaks in the absorption spectra and the existing results of resonant photo-emission. The comparison showed that the fine structure below the threshold coincided in energy with the multiplet structures in the absorption spectrum, and that the intense emission peak was located in the energy region where the electron-emission peak due to the direct recombination of the 4f electron with the 4d hole was observed in resonant photo-emission. The peaks observed in the energy region below and above the N4,5 threshold were attributed to the radiative decay of the above excited states.

Radiative Decay of 4d94fn+1 Excited States in LaB6 and CeB6. Ichikawa, K., Nisawa, A., Tsutsumi, K.: Physical Review B, 1986, 34[10], 6690-4