Charge-transfer-induced multiplet structure in the N4,5O2,3 soft-x-ray emission spectrum of lanthanum

Soft-x-ray emission spectra for the La N4,5O2,3 transitions in lanthanum aluminate LaAlO3 include contributions from several relatively intense multiplet lines near 80 eV. The appearance of this spectrum contrasts sharply with the three diagram lines observed for the N4,5O2,3 emission spectrum of Ba in BaF2. An atomic model of the La N4,5O2,3 transition, assuming single occupancy of the 4f shell by a spectator electron, provides a good approximation of the measured spectrum. Emission features due to the low-energy 3Po and 3Do terms of the 4d94f configuration are also apparent in the LaAlO3 emission spectra, but not in emission spectra from BaF2. Reflection measurements indicate that the 4f level is not occupied in the ground state in LaAlO3. The data suggest that charge transfer from ligand orbitals following creation of a 4d vacancy prior to the emission process is the predominant mechanism giving rise to the required 4f occupancy