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 {ital N}{sub 4,5}{ital O}{sub 2,3} transitions in lanthanum aluminate LaAlO{sub 3} 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 {ital N}{sub 4,5}{ital O}{sub 2,3} emission spectrum of Ba in BaF{sub 2}. An atomic model of the La {ital N}{sub 4,5}{ital O}{sub 2,3} transition, assuming single occupancy of the 4{ital f} shell by a spectator electron, provides a good approximation of the measured spectrum. Emission features due to the low-energy {sup 3}{ital P}{sup {ital o}} and {sup 3}{ital D}{sup {ital o}} terms of the 4{ital d}{sup 9}4{ital f} configuration are also apparent in the LaAlO{sub 3} emission spectra, but not in emission spectra from BaF{sub 2}. Reflection measurements indicate that the 4{ital f} level is not occupied in the ground state in LaAlO{sub 3}. The data suggest that charge transfer from ligand orbitals following creation of a 4{ital d} vacancy prior to the emission process is the predominant mechanism giving rise to the required 4{ital f} occupancy.