Atomic origin of 3d(9)4 f(1) configuration in La(3+) solids

We have studied the excited electronic structure of LaBr3(Ce) scintillator by soft x-ray spectroscopy such as x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES). The La 3d XAS and XES spectra of LaBr3(Ce) are compared with those of other La(3+) solids (LaF3, La2O3, and La metal). From this comparison, it turns out that the La 3d XAS and XES spectra from all the La(3+) solids considered here appear at almost the same energy, even though the corresponding binding energies of the 3d core holes determined by XPS (x-ray photoelectron spectroscopy) are very different. As a result, we argue that the atomic nature of the 3d⁹4f¹ configuration created by 3d¹⁰4f⁰ → 3d⁹4f¹ x-ray absorption process in La(3+) solids is maintained via the localized 4 f (1) state, which screens the 3d core holes differently from one La(3+) solid to another.