Role of la 5p in Bulk and Quantum-Confined Solids Probed by the la 5p54f13D1Excitonic Final State of Resonant Inelastic X-ray Scattering

Abstract

The varied electronic localization of rare earth elements is essential to functional materials and a key to tailoring their properties. We establish with unprecedented spectral resolution the excitonic nature of the lanthanum 5p54f13D1and 3D2final states of resonant inelastic X-ray scattering (RIXS) at the La N4,5edges. We extract the intrinsic lifetime, energy distance, and relative intensity ratio from single crystal LaAlO3and construct an empirical model. With help of the model, we precisely determine the RIXS 3D1final state position and identify La 5p as a descriptor of covalency with the host material. For metallic lanthanum, La3+ions in mixed-covalent-ionic simple oxides and phosphates, and ionic salts alike, we find a sizable chemical shift, indicating band-like and free-ion-like La. The different electronic relaxation of the La 5p5hole and the La 4f1electron is discussed with local and nonlocal screening contributions. In addition, the energetics of the excitonic La 5p54f1Coulomb attraction is quantified in its variation from lanthanum metal to mixed-covalent-ionic La2O3and the ionic LaF3salt. The power of the approach and analysis is applied to map the influence of geometric quantum confinement to La 5p sharing within quantum dots and quantum wires in comparison to bulk-like microrods of monoclinic LaPO4