Ligand field density functional theory calculation of the 4f2 → 4f15d1 transitions in the quantum cutter Cs2KYF6:Pr3+

Abstract

Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4fⁿ → 4fⁿ⁻¹5d¹ transitions in rare earth compounds and apply it for the characterization of the 4f² → 4f¹5d¹ transitions in the quantum cutter Cs₂KYF₆:Pr³⁺ with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f² and 4f¹5d¹ are calculated, where the praseodymium ion may occupy either the Cs⁺-, K⁺- or the Y³⁺-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr³⁺ and K⁺ as well as Cs⁺ lead to the distortion of the K⁺- and the Cs⁺-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.