Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4fn → 4f n-15d1 transitions in rare earth compounds and apply it for the characterization of the 4f2 → 4f15d 1 transitions in the quantum cutter Cs2KYF 6: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. © 2013 The Owner Societies.