A theoretical protocol to study the sensitization and emission mechanism in lanthanide compounds on the basis of multireference CASSCF/PT2 calculations is proposed and applied to [Eu(NO3)(3)(dppz-CN)] and [Eu(NO3)(3)(dppz-NO2)] compounds synthesized and characterized herein. The method consists of a fragmentation scheme where both the ligand and the lanthanide fragments were calculated separately but at the same level of theory, using ab initio wave-function-based methods which are adequate for the treatment of quasi-degenerate states. This is based on the fact that the absorption is ligand-localized and the emission is europium-centered. This characteristic allowed us to describe the most probable energy transfer pathways that take place in the complexes, which involved an ISC between the S-1 to T-1 ligand states, energy transfer to D-5(2) in the lanthanide fragment, and further D-5(0) -> F-7(J), emission. For both compounds, the triplet and D-5(2) states were determined at the CASPT2 level to be around similar to 26000 and similar to 22400 cm(-1), respectively. This difference is in the optimal range for the energy transfer process. Finally, the emissive state D-5(0) was found at similar to 18000 cm(-1) and the emission bands in the range 550-700 nm, in good agreement with the experimental results.