It is often said that promising phosphors for white-LEDs are Ce 3+/Eu 2+-doped multinary oxynitrides/nitrides, mainly because they are more covalent than conventional oxide phosphors so as to be effectively excited by blue or near-ultra-violet light. In this paper, detailed discussions are given to clarify factors affecting 5d levels of the rare-earth ions in nitride/oxynitride phosphors by examining some examples: LaSi 3N 5:Ce (blue phosphor)/La 3Si 6N 11:Ce (yellow phosphor) and BaSi 2O 2N 2:Eu (bluish green phosphor)/Ba 3Si 6O 9N 4:Eu (bluish green phosphor)/Ba 3Si 6O 12N 2:Eu (green phosphor). It is stressed that dielectric constant/refractive index (as an indicator of polarizability of ligand) along with coordinate bond length should be examined rather than covalency to grasp the trend of 4f–5d transitions. For this purpose, some useful rules-of-thumb are addressed.