The development of narrow band red emitters, that are based on the luminescence of Mn⁴⁺, is an important goal of current LED phosphor research. It is of fundamental interest to understand the “Mn⁴⁺-host” interaction that can tailor the luminescence of Mn⁴⁺ ions to match the requirements of the LED device. This talk will discuss the approach to understanding this interaction by examining the luminescence of Mn⁴⁺ in a wide variety of host materials (fluorides and oxides). The influence of compositional variations on the strength of the crystal-field and covalence of Mn⁴⁺ -ligand bonding will be explored. These factors tune the optical properties of the Mn⁴⁺ ion and their understanding is important in designing phosphors that will fulfill the requirements of the modern-day LED devices.