Review-Narrow-Band Emission of Nitride Phosphors for Light-Emitting Diodes: Perspectives and Opportunities

Searching for narrow-band red-emitting and thermally stable phosphors is the ultimate strategy toward enhanced performance of phosphor converted light emitting diodes (pc-LED). The red emission is assured by the nitride host because of its relatively more covalent character than oxides and sulfides; however, the narrow emission is attributed to crystallographic, morphological, and electronic considerations. The symmetric coordination site ensures equal ligand effect in all direction fits well with the configuration of Eu2+ f orbitals in the excited state, as observed in cuboid nitrides. Further, thermal stability is ascribed not only to suitable bandgap butmore specifically, a relatively distant location of the lowest 5d level from the bottom of the conduction band (CB) that consequently entails high energy to quench excited electrons by exciting them further up to the CB. Modes toward the development of new nitride hosts with potentially narrow-band emission have been identified. A viewpoint on light-emitting diode (LED), backlighting, and laser lighting, which remains the most economically-rewarding phosphors application, is presented. Other exciting frontiers, such as agricultural illumination and persistent luminescence, maximize nitride systems that have other properties other than the stringent narrow-band red emission and excellent thermal stability required for the desired improvement of the mainstream LED application. (c) The Author(s) 2017. Published by ECS. All rights reserved.