On a blue emitting phosphor Na3RbMg7(PO4)6:Eu2+ showing ultra high thermal stability

Abstract

This work concerns a novel blue emitting LED phosphor activated by Eu²⁺. It was found that this luminescent material can be efficiently pumped by near UV or UV-A radiation sources while it exhibits a high quantum yield at a doping level between 0.3 and 3.0%. More impressively, this material has a very high quenching temperature T_1/2 and will thus be applicable on-chip in high power phosphor converted LEDs or even in laser diodes. The emission and thermal stability are almost identical to that of BAM:Eu²⁺ while the absorption band is broader and reaches into the near UV range. Therefore, Na₃RbMg₇(PO₄)₆:Eu²⁺ is a promising candidate as a blue emitter in high CRI full conversion LEDs. To investigate the site preference of Eu²⁺, DFT and Ligand Field Theory based calculations were performed to successfully predict the emission spectrum. An unusual decay behavior was observed at low temperatures and the underlying mechanism involving spin-forbidden transitions of Eu²⁺ is discussed.