Novel high-saturated red-emitting phosphor Sr9(Mg0.5Mn0.5)K(PO4)7: Eu2+ with great quantum efficiency enhancement by La3+ codoping for white LED application

In this work, a novel whitlockite-structure red-emitting phosphor host, Sr9(Mg0.5Mn0.5)K(PO4)7, is designed and successfully synthesized via a solid-state reaction. Upon X-ray diffractometer Rietveld refinement, it is revealed that this compound possesses compact Eu2+-Mn2+ distance (3.6809 Å) and large intra-Mn2+ distance (8.9905 Å), which is beneficial to the high-efficient Eu2+-Mn2+ energy transfer. By Eu2+ sensitization, our new phosphor exhibits a high-saturated and bright red Mn2+ emission at 620 nm with high color purity of 97.9%. Great emission enhancement up to 245 times than host is achieved by La3+ heterovalent substitution, which can be ascribed to the La3+-induced further structural confinement effect. Moreover, the quantum efficiency is boosted by twofold. The as-fabricated white phosphor-converted LEDs device shows bright warm white light with correlated color temperature (CCT) of 3,487 K, color-rendering index (CRI) of 92.4, and luminous efficacy of 31.59 lm/W. This work proves the feasibility of chemical unit co-substitution strategy in emission engineering of Mn2+-based phosphors, which can stimulate further studies on the red-emitting phosphor materials.