Greenish-yellow emitting Ca9MgLi(PO4)7:Dy3+ phosphors – Photoluminescence and thermal stability

Abstract

In this work, the photoluminescence features, decay lifetime, internal quantum yield, and thermal stability of whitlockite structured phosphors of Ca9MgLi(PO4)7:Dy3+ were investigated. The phosphor exhibit the capability of being efficiently excited by near-UV (350, 364, 387 nm) and blue light (451 nm), exhibiting the characteristic greenish-yellow emission with two strong peaks at 487 and 577 nm, ascribing to the transitions of 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. The phosphor synthesized using a conventional solid-state reaction method at 1350 °C also show high phase purity with good compositional homogeneity and crystallinity. The Ca9MgLi(PO4)7:0.1Dy3+ phosphor showed the optimal photoluminescence emission intensity and quantum yield. The electronic transition mechanism is direct exchange interaction between activators, contributing to the concentration quenching. The phosphor was able to retain 67% of its intensity without significant colour change at an elevated temperature up to 300 °C. This work illustrates the potential of Ca9MgLi(PO4)7:Dy3+ phosphors for the application in white LED devices pumped with an n-UV or blue-emitting chip.