Photoluminescence control and abnormal Eu3+ orange emission in Ln3+ (Ln3+ = Ce3+, Eu3+)-doped oxyapatite-type phosphors
Establishing effective methods to optimize luminescence materials has been a significant challenge for white light-emitting-diodes (WLEDs) application. Herein, we successfully realize the photoluminescence adjustment and thermal stability enhancement in Ln3+ (Ln3+ = Ce3+, Eu3+)-doped Ca10-x/yBax/y(PO4)6O phosphors. First, the Ba2+ ions from BaCO3 raw material realize the spectral red-shift from 464 nm to 506 nm, which should be ascribed to a synergistic effect of the centroid shift and crystal field splitting. While using BaHPO4 as raw material, the PL intensity is 6.5 times than the initial intensity. Surprisingly, thermal stability is also improved because the increasing lattice distortion introduces large amounts of traps. Second, the Ca10(PO4)6O:Eu3+ red phosphor exhibits abnormal emission phenomenon that 5D0→7F0 peak at 575 nm becomes the strongest emission peak, while the 5D0→7F1 peak at 585 nm is particular weak. It is speculated that the site symmetry and charge transfer states are closely related with this phenomenon. The charge transfer states are not only correlated with the crystal field strength, but also related to f-electron delocalization, which significantly influence the energy-level structure of Eu3+. More importantly, according to the relationship of the ratio of I(5D0→7F0)/I(5D0→7F1) and the lattice structure, Eu3+ in Ca10(PO4)6O compound could be applied as a probe to explore the matrix information, which provides a helpful method to investigate lattice structure of compounds and also guides researchers to design newly suitable red phosphors.