Multiple Substitution Strategies toward Tunable Luminescence in Lu2MgAl4SiO12:Eu2+ Phosphors

The equivalent or heterovalent substitution strategy is an efficient way to stimulate photoluminescence tuning or to optimize the luminescence performances of phosphor materials. Garnet-type compounds receive much attention as phosphor hosts because of their flexible structural frameworks. Herein, a garnet-type Lu2MgAl4SiO12:Eu2+ phosphor with broad-band blue-green emission is first explored with two-site occupation by varying the Eu2+ content. Two host-substitution approaches to controlling the luminescence behavior of Lu2MgAl4SiO12:Eu2+ phosphor are implemented. The cation substitution strategy of Ca2+ for Mg2+ achieves tunable emission from 463 to 503 nm together with broadening emission bands in Lu2Mg1-yCayAl4SiO12:Eu2+ phosphors. Moreover, chemical unit cosubstitution of [Ca2+-Ge4+] replacing [Lu3+-Al3+] results in Lu2-zCazMgAl4-zGezSiO12:Eu2+ phosphors, which induce a red shift of the emission peak of about 60 nm and a broadening in the emission spectra with increasing Ca2+ and Ge4+ concentrations. The possible photoluminescence tuning mechanism is ascribed to the coordination sphere variation in the EuO8 polyhedron depending on the changing neighboring cations. The proposed approaches on equivalent or heterovalent substitution can contribute to the development of Eu2+-activated garnet-type phosphors with regulation of the luminescence performance and further initiate research discovering new phosphors for white-light-emitting diodes.