Intriguing luminescence properties of (Ba, Sr)3Si6O9N4: Eu2+ phosphors via modifying synthesis method and cation substitution

Synthesizing pure phase Ba3Si6O9N4 by the conventional solid-state reaction method is challenging because of easily formed secondary phase Ba3Si6O12N2 showing similar crystal structure. In this work, an alternative low temperature synthesis method is presented, and a series of green to blue emitting (Ba, Sr)3Si6O9N4: Eu2+ phosphors were prepared by a mechanochemical activation route. Variations in photoluminescence properties and crystal structure, as induced by the change in phosphor composition, were investigated. Under ultraviolet-light excitation, Ba3Si6O9N4: Eu2+ phosphor exhibited a strong narrow green emission at 518 nm and simultaneously a weak emission at 405 nm, which are ascribed to different Eu/Ba sites in Ba3Si6O9N4 lattice proved by Density Functional Theory (DFT) calculations. A continuous green to blue emission in (Ba, Sr)3Si6O9N4: Eu2+ phosphors could be achieved by tuning the crystal structure and local coordination environment acting on Eu2+ with Sr/Ba substitution. More Sr/Ba substitution improved thermal quenching and resulted in a different characteristic of emission peak shift upon increasing the temperature.