Color-Tunable Phosphor [Mg1.25Si1.25Al2.5]O3N3:Eu2+—A New Modified Polymorph of AlON with Double Sites Related Luminescence and Low Thermal Quenching

Aluminum oxynitride (AlON) was commonly used in functional ceramic materials, including phosphors for white light-emitting diodes (LEDs). In the current work, a new polymorph of AlON structure, single phase [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3, has been devised and synthesized through the solid-state reaction at a rather low temperature of 1550 °C. Its structure has been calculated by the Rietveld refinement. The [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3 crystallizes in trigonal with lattice parameters of a = b = 3.0312 Å, c = 41.5758 Å, V = 330.83 Å 3, respectively, and it is formed by Mg 2+ and Si 4+ ions replacing partical Al 3+ ions of Al 5 O 3 N 3 . The photoluminescence spectra of a series of Eu 2+ doped [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3 show a tunable light ranging from cyan to orange with a full-spectrum-covered emission and a wide excitation band with two peaks located at 290 and 335 nm. This is resulted from the two possible sites offered by the cation substitution for Eu 2+ to occupy and thus broadening the emission spectra, which significantly enrich the monotonous luminescent properties of conventional AlON phosphors. Additionally, the energy transfer from one site to another has been identified using the decay curves and time-resolved emission spectra. The scanning electron microscopy and transmission electron microscopy characterization confirmed the sample’s great crystallinity and the thermal stability with more than 85% of the initial intensity at 250 °C further indicates its potential in white LED applications.