Reaction mechanism and luminescence properties of orange-red SrAlSi4N7:Eu2+ phosphor for white-LEDs

The well-crystalline SrAlSi4N7:Eu2+ phosphor could be synthesized by the solid-state reaction method using different types of Si3N4 raw material. The corresponding reaction mechanism was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and fluorescence spectra. It was found that the structural difference between alpha-Si3N4 and beta-Si3N4, and the rearrangement of Si3N4 microstructures at high temperature had an important influence on the formation of SrAlSi4N7 phase. Results showed that the a alpha-beta transformation of Si3N4 was included in the synthesis reaction of SrAlSi4N7. So the reaction mechanism of SrAlSi4N7:Eu2+ phosphor should be: alpha-Si3N4 ->beta-Si3N4; beta-Si3N4+AlN+Sr2N -> SrAlSi4N7. The beta-Si3N4 seeds addition were actually helpful to the grain growth of alpha-beta transformation of Si3N4 and then increased the synthesis reaction rate of SrAlSi4N7. Pure SrAlSi4N7:Eu2+ phosphor with higher luminous efficacy and better crystal morphology was finally obtained, indicating that the as-synthesized phosphor was an attractive candidate material as an orange-red component for warm white light LEDs.