The site occupation and valence of Mn ions in the crystal lattice of Sr4Al14O25 and its deep red emission for high color-rendering white light-emitting diodes

•Different valences of Mn ions in Sr4Al14O25 were identified using XANES and EPR.•Red luminescence was attributed to Mn4+ occupying the center of AlO6 octahedron.•The Mn3+ incorporated in the center of AlO4 tetrahedron was non-luminescent.•The bond-valence theory was used to analyze the effective valences of cations.•A white LED device with CRI up to Ra 93.23 was packaged by using the red phosphor.

The synthesis and component of red phosphor, Sr4Al14O25: Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr4Al14O25 were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr2+ and Al3+ in Sr4Al14O25. As a result, the strong covalence of Al3+ in the AlO4 tetrahedron other than in the AlO6 octahedron is disclosed. The deep red emission is attributed to Mn4+ occupying the center of AlO6 octahedron. The mechanism of energy transfer is mainly through dipole–dipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability.

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