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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