Synthesis, Crystal Structure, and Luminescence Properties of a White-Light-Emitting Nitride Phosphor, Ca0.99Eu0.01AlSi4N7.

Colorless transparent single crystals of a new europium-doped calcium aluminum silicon nitride, Ca0.99Eu0.01AlSi4N7, were synthesized by heating a mixture of binary nitrides (Ca3N2, EuN, AlN, Si3N4, and Mg3N2) at 2150 °C under a nitrogen gas pressure of 0.85 MPa. The X-ray diffraction reflections from a single crystal were indexed with orthorhombic cell parameters a = 11.6819(3) Å, b = 21.0193(6) Å, and c = 4.91770(10) Å. The crystal structure was isomorphic to that of SrAlSi4N7:Eu (space group Pna21). One of the Ca/Eu sites was split into two sites of 4-fold and 8-fold nitrogen coordination. A white-light emission spectrum with two peaks at wavelengths of 498 and 614 nm was observed from the single crystals under 400 nm near-ultraviolet-light irradiation. The CIE1931 chromaticity of the white light was plotted at x = 0.378 and y = 0.429; the mean color-rendering index Ra was 81.