Domination of Second-Sphere Shrinkage Effect To Improve Photoluminescence of Red Nitride Phosphors

Red Ca0.99Al1–4δ/3–x ­Si1+δ+xN3–x C x :Eu2+ 0.01 (δ = 0.345; x = 0–0.2) nitride phosphors exhibit a blue-shifted emission with increased eye sensitivity function and excellent thermal stability. The variations in the photoluminescence in the Ca0.99Al1–4δ/3–x Si1+δ+x N3–x C x :Eu2+ 0.01 (δ = 0.345; x = 0–0.2) system are thoroughly investigated. The enhanced emission energy and the improved thermal stability with increasing x are dominated by the second-sphere shrinkage effect via the substitution of small Si4+ for large Al3+ with simultaneous charge compensation. Related proofs of the second-sphere shrinkage effect control for photoluminescence are confirmed via high-resolution neutron powder diffraction, EXAFS, and 29Si solid-state NMR techniques.