Domination of second-sphere shrinkage effect to improve photoluminescence of red nitride phosphors
Red Ca0.99Al1-4δ/3-xSi1+δ+xN3-xCx: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-xSi1+δ+xN3-xCx: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.