Synthesis, composition optimization, and tunable red emission of CaAlSiN₃:Eu²⁺ phosphors for white light-emitting diodes

Ca0.98Eu0.02Al1-4δ/3Si1+δN3 (δ = 0-0.36) red-emitting phosphors were prepared by carbothermal reduction and nitridation method with stable and inexpensive CaCO3 as Ca source. Optimal nominal composition was obtained at δ = 0.18, showing intense emission peaked at 625 nm and high external quantum efficiency of 71%. The emission wave length could be successfully tuned from 630 to 606 nm with increasing δ value. Ca0.98Eu0.02Al1-4δ/3Si1+δN3 phosphors provided two coordinated environments for Eu²⁺ ions, resulting in two fitted Gaussian peaks. Energy transfer from Eu²⁺ sites in Si-rich environments to those in Si/Al-equivalent modes has been confirmed by analysis of the decay curve of each peak. The decay behaviors suggested that energy transfer effect slowed with higher δ value. Finally, warm white light was created by combining as-prepared red-emitting Ca0.98Eu0.02Al0.76Si1.18N3 and yellow-emitting YAG:Ce³⁺ phosphors with a blue-emitting chip, exhibiting a color rendering index R a of 91 at a low correlated color temperature of 3500 K with a luminous efficiency of 79 lm/W.