Photoluminescence of CaAlSiN3:Eu2+-based fine red-emitting phosphors synthesized by carbothermal reduction and nitridation method

• Various Ca1−xEuxAl0.76Si1.18N3 (x = 0.01 ∼ 0.1) red phosphors were prepared by simple CTRN method with stable CaCO3 as Ca source at 1600 °C for 4 h, and the C/O ratio of 1.5:1, respectively.
• The fabricated warm white LED gave color rendering index of 93 at correlated color temperature of 3295 K.
• The as-prepared red phosphors by economical CTRN was confirmed to be high-quality phosphors for white LEDs.

In this research, we have presented the synthesis and characterization of the various Ca1−xEuxAl0.76Si1.18N3 (x = 0.01 ∼ 0.1) red-emitting phosphors, which were successfully prepared by carbothermal reduction and nitridation (CTRN) method without the strict needs of high pressure. Here, raw materials were CaCO3, AlN, Si3N4, Eu2O3, and C. In particular, C was considered as efficient and robust reducing agent. The influences of reaction temperature, holding time, C content, and Eu2+ concentration were investigated in the crystal phase compositions and photoluminescence properties of the as-prepared phosphors. Importantly, CaAlSiN3:Eu2+-based red phosphors with interesting properties were obtained with reaction temperature at 1600 °C for 4 h by atmospheric N2–10%H2 pressure, and the C/O ratio of 1.5:1, respectively. The emission peak positions of as-prepared phosphors were red-shifted from 607 nm to 654 nm with Eu2+ concentration from 1 mol% to 10 mol%. Meanwhile the highest luminescence intensity was achieved with 2 mol% of Eu2+ concentration, which showed high external quantum efficiency up to 71%. Combining the phosphor blend of green-emitting β-sialon:Eu2+, yellow-emitting Ca-α-sialon:Eu2+, and red-emitting Ca0.98Eu0.02Al0.76Si1.18N3 with a blue LED (light emitting diodes), warm white LED can be generated, yielding the color rendering index (Ra) of 93 at correlated color temperature (CCT) of 3295 K. These results indicate that CaAlSiN3:Eu2+-based red-emitting phosphors prepared by facile CTRN are highly promising candidates for warm white LEDs.