NaCaTiTaO6:Sm3+: A novel orange-red-emitting tantalate phosphor with excellent thermal stability and high color purity for white LEDs

Novel orange-red-emitting tantalate NaCaTiTaO6 (NCTT):xSm3+ (x = 0.005–0.25) phosphors are synthesized via a solid-state reaction technique at 1300 °C. The phosphors exhibit an orthorhombic perovskite structure with a space group of Pnma (No. 62). At 407 nm excitation, the phosphors show the strongest emission peak at 647 nm belonging to the 4G5/2 → 6H9/2 transition. The optimal Sm3+ concentration is 0.05 mol, and concentration quenching is caused by dipole–dipole interaction. The NCTT:0.05Sm3+ phosphor exhibit a broad bandgap of 3.44 eV and a high color purity of 99.9%. At 420 K, the decrease in intensity is only 10% of the initial value at 300 K for NCTT:0.05Sm3+ phosphor but 15% for Y3Al5O12:Ce3+ phosphor. Consequently, the fabricated white light-emitting diodes exhibit a high rendering index value of 89, a good correlated color temperature of 5257 K, and CIE coordinates of (0.339, 0.364). Hence, the Sm3+-doped orange-red-emitting NCTT phosphors have potential applications for w-LEDs.