Novel highly luminescent double-perovskite Ca2GdSbO6:Eu3+ red phosphors with high color purity for white LEDs: Synthesis, crystal structure, and photoluminescence properties

High-efficiency red-emitting phosphors are required to fabricate high-performance white light-emitting diodes (LEDs). Herein, the novel highly efficient Eu 3+ -activated Ca 2 GdSbO 6 double-perovskite red phosphors with good thermal stability toward warm-white LEDs were reported. A series of Ca 2 Gd (1- x ) Eu x SbO 6 red phosphors with different Eu 3+ doping concentrations ( x  = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by using high-temperature solid-state reaction method. Under the excitation of 396 nm near-ultraviolet light, these Ca 2 Gd (1- x ) Eu x SbO 6 phosphors showed intense red emissions peaking at 612 nm due to the 5 D 0 → 7 F 2 transition of Eu 3+ ions. The strongest luminescence intensity reached when Eu 3+ doping concentration was x  = 0.5, and the critical distance between Eu 3+ activators was calculated to be 7.97 Å. The concentration quenching mechanism was due to the dipole-dipole interaction of Eu 3+ ions. The CIE color coordinates of the optimal Ca 2 Gd 0.5 Eu 0.5 SbO 6 phosphors were determined to be (0.6629, 0.3367), and the corresponding color purity reached about 94.9%. Importantly, the Ca 2 Gd 0.5 Eu 0.5 SbO 6 phosphors revealed outstanding internal quantum efficiency of 73% and good thermal stability. The emission intensity of Ca 2 Gd 0.5 Eu 0.5 SbO 6 phosphors at 423 K still remained about 73% of its initial value at 303 K. Finally, a prototype white LED device was fabricated by coating the phosphor blend of commercial blue-emitting BaMgAl 10 O 17 :Eu 2+ , green-emitting (Ba, Sr) 2 SiO 4 :Eu 2+ and our as-prepared red-emitting Ca 2 Gd 0.5 Eu 0.5 SbO 6 on a 395 nm LED chip. Under 20 mA driven current, the device showed bright warm-white light with CIE color coordinates of (0.3888, 0.3943), correlated color temperature of 3911 K, and color rendering index of 88.4. The results demonstrated that the developed novel red-emitting Ca 2 Gd 0.5 Eu 0.5 SbO 6 phosphors could be used as potential color converters in white LEDs.