Novel double perovskite Ca2Gd0.5Nb1-W5/6O6:0.5 Eu3+ red phosphors with excellent thermal stability and high color purity for white LEDs

High color rendering index (CRI), low correlation color temperature (CCT) and excellent thermal stability are crucial indicators to evaluate the practical applications of the white light-emitting diodes (WLEDs), and the red phosphor is a key component that restricts the performances of the WLEDs. Herein, we have designed a novel W6+-doping double perovskite compound, and a series of the proposed Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ (x = 0–0.2) red phosphors were synthesized by the traditional high-temperature solid-state method at 1300 ℃. The influences of W6+-doping concentration on the microstructures and luminescence properties of the phosphors were investigated in detail. It is found that the concentration of W6+ ion has little effect on the microstructures of the Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ phosphors, whereas significantly influences their luminescence properties. All the obtained Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ phosphors can be efficiently excited by 393 nm near-ultraviolet and 464 nm blue light, exhibiting a very strong red emission at 614 nm and a weak orange emission at 591 nm. Compared with Ca2Gd0.5NbO6:0.5Eu3+ phosphor, the excitation intensity and the emission intensity of the Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ (0 < x ≤ 0.2) phosphors are enhanced, displaying an initial increase and then decrease tendency with ascending x. Due to the optimal regulation effect in the local environment of Eu3+ and the band gap, the as-obtained Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ (x = 0.05) phosphor exhibits the best luminescence properties including CRI, thermal stability and quantum efficiency. Using the Ca2Gd0.5Nb1-xW5x/6O6:0.5Eu3+ (x = 0.05) phosphor as the red light component, the assembled WLED device shows bright warm-white light with the higher CRI of 91 and the lower CCT of 5386 K. This work provides an effective and facile strategy for boosting the luminescence of double perovskite oxide phosphors.