Enhancing luminescence properties of NaBiF4:Eu3+,Tb3+ red-emitting phosphor for near-ultraviolet stimulated pc-WLED

Red-emitting phosphors efficiently excited by near-ultraviolet (NUV) light are desired for high-quality phosphor-converted white LED (pc-WLED) devices. In this work, Eu 3+ /Tb 3+ codoped NaBiF 4 phosphors were designed as promising NUV-excitable candidates for the red component in pc-WLEDs. Under 379 and 395 nm excitation, the NaBiF 4 :Eu 3+ ,Tb 3+ samples yield intense red emissions, predominantly at 616 nm due to the 5 D 0 → 7 F 2 transition of the Eu 3+ ion. The Tb 3+ dopants bring in synergistic effects in greatly enhancing the Eu 3+ red luminescence, i.e. resonant energy transfer (ET) from Tb 3+ to Eu 3+ and crystal field perturbation surrounding Eu 3+ . The relevant spectroscopic properties were systematically studied using steady-state and time-resolved fluorescence spectroscopy. The optimized NaBiF 4 :20%Eu 3+ ,15%Tb 3+ sample features a nearly complete Tb 3+ → Eu 3+ ET, leading to a pure Eu 3+ red luminescence, and showing quantum yield values of 44.2% and 51.6% upon 379 and 395 nm excitation, respectively. Notably, the red luminescence from the NaBiF 4 :20%Eu 3+ ,15%Tb 3+ system has a high thermal stability, which at 398 K sustains 80.2% of its room-temperature luminescence intensity under 395 nm excitation. Via coating a mixture of commercial BaMgAl 10 O 17 :Eu 2+ blue- and (Ba,Sr) 2 SiO 4 :Eu 2+ green-emitting phosphors and the optimized phosphor on NUV ∼ 380 and 395 nm LED chips, the homemade 395 nm-excited pc-WLED exhibited interesting warm lighting performance, i.e. color rendering index (Ra) ∼ 90 and correlated color temperature (Tc) ∼ 3884 K, while the 380 nm-excited pc-WLED had Ra ∼88 and Tc ∼ 4685 K. That is, the NUV ∼395 nm chip (illumination also overlapping with the Tb 3+ absorption around 380 nm) is practically preferable to excite the Tb 3+ /Eu 3+ pc-LED for high-qualified warm white lighting. All the results unveil the viable schemes to develop the Eu 3+ /Tb 3+ co-activated red-emitting phosphors, offering promising prospects for novel NUV-excitable pc-WLED light sources.