Highly efficient broadband blue-emitting phosphors are urgently needed for full-visible-spectrum white light-emitting diodes (WLEDs). Herein, we report a new highly luminescent garnet-type Ca 2 LuHf 2 GaAl 2 O 12 :Ce 3+ (abbreviated as: CLHGAO:Ce 3+ ) blue phosphor enabling full-visible-spectrum LED lighting. These CLHGAO:Ce 3+ phosphors doped with different Ce 3+ concentrations have been prepared by using a high-temperature solid-state reaction approach, and their phase purity, crystal structure, luminescent properties, CIE color coordinates, and quantum efficiency have been systematically studied. Importantly, CLHGAO:Ce 3+ blue phosphors show a broadband excitation spectrum in the 300–450 nm spectral range peaking around 398 nm, matching well with the emission wavelengths of commercial near-ultraviolet LED chips (380–420 nm). Upon 398 nm excitation, the optimal CLHGAO:2%Ce 3+ phosphor sample generates a bright broad blue emission band (emission peak: 472 nm; bandwidth: 84 nm) with high internal quantum efficiency of 79.2% and external quantum efficiency of 55.3%. Notably, the emission intensity of CLHGAO:2%Ce 3+ phosphor is about 1.87 times higher compared to the commercial BaMgAl 10 O 17 :Eu 2+ blue phosphor (emission peak: 451 nm; bandwidth: 53 nm). Finally, a white LED device is fabricated with a 395 nm near-UV LED chip with CLHGAO:2%Ce 3+ blue phosphor and commercial (Ba,Sr) 2 SiO 4 :Eu 2+ green phosphor as well as commercial CaAlSiN 3 :Eu 2+ red phosphor, and the device demonstrates bright warm-white emission with an ultrahigh color rendering index (Ra = 95.1, R9 = 97.8, R12 = 88.4) and low correlated color temperature of 3540 K. These results show that as-developed blue-emitting CLHGAO:Ce 3+ garnet phosphors with superior photoluminescence properties can potentially be used in phosphor-converted full-visible-spectrum WLEDs.
Highly efficient cyan-green-emitting phosphors are urgently needed for high-color-quality full-visible-spectrum white light-emitting diodes (LEDs). Herein, we report on efficient near-ultraviolet-excited cyan-green-emitting Ca 2 La 1- x Lu x Hf 2 Al 3 O 12 :Ce 3+ (CLa 1- x Lu x HA:Ce 3+ ) garnet phosphors, which are developed based on the solid-solution design of chemical cation substitution. All phosphor samples present a garnet crystal structure with the I a 3 ‾ d space group; with increasing Lu 3+ ions content, the lattice could be gradually contracted, along with a high symmetry as well as rigidity. Furthermore, under the 408 nm excitation, the cyan-green emissions of CLa 1- x Lu x HA:Ce 3+ phosphors are progressively enhanced with a slight blue-shift, due to crystal field splitting and Stokes shift . Importantly, quantum efficiency and thermal stability performances are greatly improved by introducing smaller Lu 3+ ions to replace the bigger La 3+ ions, owing to the high rigidity structure with high symmetry. The optimized CLa 0.5 Lu 0.5 HA:Ce 3+ phosphor exhibits an intense cyan-green emission band with high internal quantum efficiency of 76.4% and external quantum efficiency of 54.4%. Through employing the as-prepared CLa 0.5 Lu 0.5 HA:Ce 3+ cyan-green phosphor, we have successfully fabricated a full-visible-spectrum LED device, demonstrating a bright warm-white light emission with an extremely high color rendering index (Ra = 98.0, R9 = 95.9, and R12 = 94.3) and low correlated color temperature (3497 K) under 100 mA driving current. This study not only reveals the correlation between the crystal structure evolution and luminescent properties of phosphor materials, but also provides new strategies for the design and development of novel efficient luminescent materials for high-quality full-visible-spectrum LED lighting.
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