At present, near-ultraviolet-pumped white light-emitting diodes (LEDs) based on tri-color (blue, green, and red) phosphors still suffer from insufficient color rendering index (CRI), due to the presence of cyan gap in the 480–520 nm spectral range. To solve this problem, it is urgent to develop an efficient cyan phosphor with emission peak around 490 nm and absorption band in the near-ultraviolet range of 380–420 nm. Herein, a highly efficient cyan-emitting Ca 2 GdHf 2 (AlO 4 ) 3 :Ce 3+ (CGHA:Ce 3+ ) garnet phosphor with internal quantum efficiency as great as 80% is reported. Impressively, the CGHA:1%Ce 3+ sample showed a broad excitation band ranging from 350 to 470 nm with a maximum at 408 nm, and upon 408 nm excitation it exhibited an intense broad cyan emission band in the 420–700 nm wavelength range with peak at 489 nm and a full width at half-maximum of 103 nm. Importantly, by applying the newly discovered cyan-emitting CGHA:1%Ce 3+ phosphors as color converter, the CRI value of the fabricated warm-white LED device is greatly enhanced from 80.5 to 91.6. This work demonstrates that the novel developed CGHA:Ce 3+ cyan phosphors could compensate for the cyan gap and realize full-visible-spectrum lighting, which have a bright prospect in high-quality solid-state white lighting.
Yellow-emitting phosphors activated by Ce3+ are key components of white light-emitting diodes (LEDs) based on the blue (Ga,In)N LED. The need to replace incandescent and/or halogen lamps with warm white LEDs has driven LED phosphor development toward compositions beyond the Ce3+-doped garnets used in cool white LED packages. In this contribution, for pointing out how chemical substitutions play a crucial role in tuning the optical properties, we investigate the structural and optical properties of oxyfluoride solid-solutions and borate phosphors, specifically the (La,Ca)3(Al,Si)O4(O,F):Ce3+ yellow-green phosphors and the Ca3La3(BO3)5:Eu3+ red phosphors, via a combination of density functional theory, synchrotron X-ray detection, pair-distribution-function analyses and spectroscopy measurements. By incorporating these phosphors with a new phosphor-capping method on InGaN light-emitting diodes, we obtain the warm white light that meets the spectral and efficiency requirements for high-efficacy solid state warm white lighting lamps. We believe that solid-solutions between distinct and structurally related phosphor systems can be a good strategy to broaden possibilities for using in warm white LED phosphors.
Near-ultraviolet-pumped white light-emitting diodes (LEDs) based on the combination strategy of traditional RGB phosphors (blue/green/red) or blue/yellow phosphors have the drawback of inadequate color rendering index due to the cyan-gap (480–500 nm) in the emission spectrum . It is quite promising to find efficient cyan-emitting phosphors that can offset the cyan-gap to produce white LEDs with full-spectrum emission. In our work, we synthesized a Ce 3+ -activated ScCaO(BO 3 ) (SCB:Ce 3+ ) phosphor with a broadband blue-cyan emission. Under near-ultraviolet 396 nm excitation, the optimum SCB:0.005Ce 3+ sample shows a blue-cyan emission band with a peak of 473 nm, which is competent for filling the cyan-gap. Meanwhile, the SCB:0.005Ce 3+ blue-cyan phosphor possesses a high quantum efficiency (internal quantum efficiency = 66.5%, external quantum efficiency = 38.5%) and weak chromaticity shift (ΔE s = 1.29 × 10 −2 ). We produce white LED devices based on 395 nm LED chips and RGB or blue/yellow/red phosphors strategies. By comparing the performance parameters of white LED devices with or without blue-cyan SCB:0.005Ce 3+ phosphor, it is proved that SCB phosphor can offset the cyan gap of commercial RGB phosphors and the cyan emission lack of commercial Y 3 Al 5 O 12 :Ce 3+ phosphor. Furthermore, SCB:0.005Ce 3+ phosphor can substitute for commercial BaMgAl 10 O 17 :Eu 2+ phosphor in RGB or blue/yellow/red phosphors combinations. The prepared white LEDs based on SCB:0.005Ce 3+ blue-cyan phosphor, green/red or yellow/red phosphors show a lower proportion of high-energy blue light and are suitable for healthy lighting applications.
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