A tunable blue–cyan dual emission phosphor in Ca_4−xLu_2xHf_1−xGe₃O₁₂:Bi³⁺ via forming segregation structure for WLEDs

Abstract

White light-emitting diodes (WLEDs) are always fabricated by a combination of the near-ultraviolet (n-UV)-emitting LED chip with tricolor emitting phosphors.However, improving the color rendering index (CRI) is limited due to the absence of cyan composition for common commercial combinations. Based on this, a series of blue-cyan dual-peaks emission Ca 4−x Lu 2x Hf 1−x Ge 3 O 12 (CLHGO):Bi 3+ phosphors with unique adjustability are developed by the solid solution design strategy. All the samples belong to the garnet structure with the Ia3d space group. Two relatively independent segregation structures [Ca 4 HfGe 3 O 12 ] and [Ca 3 Lu 2 Ge 3 O 12 ] are established in the samples. When Bi 3+ ions enter into the highly symmetrical hexagon coordination environment, a special phenomenon appears that the emission peaks consist of two stabilized narrowband emission bands at 435 and 475 nm, their intensity ratio could change continuously with the increase of solid solubility. All these results are confirmed by means of excitation and emission spectra, first principles calculation and decay curves. The Ca 3.4 Lu 1.2 Hf 0.4 Ge 3 O 12 :Bi 3+ sample, with a high efficiency around 84.1% and an excellent thermal stability (65.6%@150 • C), is chosen as the optimal sample to improve the blue and cyan compositions for full spectrum emission. Using the Ca 3.4 Lu 1.2 Hf 0.4 Ge 3 O 12 :Bi 3+ , commercial green (Ba, Sr) 2 SiO 4 :Eu 2+ phosphor, and commercial red CaAlSiN 3 :Eu 2+ phosphor on a 360-nm n-UV LED chip to fabricate WLED, which successfully bridge the cyan gap and the CRI value of the as-fabricated warm-white LED reaches 90.2. The previous results confirmed that CLHGO:Bi 3+ phosphors have promising application prospect in the development of n-UV-pumped warm-white LEDs with high-CRI values. The unique property performance originating from independent segregation structures provides more reference for the research on photoluminescence mechanism.

Overcoming the cyan gap for full‐spectrum lighting using cation‐substitution‐induced rigid Ca2YZr2Al3O12:Ce3+

“…[15][16][17] However, the cyan gap at 470-520 nm reduces the CRI value and limits the obtainment of full-spectrum lighting in devices combining commercial red, green, and blue phosphors with violet chips. [18][19][20][21] Therefore, to obtain fullspectrum illumination, there is an urgent need to explore high-performance violet light-excited cyan fluorescent materials.…”

“…Therefore, as an alternative to overcome the drawbacks mentioned above, the combination of violet (380–420 nm) chips with multicolor phosphors to obtain full‐spectrum illumination has been proposed 15–17 . However, the cyan gap at 470–520 nm reduces the CRI value and limits the obtainment of full‐spectrum lighting in devices combining commercial red, green, and blue phosphors with violet chips 18–21 . Therefore, to obtain full‐spectrum illumination, there is an urgent need to explore high‐performance violet light‐excited cyan fluorescent materials.…”