Ca[B₈ O₁₁ (OH)₄ ] : Eu²⁺ - A Highly Efficient Deep Blue-Emitting Phosphor Prepared by Low-Temperature Self-reduction

Area of Science:

• Materials Science
• Solid-State Chemistry
• Luminescence

Background:

• Highly efficient inorganic phosphors are essential components for advanced solid-state lighting applications.
• Developing phosphors with desirable optical properties, such as deep blue emission and high quantum yield, is critical for improving lighting technologies.
• Existing synthesis methods may involve high temperatures or reducing atmospheres, posing limitations for certain materials.

Purpose of the Study:

• To synthesize a novel, highly efficient deep blue-emitting phosphor, Ca[B8 O11 (OH)4 ]:Eu2+ (CBH:Eu2+), using a low-temperature self-reduction method.
• To comprehensively investigate the structural, chemical, and photoluminescence properties of the synthesized CBH:Eu2+ phosphor.
• To evaluate the potential of CBH:Eu2+ as a blue-emitting component in white light-emitting diodes (WLEDs).

Main Methods:

• Preparation of Ca[B8 O11 (OH)4 ]:Eu2+ (CBH:Eu2+) phosphor via a low-temperature self-reduction technique under a non-reducing atmosphere.
• Characterization of crystal structure, morphology, and chemical state using various analytical techniques.
• Photoluminescence (PL) properties, including excitation and emission spectra, quantum yield (PLQY), external quantum efficiency (EQE), and thermal stability, were measured.
• First-principles calculations using the screened hybrid function (HSE06) to determine the band gap (Eg) of the CBH host.
• Fabrication and performance evaluation of WLEDs incorporating the CBH:Eu2+ phosphor.

Main Results:

• The calculated band gap of CBH is 7.48 eV, indicating suitability for high quantum yield phosphors.
• The low-temperature self-reduction method effectively reduced Eu3+ to Eu2+ within the CBH crystal lattice without a reducing atmosphere.
• CBH:Eu2+ exhibits broad excitation bands (220-400 nm) and a narrow blue emission band (centered at 428 nm, fwhm=42.35 nm).
• The optimized phosphor (CBH:2%Eu2+) achieved a high PLQY (95.0%), EQE (31.1%), and excellent color purity (97.6%).
• The phosphor demonstrated good thermal stability, retaining 62.6% of its initial intensity at 150°C.
• WLEDs fabricated with CBH:2%Eu2+ showed promising performance: luminous efficacy (13.9 lm/W), CRI (89.4), and CCT (5825 K).

Conclusions:

• The developed low-temperature self-reduction method is effective for synthesizing highly efficient deep blue-emitting CBH:Eu2+ phosphors.
• CBH:Eu2+ exhibits excellent photoluminescence properties and thermal stability, making it a promising candidate for blue-emitting phosphors in WLEDs.
• The synthesis strategy offers a versatile approach for designing and preparing other novel, high-performance phosphors.