Spinel-Based ZnAl₂O₄: 0.5%Cr³⁺ Red Phosphor Ceramics for WLED

Area of Science:

• Materials Science
• Solid-State Lighting
• Luminescence

Background:

• Traditional white light-emitting diodes (WLEDs) often lack sufficient red light emission.
• Cerium-doped Yttrium Aluminum Garnet (Ce³⁺: YAG) encapsulated blue LEDs are common but have limitations in color spectrum.
• Developing efficient red phosphors is crucial for improving WLED performance.

Purpose of the Study:

• To synthesize and characterize a novel spinel-based Cr³⁺-doped red phosphor ceramic.
• To investigate the luminescent properties, thermal stability, and quantum efficiency of the developed phosphor.
• To evaluate its performance in compensating for red light deficiencies in WLEDs.

Main Methods:

• Spark plasma sintering (SPS) was used to prepare ZnAl₂O₄: 0.5%Cr³⁺ phosphor ceramics.
• Phase and spectral analysis were conducted to confirm material structure and luminescence.
• Concentration quenching modeling was employed to understand emission mechanisms.
• Thermal conductivity and thermal quenching were evaluated at elevated temperatures.

Main Results:

• SPS-sintered ZnAl₂O₄: 0.5%Cr³⁺ exhibited good density with Cr³⁺ incorporated into [AlO₆] octahedra.
• Narrow-band emission and millisecond-level lifetime were attributed to the four-quadrupole interaction mechanism.
• The phosphor showed excellent thermal stability, with high thermal conductivity (14 W·m^-1·K^-1 at 150 °C) and maintained 70% PL intensity at 687 nm.
• An internal quantum efficiency (IQE) of 78% was achieved.

Conclusions:

• The Cr³⁺-doped ZnAl₂O₄ ceramic is a promising red-emitting phosphor for WLED applications.
• Its superior thermal properties and high IQE contribute to improved WLED performance.
• Encapsulation with Ce³⁺: YAG effectively compensates for red light deficits, enhances color temperature, and boosts the color rendering index (R9).