Color Tunable Composite Phosphor Ceramics Based on SrAlSiN₃:Eu²⁺/Lu₃Al₅O₁₂:Ce³⁺ for High-Power and...

White LEDs require phosphor materials to convert blue light into a broad spectrum. While single phosphor systems are common, they often fail to achieve high color rendering and brightness simultaneously. Prior research has shown that phosphor ceramics offer better thermal stability than powders. However, no prior work had resolved how to combine multiple phosphor layers to optimize both color quality and efficiency. This gap motivated the investigation of composite phosphor structures. Researchers have already demonstrated that vacuum sintering improves ceramic density. Yet, the role of layering different phosphor types remained unclear. The need for tunable white light with high R9 values was unmet in current technologies. This study aimed to address these limitations by exploring bi-layer phosphor configurations.

The goal was to develop a bi-layer phosphor system that enhances both color rendering and brightness in white LEDs. The specific problem addressed was the inability of single-layer phosphors to balance high R9 values with high luminous efficacy. The motivation stemmed from the demand for high-quality lighting in commercial and industrial settings. The researchers sought to determine if combining LuAG:Ce³⁺ ceramics with SrAlSiN₃:Eu²⁺-PiG could yield tunable color output. They also aimed to evaluate thermal and optical stability under high-power conditions. The study focused on optimizing phosphor layer thickness and doping concentration. By using vacuum sintering and low-temperature sintering, the team aimed to fabricate a stable composite structure. The ultimate purpose was to propose a practical solution for high-color-rendering white LEDs.

The team fabricated LuAG:Ce³⁺ phosphor ceramics using vacuum sintering. They then prepared a bi-layer composite by low-temperature sintering. A layer of SrAlSiN₃:Eu²⁺-phosphor-in-glass (PiG) was applied to the ceramics. Each component was analyzed separately for optical properties. Thermal stability was assessed through temperature-dependent emission measurements. Colorimetric data was collected using spectrophotometry. The researchers tested the composite phosphors with blue LED chips. They varied the doping concentration and layer thickness to evaluate color tunability.

The bi-layer phosphor system allowed for adjustable emission spectra by changing SrAlSiN₃:Eu²⁺-PiG concentration. Maximum color rendering index (CRI) reached 86 in white LEDs. The R9 value, which measures red color rendering, was 61. Under laser diode excitation, phosphor conversion efficacy peaked at 120 lm/W. The CRI under laser excitation was 83, with a correlated color temperature of 4534 K. These values suggest improved performance over single-layer systems. The thermal stability of the composite was confirmed through repeated testing. The results indicate that the bi-layer structure supports high-brightness lighting applications.

The authors propose that the bi-layer phosphor system is a viable solution for high CRI white LEDs. They suggest that the combination of LuAG:Ce³⁺ ceramics and SrAlSiN₃:Eu²⁺-PiG enables color tuning. The findings support the claim that this composite structure improves both color rendering and brightness. The researchers propose that varying phosphor concentration and layer thickness affects the output spectrum. They suggest that the system's thermal stability makes it suitable for high-power applications. The authors state that the phosphor conversion efficacy of 120 lm/W is a key result. They propose that the composite structure could be used in high-brightness lighting. The study concludes that this approach is promising for next-generation LED lighting.