A Novel Substrate‐Free Ultrathin Cyan‐Emitting Phosphor‐Glass Composite Based on Ce‐Activated Ca₂YAlGa₂Si₂O₁₂ Microcrystal

The substrate‐free ultrathin phosphor‐glass composite (PGC) provides significant advantages for all‐inorganic light‐emitting diodes (LEDs), offering enhanced resistance to light radiation and chemical corrosion. However, achieving a PGC thickness below 100 µm remains challenging due to its brittle nature. Herein, this work presents a novel strategy to fabricate an ultrathin cyan PGC for all‐inorganic LEDs, based on our home‐synthesized Ce‐activated Ca 2 YAlGa 2 Si 2 O 12 phosphor (CYAGS:Ce). The phosphor emits bright cyan light centered at λ em 497 nm with a FWHM of 93 nm and an internal quantum yield (IQY) greater than 60%. The luminescence mechanism, including concentration and thermal quenching, is investigated in detail. Using tape‐casting and low‐temperature co‐firing, an ultrathin PGC with a thickness of 98 µm is achieved. Structural and luminescence properties are compared to highlight the glass matrix's influence. Furthermore, based on as‐prepared ultrathin PGCs, a compact LEDs with a low correlated color temperature (CCT, 3384 K) and high color‐rendering index (CRI, R a = 85.7) is obtained by integrating both red and cyan PGCs with a commercial 420 nm blue chip. This work advances the understanding of CYAGS:Ce cyan phosphor and provides a versatile strategy for fabricating ultrathin PGCs, highlighting their potential applications in all‐inorganic LED lighting.