Cold Sintering of Highly Transparent Calcium Fluoride Nanoceramic as a Universal Platform for High‐Power Lighting

Abstract A thermally robust all‐inorganic color converter is imperative to high‐power light‐emitting diode (LED) lighting. However, it remains challenging to find a universal inorganic matrix for encapsulating multicolor phosphors due to the hurdle of achieving a highly transparent medium at a moderate temperature. Here, the densification of calcium fluoride (CaF 2 ) nanoceramic with visible transmittance up to 75% at merely 350 °C, benefiting from an acid‐mediated cold sintering process of oxygen‐segregated CaF 2 nanoparticles is reported. Using the optically isotropic CaF 2 as a transparent platform, a Y 3 Al 5 O 12 :Ce 3+ (YAG: Ce) phosphor‐based phosphor‐in‐ceramics (PiC) converter with luminous efficacy as high as 190 lm W −1 is fabricated. The ultralow temperature enables the PiC converter to be further combined with red‐emitting CaAlSiN 3 :Eu 2+ (CASN:Eu), delivering a color‐rendering index of 92. The cold‐sintered CaF 2 nanoceramic demonstrates great potential as a general solution for next‐generation high‐power LED lighting.