Reaction‐Inert Fluoride Glass Preserves K 2 SiF 6 :Mn 4+ Phosphors for High‐Brightness Laser Display Converters

High‐brightness laser phosphor displays require phosphor‐in‐glass (PiG) converters combining all‐inorganic robustness, high conversion efficiency, and narrowband primary emission for wide‐gamut projection. K 2 SiF 6 :Mn 4+ (KSFM) provides narrowband red emission, but its integration into PiG requires preservation of the fluorosilicate host framework and Mn–F coordination during glass embedding. Here, a reaction‐inert fluoride‐glass matrix strategy is developed for KSFM‐PiG converters. Interfacial reaction thermodynamics are used to compare oxygen‐containing glass constituents with fluoride constituents, indicating that indicates that oxygen‐containing glass chemistry drives KSF decomposition, whereas ZBLAN‐related fluoride constituents show lower reactivity toward KSF host. Based on this guideline, KSFM‐ZBLAN PiG composites are fabricated by rapid spark plasma sintering. The PiG retains 72.75% of the external quantum efficiency of the corresponding pre‐sintered KSFM/ZBLAN compact, compared with 63% reported for sapphire‐supported KSFM‐in‐glass films. Co‐embedding KSFM and β‐SiAlON:Eu 2+ enables red/green PiGs for wide‐gamut conversion. In a rotating phosphor wheel, the multicomponent PiG delivers 2612 lm at 23.58 W mm −2 , corresponding to a laser‐to‐luminous efficacy of luminous efficacy of 292.95 lm W −1 , compared with a reported value of 87 lm W −1 . These results demonstrate chemically guided fluoride‐matrix selection as a viable approach for integrating fluorosilicate phosphors into laser display converters.