Highly Stable, Hydroxyl-Functionalized Submicron K ₂ SiF ₆ :Mn ⁴⁺ by a Minimal-Water One-Pot Method

While microlight sources are set to revolutionize the display and lighting industries, their progress is hampered by the persistent “red micro-LED gap”. Submicron K2SiF6:Mn4+ (KSFM) phosphors have emerged as ideal candidates to fill this gap. However, the rapid valence changes of Mn4+ ions make it exceedingly difficult to synthesize these submicrometer phosphors without compromising their luminescent performance. Herein, a minimal-water aqueous system (<40 vol % water) is proposed to effectively suppress Mn4+ valence changes for over 2 h and inhibit Ostwald ripening for more than 5 h. Concurrently, the method functionalizes KSFM with Si–O–Si polymers, yielding a hybrid material (hf-KSFM) with a unique, controllable transition between powder and colloidal states, thereby imparting solution-processability. Compared to commercial KSFM, hf-KSFM exhibits remarkable improvements: a 4-fold enhancement in Mn4+ stability within the reaction system and vastly superior water resistance, retaining 99% of its initial emission intensity after 96 h of water immersion. Our work provides a one-pot method and a viable structural design for advancing solution-processable micro-LED technology.