Inorganic K ₂ SiF ₆ : Mn ⁴⁺ Luminescent Layers @ Cu Composites Prepared via Sintering‐Free Process for Laser‐Driven Projection Display

High‐brightness narrow‐band red color converters are essential for laser‐driven wide‐color‐gamut displays, but challenges remain in their practical development. Although K 2 SiF 6 : Mn 4+ (KSF: Mn 4+ ) phosphors offer ultra‐narrowband emission and high color purity, their integration into bulk converters often suffers from thermal degradation, interfacial damage, and severe luminescence quenching under high‐power blue laser excitation. Here, a KSF: Mn 4+ inorganic luminescent layer is coupled with a metal substrate via a sintering‐free fabrication strategy, facilitating the development of a KSF: Mn 4+ ‐TiO 2 /BN@Cu composite (K‐TB@Cu). In this architecture, a TiO 2 /h‐BN transition layer is deliberately introduced to simultaneously enhance the optical reflectivity of the substrate and promote efficient heat dissipation from the KSF: Mn 4+ phosphor to the Cu substrate. The optimized composite delivers a red output power of 399.7 mW in the static reflective mode and up to 3029 mW in the rotated reflective mode, while maintaining a low surface temperature (∼52.4°C). Further, revealed from comparative evaluations in a laser‐driven projection display system, among the investigated composite configurations, K‐TB@Cu uniquely delivers ultra‐narrowband red emission with high color purity, intense brightness, and robust operational stability. These characteristics position K‐TB@Cu as a highly promising candidate for next‐generation laser‐driven display applications.