From Phosphor Ceramics to Intelligent Light‐Conversion Materials: High‐Flux Luminescence, Glassy Composite Interface, and Machine‐Learning‐Guided Design

High-power LED/LD and NIR applications demand phosphors that remain efficient and stable under high-flux excitation, whereas conventional phosphor/organic systems are limited by heat buildup, interfacial degradation, and luminescence saturation. Phosphor ceramics provide a robust all-inorganic alternative, but their photothermal coupling mechanisms and cross-scale design principles remain insufficiently summarized. Here, we review recent advances in phosphor ceramics with a particular focus on photothermal coupling in high-flux light conversion. We establish a composition-structure-photothermal behavior-device performance framework that connects activator ions, host chemistry, defects and grain boundaries with light absorption, scattering regulation, thermal-transport pathways, and device-level output. Recent advances in garnet-based, multiphase, multicolor visible, and NIR phosphor ceramics are discussed, with emphasis on compositional regulation, ceramic processing, microstructure engineering, and LED/LD integration. We clarify key relationships among transparency, absorption efficiency, scattering strength, thermal conductivity, interfacial thermal resistance, and luminescence saturation thresholds, which collectively determine high-brightness reliability under extreme photon and heat loads. Emerging glassy composite interfaces are further highlighted for low-temperature integration, heterogeneous packaging, and multimaterial coupling. Finally, we discuss machine learning as an enabling tool for candidate screening, processing-window optimization, property prediction, and multi-objective device design, offering guidance for next-generation stable, intelligent light-conversion materials.