Reactive SPS of Al₂O₃–RE:YAG (RE = Ce; Ce+Gd) composite ceramic phosphors

Ultrafine-grained Al₂O₃–rare earth:yttrium aluminium garnet (Al₂O₃–RE:YAG) (RE = Ce; Ce+Gd) composite ceramics were obtained for the first time by reactive spark plasma sintering (SPS) using commercially available initial oxide powders. The effect of key sintering parameters (temperature, dwell time, and external pressure (P_load)) on densification peculiarities, structural-phase states, and luminescent properties of composites was studied comprehensively. Differences in phase formation and densification between Ce-doped and Ce,Gd-codoped systems were shown. Parameters of reactive SPS, at which there is partial melting with the formation of near-eutectic zones of the Al₂O₃–YAG system/coexistence of several variations of the YAG-type phase, were established. Pure corundum–garnet biphasic ceramics with an optimal balance between microstructural and luminescence performance were synthesized at 1425 ℃/30 min/30–60 MPa. The external quantum efficiency (EQE) of the phosphor converters reached 80.7% and 72% with close lifetime of ~63.8 ns, similar to those of commercial Ce:YAG materials, which is promising for further applications in the field of high-power white light-emitting diodes (WLEDs) and laser diodes (LDs).