Ultrafine-grained Al2O3−RE:YAG (RE=Ce; Ce+Gd) composite ceramics were obtained for the first time by reactive SPS using commercially available initial oxide powders. The effect of key sintering parameters (temperature and dwell time, external pressure) on densification peculiarities, structural-phase state, 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°C / 30 min / 30-60 MPa. The external quantum efficiency of the phosphor converters reached 80.7% and 72% with close lifetimes of ~63.8 nsec, similarly to commercial Ce:YAG materials, which is promising for further application in the field of high-power white LEDs and LDs.
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