Synthesis of nano-sized YAG:Eu³⁺ phosphor in continuous supercritical water system

Luminescent yttrium aluminum garnet (Y₃Al₅O₁₂) nanoparticles doped with Eu (YAG:Eu³⁺) were continuously synthesized by directly feeding potassium hydroxide solution and metal salt solution to supercritical water (SCW). Effects of Eu concentration, pH, and residence time on photo-luminescence were studied using a continuous tubular reactor. Residence time played a key role in producing single-phase YAG:Eu³⁺ nanoparticles. The residence time of 20 s under SCW conditions (400 °C and 280 bar) was enough to form YAG:Eu³⁺ phosphor without any intermediate phases. At this residence time, the Eu concentration and pH condition under SCW contributed to improving the size, morphology and luminescent property of YAG: Eu³⁺ nanoparticles. The average size of the prepared phosphor nanoparticles at 10 at.% and pH of 9.10 was 74 nm and the morphology was identified as nearly uniform and spherical-like in shape. Without further thermal treatment, the phosphor YAG:Eu³⁺ synthesized in the continuous reactor under SCW conditions showed strong luminescence properties and red emission spectra.