Stepwise synthesis of fine crystalline Ce-doped yttrium aluminum garnet in water medium in subcritical and supercritical conditions

In this paper the continuous stepwise method of a production of fine crystalline yttrium aluminum garnet doped with cerium (YAG: Ce³⁺) in supercritical water fluid (SCWF) are represented. The synthesis was carried out in water medium in two stages: first in subcritical conditions and then in an atmosphere of supercritical water fluid. The stoichiometric mixture of yttrium oxide and aluminum hydroxide in a water solution of cerium nitrate was maintained the certain time at 280°C and under vapor water pressure 6.3 MPa. Then temperature and pressure were risen up to a supercritical condition (T = 392–400°C, P_{H2 O}P_{H_2 O} = 22 MPa). The concentration of cerium ions in reaction medium was changed in the interval 0.012–0.706 wt %. The products, obtained on various stages of synthesis, were investigated by physical-chemical methods. During the first stage, the crystals of boehmite and yttrium hydroxide under hydrothermal conditions were arising, and eventually poorly formed YAG: Ce³⁺ were appearing. At this stage, the diffusion of cerium ions into intermediate products takes place. Because of this, at the second step of synthesis, in supercritical conditions, YAG: Ce³⁺, phosphor with high luminescence intensity at 530 nm, was obtained. In supercritical conditions well-faceted crystals of 0.5–3.0 μm with rhombododecahedral habitus were produced.