A Fast and Template Free Synthesis of Tb:Y<sub>2</sub>O<sub>3</sub> Hollow Microspheres Via Supercritical Solvothermal Method

The design of template-free hollow microspheres in a very short period of time will be of great importance to save energy and time and allow rapid production. We succeeded in the rapid synthesis of precursor material via a supercritical solvothermal method followed by subsequent heating to obtain Tb:Y<sub>2</sub>O<sub>3</sub> hollow microspheres. The prepared precursor material was actually composed of Y(OH)<sub>3</sub> and Y(OH)CO<sub>3</sub> phases. The hollow microspheres seemed to be formed through the aggregation of nanoparticles under supercritical conditions. The formation mechanism of hollow microspheres in the present synthesis is the Ostwald ripening process. Effects of reaction temperature and pH of the starting solution were investigated to understand the effect on the formation of hollow microspheres. Well-shaped Tb:Y<sub>2</sub>O<sub>3</sub> hollow microspheres showed strong green emission at 540 nm under 304 nm light excitation. The effect of doping concentrations and calcinations temperature was investigated.