Yolk-shell structured Gd₂O₃:Eu³⁺ phosphor prepared by spray pyrolysis: The effect of preparation conditions on microstructure and luminescence properties

Gd₂O₃:Eu³⁺ yolk-shell phosphor powders with high photoluminescence intensity were prepared by spray pyrolysis. Preparation temperature and spray solution concentration were varied to find the optimum process conditions for preparation of Gd₂O₃:Eu³⁺ with yolk-shell structure. The formation mechanism of yolk-shell Gd₂O₃:Eu³⁺ was systematically investigated by observing the microstructures of particles produced under various preparation conditions. The morphological structure of Gd₂O₃:Eu³⁺ powders was clearly dependent on reactor temperature and on the precursor solution concentration. Eventually, pure yolk-shell structured Gd₂O₃:Eu³⁺ powders were obtained for a reaction temperature of 1000°C and concentration of the spray solution below 0.2 M. Also, the yolk-shell structure formed showed high thermal stability, making it possible to maintain the original spherical yolk-shell structure through calcination at high temperatures. As a result, highly crystalline Gd₂O₃:Eu³⁺ phosphor powders having yolk-shell structure and an agglomeration-free spherical shape were successfully synthesized by spray pyrolysis. These phosphor powders were shown to have good photoluminescence characteristics.