Gd2O3:Eu phosphor particles of spherical shape, filled morphology, and high brightness were prepared by large-scale spray pyrolysis. The morphology control of Gd2O3:Eu particles was attempted by adding organic precursors in a spray solution. The influence of chain length of organic additives and introduction of esterification reaction within the droplet on the morphological and luminescent characteristics of Gd2O3:Eu particles was studied. The particles prepared from aqueous solution with no organic additive showed the hollow and porous shell structure and poor brightness, while those particles prepared from solutions with only polyethylene glycol (PEG) exhibited relatively filled structure and high brightness. The longer the chain length of added PEG is, the better morphological and luminescence characteristics the particles showed. The introduction of esterification reaction within the droplet by adding citric acid (CA) and ethylene glycol (EG) or PEG with various molecular weight enhanced the morphological characteristics and significantly improved photoluminescence characteristics regardless of chain length of PEG. The particles prepared from solution containing 0.1 M CA and 0.1 M PEG (M.W. 1500) showed the maximum photoluminescence intensity, which was 148% that of commercial product.