The post-heat treated (Y(1-x-y)Gd(x)Eu(y))BO3 (0 < or = x < or = 0.36, 0.06 < or = y < or = 0.13) powders crystallized in a solution of (Y(1-x-y)Gd(x)Eu(y))BO3 with the hexagonal vaterite crystal structure, irrespective of composition. The lattice parameter of the (Y(0.9-x)Gd(x)Eu(0.1))BO3 (0 < or = x < or = 0.36) powders slightly increased with an increase in Gd content. The average powder sizes were sub-micron order and the powders showed relatively uniform size distribution and smooth surface. We obtained improved powder morphologies by adding organic additives such as ethylene glycol and citric acid. For the post-treated (Y(0.9-x)Gd(x)Eu(0.1))BO3, the emission intensity became stronger with increasing Gd content up to x = 0.27. In addition, for the post-treated (Y(0.73-y)Gd(0.27)Eu(y))BO3, the emission intensity gradually increased with Eu content up to y = 0.13. In particular, the emission intensity of the (Y(0.6)Gd)0.27)Eu(0.13))BO3 powders synthesized was higher than that of the commercial (Y,Gd)BO3:Eu3+ product.