| abstract |
It has been difficult to suppress the production costs of conventional rare earth metal compound sols, since they are organic sols and thus require an explosion protection system during their production or use. Disclosed in claim 1 of the present invention is an aqueous sol of a rare earth metal compound wherein a rare earth metal compound is dispersed in water so that the molar ratio between a carboxylic acid having three or more carbonyl groups and at least one rare earth metal selected among Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu (carbonyl group/rare earth metal) is from 1.2 to 3. |