A method that provides a new way to embed rare earth fluorides into silicate (or germania-doped silica) glasses by means of solution chemistry. Embedding rare earth fluorides into a silicate (or germania-doped silica) glass comprises the following steps. First, form a porous silicate core preform. Second, submerge the preform into an aqueous solution of rare earth ions. Third, remove the preform from the solution and wash the outside surfaces of the preform. Fourth, submerge the preform into an aqueous solution of a fluorinating agent to precipitate rare earth trifluorides from the solution and deposit in the pores or on the wall of the preform. This is followed by drying.