A novel method is employed for the formation of rare earth phosphate solid solution compounds with unique mesoscopic structures. Europium-and lanthanum-doped sodium borate glass microspheres and particles, ranging in sizes from 50 to 300 mu m, were reacted in 0.25 M K2HPO4 solution to form hollow spheres of nanocrystalline rare earth phosphate compounds by dissolution- precipitation reactions. The initially X-ray amorphous precipitated rare earth phosphate materials were heat-treated at 700 degrees C for 2 h to form nanocrystalline compounds. Differential thermal analysis (DTA) experiments yield an average activation energy for crystallization of 394 +/- 26 kJ/mol. X-ray diffraction (XRD) data indicate that samples crystallized to the monazite structure (monoclinic P2(1)/n) with unit cell volumes ranging from 306.5 angstrom(3) for LaPO4 to 282.5 angstrom(3) for EuPO4 and with crystallite grain sizes of 56 +/- 14 nm. Compositions containing both rare earth elements formed solid solutions with the composition La(1-x)EuxPO4. Raman spectroscopy indicates that the P-O symmetric stretching vibrations (v(1)) change systematically from 963 cm(-1) for LaPO4 to 986 cm(-1) for EuPO4, consistent with a systematic decrease in average P-O bond length. Photoluminescence measurements show maximum emission intensity for the La0.65Eu0.35PO4 composition.