Two different types of structure called X 1 and X 2 are existing in Y 2 SiO 5 at normal conditions. In X 1 type, Y 3ϩ ions occupy two sites where they are surrounded respectively by nine and seven oxygen ions, while in X 2 structure, only six and seven oxygen ions are involved. Nanometric scale X 1 -Y 2 SiO 5 crystals were prepared by sol-gel method with particle size around 50 nm. Site selective excitation at low temperature has shown four different luminescent centers. Two of them belong to Eu 3ϩ embedded in X 1 -Y 2 SiO 5 , the other two are attributed to Y 2 O 3 :Eu phase and to a particular site on the surface. The occurrence of the latter site may be related to the nanometric size of the sample. A pronounced excitation energy transfer from site 2 to site 1 was also observed on excitation spectra. The energy transfer rate increases rapidly with increasing Eu 3ϩ concentration and for x ϭ0.7 in Y 2Ϫx SiO 5 :Eu x , no fluorescence takes place in site 2 at 15 K. The lifetimes of the 5 D 0 levels of Eu 3ϩ in the two sites were measured as a function of Eu 3ϩ concentration. The results have shown that the lifetime of the 5 D 0 level of Eu 3ϩ in site 2 decreases with increasing Eu 3ϩ concentration. The energy transfer rate dependence upon temperature was studied in detail and compared to a theoretical simulation.