Europium (III) (Eu3+)-doped nanoporous silica spheres were synthesized, and the states of Eu3+ ions in the silica framework structure were investigated. The ordered nanopores were preserved with the doping at the Eu3+ molar concentration to Si up to 10 mol%, and the O-Si-O and Si-OH groups in the structures were clearly rearranged with the doping, indicating the interaction of Eu3+ with the O atoms. The significant morphological changes in the spheres were observed with the doping. The photoluminescence spectral shapes due to the transitions of D-5(0)-F-7(1) and D-5(0)-F-7(2) were indicative of the presence of the Eu3+ in an environment of a low symmetry. It was found that the Eu3+ was located inside the silica framework to electrostatically interact with the environmental O atoms, which would prevent the aggregation among Eu3+ ions to show the efficient luminescence. Therefore, the interactions between the Eu3+ ions and silica framework structures in the spheres were successfully clarified. (C) 2011 Elsevier Inc. All rights reserved.