The difference in the ionic radii between Y3+ and M3+ in Y0.7M0.2NbO4:0.1Eu(3+) powders caused a change in the luminescent properties by modifying the crystal field surrounding the Eu3+ ions. By co-doping Y0.7Al0.2NbO4 with 0.01Sm(3+) and 0.09Eu(3+), the excitation peak at 406 nm corresponding to the H-6(5/2)-> K-4(11/2) transition of Sm3+ was significantly enhanced and broadened. When Y0.7Al0.2NbO4:xEu,ySm was excited by 406 nm, only the emissions due to the D-5(0) -> F-7(J) transition of Eu3+ appeared, whereas those generated by the (4)G(5/2)-H-6(J) transition of Sm3+ were not observed. This confirms the existence of an energy transfer from Sm3+ to Eu3+ ions. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3456549] All rights reserved.