We have studied the dependence of structural and scintillation characteristics of Lu2xGd2-2xSiO5:Ce (LGSO:Ce) crystals on cation composition. LGSO:Ce crystals at x=0-1 have been obtained by the Czochralski method. We report here a strong correlation between ionic radii of trivalent cations and their distribution between non-equivalent sites in lattice. By choosing the optimal Lu/Gd ratio and Ce concentration we were able to obtain the light output by similar to 70%, as compared to LSO:Ce crystals, and energy resolution similar to 7 at% 662 KeV (Cs-137): the afterglow level was decreased by 1-3 orders of magnitude as compared to LSO:Ce. We also discuss the possible mechanisms of control on scintillation characteristics of mixed orthosilicates. (C) 2009 Elsevier B.V. All rights reserved.