GdPO4:Tb3+ submicron cubes were synthesized by a sol-precipitation-hydrothermal process. The XRD result indicated that GdPO4:Tb3+ submicron cubes have pure hexagonal phase. The SEM and TEM images confirmed the formation of cubic morphology. Under the excitation at 273 nm, GdPO4:Tb3+ submicron cubes show emission bands corresponding to Gd3+ and Tb3+. With the increasing Tb3+ concentration, the emission intensities originating from Gd3+ and D-5(3)-> F-7(j) transition of Tb3+ decrease, but the emission intensities originating from D-5(4)-> F-7(j) transition of Tb3+ increase. These results suggested energy transfer from Gd3+ to Tb3+ and the occurrence of cross-relaxation processes in GdPO4:Tb3+ submicron cubes. (C) 2016 Elsevier B.V. All rights reserved.