The single crystal of GdP 5O 14 :Sm 3+ ,Pr 3+ (GdPP:Sm,Pr) was grown by the hydrothermal method. The crystal belongs to the monoclinic space group P2 1/ C by X ray powder diffraction results. The dependence of Pr 3+ ion concentration in GdPP:Sm,Pr crystals on the emission intensity of 4 G 5/2 → 6 H 7/2 transitions of Sm 3+ ion and the energy transfer between Sm 3+ and Pr 3+ ions have been investigated and discussed.