The energy dissipation of Tb3+/Eu3+ cations in both heterolanthanide multinuclear polyoxometalates, K15H3[Tb1.4Eu1.6(H2O)(3)(SbW9O33)(W5O18)(3)]. 25.5H(2)O and Na7H19[Tb4.3Eu1.7O2(OH)(6)(H2O)(6)Al-2(Nb6O19)(5)]. 47H(2)O is studied by crystal structures, emission and excitation spectra, and emission decay dynamics. The excitation of the Tb3+ F-7(6) --> D-5(4) transitions produces not only the emission lines of Tb3+ but also chose of Eu3+, accompanied by nonexponential rise and decay curves of the emission from Tb3+ and Eu3+. There is no significant exchange interaction between the lanthanide ions, as a result of the coordination of aqua and/or hydroxo ligands to the lantahanide ions. The mechanism of the Tb3+ --> Eu3+ energy transfer is identified as a Forster-Dexter-type energy transfer from Tb3+ (donor) to Eu3+ (acceptor). At low temperatures D-5(4)(Tb) + F-7(0)(Eu) --> F-7(4)(Tb) + D-5(0)(Eu) governs the transfer process, and at high temperatures it is governed by D-5(4)(Tb) + F-7(1)(Eu) --> F-7(5)(Tb) + D-5(1)(Eu), D-5(4)(Tb) + F-7(1)(Eu) --> F-7(4)(Tb) + D-5(0)(Eu), and D-5(4)(Tb) + F-7(2)(Eu) --> F-7(5)(Tb) + D-5(1)(Eu) interactions which involve the thermally populated F-7(1) and F-7(2) levels. The nearest-neighbor energy-transfer rates by electric dipole-dipole interactions between a Tb-Eu pair at 4.2 K are estimated to be 4.5 x 10(4) and 4.7 x 10(5) s(-1), and the critical radii at 4.2 K are 10.3 and 10.0 Angstrom for K15H3[Tb1.4Eu1.6(H2O)(3)(SbW9O33)(W5O18)(3)]. 25.5H(2)O (with Tb-Eu separation of 5.05 Angstrom) and Na7H19 [Tb4.3Eu1.7O2(OH)(6)(H2O)(6)Al-2(Nb6O19)(5)]. 47H(2)O (With 3.76 Angstrom separation), respectively. The low symmetry (C-s for the former and C-1 for the latter) of the LnO(8) (Ln = Tb and Eu) coordination polyhedra allows the nonvanishing electric dipole transition probability for the F-7(J) <----> D-5(0) (J = 0,1) transitions which leads to a faster transfer rate at high temperatures.