ENERGY-TRANSPORT IN PHOTOEXCITED CRYSTALS OF K-3[TB(C2O4)(3)(H2O)]CENTER-DOT-2H(2)O - TRANSFER FROM TB3+ TO ND3+ AND EU3+

The luminescence decay dynamics of Tb3+(D-5(4)) and Eu(D-5(0)) in triclinic (P ($) over bar 1) crystalline K-3[Ln(C2O4)(3)(H2O)]. 2H(2)O solids was studied between 10 and 298 K in order to establish the energy-transport characteristics. The luminescence decay rate of Tb3+ (740 s(-1) for Ln=Tb3+) is temperature independent for the pure terbium complex; with introduction of Ln(3+) dopants (e.g., Ln=Nd, Eu) faster decay rates which are temperature dependent are obtained. For the EU(3+) dopant, excitation buildup on the EU(3+)(D-5(0)) decay curve upon Tb3+(D-5(4)) excitation confirms that energy transfer from Tb3+(D-5(4)) to Ln(3+) is active. The temperature dependence of the energy-transfer process in the K-3[Eu0.83Tb0.17(C2O4)(3)(H2O)]. 2H(2)O mixed complex is well described by a relatively simple empirical expression based on Boltzmann's statistical dynamics of EU(3+) electronic energy among the F-7(J) (J=0,1,2) terms. The limiting EU(3+)-Tb3+ transfer rates are similar to 5.4 X 10(3) and 5.3 X 10(4) s(-1) at 77 and 298 K, respectively. Energy migration on the terbium sublattice was confirmed by comparing Huber's [Phys. Rev. B 20, 2707 (1979)] trapping functions for K-3[Eu0.4Tb0.6(C2O4)(3)(H2O)]. 2H(2)O and K-3[Eu0.4Tb0.1Gd0.5(C2O4)(3)(H2O)]. 2H(2)O (Gd3+ serving as a scatterer for Tb3+ excitation). Although the structure of the complexes features a one-dimensional zigzag array of Ln(3+) ions, energy transport is diffusive and not one dimensional.