Energy transfer and emission decay kinetics in mixed microporous lanthanide silicates with unusual dimensionality

We have investigated the energy transfer dynamics in mixed lanthanide open-framework silicates, known as Ln-AV-20 materials, with the stoichiometric formula Na(1.08)K(0.5)Ln(1.14)Si(3)O(8.5)center dot 1.78H(2)O (Ln = Gd3+, Tb3+, Eu3+), using steady-state and time-resolved luminescence spectroscopy. Energy transfer between donor and acceptor Ln(3+) ions is extremely efficient, even at low molar ratios of the acceptor Ln(3+) (< 5%). The presence of two different Ln(3+) environments makes the Ln-AV-20 intralayer structure intermediate between purely onedimensional (ID) and two-dimensional (2D). The unusual dimensionality of the Ln-AV-20 layers prevents modeling of energy transfer kinetics by conventional kinetic models. We have developed a computer modeling program for the analysis of energy transfer kinetics in systems of unusual dimensions and show how it may be applied successfully to the AV-20 system. Using the program, nearest neighbor energy transfer rate constants are calculated as (5.30 +/- 0.07) x 10(6) and (6.00 +/- 0.13) x 10(6) s(-1), respectively, for Gd/Tb- and Tb/Eu-AV-20 at 300 K. With increasing acceptor concentration, the energy transfer dynamics tend toward purely one-dimensional behavior, and thus, with careful selection of the ratio of individual Ln(3+) ions, it is possible to tune the energy transfer dimensionality of the AV-20 layers from pure I D to something intermediate between ID and 2D.