Energy Transfer and Emission Decay Kinetics in Mixed Microporous Lanthanide Silicates with Unusual Dimensionality

Abstract

We have investigated the energy transfer dynamics in mixed lanthanide open-framework silicates, known as Ln-AV-20 materials, with the stoichiometric formula Na1.08K0.5Ln1.14Si3O8.5·1.78H2O (Ln = Gd3+, Tb3+, Eu3+), using steady-state and time-resolved luminescence spectroscopy. Energy transfer between donor and acceptor Ln3+ ions is extremely efficient, even at low molar ratios of the acceptor Ln3+ (<5%). The presence of two different Ln3+ environments makes the Ln-AV-20 intralayer structure intermediate between purely one-dimensional (1D) 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) × 106 and (6.00 ± 0.13) × 106 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 Ln3+ ions, it is possible to tune the energy transfer dimensionality of the AV-20 layers from pure 1D to something intermediate between 1D and 2D.