Energy Transfer in Lanthanide-based Nanomaterial

Abstract

The respective fields of lanthanide-based nanoparticles and microwave-assisted synthesis are well established, but still ongoing, topics of research. Yet, there has been scarce attempts to join these areas of research together. The first part of the thesis presented here is the result of an effort to develop the very first phase-selective, microwave-assisted synthesis of small (sub-10 nm) and ultrasmall (sub-5 nm) photoluminescent NaGdF4:Yb3+(20%),X3+-based nanoparticles (X= Er, Tm). The choice of these lanthanide ions is important, as it endows the nanoparticles with the capacity to undergo upconversion and downshifting, two optical processes that allow for visible and near-infrared emission upon near-infrared excitation. The approach described here focuses on the precursor chemistry to control the size, the crystalline phase, and therewith the optical properties of NaGdF4:Yb3+(20%),Er3+(2%) nanoparticles. Furthermore, the precursor-dependent growth mechanism was investigated as a function of the microwave-assisted reaction temperature and time. Upconverting nanoparticles are well known for their long photoluminescent lifetime and as such, are often used to transfer energy to energy acceptor-like fluorescence dyes and other nanomaterials. Little work has been done on a hybrid system made of upconverting nanoparticles and inorganic lanthanide complexes. To address this, the second part of the work presented here describes a straightforward method to prepare a hybrid system containing NaGdF4:Yb3+(20%),Tm3+(0.5%) nanoparticles and either [Tb2(bpm)(tfaa-)6] or [Eu2(bpm)(tfaa-)6] complexes. The optical behavior of the hybrid system was assessed with steady-state and lifetime analysis. Furthermore, this is the first report of hyperspectral imaging used to characterize energy transfer process in thin film. The last part of this thesis describes some strategies to modify the surface of NaGdF4:Yb3+(20%),Tm3+(0.5%) nanoparticles, so they become water-dispersible. Furthermore, the effect of the aqueous solvents on the photoluminescence is also described.