Hydrophobic Versus Hydrophilic Polyelectrolyte Multilayers\nfor Emissive Europium Films

Abstract

Films containing lanthanide ions,\nhaving exceptionally narrow emissive\nbandwidths, are often used for high-performance photonic materials.\nThe lanthanide ion is commonly coordinated with organic ligands to\nenhance emission intensity. However, the light output is influenced\nby the environment, such as the presence of water, surrounding the\nligated metal center. In this work, hydrophobic and hydrophilic ultrathin\npolyelectrolyte films made using the multilayering technique were\ncompared as hosts for Eu^III tris­(dipicolinate), [Eu­(DPA)₃]^3–, complexes. The concentration of a complex\nwithin the film depended on the number of residual excess positive\npolyelectrolyte repeat units, which in turn was controlled by the\nmethod of multilayer assembly. Because the hydrophobic polyelectrolyte\nmultilayer excluded water more efficiently, the [Eu­(DPA)₃]^3– emission intensity and lifetime decreased only\nslightly on exposure of the emissive film to ambient humidity and\nmaintained a quantum yield of 48%.