Dramatic Enhancement of One and Two Photon-Excited Emission of a Stilbazolium Dye Coupled to Laponite Platelets

Natural clays are the oldest example of two-dimensional materials and have been extensively investigated for their structural, morphological, and viscoelastic properties. Although there are reports of optical studies in clay-containing media, clay has traditionally been considered highly scattering, and thus, its optical and nonlinear optical applications have not been extensively examined. Nonlinear optics plays a key role across multiple fields of research and application, including biomedicine, photonics, optoelectronics, and surface science. Nonlinear optical characteristics of two-dimensional materials and of organic-inorganic hybrid materials are of particular interest in recent years. Here, we provide the first demonstration that Laponite, a synthetic clay material, can be a highly promising medium to dramatically enhance the efficiency of emission by both linear and nonlinear excitation of a polar dye, because of its interaction with the ionic microenvironment of Laponite. We show that adsorption of this cationic dye onto the negatively charged faces of Laponite platelets in an aqueous dispersion produces a remarkable enhancement in fluorescence intensity by up to a factor of 15. Notably, the stilbazolium dye exhibits a longer fluorescence lifetime of 480 ps in the presence of Laponite, an order of magnitude longer than that in pure water, revealing that nonradiative processes are slowed via the interaction with Laponite. To probe the origins of this effect, we conducted an array of experiments that investigated the interaction between organic dye and Laponite, including viscosity measurements, ionic conductivity measurements, dynamic light scattering, and small-angle X-ray scattering. These experiments and analysis reveal that modification of the local molecular environment of the dye via interaction with Laponite platelets suppresses nonradiative recombination pathways to dramatically enhance both linear and nonlinear fluorescence in this novel hybrid system. The Laponite dye hybrid displays significant potential for applications in biosensors, optical sensors, fluorescent probes, and other fields, which require high emissive properties.