Luminescence of a laser dye in organically-modified layered silicate pigments

Abstract

The main focus of the present work was the development of pigments based on layered nanomaterials exhibiting luminescent properties. Two layered silicates, montmorillonite (Mt) and saponite (Sap), differing in their cation exchange capacity (CEC), were modified with cationic organic surfactants (tetraoctylammonium and tetraoctylphosphonium) in various amounts relative to the CEC (25–100%) and with a laser dye, rhodamine 6G (R6G), with dye/silicate ratios of 0.001–0.08 mmol g−1. The photoluminescence and its dependence on the surfactant amount, dye concentration, and the layered silicate type were evaluated. Modification by the surfactants played a key role and caused an increase in fluorescence, particularly for Mt, whose hybrids were non-active without the modification. The intensity increased significantly even for samples modified with amounts of surfactants equal to 25% of the CEC values. Dye concentrations above 0.02 mmol g−1 caused a diminishing of the fluorescence intensities due to the formation of non-luminescent molecular aggregates of the dye. Advanced chemometric and statistical analysis was applied for better differentiation of the components in fluorescence spectra. By selecting suitable organic cation and dye components, it was possible to prepare pigments exhibiting high fluorescence and at (for R6G) unusually long wavelengths, approaching the near-infrared region (650–700 nm).