Optical imaging and spectroscopy of SnO₂-rhodamine 6G composite's desiccation patterns

In this study, we produced self-assembly structures (desiccation patterns) in the drying sessile drops of SnO₂-R6G colloidal suspension that have functional applications. Colloidal suspensions of SnO₂ nanoparticles were synthesized using the sol-gel method and, subsequently, R6G molecules were added into the suspension. Centimeter-sized honeycomb- or tree-like self-assembled structures of the nanoparticle-dye composite are formed from the evaporating droplets on a flat glass surface. The usual “coffee ring” effect observed in the case of drying of a sessile drop of dye solution is inhibited this way, which is desirable in many applications. The structures were investigated using optical microscopy and spectroscopy. The resemblance between transmission and fluorescence images illustrates the feasibility of organizing dye molecules in a specific way using self-assembled nanoparticles as a template. However, dye fluorescence from the self-assembly is very weak, which might be due to photoinduced interfacial electron transfer from the excited dye molecules to the nanoparticles.