Xanthene dyes are a class of fluorescent materials that are readily available and commonly used as laser dyes. These compounds have strong absorbance in the visible region of the spectrum and are highly emissive, with many having quantum yields in solution approaching 1. When cast as thin films the properties of these dyes change, with a typical response being a significant quenching of the fluorescent when the films are more than a few nm thick. Further, the underlying substrate can also influence the photophysics of the dye.
Spin casting is a common method for creating smooth polymer films with thicknesses from hundreds of nanometers to tens of microns. Under certain circumstances, a spin-cast film can result in a structured surface that has the form of periodic wrinkles. We have found that the wrinkles have wavelengths on the order of tens of microns and amplitudes of tens of nanometers. The wrinkle pattern is influenced by the concentration of the polymer solution used in spin-casting, the angular velocity used, and the polymer molecular weight. We are not aware of any theory that can explain these observations so we are working to develop an empirical description.