Fluorescence is the spontaneous emission of light briefly after a substance is excited by electronic transitions. The emitted light has usually less energy than the previously absorbed light.
Figure 1: Absorption and emission spectra
Figure 1 shows that the fluorescence (emission) is long-wave (less energetic) than the excitation by absorption.
This is documented nicely in the resist structures of the new fluorescent e-beam resist. For the production of the new resists, both PMMA and CSAR 62 polymers were prepared in a solvent mixture which also dissolved the fluorescence dyes to a sufficiently high degree. These resists were then irradiated and developed at the company Precision Optics Gera GmbH using electron beam lithography. The structures could be generated residue-free in a developer optimised for this purpose. If excited by UV light as shown in the two pictures, they begin to fluoresce brightly.
Figure 2: Fluorescent PMMA structures yellow-green
Figure 3: Fluorescent PMMA structure red
Due to the properties of these e-beam resists are resolutions down to the range of 10 – 20 nm possible. The focus of the applications is in the optical industry; these materials are e.g. required for night vision devices.
Figure 4: Poster MNE 2017