Dye molecules embedded in different matrices in the form of thin films are the basis of specific materials used for laser cavities, optical filters, optical gas sensors, etc. Usually, the synthesis of this type of thin films is intended by sol/gel and similar wet methods. These procedures present some inconvenient as, for example, the need of different steps for drying, annealing, etc. Other limitations come from the microstructure of the films (e.g., surface roughness), that impose some restrictions when these materials have to be integrated in optical and photonic devices. Trying to circumvent these problems dye thin films have been prepared by sublimation techniques. However, the resulting films are formed by small crystalline aggregates whose size increases with time and that are easily removable from the substrates during they manipulation.
In the present communication we discuss a new methodology based on the plasma polymerization of dye molecules that circumvent the above mentioned problems. It permits a tailored synthesis of optically active thin films containing dye molecules which are active as absorbent or fluorescence emitters (i.e., coloured and fluorescent films). The principle of this new procedure is the partial polymerization of dye molecules that are evaporated over a substrate while exposed to a remote Ar plasma. As a result of this process a polymeric thin film is produced where some dye molecules keep intact their optical activity (although eventually, their optical response can be slightly modified by matrix effects. By comparison with conventional thin films containing dyes prepared by sol/gel and similar procedures, this new type of dye thin films are much thinner (for example some tenths of nms are enough to get similar extinction coefficients that several micron films prepared by wet routes), are very flat and permit a very easy control of the matrix effects that influence the optical response of the dye molecules.
To illustrate the possibilities of the technique we pre-sent here results for different dye molecules, as perylene dyes, the Ethyl red, a neutral azoic dye used as pH sensor, and several xanthene and oxazine derivative cationic dyes which are typically used as gain media in tuneable laser dyes.
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