Thermo-optic properties of hybrid sol–gel thin films doped with Rhodamine 6G at high vacuum conditions

Abstract

An inorganic–organic hybrid thin film doped with Rhodamine 6G prepared by the sol–gel technique has been studied at thermal vacuum conditions by variable angle spectroscopic ellipsometry in order to assess the suitability of using these films in aerospace applications. The thermo-optic properties of the Rhodamine 6G-doped thin film, i.e., the thermo-optic coefficient dn/dT (dependence of the refractive index on temperature) and its linear thermal expansion coefficient α (dependence of the thickness of the film on temperature) were studied in the 343–77 K temperature range obtaining a negative thermo-optic coefficient of −5 × 10−5 K−1 and a linear thermal expansion α of 5.8 × 10−5 K−1. The stability of the Rhodamine 6G molecules in the sol–gel matrix was studied at 303, 323, and 343 K at high vacuum (10−6 mbar) and no significant outgassing or thermal decomposition of the Rhodamine 6G molecules were found, which assures the performance of the hybrid thin films at high vacuum conditions up to the temperature of 343 K. The spectroscopic properties of the Rhodamine 6G molecules showed a dependence on temperature based on a Boltzmann distribution of the vibrational and rotational energy levels that was characterized in the 343–77 K temperature range. We have found that both the hybrid sol–gel thin film and the embedded Rhodamine 6G molecules successfully withstand the extreme temperatures and high vacuum studied, which make these materials promising components for space missions and open new opportunities for the usage of the hybrid sol–gel materials in the aerospace industry.