Temperature dependent non-radiative effects in the disorder-to-order transition in cyclopentanone and cyclohexanone films on Al2O3 (0001)

The excited electronic states of molecules can serve as sensitive probes of the microenvironment. Cyclopentanone and cyclohexanone thin films were prepared by vacuum deposition of these molecules onto a cryostatically cooled Al2O3 (001) surface. As the surface was heated, the films underwent several glass and crystalline transitions that were clearly identifiable by the large increase in the radiative intensity. The surface temperature was ramped to these transition temperatures, and the emission was found to exhibit decays that were kinetically different. Very importantly, the non-radiative relaxation in these films is thermally sensitive, and competes effectively with the radiative process.