Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The relaxation process of excited molecules, in homogeneous systems, is routinely studied through the measurements of fluorescence lifetimes and fluorescence quantum yields. From these data, the radiative decay rate, and hence the non-radiative decay rate, can be easily derived. Effort has been made, in the present work, to conduct such a fundamental study with molecules adsorbed on silica gel surfaces.;The photophysics of six polycyclic aromatic hydrocarbons (PAH), comprising phenanthrene, chrysene, pyrene, perylene, benzoperylene and coronene, adsorbed on variously dehydroxylated silica gel surfaces, has been investigated in this work. It has been observed that the fluorescence lifetimes of these adsorbed PAHs are dispersed into distributions, and that the recovery of these distributions is highly unstable, known as an "ill-conditioned" problem. In this thesis is discussed, in detail, the problem of the instability of lifetime distribution analysis. The regularization method of Phillips is used to obtain stable solutions. Based on these studies, a bimodal lifetime distribution, which represents the PAH molecules adsorbed on two types of surface sites, is suggested to describe the photophysical behaviour of the PAHs on the silica gel surfaces.;The fluorescence quantum yields of these PAHs have been measured by a diffuse reflectance method and also by an integrating sphere method. These results are then used, in conjunction with the measured lifetime distributions, to derive the radiative decay rates and the non-radiative decay rates for the PAH molecules adsorbed on each type of surface sites.;The so obtained lifetime distributions and quantum yields, as well as the derived radiative and non-radiative decay rates, seem to be physically plausible and self-consistent, which suggests that the techniques used are justifiable. The photophysics of the PAH adsorbed on silica gel surfaces is then discussed on the basis of these data.



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