Optical pumping of dye-complexed and -sensitized porous silicon increasing photoluminescence emission rates

Distinctly structured nanoporous and combined hybrid macroporous-nanoporous porous silicon (PS) structures have been fabricated and treated with the dyes 3,3'-diethyloxadicarbocyanine iodide (DODCI) and Rhodamine 700, both of which have negligible absorption at the wavelengths of maximum absorption for porous silicon. After an extended period of aging in darkness (air) these dye-treated samples are pumped (PLE) at 337.1 nm (nitrogen laser) near the maximum in the PS absorption spectrum (far from. the major absorption regions of the impregnating dye) and the subsequent photoluminescence from these treated samples is monitored and compared to that obtained for the untreated PS structures. The first time-dependent photoluminescence (PL) histograms obtained for these systems indicate that the resulting luminescence, initiated through the pumping of a modified PS surface, displays the manifestation of a significant interaction between the surface-bound fluorophors which characterize PS and the dye (DODCI). It is suggested that this interaction results in the creation of a distribution of PS-dye complexes which greatly enhance the nominal PL emission rate from the untreated PS surface. This enhancement not only facilitates the observation of luminescence from a formed photoluminescing PS "green" precursor state but also the mapping of its time-dependent oxidation to form the more commonly observed "orange-red" emitter. Both emitters are attributed to surface-bound silanone-based silicon oxyhydride fluorophors. The degree of PS-dye interaction, in addition to being dye dependent, is found to be PS-structure dependent. Thus the photoluminescent histograms obtained in this study also appear to provide evidence for the influence of PS morphology on the surface interaction.