Photophysics of Rare Earth Chelates Under High Pressure

132 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.The pressure dependence of luminescence intensities, energies, and decay times of several tris rare earth betadiketonates has been investigated in crystalline and plastic media over the pressure range of 0-120 kilobars. Temperature studies were also conducted from 110 to 300 K. The optical properties of Eu dibenzoylmethide and Eu thenoyltrifluoroacetylacetonate were examined in great detail. The model developed from these cases successfully explains the results for other Eu chelates and some Sm and Tb complexes.Application of pressure shifts the ligandlocalized energy levels relative to the ionlocalized levels. By thus "tuning" the energy levels with pressure and comparing the results for excitation into various excited levels, it has been found that the ligandlocalized triplet plays a major role in energy transfer processes between the ligand and ion localized levels. Radically different behavior under pressure was observed for some chelates in the solid state v.s. in solution but was explained by the assignment of different triplet levels energies at one atmosphere in the two cases. For a given triplet energy, energy migration appears to be basically similar in different media, although in a detailed analysis the dissimilar environmental interactions (e.g. thermal energy barriers) should be considered. The results for chelates in PMMA confirm the findings of previous investigators on liquid solutions. No evidence for energy transfer from the ligandlocalized singlet to the ionlocalized levels was found for these systems. In addition to the energy transfer studies, the localized photophysical properties of the ligand and of the ion have also been examined. The pressure dependence of the phosphorescent emission from the ligandlocalized triplet is very similar to general results found for luminescent organic systems. The major effect of pressure on the rare earth ionlocalized system is a small increase in the radiative rate with pressure. The findings support the model of these systems which divides the total set of energy levels into those localized to the ligand and those localized to the ion. The pressure tuning technique has been found to be a powerful means for elucidating how energy migrates through a complex set of excited states.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD