Optical dephasing and energy transfer in ordered and disordered solids : studies by laser spectroscopy and optical-microwave double resonance

Citation

Smith, Duane D. (1981) Optical dephasing and energy transfer in ordered and disordered solids : studies by laser spectroscopy and optical-microwave double resonance. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1gza-t381. https://resolver.caltech.edu/CaltechETD:etd-04072008-141328

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Electronic energy transfer and optical dephasing of ordered and disordered molecular crystals is studied theoretically and experimentally. Data on impurity band transport are presented which are consistent with the Anderson transition. The effect of dimensionality on trap-trap energy transfer thresholds is experimentally measured and modeled. Experiments focus on 1,4-dibromonaphthalene whose lowest triplet exciton is quasi-one-dimensional. Steady state and transient line narrowing laser spectroscopy provide the first unequivocal measurement of the inelastic scattering rate amongst the band states. The inelastic scattering rate (intraband exchange rate) is slow and of the order of 10 [...]sec at 20 K. Further, the elastic scattering rate is ~10 psec at 20 K and is describable as Raman scattering by ~ a 42 cm[...] phonon. It is significant that there is a six order of magnitude separation of time scales for the elastic and inelastic scattering, demonstrating that pure dephasing dominates the intraband exchange. From the broadening and the lack of a relative shift of the two sublattice [...] absorptions, it is concluded that the interband exchange rate is negligible compared to the pure dephasing. It is found that disordering [...] DBN with up to 16% [...] DBN, the inelastic scattering rate is unaltered, being 10 gsec at 20 K! Pumping the [...] state of the upper sublattice, relaxation is exclusively to the [...] state of the lower sublattice, implicating single phonon resonant relaxation. For heavily trap-disordered DBN (up to 24% [...]/[...]) it is found that (1) excitation migration is step-wise incoherent, (2) energy transfer to deep traps is best fit with a [...] energy transfer rate, (3) there are no mobility edges in the trap inhomogeneous profile and (4) an upper limit for the trap homogeneous linewidth at 1.3 K is 9 Ghz. Using lifetimes and temperature-dependent lineshapes, optical dephasing of F and [...] center triplet states in CaO is is consistent with Raman scattering by effective oscillators of 89 and 151 cm[...], respectively. Vibrational dephasing of the CO stretch for benzophenone matrix-isolated in 4,4'-dibromodiphenyl ether at 2.1 K was investigated with a novel application of emission spectroscopy. It was found that the total dephasing rate of the CO stretch was linear in the CO quantum number, consistent with recent theoretical predictions for carbonyl moieties.

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