Recently, lead halide perovskites which are organic-inorganic hybrid structures, have been discovered to be highly efficient as light absorbers. Herein, we show the investigation of the excited state dynamics and emission properties
of non-stoichiometric precursor formed lead halide perovskites grown by interdiffusion method using steady-state and time-resolved spectroscopic measurements. The influence of the different ratios of the non-stoichiometric precursor solution was examined. The observed photoluminescence properties were correlated with the femtosecond
transient absorption measurements.
Gold clusters with the sizes close to the Fermi wavelength of electron shows interesting quantum size effects. Linear and
nonlinear optical properties show dramatic trends when the sizes of clusters are in the range of quantum confinement.
We have investigated the size dependence of the non-linear optical property of two-photon absorption (TPA) cross-sections
of the gold clusters. Absolute TPA cross-sections are measured by a combination of one and two-photon excited
fluorescence upconversion measurements. Large cross-sections and abrupt changes in the trend of cross-sections are
observed in the size-dependence when size is reduced from nanoparticles to cluster. The results can be attributed to the
appearance of quantum confinement in these monolayer protected gold clusters.
In this contribution we report two-photon excited time-resolved fluorescence and fluorescence anisotropy for several
macromolecular systems of different symmetry such as cyclic (single ring) thiophene-based annulenes, triphenylaminecentered
branched trimers with pyridine acceptor groups, and linear chromophores possessing high TPA-cross-section.
We have compared the ultrafast fluorescence anisotropy dynamics for one- and two-photon excitation routes using timeresolved
fluorescence up-conversion setup with femtosecond time resolution. For linear systems the initial anisotropy
was found to be about factor 1.4 higher than that for one-photon excitation as predicted by theory. For macromolecular
strongly coupled planar systems under two-photon excitations we observed a relatively low initial fluorescence
anisotropy (~0.1) and specific femtosecond anisotropy dynamics. Two-photon excited fluorescence anisotropy is
strongly correlated to the orientation and value of the transition moment from the excited state to the second and higher
lying states and can be used as a direct indicator of strong coupling regime.
The measurements of the ultra-fast fluorescence anisotropy decay in conjugated dendrimers and in model branched dendritic molecules of different symmetry are reported. The excited state relaxation of carbon and adamantane-centered tetramers was investigated by polarized fluorescence upconversion spectroscopy. Fluorescence anisotropy was found to decay to the residual value in femtosecond time range. A comparison between the tetramer systems and a nitrogen cored distyrylbenzene dendrimer is provided. For the model system bis-MSB representing the linear building block of the investigated systems a fluorescence anisotropy decay time of 82 ps was obtained which agrees with rotational diffusion. Ultrafast anisotropy decay for these branched systems was explained in terms of interchromophore interactions. The results of these ultrafast anisotropy measurements are important to the understanding of the characteristics of excitations in organic dendrimers.
The nonlinear optical properties are reported for a novel organic dendrimer using femtosecond pulses. The organic dendrimer showed strong nonlinear refraction when measured at 790 nm, a wavelength far from the linear resonance. The nonlinear refractive index was measured by the z-scan technique and the magnitude was measured to be 1.1*10-4 cm2/GW. The presence of two photon absorption was observed and a related nonlinear absorption coefficient was found to be 1.2*10-2 cm/GW. A strong two-photon luminescence was detected resulting from this nonlinear absorption, and the power dependence and spectral characteristics were measured. The presence of a higher order, (chi) (5), nonlinear optical effect was also detected. The ultra-fast dynamics of the organic dendrimer using fluorescence upconversion spectroscopy are reported. At higher emission energies we observe femto-second decay, and at lower energies a rise time of the luminescence intensity was observed.
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