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Abstract: Effects of thermal treatment on the third-order optical nonlinearity and ultrafast dynamics of Ag nanoparticles embedded in glasses were investigated by femtosecond time-resolved OKE and femtosecond pump–probe techniques. The results indicate that the third-order susceptibility increases from 1.1×10−11 esu to 1.48×10−9 esu with increasing the annealing temperature. The fast decay process is accelerated and its amplitude ratio increases with the thermal treatment, which could be attributed to an increase of the electron–phonon coupling through the process of treelike Ag nanoparticle aggregation. The slow relaxation time ranges from 25ps to 140ps, depending on the thermal conductivity of the matrix material. [Copyright &y& Elsevier]

Abstract: We studied the photoluminescence (PL) properties of self-organized para-sexiphenyl (PSP) nano-needles with linear and nonlinear optical excitation. Excited by femtosecond pulses, two-photon absorption (TPA) induced PL emission peaks corresponding to the vibronic transitions in PSP molecules were observed. Polarization-dependent photoluminescence measurements reveal that the TPA induced PL in the highly-ordered structures, similar with the linear excitation case, is strongly dependent on the excitation polarization. The mechanism that the nonlinear transition dipole moment is oriented parallel to the long axis of the molecular for the π–π∗ absorption in PSP is suggested to explain these strong polarization effects. [Copyright &y& Elsevier]

Abstract: The energy relaxation dynamics in Ag:Bi2O3 nanocomposite films with high density of Ag nanoparticles were investigated by femtosecond pump–probe technique. For the films with relatively low Ag concentration (13.2–35.7at.%), the energy relaxation is nearly completed within 1picosecond (ps) at moderate excitation regime. For the film with 52.0at.% Ag concentration, the relaxation process consists of a fast power-dependent component (1–2ps) and a long-lived one. The different relaxation characteristics are suggested to be resulted from the differences in the structural and thermal properties of the surrounding Bi2O3 matrix coupling with Ag nanoparticles. [Copyright &y& Elsevier]

Abstract: Femtosecond degenerate pump–probe spectroscopy was carried out on thin films of a series of axially substituted phthalocyanines including tBu4PcInCl(tBu4=tetra-(tert-butyl)), tBu4PcTiO, tBu4PcIn(p-TMP) [p-TMP=p-trifluoromethylphenyl], tBu4PcGa(p-CPO) [p-CPO=p-chlorophenoxy], and μ-oxo-bridged phthalocyanine dimers, e.g., [tBu4PcIn]2O, tBu4PcIn–O–GaPctBu4 and [tBu4PcGa]2O. We demonstrate that the long lived state of the dynamics is the triplet state and the behavior of the degenerate pump–probe was determined by exciton–exciton annihilation (E-EA), nonradiative recombination (NR) and intersystem crossing (ISC) processes. The E-EA process is via the long-range dipole–dipole interaction between excitons or motion-limited diffuse other than exciton hopping migrations. The dimers shows much efficient E-EA and the indium-contained samples have larger ISC rate than the others. [Copyright &y& Elsevier]