Applying forced Rayleigh scattering to monitor the drying behavior of poly(n-butylmethacrylate-co-acrylic acid) dispersions (T > Tg + 5 K) via the diffusion of a hydrophobic dye, we find a characteristic length scale dependence of the tracer diffusion coefficient Dapp(Λ) (Λ ) 0.17-10 µm), which allows one to quantitatively describe the transition from a wet, inhomogeneous to a dry, homogeneous polymer latex film within a two-state diffusion model. Dapp(Λ) showed an enhancement of up to 2 orders of magnitude when increasing the length scale. These findings can be quantitatively rationalized within the two-state model assuming Fickian diffusion proceeding slowly in the latex cores and fast diffusion in a heavily plasticized, interfacial phase. From the water content dependence of the model parameters we conclude that the drying process proceeds first by exclusive water loss from the interfacial phase, while the properties of the particle cores remain unchanged. When the Λ dependence of D app(Λ) disappears, water withdraws also from the cores and a homogeneous polymer film forms. Our approach allows one to quantitatively follow property changes in the different compartments of a drying latex dispersion.

By dissolving tracer quantities of 9,10-phenanthrenequinone (PQ) in poly(methyl methacrylate) (PMMA) it was possible to study by forced Rayleigh scattering (FRS) the tracer diffusion of the unbleached PQ as well as the photoproduct which is covalently bound to the PMMA molecules. The PMMA samples with molecular weights, M w, of 10 3 -10 5 were intermittently annealed at 80 °C for diffusion times of up to one year. From the results we conclude that polymer chain diffusion may be possible at temperatures more than 20 K below the glass transition temperature Tg, but further experiments are necessary, in particular, since we cannot exclude that our results are due to yet unexplained long time aging effects in PMMA. The translational diffusion coefficients of the unbleached PQ are enhanced by several decades in comparison with predictions from rotational correlation times that were determined by using a modified FRS technique.

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We present an analysis of methods for calibration of the spectral sensitivity of instruments in the near IR region of the spectrum (0.90-2.05 μm), using as an example recording of the luminescence spectra of PbS semiconductor quantum dots using a diffraction monochromator and an InGaAs photodiode as the detector. We show that when high-sensitivity detectors are employed for calibration using the emission spectrum of an ideal black body, the problem of attenuation of the radiation flux is still important. Instead of neutral density glass and mesh light filters for attenuation of the radiation, we propose using UFS ultraviolet optical glasses (together with PS purple glasses), the maximum optical density of which is within the region of maximum spectral sensitivity of InGaAs photodiodes. We give examples of spectral calibration, taking into account instrumental characteristics and the effect of absorption by water vapor in the air, and also corrections of the luminescence spectra of quantum dots.

A CdSe/ZnS QD-TPP nanocomposite and energy transfer from QDs to (i) TPP monomers to oxygen generating singlet oxygen (SO) and (ii) TPP aggregates cannot generate SO in chitosan solution.

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Surface channel waveguides (WGs) were fabricated in a monoclinic Tm 3 :KLuWO 4 2 crystal by femtosecond direct laser writing (fs-DLW). The WGs consisted of a half-ring cladding with diameters of 50 and 60 μm located just beneath the crystal surface. They were characterized by confocal laser microscopy and μ-Raman spectroscopy, indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In continuous-wave (CW) mode, under Ti:sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm, corresponding to a slope efficiency η of 37.8% for the 60 μm diameter WG. The WG propagation loss was 0.7 0.3 dB∕cm. The top surface of the WGs was spin-coated by a polymethyl methacrylate film containing randomly oriented (spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched (PQS) operation was achieved. The PQS 60 μm diameter WG laser generated a record output power of 150 mW at 1846.8 nm with η 34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics (energy/duration) were 105.6 nJ/98 ns at a repetition rate of 1.42 MHz.