Multiway analysis through direct excitation-emission matrix imaging.

In this work, a direct in-flow methodology for the acquisition of excitation-emission fluorescence matrices is presented. The system is particularly suited for measurements in the order of tens of milliseconds. A light source operated in continuous mode is dispersed through a grating and focused onto a square-section capillary. Under the spatially resolved excitation, the emission is collected, dispersed through a second grating and further focused onto a CCD array sensor. To allow the wavelength accuracy, a spectral calibration was performed registering the scattering signal of a dispersive element using interference filters ranging from 340 nm to 740 nm. The theoretical performance of the method was analyzed and second-order data obtained for different analyte mixtures are presented and discussed. PARAFAC was applied to evaluate the trilinearity of the obtained data. Mathematical evaluation by means of the criterion of similarity corroborates the agreement between experimental pure spectra and spectral profiles retrieved from PARAFAC. Moreover, the feasibility of the spectrometer to obtain second-order data for analyses with quantitative aims was demonstrated. Finally, fast data acquisition was proved by monitoring a chromatographic analysis of dye mixtures for the generation of third-order LC-EEM data. Here, an improvement in the resolution of the different instrumental modes was demonstrated.

CeIV -GdIII Mixed Oxides as Hosts for ErIII -Based Upconversion Phosphors.

A family of ErIII and ErIII -YbIII based nanophosphors, hosted in monophasic oxidic CeIV -GdIII binary solid solutions, was prepared. The samples were formulated with a constant ErIII content as the activator, with the eventual addition of YbIII as a sensitizer. The amorphous Ce0.94-x Gdx Er0.06 (OH)CO3 ⋅H2 O and Ce0.94-x Gdx Er0.05 Yb0.01 (OH)CO3 ⋅H2 O precursors were prepared by following the urea method to obtain monodispersed spheres of tunable size ranging from 30 to 450 nm. After being decomposed at 1273 K under an atmosphere of air, the precursors of 200 nm in diameter evolved into monophasic polycrystalline particles preserving the parent shape and size. The role of the composition of the binary matrices in the emission properties was evaluated for two different excitation wavelengths (976 nm and 780 nm) based on the upconversion (UC) emission spectra and their dependence on the incident power. The yield of the UC process is discussed in the framework of established and novel alternative mechanisms. The number of vacancies and mainly the symmetry of the ErIII environment play major roles in the deactivation pathways of the UC emission mechanisms. However, the colours obtained by employing bare CeIV or GdIII hosts are preserved in the related monophasic CeIV -rich or GdIII -rich binary hosts.

Rich stochastic dynamics of co-doped Er:Yb fluorescence upconversion nanoparticles in the presence of thermal, non-conservative, harmonic and optical forces.

The stochastic dynamics of individual co-doped Er:Yb upconversion nanoparticles (UCNP) were investigated from experiments and simulations. The UCNP were characterized by high-resolution scanning electron microscopy, dynamic light scattering, and zeta potential measurements. Single UCNP measurements were performed by fluorescence upconversion micro-spectroscopy and optical trapping. The mean-square displacement (MSD) from single UCNP exhibited a time-dependent diffusion coefficient which was compared with Brownian dynamics simulations of a viscoelastic model of harmonically bound spheres. Experimental time-dependent two-dimensional trajectories of individual UCNP revealed correlated two-dimensional nanoparticle motion. The measurements were compared with stochastic trajectories calculated in the presence of a non-conservative rotational force field. Overall, the complex interplay of UCNP adhesion, thermal fluctuations and optical forces led to a rich stochastic behavior of these nanoparticles.