Theory of the kinetics of luminescence and its temperature dependence for Ag nanoclusters dispersed in a glass host.

We have measured and fitted the kinetics of luminescence of Ag nanoclusters homogeneously dispersed within the bulk of an oxyfluoride glass, with various sample temperatures. The balance equations for the populations of the excited singlet and triplet states of the Ag nanoclusters are proposed and used in this fitting while taking into account inter-system crossing between the singlet and triplet states and their wavelength dependent spontaneous decay to the ground singlet state. The involved energy barriers and rate constants and spontaneous emission cross-sections for the excited singlet and triplet states are evaluated.

Experiment and theoretical modeling of the luminescence of silver nanoclusters dispersed in oxyfluoride glass.

Density functional theory (DFT) and complete active space perturbation theory (CASPT2) have been applied for modeling the configuration, charge, energy states, and spin of luminescent Ag nanoclusters dispersed within the bulk of oxyfluoride glass host. The excitation spectra of luminescence of the Ag nanoclusters have been measured and simulated by means of the DFT and CASPT2. Electron spin resonance spectra have been recorded and suggest diamagnetic state of Ag nanoclusters. The silver nanoclusters have been argued to consist mostly of pairs of Ag(2) (+) dimers, or Ag(4) (2+) tetramers, with different extent of distortion along the tetramer diagonal. The sites for the Ag nanoclusters have been suggested where the pairs of Ag ions substitute onto metal and hole cation sites and are surrounded by fluorine ions within a fluorite-type lattice.

Diffuse reflectance spectroscopy characterization of hemoglobin and intralipid solutions: in vitro measurements with continuous variation of absorption and scattering.

Absorption and scattering processes in biological tissues are studied through reflectance spectroscopy in tissue-like phantoms. For this aim, an experimental setup is designed to independently control both processes in hemoglobin and intralipid solutions. From the analysis of the obtained spectra, a simple empirical power law equation is found that relates absorbance with scattering and absorption coefficients. This relationship includes three wavelength independent parameters, which can be determined geometry from in vitro measurements for each particular optical optode. The dependence of the optical path length on the absorption and scattering coefficients is also analyzed, and estimations of this parameter for physiological conditions are presented. This study is useful to better understand the scattering phenomena in biological tissue, and to obtain absolute concentration of absorber particles when a homogeneous medium can be assumed.

In vivo spectroscopy: a novel approach for simultaneously estimating nitric oxide and hemodynamic parameters in the rat brain.

Nitric oxide (NO) is a versatile molecule involved in a wide range of biological processes. Under physiological conditions, NO reacts with oxyhemoglobin (OxyHb) to form methemoglobin (MetHb) at a very high rate. Microdialysis studies have used hemoglobin solutions as a trapping method to quantify NO in vivo. The methodology described here uses the microcapillary network with endogenous OxyHb instead of microdialysis probe with exogenous OxyHb for monitoring MetHb as an indirect index of NO levels by in vivo spectroscopy using optical fibers. This new method has been validated in rat cerebral cortex by the infusion of NO or well-known drug-induced changes in NO concentration (NMDA agonists and a NO-synthase inhibitor) and by comparing results with simultaneous voltammetric recordings. Results indicate that this spectroscopy technique is able to record large increases in MetHb levels and to detect reductions of its basal levels. In addition, data show that similar changes and kinetics can be observed with both techniques. Thus, intravascular MetHb can be used as an indirect index of NO levels. It is proposed that in vivo spectroscopy may be a useful tool to gain insight into the roles of NO in hemodynamic parameters and in other physiological processes such as the regulation of the mitochondrial respiratory chain.

Synthesis, X-ray structure, polarized optical spectra and DFT theoretical calculations of two new organic-inorganic hybrid fluoromanganates(III): (bpaH2)[MnF4(H2O)2]2 and (bpeH2)[MnF4(H2O)2]2.

Two new fluoromanganates(III) of 1,2-bis(4-pyridyl)ethane (bpa) and trans-1,2-bis(4-pyridyl)ethylene (bpe), LH(2)[MnF(4)(H(2)O)(2)](2) (L = bpa or bpe), have been prepared and their structure have been solved by single-crystal X-ray diffraction. The [MnF(4)(H(2)O)(2)](-) anion displays an octahedral geometry with a strong Jahn-Teller tetragonal distortion along the H(2)O-Mn-OH(2) axis. The equatorial metal-ligand distances (Mn-F 1.827(1)-1.859(2) A) are shorter than the axial ones (Mn-O 2.203(2)-2.234(2) A). Three polarized absorption bands at 22,500, 18,300 and 14,500 cm(-1) are observed in the optical spectra of (bpaH(2))[MnF(4)(H(2)O)(2)](2). Finally, we present theoretical calculations on the equilibrium bond distances as well as the crystal-field electron structure using density functional methods. The calculated Mn-F bond distances (1.85 A) are in agreement with the experimental data but the obtained Mn-O distances (2.53-2.56 A) are higher than the experimental one as usually found in similar Jahn-Teller distorted systems. The calculated d-d transition energies are compared with experimental energies derived from the optical spectra. The variation of the HOMO energy and transition energies against the Mn-O distance is also shown.