RESUMO
The spectral properties of the emission of a colloidal suspension of titanium dioxide particles in Rhodamine 640 perchlorate were studied systematically. The particle density rho, the dye concentration c, and the energy of the pump pulse were varied over several orders of magnitude; the dependence of the spectra on these three parameters is discussed. We discovered a strong correlation between the particle density and the dye concentration. The amplification by stimulated emission was found to be strongest when the absorption length l(a) and the mean-free-path length l(*) had approximately the same magnitude. The respective l(*) values were determined by a pulsed transmission experiment.
RESUMO
Molecular electronic states are extremely sensitive to changes in their environment. Therefore, by inserting probe molecules into a host material and monitoring the ensuing changes in the widths and spectral positions of the electronic absorption bands, interactions of probe and host molecules can be studied. A statistical mechanical model used to analyze these data can also be employed to extract from pressure-induced changes of the band shape information about the local environment of the probe molecule. Dye-doped solid rare gases are ideal model systems to test the basic assumptions of the statistical model, revealing its potential and limitations.
Assuntos
Gases Nobres/química , Modelos Químicos , PressãoRESUMO
A simple reflection method that is based on ellipsometry and the electro-optic Pockels and Kerr effects is adapted for the determination of the electro-optic susceptibilities χ((2))(-ω; 0,ω) and χ((3))(-χ; 0, 0, ω). Measurements were made on materials that consist of centrosymmetric molecules like the polydiacetylene poly-(butoxycarbonylmethyleneurethane) (poly-4BCMU) and on a noncentrosymmetric poled sidechain polymer that contains dimethylaminonitrostilbene (ANS). The results are compared with those acquired by other methods (e.g., second-harmonic generation, third-harmonic generation, and degenerate four-wave mixing). Large differences occur, especially for the χ((3)) values. The effects of mechanical strains from electrostatic forces and from the field-dependent change of the absorption are discussed.
RESUMO
A photochromic reaction in Zn-tetrabenzoporphyrine-doped poly(methyl methacrylate) was investigated at room temperature. A one-quantum thermoreversible photoreaction could be initiated in the sample with 633-nm He-Ne laser irradiation. The photoreaction quantum yield depended strongly on the concentration of an additional electron acceptor. The changes of the refractive index were also measured.