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  • 1
    Electronic Resource
    Electronic Resource
    Dipole moment differences of nonpolar dyes in polymeric matrices: Stark effect and photochemical hole burning. I (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5316-5322 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The difference of the induced dipole moments Δμind between the ground and excited state of (centro-)symmetric dye molecules (tetraphenylporphin and tetrapropylporphycene) embedded in different nonpolar and polar polymers is investigated. The technique of photochemical hole burning combined with Stark effect measurements was used to determine the values as a function of the burning frequency. For almost all systems an increase of Δμind from higher to lower optical frequencies was found. A plot of the 〈Δμind(approximately-greater-than) values measured at the absorption band maximum vs the low-temperature values of the dielectric constant ε shows a clear correlation between the dipole moment difference and the low-temperature ε values over the whole investigated range which is accessible with commercially available polymers. In order to evaluate the data the dielectric constant ε of each sample was determined in a series of separate experiments as a function of frequency and temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463791
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  • 2
    Electronic Resource
    Electronic Resource
    Stochastic theory of inhomogeneous spectroscopic line shapes reinvestigated (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5574-5581 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The inhomogeneous distribution of an ensemble of absorption or fluorescence lines in a disordered matrix can be described by a stochastic theory whose fundamental ideas have been known for many decades. Due to its very general principles, it can be applied to inhomogeneous effects of many different types, including inhomogeneous broadening in optical spectra and spectral diffusion in magnetic resonance and line-narrowed optical experiments. In the case of absorption and luminescence bands, it is often convenient to perform the so-called Gaussian approximation, which is valid in the limit that the density of the matrix molecules is high compared to the reciprocal volume of the cavity containing the absorbing or fluorescing center; this leads to the analytical result that the line shapes of the optical bands are Gaussian. Numerical calculations beyond the Gaussian approximation help to clarify its physical meaning and to interpret inhomogeneous bandwidths from a statistical point of view. Three types of intermolecular potentials are examined, namely, dipole–dipole, van der Waals, and a modified Lennard-Jones-type interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461631
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  • 3
    Electronic Resource
    Electronic Resource
    Pressure effects on hole-burning spectra in glasses: Calculation beyond the Gaussian approximation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 846-853 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In a recent publication, Laird and Skinner [J. Chem. Phys. 90, 3274 (1990)] proposed a microscopic statistical theory describing the effects of external hydrostatic pressure on hole-burning spectra of impurity molecules in amorphous solids. Using the so-called Gaussian approximation, which is valid in the limit that the density of the solvent molecules is high, the theory predicts the pressure kernel of a hole spectrum as well as the shape of the inhomogeneous band to be characterized by Gaussian profiles. Whereas the maximum position of the kernel increases from lower to higher solvent shift values in the inhomogeneous distribution, its width is constant. Numerical calculations performed without this approximation, however, show that for the data of poly(ethylene) and poly(styrene) doped with free-base phthalocyanine, not only the pressure shift but also the pressure broadening of hole-burning spectra increases from the blue to the red edge of the absorption band. Moreover, the hole spectra are predicted to become asymmetric when the sample is exposed to hydrostatic pressure. These deviations from the results of the Gaussian approximation are distinctly more pronounced than the deviations of the inhomogeneous band shapes from Gaussian profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461092
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  • 4
    Electronic Resource
    Electronic Resource
    Wavelength dependence of external-field effects on persistent hole-burning spectra: Analytical approximation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7-11 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: External perturbations such as, for instance, hydrostatic pressure in general give rise to a shift and a concomitant broadening of persistent hole-burning spectra. The magnitude of both effects usually varies with the optical frequency in the inhomogeneous absorption band. Within the framework of a stochastic theory of dye-matrix interaction, an extended Gaussian approximation is used to derive general analytical expressions for the variation of both the shift and the broadening parameter. The results are compared with numerical calculations. Furthermore, the obtained expressions are generalized to take correlations between the matrix molecules into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465706
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  • 5
    Electronic Resource
    Electronic Resource
    Photoluminescence frequency up-conversion in GaSe single crystals as studied by confocal microscopy (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1081-1086 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence spectrum of melt-grown GaSe single crystals was investigated with a confocal Raman microscope equipped with a HeNe laser. Three luminescence bands of different intensity were observed, which are mainly located to the blue of the laser line. The luminescence signals show a quadratic dependence on excitation intensity. The effect is interpreted as second-harmonic generation in the strongly optically nonlinear material followed by the excitation of electrons into the conduction band and luminescence emission from direct-gap Wannier excitons. The relative intensities of the three luminescence peaks exhibit a spatial variation on the crystal surface, which was mapped with the confocal microscope. Possible explanations of this effect are discussed. In an external electric field the luminescence shows a strong increase and a quadratic redshift, whose magnitude is consistent with the Franz–Keldysh mechanism. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421215
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  • 6
    Electronic Resource
    Electronic Resource
    Fine structure in the χ(2) signals of inorganic-organic nanocomposites (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2709-2711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of organically modified ceramics with nonlinear-optical-active chromophores produced in a sol-gel process exhibit Maker fringe signals which are superimposed by a periodic fine structure. The fine structure is shown to be due to Fabry–Perot resonances of the second-harmonic light which are stronger as compared to the amplitude corresponding to the regular Fresnel surface reflectivity by one to two orders of magnitude. The effect which is also observed on unpoled samples is tentatively ascribed to an accumulation and partial spontaneous orientation of the chromophores at the film surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356201
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  • 7
    Electronic Resource
    Electronic Resource
    Optical detection of injected charge carriers in polymer films via Stark spectroscopy (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4226-4230 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Persistent spectral holes in a thin film of poly(vinyl butyral) doped with a substituted Zn-tetrabenzoporphin show irreversible broadening effects when high electric field strengths (some hundred kV/cm) are applied. A small field (a few kV/cm) with opposite sign, however, cancels the broadening almost completely and restores the original hole width. Therefore, the broadening is not due to field-induced spectral diffusion, but to permanent electric fields generated in the sample. Our interpretation in terms of electret theory shows that the source of these fields is charges near the surface of the sample, which are injected from the electrodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339094
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  • 8
    Electronic Resource
    Electronic Resource
    Kramers–Kronig relations in nonlinear optics (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2938-2939 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the vicinity of the phase-matching angle of second-order nonlinear optical crystals, the fundamental light wave experiences an intensity-dependent phase shift which is connected with the effective attenuation due to second-harmonic generation. It is demonstrated that in the limit of weak pump depletion, the Kramers–Kronig relations can be used to derive a simple analytical expression for the phase shift as a function of the phase-mismatch angle. For certain mismatch angles, a large phase shift occurs without any attenuation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114235
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  • 9
    Electronic Resource
    Electronic Resource
    Phase-matched second-harmonic generation at 789.5 nm in a GaSe crystal (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 731-733 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phase-matched second-harmonic generation in the highly χ(2)-active layered semiconductor GaSe is demonstrated in the near-infrared frequency region. Due to the high indices of refraction, the internal phase-matching angle of about 30° is beyond the critical angle of total reflection for a z-cut crystal. This problem is overcome by sandwiching the crystal between two half-cylindrical glass rods, which leads to a shift of the critical angle to larger values. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117873
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  • 10
    Electronic Resource
    Electronic Resource
    Relation between hole-burning parameters and molecular parameters: free-base phthalocyanine in polymer hosts (1986)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 90 (1986), S. 1264-1270 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100398a013
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