The photorefractive properties of poly(N-vinylcarbazole) doped with a variety of nonlinear optical chromophores and sensitizing agents are surveyed. Steady-state diffraction efficiencies of greater than 10(-3) and two-beam coupling gain exceeding the absorption loss are found in six materials combinations. The effect of the structure of the nonlinear optical chromophore on the photorefractive properties is discussed.
A study is made of self-trapped excitons in AgCl using cw and pulsed EPR techniques at 95 GHz. This type of spectroscopy, owing to its superior resolution and its time-resolved character, allows us to obtain detailed information about the properties of these excitons. The singlet-triplet splitting is determined with great accuracy and the result confirms that the exchange interaction, present between the electron and the hole making up the exciton, is very small. From a measurement of the dynamic properties of the exciton in the triplet state it appears that a tunneling process takes place between the different Jahn-Teller distorted configurations of the (AgC16) complex at a rate of 10' s ' at temperatures as low as 1.2 K.
The molecularly doped polymer system polyvinylcarbazole:Lophine 1:2,4,7-trinitro-9-fluorenone, which is both photoconductive and optically nonlinear, forms a grating whose diffraction efficiency is strongly dependent on the externally applied electric field. Two-beam coupling measurements show no energy transfer between the beams and grating translation measurements and reveal an index of refraction grating that is not phase shifted relative to the light intensity pattern at any value of the externally applied field. These results lead to the conclusion that, even though diffraction is field dependent, the grating is not photorefractive in origin. This illustrates the importance of two-beam coupling measurements for characterization of potentially photorefractive polymers. A possible origin of the nonphotorefractive grating based on quadratic electroabsorption is discussed.
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