Holographic and photoelectric characterization of a novel photorefractive organic glass

We present a detailed study of the photoelectric as well as the holographic properties of a novel organic photorefractive glass based on triphenylamine. We studied the quantum efficiency Phi of the photogeneration of charges by means of photoinduced discharge measurements. The photoconductivity a and the charge carrier mobility mu were obtained via de photoconduction and pulsed time-of-flight experiments, respectively. The holographic characterization was performed by two-wave and degenerate four-wave mixing experiments allowing for the determination of properties such as diffraction efficiency eta, modulation of the refractive index Delta n, gain coefficient Gamma, and phase-shift phi(p) of the investigated system. The experimental data for Phi could be successfully described by the Onsager formalism with a thermalization radius of r(0) = 24 Angstrom and a primary quantum yield of Phi(0) = 40%. We evaluated the E field and temperature-dependent measurements of mu using the Bassler formalism yielding a width of the density of states of sigma = 0.13 eV and a disorder parameter Sigma = 3.6. On this basis the lifetime and the average drift length of the charge carriers could be estimated from the dc photoconduction experiments. From the photoelectric measurements we also calculated the holographic response time that matched very well to the measured response time and described the E-field dependence satisfactorily. The presented photorefractive system shows outstanding optical properties and stability with respect to degradation. We measured a gain coefficient of Gamma = 90 cm(-1), and a diffraction efficiency of eta = 27% at a response time of 30 ms for only 40-mu m-thick samples. Orientational enhancement was observed and evaluated quantitatively. To our knowledge, this work presents the first determination of each of the above quantities all in one single organic photorefractive material.