A photo-oxidation mechanism for patterning and hologram formation in conjugated polymer/glass composites

Improved diffraction efficiency was observed in holograms stored in disorde red conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylne) analogs and the glass matrices we re zirconia-organosilica xerogels. Investigation of the mechanism of hologr am formation revealed evidence of a photochromic process consisting of ligh t induced photo-oxidation (bleaching) of the embedded conjugated polymer re sulting in the formation of an absorption grating and a phase grating. Inve stigation of the hologram formation revealed that the process was oxygen de pendent. Oxygen removal increases hologram formation time by more than an o rder of magnitude and halves the total hologram efficiency. The oxygen depe ndence was also highly correlated with photobleaching of the samples and be am interaction of the writing beams. The chemical transformations upon phot obleaching were shown by infrared and Raman spectroscopy to involve chain s cission and oxidation of the polymer at the vinylic position of the conjuga ted polymer. Film preparation of the composites was optimized showing a ten fold improvement in the holographic properties compared to our previous res ults. The optimized treatment method allows for a high, > 20%, diffraction efficiency, eta, to be obtained for the 2.5-mu m-thick polymer/glass films. Light sensitivity was compared for several polymer/glass composites and wa s correlated to the absorption curves and holographic diffraction efficienc y showing that the new composites and film preparation techniques are promi sing for holographic materials sensitive in the blue and ultraviolet spectr al regions. A method of information fixing by preventing oxygen entry to th e composite film resulted in a fourfold increase of the erasure time. These findings suggest that holograms can be fixed for a long term by nonoxygen permeable coating, applied after hologram formation. (C) 2000 American Inst itute of Physics. [S0021- 8979(00)07114-0].