Diffraction efficiency and phase stability of poly(N-vinylcarbazole)-basedphotorefractive polymer composites as a function of azo-dye concentration

Diffraction efficiency and phase stability of photorefractive polymer compo sites doped with alkylether-substituted azobenzene dyes are studied as a fu nction of dye concentration. Composites doped with 2,5-dimethyl-4-(4'-nitro phenylazo)phenyl benzyl ether (DMNPAPBE) are phase stable at all concentrat ions studied while composites doped with 2,5-dimethyl-4-(4'-nitrophenylazo) phenyl octyl ether (DMNPAPOE) exhibit a critical concentration of 47% above which the composite rapidly degrades due to dye crystallization. The glass transition temperatures T-g of DMNPAPBE- and DMNPAPOE-doped composites are approximately 67 and 57 degrees C, respectively. Diffraction efficiency me asurements of DMNPAPOE-doped composites show a threefold increase at 100 V/ mu m over DMNPAPBE-doped composites at the same dye concentration and appli ed field. (C) 2000 American Institute of Physics. [S0021- 8979(00)08620-5].