Effect of plasticizer and temperature on the photorefractive phase shift in fully functionalized polymethacrylates

Abstract

We have analyzed the evolution of the photorefractive phase shift and the photoconductivity in three fully functionalized photorefractive polymethacrylates with increasing temperature and plasticizer concentration. Apart from a strong increase in refractive index modulation amplitude, the polymers show a larger phase shift and photoconductivity as the measurement temperature is raised. When the measurement temperature is kept at 21 ³C, the photorefractive performance can be improved by reducing the glass transition temperature of the polymers by adding an external plasticizer. Two types of plasticizer were used. When doped with 10 or 20 wt% of an inert plasticizer (IP), diffraction ef®ciencies and gain coef®cients are improved substantially. Due to a dilution of the charge transporting groups, however, the photoconductivities and the phase shifts start to decrease when more than 10 wt% of inert plasticizer is added. A detailed analysis of this behaviour is presented. When the carbazole-functionalized copolymers with carbazole as the only charge transporting group are doped with 20 wt% of N-ethylcarbazole, the concentration of the charge transport molecules is increased. Together with the lowering of T g , this produces a larger phase shift. In all experiments, a good correlation between photoconductivity and photorefractive phase shift was observed.

Dynamics and steady-state properties of photorefractive poly(N-vinylcarbazole)-based composites sensitized with (2,4,7-trinitro-9-fluorenylidene)malononitrile in a 0–3 wt % range

“…͑5͒ the photoconductivity is split up into a charge generation factor ͑CGF͒ and a charge mobility factor ͑MF͒. 24 In the samples discussed in this paper, a similar behavior is observed upon increasing temperature. An increased photogeneration efficiency is established by promoting electron-hole separation and hampering geminate recombination through application of a larger electric field.…”

Organic Photorefractives: Mechanisms, Materials, and Applications

“…The sensitivity of the measurement can be further improved by ac phase modulation and lock-in detection . The 2BC technique in conjunction with phase shift measurements has been widely utilized to assess material parameters such as the PR trap density and electro-optic nonlinearity. ,,,,, …”

The photorefractive effect in polymeric systems

“…It was found that the larger the T e 7T g difference (T e is the temperature of the experiment), the higher the photoconductivity and the phase shift c. It was concluded that raising the temperature causes an increase in the hole path length (until trapping by deep traps), which in turn leads to an increase in c. If at a constant temperature of the experiment (T e = 21 8C) the (T e 7T g ) difference increased due to a decrease in T g caused by an increase in the concentration of plasticiser, G increased more slowly than Z. 76 This is due to a decrease in the phase shift c as a result of reduction of the mobility of charge carriers on dilution of carbazolyl transport groups with neutral plasticiser molecules. Experiments with a composite prepared from PVCz, TNF and the nonlinear optical chromophore N,N-diethyl-p-nitroaniline (EPNA) and doped with 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH) showed that the phase shift depends on the dopant concentration in a complex manner.…”