Photorefractive Properties of Poly(N-vinyl carbazole)-Based Composites for High-Speed Applications

Abstract

The photorefractive properties of polymer composites based on poly(N-vinylcarbazole), doped with the sensitizer C 60 , the plasticizer butyl benzyl phthalate, and two series of chromophores are presented. The influence of the structure and the oxidation potential of the chromophore on the photorefractive properties is discussed. These materials show promise for video-rate optical processing applications, since they exhibit fast response times (beamcoupling growth times, τ g , as small as 60 ms at 50 V/µm applied field and 200 mW/cm 2 intensity and τ g as small as 5 ms at 100 V/µm and 1 W/cm 2 ).

Photophysical and Redox NIR‐Sensitivity Enhancement in Photorefractive Polymer Composites

“…[11] was added as the EO component for all composites investigated. Azo dyes were used rather than chromophores with higher PR figures of merit [6,9,12] because they have an (irreversible) oxidation potential that is higher than that of the investigated hole conductors. In this way, the chromophores were excluded from participating directly in the charge generation, redistribution, and trapping processes, which allowed us to compare different sensitizer ± hole conductor systems without chromophore interaction.…”

Materials Design and Physics of Organic Photorefractive Systems

“…This has recently been investigated independently by Moerner and co-workers [46] and by Kippelen and co-workers. [117] Using different substituents, they were able to tune the HOMO level of their chromophores with respect to that of the PVK host.…”

“…In some references, 2BC dynamics was used to evaluate the response time of the material, [37,46] since it is a characteristic measure for applications based on 2BC. This procedure, however, is not suited for a comparison with other materials, because 2BC dynamics are governed by both the evolution of the phase and of the refractive index modulation Dn, whereas fast DFWM dynamics are only sensitive to the latter, which allows for an easier interpretation of the underlying physical processes.…”

“…[32,36,46] A significant disadvantage, however, is their lack of compositional stability: The highly polar chromophores, which are mobile in low T g systems, tend to crystallize over a time span between hours and a couple of months in the apolar photoconductive host material. [52,53] Therefore, the issue of limited shelf lifetime has to be addressed, for example by using eutectic [53] and isomeric [54] dye mixtures or by improving the compatibility of the components.…”

“…[37,46] Consequently, the important parameters to be optimized would be the internal quantum efficiency for charge-carrier generation F cg and the hole mobility m. The number of available sensitizers is rather limited, hence, there have been only few attempts to optimize F cg . [105] The hole mobility m can be tuned by both the choice of the photoconductor and of the chromophore, which may itself act as a trap.…”