Carbon nanotube-containing photorefractive polymer composites operating at telecommunication wavelengths

Abstract

The field dependences of photocurrent, the two-beam coupling gain coefficient, and the grating formation time constant in polymer composites made from polyvinylcarbazole (PVK) and single-wall carbon nanotubes (SWNTs) were measured under the conditions of one-photon SWNT excitation with continuous laser radiation at a wavelength of 1550 nm. Carbon nanotubes are responsible for optical electronic absorption up to ∼2000 nm in this composite. The dependence of the quantum efficiency of generation of mobile charge carriers on the electric field E ₀ as determined from the photocurrent coincides with the curves calculated via the Onsager equation expanded to the (E ₀)⁴ term, at a quantum yield of thermalized electron-hole pairs of η₀ = 0.07 and a charge separation distance in the pair of r ₀ = 9.8 Å. An analysis of the photorefractive characteristics showed that the admixture of fullerene C₆₀ in an amount of 3 wt % to the PVK composite with 0.26 wt % SWNT leads to a twofold increase in the beam-coupling gain coefficient. In the PVK-matrix composite containing 0.26 wt % SWNT and 3 wt % C₆₀, the beam-coupling gain coefficient Γ of a 1550-nm laser beam and the net gain Γ-α are 32 and ∼27 cm⁻¹, respectively, at a constant field of E ₀ = 140 V/μm.