Photostimulated optical SHG in BEDO‐TTF polyiodide/polycarbonate composites

Abstract

Measurements of photoinduced optical second-harmonic generation (PISHG) for the bis(ethylenedioxy)tetrathiofulvalene (BEDO-TTF)/Iodine complex in a polycarbonate matrix were performed. Two kinds of samples were studied: as-obtained, grey-violet material, showing a metal-like temperature dependence of conductivity down to liquid helium temperature (system 1), and electrochemically decoloured, transparent (slightly grey) material, showing metallic conductivity down to about 30 K and semiconductive properties below this temperature (system 2). An increase in the PISHG signal with decreasing temperature was observed below 10 K for both specimens. In the temperature range 40-88 K, an increase then a decrease in PISHG with increasing temperature was observed for specimen 2, while practically no PISHG signal was recorded for sample 1. The dependences obtained indicate unambiguously the essential influence of the BEDO-TTF(l) dopant on the PISHG of polycarbonate composites. Simultaneously, competition was demonstrated between the optical second- and third-harmonic signals at photoinducing fluxes near 1015 photons cm−2. A strong increase in the PISHG signal at low temperatures was observed for both systems (below 11 K for sample 2 and below 7 K for sample 1). In the temperature range 40-88 K a maximum of the PISHG was observed only for specimen 2. At higher temperatures the intensity of the PISHG was very low in both kinds of samples.