Photoconductivity of Polyalkanetherimide Composite Films Containing Rubrene Microcrystals and Magnetic Nanoparticles

Abstract

The effect a weak magnetic field in the hyperfine (HFI) range (Н < 1 kG) has on the yield of luminescence, excitonic photoconductivity (EPC) (spin magnetic effects, or SMEs), and the drop in SMEs upon adding magnetic nanoparticles (MNP) with lowered Curie points (40–60°C) (the SME decrement) is determined for composite polymeric films containing rubrene microcrystals at room temperature. Investigation of the photocurrent kinetics in real time scales shows that in addition to the non-inertial EPC (with times shorter than 1 s), there is a weaker inertial (time, 23.5 min) secondary thermostimulated current (TSC) caused by the capture of photo-generated current carriers by deep centers with subsequent thermal release, and lacking sensitivity to the magnetic field. It is determined that the centers of capture are MNPs with considerable affinity toward electrons. The formation of a supply of long-lived MNP−s (captured carriers) results in a marked decrement of SMEs on the EPC. A peak of MNP–s (nanoparticles with captured electrons), formed upon both the dark electron transition and the capture of photoelectrons, is observed at Н = 2830–2900 G in the spectra of the ferromagnetic resonance for the composite films. It is concluded that such a notable decrement of SMEs on the EPC is associated with the substantial change in MNP magnetic characteristics upon the capture of electrons, as was observed earlier for interaction with excitons (an indirect mechanism of interaction).