Thermally Stimulated Luminescence in Molecularly Doped Polymers

Abstract

The low-temperature thermally stimulated luminescence (TSL) technique has been applied for the first time for probing the energetic disorder of localized states in molecularly doped polymers (MDPs) as substituted triphenylamines doped into poly(styrene) (PS). TSL of both the neat MDPs, as tri-p-tolylamine (TTA) and tri-p-anisylamine (TAA) doped PS, and the doubly doped polymers, as TTA doped PS containing small concentrations of di-p-anisyl-p-tolylamine (DAT), was studied. The results are described in terms of the Gaussian disorder model and the energetic relaxation of photogenerated charge carriers, that provide reasonable understanding of all observed trends in the TSL. Analysis of both the energetic position of the TSL peak maximum and the shape of its high-energy wing allowed extraction of a parameter characterizing the energetic disorder in MDPs, which agreed well with the width of the density-of-states determined from charge transport measurements. The effect of extrinsic trapping because of DAT on TSL properties can be reasonably interpreted in terms of the effective energetic disorder and the TSL results are in good agreement with those obtained earlier by charge transport studies.