Thermally stimulated luminescence in molecularly doped polymers

The low-temperature thermally stimulated luminescence (TSL) technique has b een applied for the first time for probing the energetic disorder of locali zed states in molecularly doped polymers (MDPs) as substituted triphenylami nes doped into poly(styrene) (PS). TSL of both the neat MDPs, as tri-p-toly lamine (TTA) and tri-p-anisylamine (TAA) doped PS, and the doubly doped pol ymers, as TTA doped PS containing small concentrations of di-p-anisyl-p-tol ylamine (DAT), was studied. The results are described in terms of the Gauss ian disorder model and the energetic relaxation of photogenerated charge ca rriers, that provide reasonable understanding of all observed trends in the TSL. Analysis of both the energetic position of the TSL peak maximum and t he shape of its high-energy wing allowed extraction of a parameter characte rizing the energetic disorder in MDPs, which agreed well with the width of the density-of-states determined from charge transport measurements. The ef fect of extrinsic trapping because of DAT on TSL properties can be reasonab ly interpreted in terms of the effective energetic disorder and the TSL res ults are in good agreement with those obtained earlier by charge transport studies.