Trap states of tris-8-(hydroxyquinoline) aluminum and naphthyl-substituted benzidine derivative using thermally stimulated luminescence

The bulk trap state properties of a naphthyl-substituted benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum (Alq(3)) have been measured using thermally stimulated luminescence (TSL). The TSL spectra for both organic materials show significant trap distributions over the temperature range from 8 to 300 K. Using a general order TSL expression, the four peaks in NPB were modeled with trap states centered from 0.20 to 0.05 eV. Alq(3) has three TSL peaks over the temperature range, with the peak at 156 K modeled as a distribution of trap states from 0.25 to 0.13 eV. For both materials, the trapping mechanism involves a combination of first and second order emission. NPB and Alq(3) have trap states sufficiently deep to influence the carrier transport and recombination process in bilayer organic based light emitting. (C) 1998 American Institute of Physics.