Double Injection and Electroluminescence in p-Terphenyl Single Crystals

Abstract

Double injection currents in p-terphenyl are followed by light emission from decaying singlet excitons produced by the recombining electron-hole pairs. Only one singlet exciton is produced out of ∼ 100 recombinations, the other recombinations are non-radiative. The current densities with gold and Na-Hg amalgam as hole and electron injecting contacts, respectively, approached the limit of volume-controlled currents, but were limited to well defined spots covering only 10 ³-10 ⁴ of the contacts area.

This work is a study of double injection currents and recombination radiation in p-terphenyl. Gold and Na-Hg amalgam contacts were used as hole and electron injectors, but efficient injection took place in only 10⁻³-10⁻⁴ of the contacts area. In that area the current densities approached the limit of volume-controlled currents. The recombination radiation has the same spectral distribution as the ordinary crystal fluorescence, both result from the radiative decay of singlet excitons. The major proportion of electron-hole recombinations is non-radiative. Only about one singlet exciton is produced per about 100 recombination events.