Observations of the transient behaviour of electroluminescence in sublimation flakes have shown that quenching of the delayed electro-luminescence component by the carriers themselves becomes important at high currents. The results show quenching is of the same order as observed for carrier quenching of optically produced triplet excitons. No quenching was observed in thick crystals though carrier densities of the same order are present. This is presumably due to the difference in recombination zone width which may be larger in these thick crystals.

The time dependence of slow electroluminescence has been used as an experimental probe for studying the physical characteristics of the recombination region in anthracene. Under conditions where two injecting contacts are used, and neither carrier is trapped to a large extent, the recombination zone is found to occupy approximately 0.3 of the crystal volume for current densities of 10−5-10−8 amps cm−2. When forced hole injection is used, the recombination volume at low currents decreases, particularly at low temperatures. This decrease in recombination volume is discussed in terms of carrier trapping and filament formation.