Phase transitions in thermally annealed films of Alq3

Organic light emitting devices have improved greatly in recent years, so they are now widely used in displays and lighting. Annealing processes in different atmospheres strongly affect their performance, as when the active material is the small molecule Alq3. In particular, a significant increase in the photoluminescence is observed in thin films of this molecule between 150 and 180 °C, before physical destruction of the films sets in at higher temperatures. This phenomenon is attributed to a phase transition to a novel morphological aggregation of the molecules in the film, which has yielded a much improved optical material for luminescence applications, and seems to apply to other molecules as well.