AFM studies on formation of new phase responsible for enhanced photoluminescence in light-emitting small molecular thin films

Tris(8-hydroxyquinoline) metal complex (AlQ3) is a widely used light-emitting material in organic light-emitting devices (OLEDs). The environmental stability is still a major problem with OLEDs and needs further improvements. In this report, we examine the optical properties of the thin films of this material and the effect of environment on it. The annealing in different ambients were done with the aim to understand the physical phenomenon involved in AlQ3 thin films. An enhanced photoluminescence intensity is observed for the samples annealed in oxygen near 100 °C. Sudden change in roughness which may be as a consequence of change in surface morphology due to phase change and fraction of new phase is estimated by phase images taken by Atomic Force Microscopy (AFM). The enhanced photoluminescence is understood in terms of formation of a new phase.