The monolayer characteristics of nonamphiphilic 9-phenylcarbazole (PCB) mixed with stearic acid (SA) have been studied at the air-water interface. Miscibility studies as well as the Gibbs free energy measurements indicate a repulsive type of interaction between the two component molecules in the mixture that results in the formation of aggregates of PCB. Spectroscopic studies reveal that PCB in mixed LB films is highly fluorescent and forms organized aggregates. The high-energy phosphorescence emission bands in an ethanol-glass matrix are quenched whereas the low-energy bands are manifested in the LB films. This has been attributed to aggregation-induced reabsorption, which is unusual for singlet-triplet transitions. The large difference in phosphorescence lifetime in two different microenvironments supports the formation of small microcrystalline domains in LB films at 77 K. Scanning electron micrographs clearly demonstrate the existence of such aggregates in the films, and the size of the aggregates is in the range 0.1-4 mu m.