Abstract
Spherical amorphous Alq 3 nanoparticles of various diameters could be obtained under a cold trap by adjusting the He pressure in a vapour condensation system. The growth of nanoparticles is related to the collisions between the sublimed Alq 3 molecules and gaseous He atoms. Both the diameter and size distribution of nanoparticles decrease with a decreased He pressure. Smaller nanoparticles have no spectral blue shift but lead to stronger photoluminescence because of the increased optical absorption that results from the larger specific surface area. With a larger surface-to-volume ratio, smaller nanoparticles exhibit higher surface energy and require less enthalpy for phase transition, resulting in decreased temperatures for α-δ phase and melting transitions. © IOP Publishing Ltd.