Hexamethylenediamine-assisted hydrothermal preparation of uniform ZnO particles and their morphology-dependent photoluminescent properties

Uniform ZnO particles with ellipsoidal, needle-like and branched morphologies were prepared by a hexamethylenediamine (HMDA)-assisted hydrothermal method. The morphology of ZnO particles was simply controlled by the molar ratio of zinc nitrate to HMDA, that is, ellipsoidal particles were prepared at a [Zn2+]/[HMDA] ratio larger than 0.5, needle-like particles were prepared at a ratio of 0.1, and branched particles were prepared at a ratio of 0.02. These ZnO particles were all of well-crystallized wurtzite structure despite of their different morphologies. However, they showed interesting morphology-dependent photoluminescent properties, with the branched particles showing the most intense near-band edge ultraviolet photoluminescence (PL) and the greatest ratio of ultraviolet (UV) to visible (Vis) photoluminescence. These phenomena were discussed by considering the role of the HMDA in the growth process of ZnO particles.