Anneal-induced transformation of phase structure, morphology and luminescence of GdPO:Sm nanomaterials synthesized by a hydrothermal method.

GdPO·HO:xSm nanomaterials were synthesized via a facile hydrothermal method and the effects of Sm concentrations and annealing temperature on the crystal structures, morphologies, and luminescent properties were studied. Doping of Sm exhibited no obvious influence on the crystal structure for the non-annealed samples, which possessed a hexagonal structure and a nanorod shape. Under 401 nm excitation, GdPO·HO:xSm displays a typical emission band with several peaks at 560, 596, and 640 nm. For the optimal sample of GdPO·HO:1.75%Sm, as the annealing temperature was increased from 300 to 800 °C, the compound transformed from GdPO·HO with a hexagonal symmetry to anhydrous GdPO with a monoclinic symmetry, and the morphologies varied from nanorods to ellipse-like shapes. The length of the nanorods was about 200 nm, whereas the ellipse-like shape exhibited a length of 100 nm and a diameter of 50 nm. The luminescent intensity was enhanced with the increased annealing temperature because the compound transformed from GdPO·HO to anhydrous GdPO and the nonradiative transition was reduced due to variation in the morphology. Moreover, GdPO·HO:1.75%Sm exhibits paramagnetic performance. In addition, the potential applications in bioimaging and MRI were investigated.