Anneal-induced transformation of phase structure, morphology and luminescence of GdPO4:Sm3+ nanomaterials synthesized by a hydrothermal method.

GdPO4·H2O:xSm3+ nanomaterials were synthesized via a facile hydrothermal method and the effects of Sm3+ concentrations and annealing temperature on the crystal structures, morphologies, and luminescent properties were studied. Doping of Sm3+ 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, GdPO4·H2O:xSm3+ displays a typical emission band with several peaks at 560, 596, and 640 nm. For the optimal sample of GdPO4·H2O:1.75%Sm3+, as the annealing temperature was increased from 300 to 800 °C, the compound transformed from GdPO4·H2O with a hexagonal symmetry to anhydrous GdPO4 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 GdPO4·H2O to anhydrous GdPO4 and the nonradiative transition was reduced due to variation in the morphology. Moreover, GdPO4·H2O:1.75%Sm3+ exhibits paramagnetic performance. In addition, the potential applications in bioimaging and MRI were investigated.