Down- and up-conversion photoluminescence, cathodoluminescence and paramagnetic properties of NaGdF4 : Yb3+,Er3+ submicron disks assembled from primary nanocrystals

NaGdF4 : Yb3+,Er3+ submicron disks have been synthesized at a relatively low temperature in aqueous solution with citric acid as the structure-directing agent. The structure, luminescence, and magnetic properties of the synthesized materials have been characterized by a variety of techniques. The as-prepared NaGdF4 : Yb3+, Er3+ has hexagonal structure, and is mainly composed of submicron disks with a diameter of around 870 nm and a thickness of about 420 nm. Citrate groups selectively bonded to a certain crystal surface of the nanocrystals probably provide the driving force that makes primary particles assemble into submicron disks. The phase structure of these submicron disks is affected by the annealing temperature, while the disk morphology could be essentially preserved even when annealed at high temperatures. The annealed submicron disks exhibit prominent visible emission with different excitation sources, including ultraviolet light, low-voltage electron beam and near-infrared laser. In addition, these disks exhibit paramagnetic features with the mass magnetic susceptibility value of 9.82 x 10(-5) emu/g.Oe at room temperature. These multifunctional disks would have potential in applications as building blocks for many functional devices such as solid-state lasers, lighting and displays, magnetic resonance imaging and so on.