Upconversion And Paramagnetism Of NaGdF₄:Tm³+/Yb³+by Ball Milling Method And Its Graphene Oxide Composites

Because of the unique physical and chemical properties, there is much attention to the rare earth up-conversion luminescent materials. Rare earth ions having unfilled4f-5d electron configuration which shielded outside makes the Stokes effect much stronger, and turning infrared to visible light. Therefore, up-conversion material is widely used not only in the traditional areas, but also in the field of bioscience.First, Tm3+/Yb3+doped NaGdF4luminescent powder with different ball ratios and reaction time were synthesized by ball milling method. Yb3+as the sensitizer, Tm3+as the activator, and NaGdF4as the base material. Suitable ball milling conditions has been reserached. Then, Tm3+/Yb3+doped NaGdF4luminescent powder with different Na sources and ion ratios were synthesized by ball milling method, and part of samples treated under high temperature. In all selected molar ratios of the ions, n(RE):n(Na):n(F)=1:1:4is the best. The up-conversion luminescence of the samples with this ratio is the strongest before and after high temperature treatment. After high temperature treatment, the intensity of visible light emission increases significantly. XRD results show that Tm3+and Yb3+have doped in the lattices of NaGdF4. After high temperature treatment, part of β-phase and amorphous phase turn to a-phase, which results in the crystallinity improving. TEM image shows that the samples are micro-crystal with20nm grain size, HRTEM image also shows that α-and β-phase coexist in the sample. The excitation of980nm laser hardly has effect on the paramagnetism of the samples, but the changing magnetic field has negative effect on the up-conversion luminescence of the samples.To investigate the application of up-conversion luminescence nanoparticle composites further, graphene oxide has been prepared by redox(Hummers method). The effect of oxidation time on the shape of graphene oxide was discussed briefly. Tm3+/Yb3+doped NaGdF4and graphene oxide composites were synthesized by step hydrothermal process. Up-conversion luminescence and paramagnetism of the samples were investigated. TEM image shows the shape of the composites. The result shows that dispersibility of the composites is better. Taking a new step to explore the up-conversion luminescence nanoparticles and graphene oxide composites in the biomedical field.