Controlled Synthesis Of Heterovalent Ion Doped Rare Earth Fluoride And Vanadate Nanocrystals And Application In Heavy Metal Ion Detection

Rare earth nanomaterials are deeply studied by researchers all over the world due to their unique magnetic,electrical,mechanical and optical properties.In particular,its unique optical properties,such as sharp-line emission bandwidth,low background fluorescence,photochemical stability,and almost no damage to biological tissues,make it extremely important in various fields such as solar cells and biological imaging.However,the intrinsic defect of low fluorescence efficiency of rare earth materials limits the further practical application of these materials.There are many ways to improve the luminous efficiency of rare earth nanomaterials and realize the enhanced regulation of luminous intensity.Notably,host lattice doping is an effective way to enhance rare-earth luminescence.In this study,solvothermal and hydrothermal methods were used to find that by introducing heterovalent ions（non-rare earth metal ions）doping,the morphology change and luminescence intensity of rare earth nanoparticles could be effectively controlled,and it was used in the detection of heavy metal ions.The main research results of this paper are as follows:（1）Hexagonal Yb³⁺/Er³⁺:Na Gd F₄nanocrystals codoped with Sn⁴⁺ions were produced via an adjustive solvothermal approach.Simultaneous morphology regulation and intensified upconversion（UC）luminescence of Yb³⁺/Er³⁺:Na Gd F₄nanocrystals were achieved through Sn⁴⁺ions doping.Upon introducing Sn⁴⁺ions into the Na Gd F₄host,a part of the nanocrystals were converted to nanocubes.By optimizing the Sn⁴⁺ions doping content to 40 mol%,UC luminescence intensity of the green and red emissions were intensified by 21 and 31 times,respectively.Moreover,the possible mechanisms for morphology transformation and UC luminescence enhancement of Sn⁴⁺-doped Yb³⁺/Er³⁺:Na Gd F₄nanocrystals were discussed elaborately.Additionally,in contrast to the sample fabricated by co-precipitation method,the result indicated that the UC luminescence intensity with 40 mol%Sn⁴⁺ions doping was about2.5 times higher than the former one.（2）Two-phase Ca²⁺-doped La VO₄:Eu³⁺nanocrystals were prepared through a hydrothermal method with the help of SOD CITR and EDTA surfactants.The phase and morphology of the products were characterized by XRD and TEM,and the fluorescence performances were also recorded.The results indicated that Ca²⁺ions were doped into the La VO₄:Eu³⁺host lattice,impeding the aggregation of the nanocrystals and enhancing the luminescence intensity.The morphology transformation process and luminescence enhancement were systematacially investigated.The fluorescence intensity of the two selected samples could be completely quenched by Fe³⁺ions without the disturbance of other ions,with the mechanism being due to the adsorption of Fe³⁺ions onto the grains and a subsequent energy transfer from Eu³⁺to Fe³⁺.Therefore,the present two Ca²⁺-doped La VO₄:Eu³⁺samples can be applied as appropriate candidates for detecting Fe³⁺ions with agility and sensitivity in aqueous solution.（3）The two-phase Sr²⁺-doped La VO₄:Eu³⁺nanomaterials were constructed through a facile hydrothermal approach.The crystal phase,morphology as well as optical performance were systematically investigated in detail.The results manifested that the dopant Sr²⁺ions were doped into the host lattice,restricting the growth of grain and elevating the fluorescence intensity simultaneously.Besides,the morphology evolution process and optical performance modulation were also fully analysed.The fluorescence quenching was attributed to the adsorption of Cu²⁺ions onto the matrix surface by electrostatic attraction and succeeding energy transfer from Eu³⁺to Cu²⁺.Moreover,the materials displayed excellent detecting ability for Cu²⁺with high selectivity and sensitivity（0.514μM and 0.476μM for both two-phase samples）.Consequently,this material could be applied as a promising candidate for Cu²⁺detecting due to good reusability and facile synthesis.