Ionic Liquid-Assisted Synthesis And Multifuctional Properties Of Rare-Earth Oxyfluorides Luminescent Materials

Rare-earth oxyfluoride luminescent materials are widely used in field emission display devices,anti-counterfeiting technology,biological imaging,magnetic resonance imaging and other fields because of their merits,such as low phonon energy,high refractive index of fluoride and high chemical and thermal stability of oxide.At present,organic compounds are usually used as solvents and templates in the synthesis of micro/nano rare-earth oxyfluorides,which are mostly complex and have environmental pollution.,which limit their practical application.Therefore,exploring simple and green synthesis methods has become the goal of researchers.Ionic liquids are emerging as a vital part of chemistry and materials science on account of their unique properties.Ionic liquids can play the role as adjusting the crystal phase,regulating the morphology and size,and adjusting hydrophilicity or hydrophobicity for the products.In“all-in-one”systems,ionic liquids can act as reactants,solvents,surfactants,templates and capping agents at the same time,which can greatly simplify the reaction process,and have been utilized as green alternatives to conventional reagents.In this thesis,rare-earth oxyfluorides with different morphologies and structures were prepared by ionic liquid-assisted hydrothermal method and ionic liquid-assisted coprecipitate method using 1-octyl-3-methylimidazole-tetrafluoroborate（[Omim]BF₄）as solvent,crystal phase and morphology control agent and reaction reagent.The nucleation,growth and assembly behaviors in ionic liquid system were studied,and a series of multifunctional rare-earth oxyfluorides were prepared.The main research results are as follows:1.Gd OF:Eu³⁺and Gd OF:Yb³⁺,Er³⁺luminescent materials with high thermal stability and paramagnetic properties were synthesized by ionic liquid-assisted hydrothermal method and calcination process.By adjusting the p H value of the initial solution,various morphologies such as nanodisks,nanorods aggregates,nanoneedles and stubby nanorods were obtained.The effects of calcination process,calcination temperature and p H value on the down/up conversion luminescent properties of Gd OF:Eu³⁺and Gd OF:Yb³⁺,Er³⁺luminescent materials were discussed from various perspectives.Temperature-dependent emission spectra and the static magnetic properties characterization indicate that Gd OF:Eu³⁺and Gd OF:Yb³⁺,Er³⁺luminescent materials possess high thermal stability and paramagnetism and have potential applications in fields such as lighting and magnetic resonance imaging.2.Rare-earth doped Lu₇O₆F₉ luminescent materials with various novel morphologies were prepared by ionic liquid-assisted hydrothermal method and subsequent calcination process.The effects of reaction conditions on the morphologies of precursors and calcined products were studied and the formation mechanism was proposed.The crystal structure was further confirmed by using Eu³⁺ion as a fluorescent probe.Yb³⁺and Er³⁺co-doped Lu₇O₆F₉ luminescent materials with different concentrations of Yb³⁺were prepared and their up-conversion luminescence properties were studied.The temperature sensing behavior of Vernier phase lutecium oxyfluoride matrix was investigated for the first time and the influence of Yb³⁺concentration on the sensing sensitivity was elaborated.The results show that Lu₇O₆F₉:Yb³⁺,Er³⁺is a good material for color-tunable displaying and optical thermometers.3.The rapid preparation of rare-earth doped Lu₇O₆F₉ luminescent materials was realized by ionic liquid assisted coprecipitation and calcination process.The influences of calcination temperature,reaction temperature,reaction time and fluorine source on the phase and morphologies of precursors and calcined products were discussed in detail,and the formation mechanism was proposed.Lu₇O₆F₉:Eu³⁺and Lu₇O₆F₉:Yb³⁺,Er³⁺luminescent materials were prepared and their down/up conversion luminescent properties were studied.In addition,Lu₇O₆F₉ co-doped with Gd³⁺and Eu³⁺was prepared.The doping of Gd³⁺improved the luminescent intensity and paramagnetism of the sample.This study opens up a new way for rapid preparation of multifunctional rare-earth fluorides and oxyfluorides.