Rare Earth Doped Tungstate/Molybdate/Phosphate/Fluoride Upconversion Materials:Synthesis And Luminescent Properties

Rare earth doped materials have attracted much interest due to their novel electronic and optical properties resulting from their abundant emission colors based on their 4f-4f or 5d-4f transitions.The phosphors have potential in areas such as biomedicine,optical data storage,display,fluorescent lamps,optical fibers and X-ray intensified screens.Especially,more and more attention has been devoted to the research on upconversion?UC?luminescent materials due to their unique optical and electrical properties arising from their 4f electrons.To date,a large number of high quality rare earth-based micro/nano-crystals,such as oxides,phosphates,vanadate,and fluoride have been extensively reported.In this work,micro/nano-crystals with tailored morphologies were synthesized.The solvothermal method,hydrothermal process and water bath process were used for the synthesis of crystals.It is found that the as-prepared product exhibits regular shape,uniform size and perfect dispersion properties.The structural and kinetic factors that govern the phase and shape evolution of the materials have been systematically investigated and discussed.The formation mechanisms have also been proposed.Tunable multicolor and bright white emissions were successfully realized by precisely adjusting the doping sensitizer(Yb³⁺)and activator concentration in the host matrix.In particular,the markedly enhanced luminescence intensity can be by Li⁺ doping,the related mechanism has been discussed.Furthermore,a systematic study on the UC emissions of samples with different shapes has shown that the optical properties ofthese phosphors are strongly dependent on their morphologies and sizes.Firstly,LaPO₄:Ln³⁺?Ln = Yb,Er,Tm,Ho?nanocrystal was successfully synthesized via a facile solvothermal process in the present of oleic acid.The growth mechanism was also proposed.The UC properties of Yb³⁺/Er³⁺,Yb³⁺/Tm³⁺,and Yb³⁺/Ho³⁺ doped LaPO₄ nanoparticles were also discussed under 980 nm laser excitation.The UC luminescences property of the products can be controlled by changing the doping concentration of Yb³⁺.Secondly,well-defined NaLa?WO₄?₂ microstructures were prepared by a facile solvothermal process in the presence of oleylamine and oleic acid as a mixed surfactant.The phase,morphology,size and luminescence properties were well characterized.Upon ultraviolet?UV?excitation,the NaLa?WO₄?₂:Eu³⁺ and NaLa?WO₄?₂:Tb³⁺ exhibit the characteristic down-conversion?DC?emissions of Eu³⁺ and Tb³⁺.And Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ co-doped NaLa?WO₄?₂ samples show strong green and blue UC emission.The UC emission mechanisms in NaLa?WO₄?₂:Ln?Ln = Yb/Er,Yb/Tm?are also presented.It should be noted that the emission intensities,especially the UC emission can be markedly enhanced compared with sodium free tungstates,which can be attributed to the charge compensation.The UC luminescences property of the products can be controlled by changing the doping concentration of the rare earth lio.Thirdly,self-assembled NaLa?WO₄?₂:Ln³⁺?Ln = Yb,Er,Tm?micro-spheres were successfully prepared by a solvothermal method for the first time.The morphologies were tuned trough manipulating the reaction parameters,from which the growth mechanisms were also proposed.Upon 980 nm laser excitation,multi-color UC light was successfully achieved by properly tuning the sensitizer(Yb³⁺)and activator concentration in the host matrix.Fourthly,NaYF₄ microcrystals with a variety of morphologies,such as microsphere,hexagonal prism,microtubes and octahedron shapes have been synthesized by different reaction conditions including reaction time,pH values,fluoride sources and reaction temperature.The possible formation mechanism for the products with various architectures has been presented.The UC properties of Yb³⁺/Ho³⁺,Yb³⁺/Er³⁺ or Yb³⁺/Tm³⁺ codoped NaYF₄ samples were studied.In particular,the luminescence intensity can be markedly enhanced by Li⁺ doping.Furthermore,a systematic study on the UC emissions of Yb³⁺/Tm³⁺ codoped NaYF₄ samples with different morphologies have been discussed.In particular,the luminescence intensity can be markedly enhanced by Li⁺ doping.Finally,a facile and mild one-pot approach was employed to prepare hollow-structured SrMoO₄ using soluble sodium poly?4-styrenesulfonate??PSS?as a soft template.The phase,morphology and size of the SrMoO₄ microstructures were rationally tuned in a controlled manner by altering the amount of PSS,the concentration of reactants and the pH value of the initial solutions.Moreover,the crystal growth process was thoroughly studied through a series of time-dependent experiments and a possible formation mechanism was proposed.Tunable multicolor and bright white UC emissions were successfully realized by precisely adjusting the doping sensitizer(Yb³⁺)and activator(Tm³⁺,Ho³⁺)concentrations in the host.A doxorubicin hydrochloride?DOX?release test exhibited clear sustained drug release property.Notably,the PL intensity of the functional system increases with the amount of DOX released,thus allowing the carrier to be monitored and tracked by the change in PL intensity.A MTT?3-?4,5-dimethylthiazol-2-yl?-2,5-diphenyltetrazolium bromide?assay showed the good biocompatibility of SrMoO₄ hollow spheres,indicating the potential application of this kind of material in biomedicine and other fields.Moreover,the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carrier was investigated and the endocytosis process of drug-loaded microspheres was studied using confocal laser scanning microscopy?CLSM?and flow cytometry.