Preparation,Properties And Multifunctional Applications Of BiF₃ And Bi₇F₁₁O₅ Upconversion Luminescent Materials

Upconversion luminescence?UCL?refers to the phenomenon of nonlinear luminescence that continuously absorbs two or more low-energy photons and radiates a high-energy photon.The rare earth doped UCL materials have the advantages of good optical stability,good chemical stability,low toxicity,narrow emission band and long life.And UCL materials have a deeper penetration depth,lower background fluorescence and lower damage to biological tissues due to the excitation source is near-infrared light.Therefore,they have potential application value in the fields of safety signs,backlights,color display sources,bio-imaging,solar cells,etc.However,most of the matrix materials are generally rare earth salts,containing expensive rare earth ions,which increase the cost and have certain harm to the environment.Considering that transition metal bismuth?Bi?is the only non-toxic heavy metal and the radius of Bi³⁺is similar to trivalent rare earth ion,so it can replace trivalent rare earth ion in matrix.Therefore,the luminescence properties and mechanism of BiF₃and Bi₇F₁₁O₅ doped Yb³⁺/Ln³⁺?Ln=Er,Tm,Ho?UCL materials have been studied,and the applications of these materials in different fields have also been studied.1.Pure cubic phase and uniform BiF₃:Ln³⁺?Ln=Ho,Er,Tm?/Yb³⁺nanoparticles?NPs?were prepared by coprecipitation.The growth mechanism of BiF₃:2%Er³⁺/20%Yb³⁺NPs was proposed based on the evolution analysis with time-dependent morphology,in which BiF₃:2%Er³⁺/20%Yb³⁺were formed through the growth process of“Nucleation to crystallization and Ostwald ripening”.Upconversionluminescence?UCL?propertiesandmechanismofBiF₃:2%Er³⁺/20%Yb³⁺under the dual-wavelength excitation were also systematically investigated.The emission intensities of BiF₃:2%Er³⁺/20%Yb³⁺by the dual-wavelength excitation??=980 nm+1550 nm?was 1.49 times more than the sum excited by 1550 nm or 980 nm,respectively.Furthermore,the properties of the bright white and multicolor UCL showed that yellow,purple,green or pinkish lights could be observed by controlling the doping concentrations of Ln³⁺?Ln=Yb,Er,Tm and Ho?,indicating that they had potential applications in backlight sources of color displays and security labeling.Research on temperature sensitivity of BiF₃:2%Er³⁺/20%Yb³⁺exhibited a downward tendency and its max value was about0.0036 K^-1at 273 K.Cell toxicity test showed that the UCNPs in phospholipid aqueous solution presented low cytotoxicity.Also,in vivo imaging and X-Ray imaging revealed that BiF₃:2%Er³⁺/20%Yb³⁺NPs had deep penetration and high contrast,which was a potential probe and contrast agents in vivo optical bio-imaging.2.In order to improve the UCL properties of BiF₃:Yb³⁺/Ln³⁺?Ln=Er,Tm,Ho?materials,PAA-coated BiF₃:Yb³⁺/Ln³⁺?Ln=Er,Tm,Ho?were prepared by hydrothermal method.The structures,morphologies,UCL properties,mechanism,and temperature sensitivity were studied,compared to uncoated BiF₃:Yb³⁺/Ln³⁺materials.The UCL intensity of PAA-BiF₃:Yb³⁺/Er³⁺was the maximum 36 times enhancement of the BiF₃:Yb³⁺/Er³⁺.Compared to the sum of emission intensities excited by two single-wavelength?980 nm and 1550 nm?separately,the red emission from PAA-BiF₃:Yb³⁺/Er³⁺sample excited by two-wavelength simultaneously was enhanced by a factor of 6.The temperature sensitivity of the sample was also studied in detail.3.A novel Bi₇F₁₁O₅:Yb³⁺/Ln³⁺?Ln=Er,Tm,Ho?UCL materials were synthesized by hydrothermal method,and their structures and morphologies were characterized.Compared to the sum of emission intensities excited by two single-wavelength?980 nm and 1550 nm?separately,the red emission from Bi₇F₁₁O₅:Yb³⁺/Er³⁺sample excited by two-wavelength simultaneously was enhanced by a factor of 16.57.The temperature sensitivity was also studied.