Synthesis Of Yb³⁺/Er³⁺ Co-Doped NaLaF₄ And (Ca_0.65La_0.35)F_2.35 Powder And Study Of Their Upconversion Luminescence Properties

Upconversion luminescence is the paradoxical phenomenon in which a substance can continually absorb low energy long wavelength radiation while simultaneously emitting high energy short wavelength radiation.The rare-earth ion-doped upconversion luminescence nanomaterials have received the most attention in research.Due to their special qualities of low phonon energy,high optical stability,narrow-band emission,low toxicity and deep tissue penetration,and low background interference in living organisms,fluoride-based upconversion luminescent materials are an essential resource for catalysis,illumination,anti-counterfeiting and biomarking,as well as imaging.For instance,in order to achieve high sensitivity,the most common upconversion fluorescent probe reagents must have a greater degree of attachment in the target organism.On the other hand,the metabolic elimination mechanism of the drug in the organism requires that these materials have a small size and strong luminescence.Smaller nanoparticles have more exposed luminous ions or surface passivators（ligands,solvents,or contaminants,for example）,which can all result in a decrease in the material’s upconversion emission intensity.Thus,scientists have been looking towards highly effective and non-harmful rare earth upconversion luminous materials.In response to the current issues,they have proposed solutions include altering the matrix material,adding non-lanthanide ions,noble metal doping,adjusting the concentration of dopants,or building core-shell structures.As the primary component of the upconversion luminescent material,the matrix material creates the ideal crystal field for the luminescent ions to radiate from.Therefore,it’s crucial to select a matrix material with low lattice vibratory energy and strong chemical stability.In this paper,La F₃,Na La F₄ and(Ca_0.65La_0.35)F_2.35 matrix were synthesized by the solvothermal method.By adjusting the reaction conditions,the effect on the matrix’s crystalline size,shape,and morphology was investigated,and then the impact on the luminescence performance was examined.Yb³⁺was selected as the sensitizer and Er³⁺as the activator.The main research in this paper consists of three parts:（1）In a three-solvent system,pure hexagonal phase LaF₃:Yb³⁺/Er³⁺were effectively prepared using a simple and environmentally friendly solvothermal technique.By changing the amount of precursor La（CF₃COO）₃ reactants,the source of fluorine ions,and the reaction conditions,such as reaction temperature and reaction time,the effects on the crystalline phase,size,and morphology of the La F₃:Yb³⁺/Er³⁺were investigated,and the effects on the luminescence properties were discussed on this basis.The results show that La F₃:Yb³⁺/Er³⁺with an average size of approximately 55.44 nm were synthesized when 1 mmol of precursor,0.75mmol of Na F,5 mmol of NH₄F,and solvent systems of oleic acid（OA）,octanol（OC）and ethylene glycol（EG）were added for 36 h at 180°C.XRD（X-ray powder diffraction）,fluorescence spectrometer and SEM（scanning electron microscope）were used to characterize the results,which showed that La F₃:Yb³⁺/Er³⁺were successfully synthesized.Their samples are small in size,all of them are hexagonal phase nanodiscs,while the upconversion luminescence spectra show good green emission.（2）hexagonal NaLaF₄:Yb³⁺/Er³⁺were successfully prepared by solvothermal method.By changing the concentration of Na F,NH₄F,reaction temperature,reaction time and other reaction conditions,the effects on the crystal phase,size and morphology of Na La F₄:Yb³⁺/Er³⁺were studied,and then the effects of reaction conditions on the luminescence properties of the samples were discussed.The results showed that Na La F₄:Yb³⁺/Er³⁺with a size of about 53 nm were synthesized when2 mmol Na F,9 mmol NH₄F were added and the solvent system was OA,OC,EG at 200℃for 48 h.The samples were characterized by XRD,fluorescence spectrometer and SEM.The characterization results show that Na La F₄:Yb³⁺/Er³⁺with small size and mainly rod-like hexagonal phase are successfully synthesized,and the sample gradually grows from nano-disk to rod-like material by prolonging the reaction time.The upconversion luminescence spectrum shows better green emission.Compared with the luminescent properties of La F₃ and Na La F₄:Yb³⁺/Er³⁺,the luminescent intensity of NaLaF₄ is better.（3）The pure cubic phase(Ca_0.65La_0.35)F_2.35:Yb³⁺/Er³⁺was successfully prepared by the solvothermal method.The effects on the crystalline phase,size and morphology of the(Ca_0.65La_0.35)F_2.35:Yb³⁺/Er³⁺were investigated by varying the amount of precursor rare earth ions doped,the amount of NH₄F and Na OH in the reaction and the reaction temperature and time,and finally exploring the effects of the precursor rare earth ions doping on the luminescent properties.The results show that(Ca_0.65La_0.35)F_2.35:Yb³⁺/Er³⁺with a size of about 108)were synthesized when the precursor rare earth ions Yb³⁺doped 20%and Er³⁺doped 2%with the addition of 2 mmol Na OH,8 mmol NH₄F,240℃and 48 h.The samples were characterized using XRD,fluorescence spectroscopy,and SEM,and the results show that the precursor materials for rare earth ions,which are20%doped in Yb³⁺and 2%doped in Er³⁺,were successfully synthesized.All are cubic-phase micron rods,and the upconversion luminescence spectra demonstrate that the samples have strong red light emission.