Preparation And Performance Research Of NaYbF₄:Tm³⁺/Fe³⁺Luminescent Material By Low-temperature Self-flux Technique

Rare earth up-conversion luminescent materials have excellent up-conversion luminescence properties,and have broad application prospects in the fields of energy conversion,medical diagnosis,photodynamic therapy,security and anti-counterfeiting,and photocatalysis,and have attracted much attention.Compared with luminescent materials such as quantum dots and organic dyes,rare earth upconversion luminescent materials(especially rare earth fluoride materials)have many unique advantages,such as low toxicity,large anti-Stokes shift,longevity long wait and high quantum yield.In this paper,a series of rare earth fluorides were prepared by the low-temperature self-flux technique,and the influence of the type of raw materials,reaction temperature and other experimental parameters on the phase structure,morphology and size of the product was explored,and the corresponding evolution law was summarized.On this basis,a hexagonal NaYbF₄:Tm³⁺/Fe³⁺luminescent material was prepared,and the up-conversion luminescence and magnetic properties of the material and the role of Fe³⁺in the up-conversion emission process were studied.Below are key research findings.(1)Using low melting point Na NO₃,Ln(NO₃)₃·x H₂O(Ln=rare earth elements)and NH₄F as raw materials,a series of LnF₃ and NaLnF₄ products are prepared under the conditions of a molar ratio of 1:1:5 and different reaction temperatures.Based on the evolution law of phase structure,morphology and size,it can be divided into four categories:type I(La and Ce),type II(Pr and Nd),type III(Sm?Eu?Gd?Tb?Dy and Ho)and type IV(Er?Tm?Yb?Lu and Y).The reaction temperature has almost no effect on the phase structure of type I,type III and type IV fluorides.The type I rare earth fluorides prepared at high and low temperatures all have a hexagonal LnF₃ phase structure,while the type III and IV fluorides have a performance It is NaLnF₄ with hexagonal phase structure.When the other reaction conditions remain unchanged and only the reaction temperature is increased,the morphology of the remaining fluorides of type I gradually changes from nearly spherical to hexagonal pyramid,while the fluorides of type III and IV evolved from nearly spherical particles to rod-like bodies and hexagonal prism respectively,and the whole shows higher crystallinity and better dispersibility.In addition,the phase structure of type II rare earth fluorides is very sensitive to the reaction temperature.Under low temperature conditions,the prepared sample is a short rod-shaped hexagonal LnF₃.Under high temperature conditions,the prepared sample is a smooth rod-shaped hexagonal NaLnF₄.(2)Using low-temperature self-flux technique,using low melting point Na NO₃,Ln(NO₃)₃·x H₂O(Ln=Yb,Tm and Fe)and NH₄F as raw materials,the molar ratio is 1:1:5,and the reaction temperature is 210?,The reaction time is 4.5 h to prepare hexagonal NaYbF₄:Tm³⁺/Fe³⁺luminescent material.The results show that the NaYbF₄:Tm³⁺/Fe³⁺luminescent material has paramagnetism.The optimal substitution concentration of Fe³⁺is10 mol%.At this time,the ultraviolet and blue emission intensity of NaYbF₄:Tm³⁺/Fe³⁺materials are increased by 16 times and 20 times,respectively.In addition,the tunable emission of red(less than 9)and blue(above 9)light can be achieved by controlling the substitution concentration ratio of Fe³⁺/Tm³⁺.Since Fe³⁺plays a role in regulating the local lattice field and changing the energy transfer during the up-conversion process,NaYbF₄:Tm³⁺/Fe³⁺realizes the high-efficiency up-conversion luminescence under the conditions of high substitution and low power.