Synthesis And Luminescence Properties Of Rare Earth Fluorides With High Efficiency And Heavy Dopant

Rare earth upconversion luminescent materials have attracted much attention because of their special structure and unique properties in the fields of plasma display,biofluorescence labeling,anti-counterfeiting technology and other fields.Compared with other light conversion materials,doped rare earth upconversion luminescent materials have many outstanding advantages,such as narrow luminescence lines,large anti-stokes shifts,long luminescence lifetime,low toxicity and so on.In this paper,the low-temperature molten salt method was used to prepare rare earth fluorides to investigate the effects of the reactants such as type,component ratio,reaction temperature and reaction time on the luminescence properties of crystal structure,particle morphology and size.Based on this,the effect of Bi3+ ion on the upconversion fluorescence enhancement and luminescence mechanism were studied.The main findings are as follows.(1)The precursor Na F and Ln(NO3)3·x H2O(Ln = rare earth)react in a molten ammonium nitrate system to form Ln F3 or Na Ln F4,systems to investigate in depth the effects of rare earth ion species and crystal growth conditions(Na F/Ln molar ratio,reaction temperature and reaction time)on the crystal structure,particle morphology and size of the product rare earth fluoride.Based on this,it was divided into four groups: G1(La and Ce),G2(Pr and Nd),G3(Sm,Eu,Gd,Tb,Dy and Ho),G4(Y,Er,Tm,Yb and Lu).The crystal phase of the G1 fluoride is hexagonal Ln F3,the particle morphology of the crystal is near spherical at low temperature and short time,while the crystal particle morphology changes to thin slice at high temperature or long time.Under the condition of low temperature and short time G2 fluoride is still hexagonal Ln F3,the crystal particle morphology is nearly spherical,short prism,small rod shape,but high temperature and long time lead to the formation of hexagonal phase Na Ln F4 rod structure.G3 and G4,when the molar ratio of Na F/Ln is 3,low temperature and short time,the crystal particle morphology is transformed into orthogonal polyhedron Ln F3,while at high temperature and long time,the crystal particle morphology is gradually transformed into polyhedron,flake or polyhedron and flake mixed shape.When the molar ratio of Na F/Ln is increased to 6,for G3,the crystal particle morphology changes from polyhedron to rod-like structure Ln F3 hexagonal phase.at high temperature and for a long time,the rod-like particles of hexagonal phase will eventually be formed.As for the G4 crystal,Na F/Ln the molar ratio is increased to 6,the spherical cubic Na Ln F4 particles are produced at low temperature and short time,while the hexagonal phase is formed Na Ln F4 rod-like structure at high temperature for a long time.(2)The controlled synthesis of hexagonal Na Yb F4:Tm3+/Bi3+ upconversion luminescent materials was achieved by low temperature self-melting salt method.the optimal molar ratio between precursor Na NO3、B(NO3)3(B=Tm,Yb,Bi)and NH4 F was 1:1.2:5.The Tm3+ doping concentration can be increased from 2 mol% to 8 mol% after the introduction of Bi3+ into the Na Yb F4:Tm3+ material.High upconversion luminescence are achieved under low power conditions.When the excitation power is 1.5 W cm-2,the total upconversion quantum yield of Na Yb F4:8 mol%Tm3+/32 mol%Bi3+(60Yb8Tm32Bi)is 0.41%,while the total upconversion quantum yield increases to 1.61% as the excitation power increases to 40 W cm-2.These realize high double-doped efficient upconversion luminescence under low power conditions to provide a new way for new energy materials applications.