Synthesis And Luminescence Property Tuning Of NaLuF₄ Micron Crystals

Rare earth upconversion luminescence materials have been promising materials for decades.Compared with the traditional luminescence materials,such as organic fluorescent dyes and semiconductor quantum dots,the rare earth materials have many excellent properties,characterized by narrow emission spectra,low photobleaching,long lifetimes,high chemical stability and large Stokes shift.Due to their unfilled 4f electron orbits,lanthanide ions have a large number of intermediate levels,which can emit ultraviolet,visible,near infrared and even infrared lights.At present,as a kind of important luminescence materials,rare earth materials have been widely applied in many fields,and have broad prospects in lasers,new light sources,X ray intensifying screens and so on.In this paper,NaLuF₄ microcrystals were prepared by molten salt method and hydrothermal method.The morphology of products was controlled by changing the content of surfactants,and the fluorescence characteristics produced by doping different rare earth elements and different excitation power were studied.In this paper,the NaLuF₄ rare-earth upconversion micron crystals were prepared by the molten salt method with reaction medium of NaNO₃ and KNO₃.The crystal structure,morphology and element composition of the products were investigated by XRD,SEM and EDS.The luminescence properties of three different micron crystals including NaLuF₄:Yb³⁺,Er³⁺,NaLuF₄:Yb³⁺,Tm³⁺and NaLuF₄:Yb³⁺,Er³⁺,Tm³⁺,are studied.The influence of the content of rare earth elements in NaLuF₄:Yb³⁺,Er³⁺,Tm³⁺crystals on the luminescence color is analyzed.By adjusting the molar ratio of Er³⁺ion,the color of the micron crystals was modulated and the white light emission could be realized.The influence of the amount of Nd³⁺dopingintothreecrystalsofNaLuF₄:Yb³⁺,Er³⁺,NaLuF₄:Yb³⁺,Tm³⁺and NaLuF₄:Yb³⁺,Er³⁺,Tm³⁺on the intensity of luminescence,and then the color modulation of light was realized through the change of Nd³⁺doping amount.The NaLuF₄ rare earth upconversion micron crystals were synthesized by the hydrothermal method with citric acid as surfactant.By controlling the content of citric acid,four kinds of rare earth compounds with different morphology,including disk,short column,stick and tube,were synthesized.After sintering,the morphology of crystals became more regular.The relationship between the morphology and XRD patterns have been discussed.The morphology of the material affected the luminescence intensities of the material.By adjusting the excitation power of the laser,luminescence color changes of the rare earth micron crystals were investigated.For the crystals doped with Er³⁺and Tm³⁺activator ions,the influence of varied excitation power on different emission peaks was discussed.In Er³⁺/Tm³⁺system,by controlling the doping amount of Er³⁺,Tm³⁺and Yb³⁺,and adjusting the excitation power,a large range of color change was realized.Changing excitation power could achieve continuous fluorescence modulation,which has a good application prospect in real-time detection,display and lighting.