Up-conversion Luminesce Of Energy Transfer Of Rare Earth Doped Gadolinium Molybdate Lithium And Its Application

Rare earth-doped up-conversion luminescent materials can absorb near-infrared radiation to be converted into visible light band radiation.The luminescent material has broad application prospects in lasers,lighting,display,biomedicine,optical temperature sensing,and information transmission.The increasment of the fluorescence intensity,achievement of accurate temperature measurement,and regulation of the fluorescence color of up-converting luminescent materials have been the research directions of many researchers.The main research contents of this paper are as follows:The Gd₂?MoO₄?₃:Er/Yb nanocrystals are prepared by the sol-gel method,the effect of calcination temperature on the crystal phase and luminescence intensity of nanocrystals is studied.At different calcination temperatures,two crystal phases of Gd₂?MoO₄?₃ nanocrystals can be obtained,which are monoclinic crystal phase and orthorhombic crystal phase,respectively.Under the excitation of 980 nm laser,it is found that the orthorhombic nanocrystals had stronger fluorescence intensity.In addition,LiGd?MoO₄?₂:Er/Yb nanocrystalline materials are prepared by hydrothermal method,high temperature solid phase method,and sol-gel method.The comparison found that the sol-gel method is simple and can be prepared pure crystal phase of LiGd?MoO₄?₂ nanocrystals at 600?.Among them,citric acid is used as a chelating agent in the preparation process of the sol-gel method,which promotes the hydrolysis and polymerization processes,and at the same time can modify the surface morphology of the sample.It is found that by adjusting the ratio of citric acid and rare earth ions,LiGd?MoO₄?₂ nanocrystals with uniform particle size can be obtained.And the up-conversion luminescence intensity will change with the ratio of citric acid and rare earth ions.Changing the concentration of doped ions is one of the main means to increase the up-conversion luminescence intensity of the sample.In this work,under the excitation of 980 nm pump light,study the effect of different Er³⁺ and Yb³⁺concentrations on the luminescence intensity of LiGd?MoO₄?₂ nanocrystals,the best doping concentration of Er³⁺and Yb³⁺were obtained respectively.In addition,the energy transfer,radiative transition,non-radiative relaxation and other up-conversion luminescence mechanisms of Er³⁺ and Yb³⁺ ions are analyzed.The probability of radiative transition is calculated by the J-O theoretical model,and the theoretical model of the steady-state rate equation is established to carry out the change of luminescence intensity.The temperature sensing characteristics of LiGd?MoO₄?₂ nanocrystals in the temperature range of 298 K to 523 K were measured by fluorescence intensity ratio?FIR?technology,and the absolute sensitivity reached a maximum value of 0.0153 K-1 at 523 K.The higher absolute sensitivity illustrates.The higher absolute sensitivity indicates that the material is expected to be used in the field of temperature sensing.Finally,the up-conversion luminesce characteristics of Ce/Er/Yb doped LiGd?MoO₄?₂ nanocrystals are studied,and the fluorescence color of the nanocrystals is adjusted.It is found that the red-green ratio of LiGd?MoO₄?₂ nanocrystals changed with the increase of Ce³⁺concentration.The cross-relaxation process between Er³⁺ and Ce³⁺increases the particle number density of Er³⁺'s red band energy level 4F9/2 and infrared band 4I13/2 energy level,enhancing the sample's red-green ratio.By establishing a theoretical model of steady-state rate equations,the intensity changes of red and green light are analyzed.