Study On Preparation And Fluorescence Properties Of Double Tungstate/Molybdate Luminescent Materials

In recent years,rare earths have been used in petrochemical industry,ceramic glass,biological applications,aerospace and aviation and other fields.In a word,the study of rare earth materials is of great significance.The rare earth up-conversion luminescent materials are common and highly regarded,which could absorb low-energy photons and emit high-energy photons,sequentially generate visible light.In addition,the excitation source of near-infrared light(980 nm)can penetrate biological tissue with little damage to biological cells.Hence,up-conversion luminescent materials can be used in biological imaging,biological detection,cancer treatment and other biological applications.Cancer cells can be screened and excluded by accurate temperature detection based on the temperature difference between cancer cells and normal cells.Therefore,it is particularly critical to find a temperature sensor with fast response and high detection accuracy.In recent years,rare earth up-conversion luminescent materials based on fluorescence intensity ratio technology are ideal candidate temperature-sensitive materials because of their low toxicity,wide detection temperature range and high detection accuracy.In this paper,we selected four kinds of alkali metal double tungstate/molybdate(Na_0.5Yb_0.5WO₄,NaLu(WO₄)₂,Ag Lu(Mo_1-xW_xO₄)₂ and Ag Y(Mo O₄)₂,respectively.)with low phonon energy,low toxicity,high physical and chemical stability.At 980 nm excitation,discussed the function relationship of the fluorescence intensity ratio(FIR)and the thermally coupled energy levels(Er³⁺ions)as the temperature change.It is investigated preliminarily for the realization of accurate temperature measurement in biological applications.The specific conclusions are as follows:(1)In this paper,we prepared Na_0.5 Yb_0.5 WO₄,NaLu(WO₄)₂,Ag Lu(Mo O₄)₂ and Ag Y(Mo O₄)₂ nano/micro crystal by facile,mild and free of contamination hydrothermal method.The phase structure and morphology of crystals are analyzed through X-ray diffraction,field emission(FE-SEM),electron microscopy and transmission electron microscope(TEM).We adjusted the reaction conditions to achieve the purpose of morphological control.Na_0.5Yb_0.5WO₄ nanocrystals with various morphologies were obtained by changing the molar ratio of cation-cation and adding four different organic additives:EDTA,glycine,citrate and PVP.Na_0.5Yb_0.5WO₄nanocrystals with various morphologies,such as aggregated nanosheets and self-assembled nano-flowers,were obtained.The pony-size of NaLu(WO₄)₂ nanocrystals were obtained by introducing ions Yb³⁺/Er³⁺,Yb³⁺/Ho³⁺,Yb³⁺/Tm³⁺,Yb³⁺/Ho³⁺/Tm³⁺with larger ionic radius.Different concentrations of Yb³⁺,Er³⁺and WO₄^2-ions doped Ag Lu(Mo O₄)₂ micron crystal changed from octahedral shape to rosette shape,lotus shape and other rich morphology.(2)Rich up-conversion luminescent colors of green,orange and blue were obtained by doping Yb³⁺/Er³⁺,Yb³⁺/Tm³⁺and Yb³⁺/Ho³⁺.We got the optimal doping ratio by investigating the influence of doping concentration on the luminescence intensity.Furthermore,the Ho³⁺/Tm³⁺doping ratio in Na_0.5Yb_0.5WO₄ nanocrystals and the molar ratio of Yb³⁺/Ho³⁺/Tm³⁺in NaLu(WO₄)₂ and Ag Y(Mo O₄)₂ were respectively adjusted.What's more,the white up-conversion luminescence of Na_0.5Yb_0.5WO₄:Ho³⁺/Tm³⁺,NaLu(WO₄)₂:Yb³⁺/Ho³⁺/Tm³⁺and Ag Y(Mo O₄)₂:Yb³⁺/Ho³⁺/Tm³⁺phosphors were obtained,which were highly consistent with the international standard chromaticity coordinates.(3)Based on theoretical support fluorescence intensity ratio technology,we have studied the relationship between the fluorescence intensity ratio of the thermal coupling level(²H_11/2 and ⁴S_3/2)and the variation of temperature(with the range of 298?523 K,323?563 K,and 323?503 K)of Na_0.5Yb_0.5WO₄:Er³⁺,NaLu(WO₄)₂:Yb³⁺/Er³⁺and Ag Lu(Mo_1-xW_xO₄)₂:Yb³⁺/Er³⁺phosphors.In addition,according to the Boltzmann distribution law,we deduced the functional relationship between the fluorescence intensity ratio and the temperature,obtained the respective best absolute and relative sensitivity through calculations.The maximum absolute sensitivity of Na_0.5Yb_0.5WO₄:Er³⁺,NaLu(WO₄)₂:Yb³⁺/Er³⁺and Ag Lu(Mo_1-xW_xO₄)₂:Yb³⁺/Er³⁺are1.189%K^-1(498 K),1.38%K^-1(543 K)and 0.0173 K^-1(428 K).Compared with the sensitivity of other fluorescent materials,it is found that the application of Yb³⁺/Er³⁺-doped alkali metal rare earth bis-tungsten/molybdate in non-contact temperature sensors has obvious advantages.