Preparation And Upconversion Fluorescence Properties Of Yb³⁺/Er³⁺/Tm³⁺ Doped Y₆O₅F₈ Nanocrystals

In recent years,research on the upconversion of rare earth doped luminescent nanomaterials has achieved exciting results in domestic and worldwide,while rare earth doped fluorine oxide has a very wide application value in the environmental chemistry,life sciences,non-contact temperature measurement,white display lighting and other fields,due to its high chemical stability,light stability,long fluorescent lifetime,low toxicity,low phonon energy,high lu minous efficiency.In this thesis,the upconversion fluorescence characteristics of rare earth ion doped Y₆O₅F₈ nanocrystals were studied.The main research contents and results are as follows:The samples of Y₆O₅F₈ nanocrystals doped with rare earth ions were synthesized by hydrothermal method.The crystal structure and morphology of Y₆O₅F₈ nanocrystals were characterized by X-ray diffraction?XRD?and transmission electron microscopy?TEM?.The influence of different reaction temperature and reaction time on the crystal structure of nanocrystals was investigated.It was found that the pure orthorhombic phase Y₆O₅F₈ crystal powder could be obtained by sintering at 600 ? for 6 hours.The effect of F-/ Ln³⁺ ratio on the grain size in the reactants was analyzed.The Y₆O₅F₈ nanocrystals with different Er³⁺ ion doping concentration were prepared and the upconversion spectra were measured under the 980 nm excitation.The optimal doping concentration of Er³⁺ was found to be 1%.The upconversion mechanism of Y₆O₅F₈: Yb³⁺ / Er³⁺ nanocrystals was investigated by analyzing the double logarithmic relationship curve of the fluorescence intensity and the pumped optical power.The Y₆O₅F₈: Er³⁺ / Yb³⁺ nanocrystals samples with different doping concentration of Yb³⁺ ions were prepared.Combining with the Yb³⁺/ Er³⁺ energy levels steady state rate equation,the effect of Yb³⁺ ion concentration on the ratio of red-green fluorescence intensity was analyzed.It was found that Y₆O₅F₈: Er³⁺ / Yb³⁺ nanocrystals were subjected to upconversion fluorescence measurements over the temperature range of 300-500 K by the two thermal coupling levels?2H11/2 and 4S3/2?of Er³⁺,and the temperature sensitivity was calculated 0.012 K-1.The fluorescence lifetime of nanocrystalline samples at different temperatures was measu red,showing that the method approach has a high temperature sensitivity in the lower temperature range of 300-350 K.The optimal doping concentration of Tm³⁺ was 0.2%,which was obtained by measuring the upconversion fluorescence spectrum of Y₆O₅F₈:Yb³⁺/Tm³⁺ nanocrystals with different doping concentration of Tm³⁺ ions.The influence of the doping concentration of Er³⁺ on the fluorescence color of Y₆O₅F₈: Yb³⁺ / Tm³⁺ / Er³⁺ nanocrystals was studied.The intensity distribution of three colors of red,green and blue was analyzed,and the chromaticity coordinates?0.3299,0.3297?of the Y₆O₅F₈: 10% Yb³⁺ / 0.2% Tm³⁺ / 1.0% Er³⁺ nanocrystal samples are very close to the standard white light.The influence of the temperature of the sample and the excitation power on the white light chromaticity coordinates is analyzed.The energy transfer process in the Y₆O₅F₈: Yb³⁺ / Tm³⁺ / Er³⁺ nanocrystals is analyzed by analyzing the double logarithmic relationship curve of the fluorescence intensity and the pumped optical power.