Preparation And Properties Of Sr₂MgWO₆:Cr³⁺,Nd³⁺/Yb³⁺ Near Infrared Luminescent Materials

With the development of science and technology,especially the development of life science and technology,people have increased interest in the near infrared?NIR?luminescent materials.When NIR is used for bioimaging,it has the advantages of deep tissue penetration,low autofluorescence and low back scattering,which has become a new favorite in the field of biological optical imaging.The kind of NIR long afterglow materials are which still able to launch NIR light and continue for a period of time after the excitation of the light source halt.People can stimulate NIR materials outside organisms first,then injecting it into organisms,and perform biological research with continuous NIR light emitted from materials.Cr³⁺ions are often used as active ions for NIR long afterglow materials,and the related research has made remarkable progress.It has been reported about Cr³⁺doped materials'afterglow continue more than 360 h.Long afterglow materials about Cr³⁺doped systems are usually gallium containing materials,such as Zn₃Ga₂Ge₃O₁₀,ZnGa₂O₄,and Ca₃Ga₂Ge₃O₁₂.In order to meet the needs of the people on the NIR long afterglow materials,expand the types of NIR doped Cr³⁺long afterglow materials,and also in order to provides a new reference to better study the Cr³⁺doped NIR long afterglow mechanism,looking for new non gallium doped Cr³⁺system NIR long afterglow materials is very significant.In this paper,we adopted SrCO₃,CaCO₃,MgO,WO₃,Cr?NO₃?₃?9H₂O,Nd₂O₃,Yb₂O₃ as raw materials,synthesis a series of phosphors of Sr₂MgWO₆:Cr³⁺,Nd³⁺/Yb³⁺and?Sr,Ca?₂MgWO₆:Cr³⁺,Yb³⁺by high temperature solid phase method.The experimental results show that Sr₂MgWO₆:Cr³⁺phosphor possesses a strong wide spectrum emission band at the NIR range of 700–1000 nm.When the doping amount of Cr³⁺is 0.4%,the material exhibits the strongest NIR emission,and its intensity is nearly 3 times intense that of the Ca₂MgWO₆:Cr³⁺which reported previously.Meanwhile,the material exhibits excellent long afterglow properties.When the Cr³⁺content is 0.1%,the long afterglow effect of the material will last 11000 s.After co-doping Nd³⁺,the emission spectrum of the material extends to the second biological window.The characteristic emission band of Nd³⁺is observed under the excitation of the characteristic absorption wavelength of Cr³⁺,indicating that there is energy transfer between Cr³⁺and Nd³⁺.At the same time,the excitation spectrum and lifetime spectra further confirm the energy transfer between Cr³⁺and Nd³⁺,and the way of energy transfer is carried out through the F?rster resonance energy transfer?FRET?.After co-doping Yb³⁺,the energy transfer between Cr³⁺and Yb³⁺is also reflected in fluorescence spectra and excitation spectra.A small amount of Yb³⁺?1%–4%?does doped do not lead to other new phase formation.A large amount of Yb³⁺?>4%?will lead to the formation of new phase,and the content of the new phase increases with the increase of the amount of Yb³⁺doping.Interestingly,adding the appropriate amount of Yb³⁺can enhance the long afterglow effect of Sr₂MgWO₆:Cr³⁺materials.We have studied the phenomenon in detail.Through the analysis of the thermoluminescence and XRD spectra,we think that the new phase produced by the addition of appropriate Yb³⁺ions increases the defects of the material,thus achieving a more lasting long afterglow effect.Sr₂MgWO₆:Cr³⁺,Nd³⁺/Yb³⁺has strong fluorescence and long lasting afterglow effect in NIR region.Its emission band is located in the permeable window of biological tissue.It is expected to replace the gallium containing material to be a new kind of NIR material for bioimaging.