Preparation And Temperature Sensing Properties Of Rare Earth Doped Germanate Luminescent Materials Based On Fluorescence Intensity Ratio

As one of the fundamental physical parameters,temperature plays a vital role in many fields such as physics,chemistry and physiology.The high-powered thermometers which are contactless,uninjurious and peculiarly able to work in high temperature condition have been attracting immense interest from researchers worldwide.Recently,fluorescence thermometry has received great attention as a newfangled temperature sensing method which can enable temperature sensing in local regions by using the fluorescence intensity ratio（FIR）technique.To date,rare earth（RE）ions doped materials are usually selected as the FIR optical thermometers due to the temperature-triggered inverse particles population in thermally coupled levels of RE ions.However,these kinds of optical thermometers normally have low sensitivities on account of the small energy gap between two thermal coupled levels of RE ions.In order to better meet the demand for accurate temperature measurement in the fields of diagnostics and clinical medicine,this paper discussed the temperature measurement technology of up-/down-conversion based on rare earth Eu³⁺ions and transition metal ions Cr³⁺doped Ba₂TiGe₂O₈ phosphors,and gave corresponding mechanism explanation from the theoretical perspective.The main contents of this paper are as follows:（1）A multifunctional thermometer based on trivalent rare earth ion(Eu³⁺)doped Ba₂TiGe₂O₈ phosphor has been successfully fabricated by high-temperature solid-state method.The crystal structure,phase purity and luminescence properties have been characterized by X-ray diffraction,Fourier infrared spectroscopy,absorption spectrum,photoluminescence spectrum and variable temperature spectrum.A novel optical temperature sensing mechanismhas been proposed.The maximum relative sensitivity（S_r）of 0.93%K^-1 at 358 K,which is higher than that of most thermometers.These results demonstrate that the BTG:Eu³⁺phosphor could be a kind of promising and multifunctional material.（2）A novel optical thermometry based on Cr³⁺/Ln³⁺/Yb³⁺（Ln=Er,Ho）tri-doped BTG phosphors has been successfully fabricated by a high-temperature solid state method,and the corresponding phase formation,structure characteristics and luminescent properties have been also discussed in detail.BTG is chosen as the host material owing to the appropriate crystal field,low phonon energy and the suitability of incorporation of both Cr³⁺and Ln³⁺ions.It is confirmed by our experiments that the up-conversion luminescence of Cr³⁺can be achieved by the following energy transfer process:Yb³⁺→Ln³⁺→Cr³⁺,where Ln³⁺ions act as the energy transfer intermediary and Yb³⁺ones as the sensitizers to absorb the 980 nm phonons.The maximum relative sensitivities（S_r）of our investigated phosphors are 3.95%K^-1(Er³⁺/Cr³⁺)at 313 K and 2.67%K^-1(Ho³⁺/Cr³⁺)at 313 K,respectively,which are much higher than those of most up-conversion（UC）thermometers.All the results prove the possibility of realizing a kind of high-efficient and deep-penetration optical thermometry with high sensitivity in the biology field.