Preparation Of Yb³⁺/Er³⁺ Co-doped Red Upconversion Materials Along With The Study Of The Correspongding Temperature Sensing Properties

With the rapid development of science and technology,upconversion luminescent materials have been developed as a new kind of luminescent materials.Upconversion luminescent materials have unique advantages,such as stable emission spectrum,large anti-stokes shift and high optical stability.So upconversion luminescent materials are widely used in information storage,anti-counterfeit labels,three-dimensional display,solid-state lasers and other fields.In addition,nanomaterials own advantages of good biocompatibility,weak background fluorescence and strong tissue penetration.Which make them suitable for bioimaging,photodynamic therapy and so on.However,most up-conversion luminescence is mainly green light,which has limited penetration depth in biological tissue.Therefore,the emission wavelength can be modulated in the biological window.In this thesis,Yb³⁺/Er³⁺co-doped Na Sc F₄,Ba Y₂O₄ and Ca O-Y₂O₃upconversion red light materials were successfully prepared and the fluorescence temperature-sensitive properties were studied.The specific research contents and analysis are as follows:The first part:An approximately monochromatic red upconversion emission is successfully realized in Na Sc F₄:Yb³⁺/Er³⁺nanoparticles(NPs)through Mn²⁺ions doping without phase transition.The Mn²⁺ions play a role of bridge during the energy transfer process from green emission state ²H_11/2/⁴S_3/2 of Er³⁺to red emission state ⁴F_9/2of Er³⁺,which significantly accelerates the red UC enhancement.The strongest red luminescence is observed in the sample containing 10%Mn²⁺ions(Mn-10)with an enhancement factor of 7.5 times.Meanwhile,an ultrasensitive optical thermometry in the physiological temperature region can be realized by utilizing the fluorescence intensity ratio(FIR)between two thermally coupled Stark transitions of Er³⁺:⁴I_13/2?⁴I_15/2,locating in the near-infrared long wavelength region of the second biological window(NIR-II).Its relative sensitivity S_R can be expressed by 340/T²,which is much higher than most optical thermometers based on thermally coupled Stark sublevels reported by the previous papers.Beyond that,an ex vivo experiment is designed to evaluate the penetration depth of the red and NIR emission of Mn-10 in the biological tissues,revealing that they can reach depth of at least 3 mm and 5 mm respectively.More importantly,the increasing tissue thickness has almost no effect on the FIR values.All the results show that the present sample is a promising bi-functional nano probe which can be used for bioimaging and temperature sensing in the deep tissues through the strong red UC emission and ultrasensitive NIR optical thermometer,respectively.The secord part:BaY₂O₄:Yb³⁺/Er³⁺,a high effiffifficient red upconversion material,is first utilized as an optical thermometer in the biological window,accomplished through the FIR of thermally coupled Stark sublevels of ⁴F_9/2(FIR_(654/663)).The maximum absolute sensitivity of FIR_(654/663)is 0.19%K^-1 at 298 K,which is much higher than most previous reports about FIR-based temperature sensors located in the biological windows.More importantly,the groove of FIR_(654/663)for thermometry is nicely located in the physiological temperature range,indicating its potential thermometry application value in biomedicine.Furthermore,a simply ex vivo experiment is implemented to evaluate the penetration depth of the red emission in biological tissues,revealing that a detection depth of 6 mm can be achieved without any effect on the FIR values of I₆₅₄ to I₆₆₃.Beyond that,the temperature sensing behaviors of the thermally coupled levels ²H_11/2 and ⁴S_3/2(FIR_(523/550))are also investigated in detail.In the studied temperature range,the absolute sensitivity of FIR_(523/550)monotonously increases with the rising temperature and reaches its maximum value0.31%K^-1at 573 K.All the results imply that Ba Y₂O₄:Yb³⁺/Er³⁺is a promising candidate for deep-tissue optical thermometry with high sensitivity.The third part:A conventional high temperature solid state method was utilized to prepare Ca O-Y₂O₃,which is a potential candidate for manufacturing crucible material to melt titanium and titanium alloys with low cost.Meanwhile,Yb³⁺ions and Er³⁺ions were selected as the sensitizers and activators respectively to dope into Ca O-Y₂O₃,aimed at providing real-time optical thermometry during the preparation process of titanium alloys realized using FIR technology.The results reveal that a high measurement precision can be acquired by using the Stark sublevels of Er³⁺⁴F_9/2 to measure the temperature with a maximum absolute error of only about 3 K.In addition,by analyzing the dependence of ⁴I_13/2?⁴I_15/2 transition on pump power of 980 nm excitation wavelength,it was found that the laser-induced thermal effect has almost no influence on the temperature measurement conducted by using the FIR of the Stark sublevels of Er³⁺⁴I_13/2,which means that a high excitation pump power can be used to obtain strong NIR emission and good signal-to-noise ratio for optical thermometry without the influence of the laser-induced thermal effect.All the results reveal that Ca O-Y₂O₃:Yb³⁺/Er³⁺is an excellent temperature sensing material with high measurement precision.