Research On The Rare-earth Doped Up-converting Thermometers Based On The Fluorescent Intensity Ratio Technique

The accurate measurement of temperature is very important in many fields,such as industrial manufacture,electronics,scientific research,aerospace and defense.Among all temperature sensing methods,the fluorescent intensity ratio?FIR?technique based on thermally coupled levels?TCLs?has aroused considerable interests due to its fast response,high spatial and thermal resolution.Stimulated by the development of nanotechnology,lanthanide doped up-conversion?UC?materials have been widely proposed as potential FIR thermometers,especially in biological systems,thanks to their excellent luminescent properties,low toxicity,minimized background auto-luminescence and deep tissue penetration.This thesis aims to construct the multifunctional UC nano-platforms with optimized performances.Several strategies were adopted to improve the UC intensity,thermal sensitivity and photo-thermal effects,and the mechanisms were theoretically investigated.Finally,the feasibility of samples acting as self-monitored photo-thermal agents?PTAs?in sub-tissues and antibacterial agents was assessed.This thesis includes the following four parts:?1?A series of Yb³⁺/Ln³⁺?Ln=Ho,Er,Tm?co-doped UC phosphors with efficient green,red and blue emissions were respectively synthesized by a sol-gel process using Ba₅Gd₈Zn₄O₂₁1 with low phonon energy as the host.Spectrally pure green UC emission and dual modulation of UC color were separately realized in Yb³⁺/Ho³⁺and Yb³⁺/Er³⁺co-doped samples,and the mechanisms were proposed in detail.The thermal sensing behaviors were evaluated based on the ²H_11/2/⁴S_3/2/2 and ⁴F_9/2/2 stark levels of Er³⁺and ¹G₄ stark levels of Tm³⁺,and the effects of UC color and doping contents on the sensitivity were elaborately discussed.Photo-thermal effects of Yb³⁺/Tm³⁺co-doped samples were further assessed,which lays the foundation for the construction of multifunctional UC nano-platforms.?2?In consideration of the biological applications,a series of UC nano/micro-thermometers with precisely controlled morphology were synthesized by hydrothermal procedure using YF₃ with low phonon energy as the host,Yb³⁺as the sensitizer and Er³⁺and Tm³⁺as luminescent centers,respectively.The effects of morphology and size of YF₃:Yb³⁺/Er³⁺on UC emission and thermal sensing behavior were explored,and the sub-tissue thermometry was also assessed using rice-like nanoparticles.Through increasing Yb³⁺contents,the intensity ratio of³F_2,3?³H₆ to³H₄?³H₆ transitions was greatly improved in YF₃:Yb³⁺/Tm³⁺micro-crystals.Moreover,the thermometric ability was evaluated within the biological window based on the ³F_2,3/³H₄ TCLs,and the effects of Yb³⁺contents on the sensitivity and photo-thermal effects were elaborately studied,which provides great potential applications in sub-tissue thermometry and photo-thermal therapy?PTT?.?3?In order to optimize the thermal sensitivity,the influences of phonon energy and local site symmetry of hosts on the UC emission and thermometric ability were systematically investigated.Firstly,phase transformation from Yb³⁺/Er³⁺co-doped YF₃ to YOF and Y₂O₃was realized by controlling the annealing temperature,and the effect of phonon energy on the UC color was analyzed.By evaluating thermal sensing behavior of samples,the inner relations between phonon energy or bond covalency and sensitivity were qualitatively demonstrated according to J-O theory and first-principle calculations.Moreover,trigonal La₂O₃:Er³⁺/Yb³⁺nano-spheres were prepared using cubic Lu₂O₃ and Y₂O₃ as contrasts.The local site distortions of three hosts caused by dopants were evaluated using Eu³⁺ion to explain the big differences of samples in UC intensity.The relations between local site symmetry and thermal sensitivity were elaborately studied according to J-O theory,and sub-tissue thermometry was also realized using La₂O₃:Er³⁺/Yb³⁺nano-thermometers.Results provide efficient routes for the design of UC thermometers with desired sensitivity.?4?In order to avoid the heating effects of 980 nm irradiation on biological tissues,Nd³⁺/Yb³⁺/Er³⁺tri-doped yolk-shell GdOF@SiO₂ and olive-like LuVO₄@SiO₂@Cu₂S multifunctional UC nano-platforms were respectively constructed using Nd³⁺as the 808nm light-absorptive sensitizer and biocompatible SiO₂ as the shell.Under 808 nm excitation,the effects of yolk-shell configuration,Nd³⁺doping and Cu₂S coating on UC emission,photo-thermal effects and thermal sensitivity were investigated in detail,respectively.Moreover,the feasibility of samples acting as self-monitored PTAs in sub-tissues and antibacterial agents was assessed.Results open a general avenue for designing 808 nm light-driven nano-platforms with strong UC emission,sensitive thermometry and efficient photo-thermal conversion,which provides great potential applications in biomedical science.