Rare Earth Doped Luminescence Thermometric Nanomaterials Toward Biological Applications

With the rapid development of nanotechnology and biotechnology,such as Nano-biomedicine and other fields,new requirements for temperature measurement technology have been put forward.It is urgent to develop fluorescent thermometers with high fluorescence efficiency,high accuracy,high sensitivity and high resolution suitable for physiological temperature range.Rare earth doped fluoride nanomaterials are a kind of bio-probe materials with excellent comprehensive properties due to their high penetration depth,no background fluorescence,strong chemical stability of fluoride matrix,low phonon energy and low cytotoxicity.In this paper,two new fluorescent thermosensitive materials were designed based on the new mechanism found and proposed by our previous work that the thermal expansion of the lattice inhibits the surface fluorescence quenching caused by the energy transfer of sensitizers.First,a new fluorescence lifetime temperature probe has been developed.In Nd³⁺/Yb³⁺co-doped fluoride nanoparticles,the lifetime of the excited state(²F_5/2)of Yb³⁺ions increases monotonously with the increase of temperature.This is because increasing temperature slows down the energy migration to the surface quenching process.At present,there is no report on inorganic thermometric materials whose fluorescence lifetime increases with temperature.Therefore,based on this unique phenomenon,we designed and evaluated such fluorescence lifetime temperature probe.The maximum absolute/relative sensitivity?Sa/Sr?is as high as 2.68?s*K^-1/1.59%K^-1 in the range of biological temperature?30-70??,which indicates that the nanomaterials studied have good properties and broad application prospects in the biological field.The second part is to develop a new fluorescence intensity ratio temperature probe.In Nd³⁺/Yb³⁺/Tm³⁺co-doped fluoride nanoparticles,we constructed a fluorescence intensity ratio temperature probe using Nd³⁺excited state absorption upconversion and cross relaxation upconversion luminescence and Tm³⁺ion energy transfer upconversion luminescence.Despite the unsatisfactory performance and relative sensitivity,this method provides a useful idea for designing better temperature probes,and there is still a lot of room for optimization,and the performance can continue to improve.