Investigation On Ratiometric Temperature Sensing Of Rare-earth-doped Inorganic Luminescent Materials

Precise temperature measurement plays a significant role in all natural sciences.With the rapid development of nanotechnology,the demand for temperature detection with nanoscale resolution is increasing in the fields of nanomedicine,microelectronics and catalytic.However,conventional types of thermometers are failed to meet the requirement,and luminescent thermometers have become a hot spot because of their high spatial resolution and remote monitoring with fast response.Due to the excellent photostability,narrow-band emissions covering the entire electromagnetic spectrum and unique versatility of rare-earth doped luminescent materials,the lanthanide-based ratiometric luminescent thermometers have become very popular,which have been widely used in cell thermal imaging and microelectronic fault diagnosis.This thesis focuses on the selection and optimization of lanthanide-based ratiometric luminescent thermometers,and develops the biological window thermometers with higher penetration depth in biological tissues.The details are as follows:(1)Prediction of the performances of different thermometric materials will contribute to the design and selection of luminescent thermometers,but it's rarely noticed.Here,we unveil the typical thermal-coupled thermometry of Er³⁺based on Er³⁺/Yb³⁺codoped ten host lattices.The calculation of microstructure parameters around Er³⁺by the chemical bond theory of complex crystals reveals the luminescent properties and thermometric performances of ²H_11/2?⁴I_15/2 and ⁴S_3/2?⁴I_15/2 transitions.Through theoretical analysis,hypothesis and further result fitting,the quantitative relationship between the thermometric parameters and the defined chemical bond parameters is established for the first time,which breaks through the limitation of only evaluating thermometric performances from spectral phenomena.And the prediction of thermal-coupled thermometric performances of Er³⁺for a given host material is realized.(2)The current luminescent thermometers focus on the visible region,and have the disadvantage of low tissue penetration depth,which limits the temperature detection of deep tissues.Due to the lowest tissue absorption and scattering of biological windows,we design one ultrasensitive luminescent thermometer located in the first biological window(BW-I)utilizing phonon-assisted thermal enhancing and thermal quenching based on NaYb(MoO₄)₂:Tm³⁺nanosheets sensitized by Yb³⁺-MoO₄^2-dimers.Its relative temperature sensitivity(S_r)is as high as 6.5%K^-1 at 313 K,with98.3%repeatability and optimal temperature resolution as low as 0.16 K.The tuning of Yb³⁺-Mo O₄^2-dimers to the luminescence process and temperature sensing is studied.In addition,we explore the temperature detection of the proposed BW-?thermometer in simulated biological tissues,and successfully measure the temperature inside the chicken breast.(3)Compared with BW-?,the second and third biological windows(BW-?/?)can further improve the signal-to-noise ratio by filtering out autofluorescence,which is more suitable for in vivo temperature detection.Using the BW-? emission of Ho³⁺and the BW-? emission of Er³⁺,a new type of BW-?/? ratiometric thermometry with phonon-tuned sensitivity is proposed.We analyze the thermometric model and mechanism based on phonon-assisted energy transfer and multi-phonon relaxation processes,which are verified by Ho³⁺/Er³⁺/Yb³⁺codoped Ba Ti O₃,Gd₂O₃,Y₂O₃,Y₃Al₅O₁₂ and YVO₄ samples.It is revealed that different phonon modes contribute differently to phonon-assisted energy transfer and multi-phonon relaxation,and the temperature sensitivity can be predicted by the dominant phonon energy of host lattice.In addition,we utilize monodisperse Y₂O₃:Ho³⁺/Er³⁺/Yb³⁺nanospheres to explore their temperature sensing in aqueous solution and chicken breast tissues,and initially discuss the influence of water and chicken breast tissues on thermometric performance.(4)In the past ten years,the lanthanide-based ratiometric luminescent thermometers have drawn much attention,and researchers are committed to developing high-sensitive thermometers,including absolute temperature sensitivity(S_a)or S_r.However,whether higher S_a or S_r can improve thermometric performance and the factors that determine the accuracy are rarely considered.Through error analysis and experimental verification of eleven luminescent materials,we clarify that the intrinsic influencing factors of temperature uncertainty(?T)are S_r and the relative error of luminescent intensity(?I/I),and high S_a cannot improve?T,which corrects the previous understanding of S_a;?I/I is affected by energy level splitting.For temperature detection of biological tissues,we also need to consider the influence of external factors around thermometers.Therefore,we prepare a hydrophilic ratiometric luminescent thermometer based on NaYF₄:Er³⁺/Yb³⁺@NaYF₄-PEI,and discuss the influence of self-heating,excitation power density,emission intensity and penetration depth on thermometric accuracy.