Design And Synthesis Of Rare Earth Doped Luminescence Nanomaterials As Thermometry

Lanthanide doped nanomaterials can be applied as luminescent thermometer especially in biological and medical field, owning to its small size, fast response and high accuracy in temperature detection, based on the temperature-sensitive characteristic luminescence of lanthanide ions. Biologically, temperature is an indication of the level of metabolism of cells which reflects the physiological activity of human body. For example, the temperature of cells in the process of division is higher than that of those not, and temperature of cancer cells is also higher than that of normal ones. Thus, characterization of the biological micro-area temperature distribution and variation is of vital importance in research of cell life activities and related disease diagnosis and treatment. However, the application of current luminescent thermometers still faces strong obstacles due to their large size, toxicity, instability, non-self-calibration and low-sensitivity. In addition, the excitation and emission are usually not located in the biological window and the notorious heating effect is inevitable with certain excitation band. To circumvent the above problems we present three novel strategies for the designing of lanthanide doped luminescent thermometer, as exemplified by the experiments given below.Firstly, we designed a single-band thermometer with its excitation and emission both located in biological window. It is based on Yb3+-Er3+ co-doped KMnF3 nanoparticles. In this particles, Yb3+ ions intensely absorb 980 nm light and transfer the energy to Er3+ ions, and meanwhile Er3+ ions at levels of 2H2/9 and 4S3/2 Er3+ can transfer the excitation energy to the 1T4 level of Mn2+, followed by back-energy transfer to the 4F9/2 level of Er3+. These prepared nontoxic nanoparticles with a size of ～14.9 nm give single-band red-light (-660 nm) upconversion with a sensitivity of 6.2～6.7% K-1 at 40～100 ℃. The result is higher than ever reported for lanthanide doped luminescent thermometer. The above approach highlights the delicate design of temperature-sensitive single-band-emitting nanoparticles in the biological window utilizing the energy transfer between Er3+ and Mn2+. However, the luminescence is easily affected by factors other than temperature and is also non-self-calibrated, which largely limit its practical application in biology.Secondly, we designed dual-band nanothermometer with the aim to achieve self-calibration. Considering that single-band thermometers have to be carefully calibrated, they are therefore unable to detect the temperature precisely. Although there are some studies about dual-band thermometer, they suffer lots of drawbacks such as large-size, low-sensitivity and UV excitation. Here, we designed a lanthanide doped core-shell nanostrucrured dual-band thermometer in order to realize self-calibrated and highly-sensitive temperature sensing. NaGdF4:Tm3+/Yb3+@NaGdF4:Tb3+/Eu3+ core-shell nanoparticle was designed and synthesized via a thermal-decomposition method. Under 980 nm excitation, the luminescence intensity ratio of Tb3+(～545 nm) and Eu3+(～615 nm) depends on temperature, and a sensitivity of 1.2%K-1 at 125～300 K was achieved. This approach highlights use of novel core-shell nano-structured nanoparticle in achieving high sensitive dual-band self-calibrated temperature sensing, which presents as a new way in designing thermometer. However, the emission band is not in the biological window and hence heating effect under excitation at 980 nm is inevitable, which, to some degree, limits its practical application.Finally, based on the above results, a dual-band self-calibrated thermometer with excitation and emission band both located in the biological window and no obvious heating effect was designed and realized. This novel thermometer is based on NaYF4:Tm3+/Yb3+@NaYF4:Yb3+/Nd3+ core-shell nanoparticles with a size of 42～49 nm, which can be excited by 808 nm laser and emit at ～696 nm and 645 nm (Tm3+). The luminescence intensity ratio of ～696 nm and ～645 nm from Tm3+ changes with temperature and the highest sensitivity of 1.54%K-1 at 40～240 ℃ was achieved. This approach highlights the selection of Nd3+ as the sensitizer to utilize 808 nm laser as the excitation source because of its low heating effect. Besides, the excitation and emission band are both located in the biological window. Therefore, a novel self-calibrated thermometer with low heating effect, high-sensitivity and totally working in the biological window is achieved based on elaborately designed lanthanide-doped nanostructured nanoparticle.