Mechanism Research On Three Kinds Of Rare Earth Luminescent Sensing Materials

The research on sensing mechanism attracts great attentions nowadays due to the tremendous demand for sensor in modern society. Rare earth luminescent sensing material is one of the most important issues of concern. Due to the special luminescent properties, the rare earth ions can be used as fluorescence probes, which is important in probing short-range structure of materials and electronic structure of rare earth ions. The inorganic fluorescent probes have great potential application in biological labeling. Due to low toxicity and high stability, rare earth ions doped upconversion nanoparticles are attracting more attention. High upconversion efficiency is good to biological labeling. The temperature sensing based on rare earth luminescent materials is a good contactless temperature measuring method. One of the research focus is to improve the sensitivity. Based on these analyses, my research focuses on the fluorescence probe function of rare earth ions, upconversion naoparticles used in biological labeling and temperature sensing of rare earth luminescent material.In chapter one, we introduced the fundamental knowledge of sensor and rare earth ions. The effect of crystal field on the energy level of rare earth ions, the function of luminescent ions in fluorescence probe and the application of inorganic fluorescent probe in biological probe were introduced in detail, which focus on the fluorescent probe function of Eu3+and upconversion nanoparticles doped with rare earth ions. Additionally the temperature measuring methods and temperature sensor based on luminescence were introduced briefly.In chapter two, we investigated on luminescence properties of Eu3+ions as a fluorescence probe in NaYF4nanoparticles and CaW04nanorods.First of all, monodisiperse hexagonal phase NaYF4:2%Eu3+core and NaYF4:2%Eu3+/NaYF4core/shell NCs were synthesized through a wet chemical method using oleic acid (OA) and octadecence (ODE) as solvents. The PL properties are investigated in detail for core and core/shell samples. The relationship between the structure of the sample and the spectral structure of Eu3+emission is discussed. The fluorescence decays are also studied, the interpretation of which are in agreement with that for the emission spectra. In addition, the intrinsic quantum yields have been evaluated to analyze the experimental results.Besieds, we report the synthesis of monodisperse and uniform CaWO4:Eu3+, Li+nanorods via a solvethermal route. The PL properties are investigated in detail for:Eu3+, Li+samples. In addition, we focus our attention on the5D0lifetime of:Eu3+, Li+nanorods. The effect of the compactness and dispersion of nanorods in air on the5D0lifetimes are analyzed in detail. It is shown that the5D0lifetime is easily tuned by varying the compactness of the nanorods in air, and this is attributed to the size of the nanorods and the effective-refractive index of the medium surrounding Eu3+ions.In chapter three, we investigated on the upconversion luminescence mechanism in YbAG:Er, Mo. it has been reported that the UC properties of Er3+-Yb3+are greatly enhanced by doping Mo6+into Yb3Al5O12(YbAG) and Yb2Ti2O7. And the Er-Yb-Mo systems in oxysalt matrix exhibit an extraordinary enhancement of green UC efficiency-a four orders of magnitude enhancement relative to the Er-Yb oxides without Mo doping. However, we noticed that there are still some doubts about the exceptional UC property. Firstly, impurity phase was obviously found in the XRD patterns of YbAG:Mo6+, Er3+/Tm3+, which was not addressed in the reference. Secondly, there are remarkble differences in spectral pattern and peak positions between Er-Yb and Er-Yb-Mo systems. In addition, it has been interpreted that the anomalous UC property is due to a novel energy transfer pathway from the formed Yb3+-MoO42-dimmer to the rare-earth ions, and this is assigned as a two-photon process. However, it is also doubtful that the UC luminescence of Er-Yb-Mo systems enhanced by a factor of four orders through combination of GSA+ESA, which is usually of a relatively low efficiency. What is more, the lowest excited state of MoO42-groups is generally much higher than twice of that of980nm photon absorbed by Yb3+and the large energy mismatch should lead to a lower efficiency further. On the other hand, we also notice that Er-Yb in molybdate and tungstate host usually have a high UC efficiency. For these reasons above, we believe that it is necessary to further scrutinize these UC materials and to clarify the underlying mechanism. In order to determine what the impurity is and check whether the impurity is the origin of the observed anomaly, we conducted a series of experiments in this work and attribute the anomalous UC luminescence to mixture of Yb2(MoO4)3:Er3+ In chapter four, hexagonal phase sodium yttrium fluoride (β-NaYF4) was chosen as the host material. Under574.8nm excitation, the photoluminescence (PL) properties of Nd3+ions in β-NaYF4; Nd3+microcrystals were investigated systematically by changing the temperature of the sample. By using FIR technology, we confirmed that the thermal coupling between the4F7/2and4F3/2levels of Nd3+had been achieved, just as our prediction. And a large relative temperature sensitivity of1.12%K-1at500K is reached with the FIR of4F7/2to4F3/2levels. The thermally enhanced luminescence of4F7/2and4F5/2level of Nd3+was also investigated systematically by changing the temperature of the sample. A rate equation model that includes light pumping and multiphonon absorption via thermally coupled electronic excited states of Nd3+ions was used to explain the experimental results.