Preparation And Properties Study Of Multifunctional Nanomaterials Based On NaYF₄:Yb,Er

Rare-earth upconversion luminescence materials, converting low frequencyexcitataion light to high frequency emission light via multiphoton mechanism, haveimportant applications in the solid state laser, optical storage, sensors, solar cells andthree-dimensional presentation. In recent years, the researches of fluorescence sensorsbased on upconversion luminescence as detection singal have gradually gatheredattention by chemists, environmentalists, biologists. Upconversion nanomaterials haveshown many advantages, including low toxicity, high chemical stability, good lightstability, large Stokes shift, narrow absorbance and emission bands, simultaneously,near-infrared （NIR） irradiation has lower photo damage effect, a larger penetrationdepth in tissues, and at the same time, it can avoid the autofluorescence interferenceof biological sample and light scattering phenomenon, which reduces backgroundlight and improves signal-to-noise ratio. These excellent properties makeupconversion fluorescence sensors possessing very good application prospect inenvironmental chemistry, clinical toxicology and biochemistry fields. So functionaldesign and synthesis of upconversion nanomaterials have become a research hot spotsin the chemical, material and biomedical fields. On the basis of a vast amount ofliterature research, this thesis synthesize hexagonal phase β-NaYF4nanocrystals usingsimple high temperature organic solvent method and hydrothermal method, and thenprobe molecules and photosensitizer molecules can be combined with upconversionnanomaterials in the form of adsorption or covalently grafting, the obtainedmultifunctional nanocomposites display good ability to recognize specific metal ionor produce singlet oxygen. The major achievements obtained are as follows:1. Hexagonal phase β-NaYF₄nanocrystals was first prepared through high temperature organic solvent method, and then combined with RB-hydrazidepossessing high selectivity for copper ions. Upon NIR light as excitation source,excitation spectrum of RB-hydrazide-Cu overlaps well with upconversion greenluminescence of β-NaYF₄nanocrystals, indicating the possibility for the energytransfer between them. Decreased upconversion luminescence intensity and increasedfluorescence intensity of probe molecules realize the optical sensing for copper ion.The system can effectively and quickly identify copper ions, simultaneously, NIRirradiation displays the advantages of slight background light interference, lowerphoto damage effect, a larger penetration depth in tissues, which endows the systemwith further potential application for copper ion detection in analytical and biologicalfields.2. Core/shell-structured β-NaYF₄@SiO₂nanorods with very thin and uniform silicacoatings have been prepared via simple hydrothermal and sol-gel approaches. Becauseof the upconversion luminescence nanorods core （β-NaYF4） and fluorescent probe（RB-hydrazide） immobilized onto silica shell by covalent bonding, thenanocomposites exhibit good sensing property for mercury ion. Under NIR excitation,nanomaterials show bright upconversion green emission, as well as good selectivityand high sensitivity for mercury ion. As a fluorescence chemosensor, the obtainednanomaterial displays a good linearity between the fluorescence intensity of probemolecules and the concentration of mercury ion. NIR-to-Vis upconversionluminescence and good selectivity for mercury ion, endow the nanocomposites withfurther potential applications for mercury ion detection in analytical chemistry andbiochemistry fields.3. Ordered mesoporous silica encapsulating core-shell structured upconversionluminescence nanomaterials β-NaYF₄@SiO₂@mSiO2have been successfullysynthesized by the surfactant-assistant sol-gel coating method. The mesoporous silicashells possess uniform pore size distribution, high BET surface area and pore volume,which is favorable for loading photosensitizer molecules. Upon irradiation by NIRlight, photosensitizer molecules （Rose bengal） activated by the green emission fromupconversion nanorods can interact with surrounding oxygen molecules and producesinglet oxygen, which can cause oxidative damage to biological substrates andultimately cell death. The generation of singlet oxygen is evaluated using fluorescent indicator. These properties may develop nanocomposites potential application inbiochemistry and biomedical aspects.