Luminescent Modulation Of Rare Earth Doped Nanomaterials/Quantum Dots:Photoelectrochemical Application

In recent years,with the rapid development of nanotechnology,the nano-fluorescent materials have maked extensive attention in biosensing,fluorescent labeling,disease dignosis and treatment.However,the inevitable introducted surface defects in the preparation process might induce the fluorescence quenching,and the lower quantum efficiency of luminescence,which becomes a bottleneck problem that limits its practical application.The local light field modulation via surface plasmon resonance of noble metals and photonic crystals to enhance the optical and electrical properties is an effective method to improve the optical stability,sensitivity and detection limits of biosensing applications.On this basis,we systematically studied the fluorescence properties of nano-luminescent materials such as NaYF₄:Yb,Er/Tm,Ti₃C₂ quantum dots and inorganic perovskite quantum dots etc.We utilized the surface plasmon resonance of noble metals and photonic crystals to modulate the localized light field and greatly improve the luminescent efficiency or intensity.We realized the application of photoelectrochemical sensing from visible to near-infrared via the structures and band regulation of semiconductor composite.The main results achieved are as follows:（1）Au-Ag nanocage@NaYF₄@NaYF₄:Yb,Er core-shell hybrid was designed.A non-fluorescent NaYF₄ layer as an intermediate to inhibit the non-radiation transition and tunable plasmon resonance position from visible light to near-infrared light were applied to obtain an efficient up-conversion fluorescence enhancement of 25 times in the colloid.The mechanism of up-conversion fluorescence enhancement is mainly derived from the barrier of the intermediate layer and the coupling of Au-Ag nanocage with the excitation electromagnetic field of UCNPs.（2）A novel,high-quality ZnO inverse opal photonic crystal（IOPCs）/Ag/NaYF₄:Yb,Tm composite film was prepared by the colloidal self-assembling,vapor deposition and laser pulse deposition.In this composite structure,ZnO IOPCs and surface plasmon resonance（SPR）of Ag can greatly enhance the local excitation electromagnetic field of NaYF₄:Yb,Tm,and efficiently convert near-infrared light into visible/ultraviolet light.The ultraviolet light emitted by NaYF₄:Yb,Tm can be further absorbed by ZnO to generate photoelectrochemical response for detecting tumor markers（AFP）.And the linear range of AFP detection is from 0.05 ng/mL to100 ng/mL with a low detection limit of⁰.04 ng/ml.（3）A novel visible light-driven photoelectrochemical sensor was designed:CsPbBr_1.5I_1.5 PQDs/TiO₂ IOPCs.TiO₂ IOPCs as a framework,the stability of PQDs in PEC sensors was greatly improved.CsPbBr_1.5I_1.5 PQDs as a PEC-sensing photosensitive material,the photoelectric response range of the PEC sensor could be extended to the visible region.In addition,the photonic band gap effect of the TiO₂IOPCs on the modulation of incident light and the emitted light of PQDs can further enhance the photoelectric response.Such a PEC sensor demonstrates a sensitive detection for DA in phosphate buffer saline solution and serum,with a good linear range from 0.1μM to 250μM and a low detection limit of approximate 0.012μM.（4）Surface functionalized MXene quantum dots（QDs）Ti₃C₂ QDs were synthesized by ultrasonic cutting and hydrothermal methods.Due to size effects and surface defects,the functionalized Ti₃C₂ QDs exhibit bright and excitation-dependent blue photoluminescence（PL）.At the same time,Ti₃C₂ QDs have a high PL response to the deprotonation effect of surface defects.In addition,combined with high pH-sensitive Ti₃C₂ QDs and pH-free[Ru（dpp）₃]Cl₂,we designed a ratiometric fluorescence pH sensor to quantitatively monitor intracellular pH.（5）TiO₂ IOPCs/Ti₃C₂ QDs composite films were prepared by self-assembly method.Due to the broad absorption band of Ti₃C₂ QDs,the photocurrent response of TiO₂ IOPCs/Ti₃C₂ composite films could range from 280 nm to 900 nm,and the energy conversion efficiency can reach 26%at 350 nm.Due to the good energy level matching,Ti₃C₂ QDs and TiO₂ form a typeⅡheterojunction,which realizes efficient separation and directional transmission of charges.TheⅡ-type heterojunction PEC sensor consisting of TiO₂/Ti₃C₂/Nafion electrode has high stability,sensitivity and selectivity for the detection of glutathione in buffer solution and cell extract.