Synthesis Of Photoluminescent Manganese-Doped Semiconductor Nanocrystals And Their Study On Oxygen Sensing

Since the 1990s,the study of photoluminescence?PL?properties of semiconductor nanocrystals has been one of the important research directions in photochemistry.In the last five years,lead halide perovskite nanocrystals?LHP NCs?,as emerging ionic semiconductor nanocrystals,have exhibited better photoelectric properties than conventional semiconductor nanocrystals,including tunable emission wavelength,defect tolerance ability,high PL quantum yield,high carrier mobility and so on.Doping Mn²⁺ions can regulate the electron-hole recombination of semiconductor nanocrystals.Through an effective exchange coupling between the exciton of host nanocrystals and Mr1+ions,the doped nanocrystals show a unique PL emission?⁴T₁?⁶A₁?with a long lifetime.Due to their good optical properties,Mn-doped semiconductor nanocrystals have been used not only in photoelectric devices,but also in sensing and bioimaging.Oxygen is one of the most important elements that are closely related to life.Researches of oxygen gas and dissolved oxygen sensing are of great significance to the fields of environmental science and biomedicine.At present,optical sensing materials for oxygen are mostly phosphorescent molecules and their functionalized nanocrystal composites.There is still a large potential for oxygen sensing using the fluorescence or phosphorescence emission of semiconductor nanocrystals.In this thesis,research works focus on the synthesis of photo luminescent Mn-doped semiconductor nanocrystals and their study on oxygen sensing.A simple synthetic method of Mn-doped cesium lead chloride perovskite nanocrystals?Mn:CsPbC1₃ NCs?has been proposed,and the optical sensing performance of Mn:CsPbC1₃ NCs and Mn-doped zinc sulfide nanocrystals?Mn:ZnS NCs?for oxygen has been studied.This dissertation includes the following four chapters:In chapter I.conventional semiconductor quantum dots and LHP NCs are reviewed firstly.Then the photoluminescent metal-doped semiconductor nanocrystals and their synthetic methods are introduced.The PL properties of semiconductor nanocrystals doped with transition metals and their applications in optoelectronic devices and analytical chemistry are further introduced.On the basis of these,the research scheme of this thesis is proposed.In chapter II,a new strategy for the synthesis of Mn-doped all inorganic LHP NCs has been proposed.Mn:CsPbCl₃ NCs were successfully prepared via a "one pot"method using lead stearate as precursor.Compared with the hot-injection method,the whole process of "one pot" method could be completed under ambient atmosphere within a few minutes,which simplified the synthesis process and improved the efficiency.The composition,structure and optical properties of Mn:CsPbC1₃ NCs were investigated under different proportions of MnC1₂ precursor and synthesis temperatures.The products had good crystal structure,adjustable doping concentration and a long-lifetime phosphorescence?⁴T₁?⁶A₁?emission from Mn dopants.In addition,doping efficiency could be further improved by changing the chlorine source in synthesis.This simple and controllable synthesis method has established the basis for the study on optical sensing based on the Mn:CsPbC1₃ NCs.In chapter ?,Mn:CsPbC1₃ NCs,which were simply and economically synthesized,were used as optical sensing materials.By adjusting the amount and distribution of Mn dopants,as well as the host-dopant energy transfer process,the oxygen sensing capability of Mn:CsPbCl₃ NCs was investigated.The results showed that the fluorescence intensity of the band edge emission had a limited sensitivity to oxygen,while the Mn emission showed a fast and reversible sensing response to oxygen.Mn:CsPbCl₃ film was used for the phosphorescence oxygen sensing test at room temperature.The photoluminescence intensity of the sensor in pure oxygen was 53%lower than its maximum phosphorescence intensity in pure nitrogen.The linear range of oxygen sensing was 0-12%.After 10 cycles of alternating oxygen/nitrogen purging,the sensor still maintained good reversibility.This work has established a certain basis for the phosphorescence sensing of low oxygen concentration using Mn:CsPbCl₃ NCs,and expanded the application of doped perovskite materials in optical sensing.In chapter ?,Mn:ZnS NCs with uniform morphology,low toxicity and stability in water were synthesized and applied to the optical sensing of oxygen gas and dissolved oxygen.The results showed that the dual-emission fluorescence of Mn:ZnS NCs changed rapidly and reversibly by the change of oxygen concentration.Compared with the maximum fluorescence intensity of sensor in pure nitrogen,the intensities of ZnS emission and Mn emission in pure oxygen were decreased by 72%and 32%,respectively.The linear range of oxygen sensing was 3-12%.Sensing performance of dissolved oxygen was also reversible,and the linear range was 0.54-11.42 mg/L.This work is enlightening for the optical sensing application of photo luminescent semiconductor nanocrystals with defect states and exciton energy transfer.