Controllable Synthesis Of Near-infrared PbS Colloidal Quantum Dots

Colloidal quantum dots can be used as key materials in fields of biological imaging,photovoltaic,lasers etc.,due to their size-tunable optical properties and solution processability.Among them,lead sulfide(PbS)quantum dots have tunable photo-response in a wide near-infrared range and good stability as well,which are suitable for medical imaging and photoelectric detection applications.At present,the low-cost hot-injection method is commonly applied to synthesize PbS quantum dots,which plays a significant role on the final quality of the synthesized quantum dots.In order to control synthesis process of PbS quantum dots by hot-injection,we focus on additive effect and developing a new lead precursor in the thesis:Lead chloride as lead source was mixed with olamine(OLA),and followed by heating,in order to form lead prectursor solution.Then the elemental sulfur(S)-OLA solution mixed with a certain volume of tributylphosphine(TBP)was rapidly injected into the lead precursor solution to synthesis of PbS quantum dots.The effect of TBP on the growth of quantum dots was studied by UV-Vis-NIR absorption spectrum and transmission electron microscopy(TEM).The results show that when other conditions in the synthesis route are consistent,the higher the temperature of the lead precursor during sulfur injection,the larger the size of the PbS colloidal quantum dots;The larger the lead-sulfur mass ratio,the smaller the size of the PbS colloidal quantum dots;The smaller the TBP,the larger the size of the PbS colloidal quantum dots.It is worth mentioning that when the temperature of lead precursor is 70? and 90? the trace TBP can effectively stop the growth process of PbS quantum dots,leading to good controllability on the size or absorption properties of PbS QDs.The Pb(OH)Cl matrial was synthsized by mixing the prepared sodium chloride and basic lead acetate aqueous solutions.The obtained Pb(OH)CI was heated with OLA and oleic acid(OA)to form the lead precursor solution,and then the prepared S-OLA solution was rapidly injected into the lead precursor to obtain PbS colloidal quantum dots.After being characterized by UV-Visible-NIR absorption spectroscopy,XRD,TEM,We found that the size of the synthesized quantum dots(photoresponse range)can be adjusted by controlling the temperature of lead precursor during sulfur injection:the high injection temperature led to large size of PbS colloidal quantum dots and tuanble optical response in wide range.Secondly,the size of PbS QDs can be well controlled by injecting OA into Pb(OH)Cl-OLA solution in different temperatures,and by injecting the S-OLA into the lead precursor at a temperature of 70?.It reveals that the size of obtained PbS QDs decreased with increasing the OA injecting temperature.Importantly,the size of PbS colloidal quantum dots show poor dependance on reaction time,indicating the well-controllable synthesis of PbS QDs.With this synthesis route,we have successfully prepared near-infrared PbS colloidal quantum dots with absorption peaks ranged from 1100 nm to 1770 nm,good monodispersity and high stability.XRD,Fourier transform infrared spectrum and TEM have been employed to investigate the reaction mechanism of PbS synthesis using Pb(OH)Cl as the lead source.TEM images of Pb(OH)Cl raw materials and lead precursors show that the injection of OA into the Pb(OH)Cl-OLA turborous solution could split the rod-shaped Pb(OH)Cl in micro-scale into submicro-scale particles with cracks on the surface;then,the particle size was further decreased after the injection of S precursor,and the stable PbS colloidal quantum dot solution was successfully obtained.We speculate that S2-substituted OH-and Cl-ions in Pb(OH)DCl to form PbS on surface of large Pb(OH)Cl particles.The different the mismatch of the lattice structures between Pb(OH)Cl and PbS led to the separation of formed PbS partices from the surface of Pb(OH)Cl.The absence of nucleation process in the synthesis would have benefit the well-controllable synthesis of PbS quantum dots.