Study On The Luminescence Properties Of Ion-doped Perovskite Quantum Dots

Lead halide perovskite CsPbX₃ have outstanding advantages in wide color gamut,high color purity and high quantum yield(PL QY).Hence,it has caused great repercussions in the fields of lighting,multidimensional encryption,photoelectric detection and so on.Nevertheless,lead halide perovskite CsPbX₃have some shortcomings.For example,it contains heavy metal element lead.The photoluminescence quantum yield of CsPbCl₃quantum dots(QDs)in blue light region is relatively low.The stability of CsPbI₃QDs is poor.CsPbX₃QDs are ionic crystals,and it is easy to aion exchange between different components of perovskite.The traditional synthesis methods of CsPbX₃QDs have many problems,such as operation process,high equipment cost,and preparation in rare gas environment.Therefore,in order to solve the above-mentioned problems,we used an optimized lower temperature injection method to prepare CsPbX₃QDs to improve their yield and stability.The details are as follows:(1)In this chapter,CsPbX₃QDs were fabricated by an optimized low-temperature injection method under ambient environment.The precursors were mixed at 120?and transferred to 90?for reaction.Multicolor perovskite quantum dots were characterized by steady-state fluorescence spectrometer.The photoluminescence emission spectrum is adjustable in the range of 404?675 nm,the FHWM in the range of 13?46nm and PL QY can reach 77%.Transmission electron microscope images show that the quantum dots are homogeneous and monodispersed in cube shape.X-ray diffraction analysis showed that the structure of QDs was cubic.X-ray photoelectron spectroscopy was used to determine the composition,valence state and proportion of the elements.The method provides a new scheme for the synthesis of CsPbX₃QDs.(2)In view of the low PL QY in the blue light region and poor stability in the red light region,on the basis of the above-mentioned improved lower temperature synthesis method,we introduced Ni²⁺and K⁺ions into CsPbX₃QDs to replace Pb²⁺and Cs⁺ions.By adjusting the component concentrations of various halogen salts,we studied the incorporation of Ni²⁺and K⁺ions into CsPbX₃QDs.It is found that a certain amount of doping is beneficial for suppressing the defects and improving the lattice structure of QDs,whereas an excessive dopant may induce quenching centers of emission.The absolute PL QY of doped CsPbX₃QDs can be obtained by our method.The absolute PL QY of CsPbCl₃QDs has been increased from less than 1%to more than 5%,it is almost 80%for Cs Pb Br₃ and CsPbI₃.In addition,the stability of Ni-doped QDs has been greatly enhanced The photo-and structure-stability of the Ni²⁺doped CsPbI₃ samples retain about 2 months without degradation and deterioration.(3)Mn-doped perovskite CsPb(Cl/Br)₃ have been explored due to their unique dual-color emission characteristics,which introduce the exciton emission in blue region and the stable Mn²⁺emission peak in orange-red region by energy transfer from exciton to Mn²⁺emission.Although high doping concentration Mn²⁺could increase the Mn²⁺emission,excess Mn²⁺ions would be expelled from the host perovskite lattice.Doping secondary metal Ni²⁺into the QDs is always used to improve the Mn²⁺emission.We adopted a one-pot halogen injection into Cs-precursor under ambient environment method to prepare(Mn,Ni):CsPbCl₃ and(Mn,Ni):CsPb(Cl/Br)₃QDs,which introduces NiCl₂ in the Mn:Cs Pb(Cl/Br)₃QDs to supply halide ions and to passivate defect states or traps in the perovskite so as to enhance Mn²⁺emission.Density Functional Theory(DFT)calculations were also conducted to explain our experimental results,which revealed that Ni²⁺doping could eliminate the in-gap deep defects of the Cs Pb(Cl/Br)₃.In addition,the passivated lattice defects help to improve the stability of the perovskite QDs,preventing from electron beam irradiation.White LEDs based on(Mn,Ni):CsPbCl₃ were fabricated,and the changes of color coordinates,color rendering index and color temperature with the increase of driving current were studied.