Structure And Photoluminescence Properties Of Sesium Lead Halide Perovskite Quantum Dots

Recently,cesium lead halide perovskite quantum dots（PQDs）of cesium lead halide（CsPbX₃ X=Br,Cl,I）as a new class of fluorescent materials,which has attracted more and more attention.PQDs have high photoluminescence quantum yields（PLQYs）and extremely narrow emission bands,and their emission can be easily tuned over the entire visible spectral region by controlling the composition and the size.Therefore,it is widely used in light-emitting diodes,solar cells,biological detection,lasers,etc.However,the optical and thermal stability of perovskite quantum dots is still poor,which has led to certain limitations in the development of commercial applications,which lead to the limited development of commercial application and an important problem which puzzles researchers.Here,we prepared a variety of PQDs by controlling the reaction synthesis temperature,the effects of metal cation doping,halogen anion exchange,heat treatment,and UV-irradiation on the structure and luminescence of PQDs were studied.The results mainly focus on the following aspects:1.UV irradiation was applied to CsPbBr₃（NC495 and NC520）quantum dots（QDs）films at the room temperature.But the results showed that the grain sizes of the two（QDs）films did not change much after irradiation,the lattice constant of NC495 slightly increased,and the lattice constant of NC520 did not change.The photoluminescence（PL）intensity decreased with the increase of UV irradiation time,and the fluorescence lifetime increased.Some crystalline（PbCO₃,PbO and Cs₄PbBr₆）and amorphous（PbCO₃ and Pb）phases have been observed,which have a certain influence on the PL performance of CsPbBr₃ QDs.2.The effects of temperature on PL and structural properties of CsPbBr₂I（NC590）and CsPbBr_1.5I_1.5（NC647）QDs films were investigated.The results show that the grain size and lattice constants of QDs increase with the increase of the thermal temperature after heat treatment.Because the Cs₄PbBr₆,CsPbI₃ and the PbI₂（crystalline and amorphous）produced during the heat treatment process,the structure and size of the QDs changed,resulting in the degradation of its PL.The experiment show structural stability of QDs becomes worse with the increase of element I content.3.The structure and PL properties of Sn/Zn:Cs PbBr₃ QDs films with different doping ratios were tested.The results showed that the grain size of Sn/Zn:CsPbBr₃ QDs increasing with the increase of doping ratio,resulting in the shift of the PL spectrum due to size effect.This is because the addition of Zn/Sn ions reduces the bond length between the metal positive ions and the halides,increases stability,and enhancing optical properties.The doping of a certain number of cations plays a positive role in improving the thermal stability of PQDs,but the excessive doping will also lead to the instability of the structure.4.Mn²⁺-doped CsPbCl₃ QDs（Mn:CsPbCl₃）was prepared.It was found that Mn²⁺starts emitting when the temperature is above 160 K.According to the change of Mn²⁺PL spectra and lifetimes,the degradation mechanisms of Mn²⁺emissions were explained by the formation of the number of nonradiative recombination centers such as defects or traps in size-unchanged and grown QDs under higher temperature heat treatment.Also,under the condition of low concentration doping of Mn²⁺,the reaction temperature has little effect on the lifetime of Mn:CsPbCl₃ QDs.5.CsPbBr₃,CsPbBr₂I,and a mixture of Mn:CsPbCl₃ and CsPbBr₃ are mixed with PDMS in a certain proportion,and then coated on blue or purple chips to make green and white LEDs.The results show that the mixing of PDMS plays a decisive role in the dispersion of PQDs,and can also play a role in thermal insulation,making the devices more stable.We mainly studied the structure and PL properties of PQDs under different conditions（such as thermal degradation,UV irradiation degradation,halogen anion exchange,etc.）.And had a deeper understanding of the formation of internal defects of QDs.The lead content in perovskite can be gradually replaced or reduced by metal cation doping to make it turn to a non-toxic or less toxic metal alloy during the same time.These research contents play a positive role in improving the stability of inorganic perovskite quantum dots and their applications in LED and solar cells,which have important scientific significance and practical application value.