Synthesis And Characterization Of Luminescent Organometal Halide Perovskite Materials

Organometal halide perovskite nanocrystals?NCs?have attracted great attentions in the last few years own to their fascinating photoelectric properties,such as high photoluminescence quantum yield?PLQY?,tunable emission spanning the entire visible to near-infrared spectrum regions,narrow band width,high absorption coefficiency and high defect tolerance due to quantum confinement and size effects.These properties make them very promising for applications in light emitting diodes?LEDs?,solar cells,photodetectors and lasers.Despite the huge success of halide perovskite-based materials in optoelectronic fields,their practical applications are hindered for their poor stability upon exposure to humidity,light,oxygen and heat,which are due to their ionic nature and low formation energy.Therefore,to improve the stability of organometal halide perovskite NCs has become the key issue at present.Aim to improve the stability of lead halide pervosite based nanocrystals,this paper reports the researches on the preparation and characterization of lead halide perovskite?LHP?based nanocrystals.?1?Well-defined CH₃NH₃PbBr₃/?-cyclodextrin?MAPbBr₃/?-CD?core/shell structured nanodots were synthesized via host-guest interaction between?-cyclodextrin and the hydrophobic aliphatic chain of the capping ligand hexylamine.TEM and PL characterization indicated that the average size and emission wavelength can be tuned by changing the ligand concentration of hexylamine.Stability study showed the MAPbBr₃/?-CD nanodots have superior stability in water,under heat and UV light exposure due to the protection of?-CD shell.By optimizing the concentration of hexylamine in the precursor,the highest PLQY of 38%was obtained,illustrating the excellent luminescence property.Green light LED was demonstrated by blending MAPbBr₃/?-CD nanodots with PMMA coated on the commercial available GaN LED chip.On the other hand,the toxic lead restricts the biological applications of MAPbBr₃ nanodots.?-cyclodextrin has good biocompatibility.By introducing?-CD as shell to encapsulate MAPbBr₃ nanodots,the toxicity of the nanocrystals was reduced and the biocompatibility was improved.The resulted MAPbBr₃/?-CD nanodots are potential candidates for applying in biological and medical fields,such as bioimaging.?2?A CH₃NH₃PbBr₃/silicon oil/PDMS-urea composite was prepared by encapsulating CH₃NH₃PbBr₃ nanocrystals and silicon oil into the PDMS-urea polymer matrix.This composite shows charateristics of water-induced photoluminescence?PL?enhancement and water-driven PL recovery.After immersed in water,the photoluminescence quantum yield of the composite increases from initial26.0%to 52.2%,which is ascribed to the passivation of surface defects by the capping of polymer chains,H₃O⁺and OH^?.The composite possesses superior stability against UV light illumination in water.Furthermore,the composite film exhibits a capability of water-driven PL recovery after UV light irradiation and heat treatment.After repeated UV light/water and heat/water treatment,it is found this PL switch“off”and“on”process is reversible.Furthermore,after 3-4 cycles,the PL intensity of“off”and“on”tend to be stable and the value of“on/off”ratio reaches above 4.These advantages make this composite highly promising in applications for luminescent switching and under water lighting.?3?MAPbBr₃ nanoplatelets was synthesized through dilution of the irregular MAPbBr₃ colloidal nanocrystals prepared at 50°C.The dilution followed by self-organization of the nanocrystals result in the production of uniform square nanoplatelets with long term stability up to 6 months and high photoluminescence quantum yield about 90%.Furthermore,by using bidentate coordination molecule pyrazole as co-ligand,regular 2D structural nanocrystals with round edge and aggregation were produced.The aggregated nanoplatelets prepared at 50°C show the same self-assembly process after dilution to form uniform square nanoplatelets.