| Recently,organic-inorganic halide perovskite luminescent materials have been widely researched in the optical fields such as light-emitting diodes(LEDs),lasers,and photodetectors owning to their high fluorescence luminous efficiency,high color purity,and continuous adjustable wavelength.Generally,the three-dimensional(3D)perovskites exhibit excellent luminescence properties,however,due to their poor intrinsic structural stability,these 3D perovskites are facing the fatal defect of poor environmental stability,which can be easily decomposed by heat,water or oxygen.In order to overcome the disadvantage of poor stability,researchers have done a lot of works.The researchers demonstrated that the dense coating methods can effectively protect perovskite from water and oxygen,thereby significantly improving the environmental stability of perovskites.On the other hand,researchers declared that the low generation energy of 3D perovskite is one of the main reasons which led to the poor stability of the material.Therefore,they have synthesized many low-dimensional(quasi-2D,2D,1D and 0D)perovskites.These low-dimensional materials have large formation energies,which exhibit better environmental stability.In summary,these methods have effectively improved the stability of perovskites,however,the mechanisms which affect the stability of perovskites are still unclear.Therefore,in order to systematically explore the relevant factors affecting the stability of perovskites,we have investigated the water-stability and luminescence properties of lead bromide perovskites via hydrophobic coating,doping and structural dimensionality reduction methods.The coating method improves the environmental stability of perovskite through“physical isolation”;the doping and structure dimensionality reduction methods optimized the perovskite structure to increase the formation energy and exciton binding energy,which effectively improved the intrinsic stability of the perovskite.As a result,in this paper,the“physical isolation”and“structure optimization”are carried out to provide new ideas for the development of highly stable perovskite luminescent materials.And the specific works are as follows:(1)Ultrastable Carbon Quantum Dots-Doped MAPbBr3Perovskite with Silica Encapsulation.Having suffered from intrinsic structural lability,perovskite quantum dots(PQDs)are extremely unstable under high-temperature and moisture conditions,which have greatly limited their applications.In this work,we propose a novel method to synthesize ultrastable carbon quantum dots(CQDs)-doped methylamine(MA)lead bromide PQDs with SiO2encapsulation(CQDs-MAPbBr3@SiO2).The kernel CQDs-MAPbBr3is formed by the interaction of carboxyl-rich CQDs with MAPbBr3via H-bond,which greatly improves the thermal stability of CQDs-MAPbBr3.Furthermore,highly compact SiO2encapsulates the proposed CQDs-MAPbBr3via a facile in situ growth strategy,which effectively enhances the water resistance and air stability of CQDs-MAPbBr3@SiO2.As a result,the proposed nanomaterial shows extremely high water stability in aqueous solution for over 9 months and ideal thermal stability with strong fluorescence(FL)emission after 150°C annealing.Based on the superior stability and ultrahigh FL efficiency of this proposed nanomaterial,a primary sensing method for ion(Ag+and Zn2+)FL detection has been developed and the mechanism of PQDs-based ion determination has also been discussed,thus exhibiting the potential applications of CQDs-MAPbBr3@SiO2in the area of FL assay and environment monitoring.(2)Highly Luminescent and Stable Quasi-2D Perovskite Quantum Dots by Introducing Large Organic CationsIn our previous work,we have synthesized a highly stable perovskite through SiO2-encapsulating,but this“physical isolation”method can not improve the intrinsic stability of the material.In order to improve their instinct stability,herein,an ultra-stable quasi-two-dimensional perovskite quantum dots(quasi-2D PQDs)is synthesized by introducing butylamine cation(BA+)into methylamine lead bromide perovskite(MAPbBr3).By reducing the dimensionality of perovskite structure,the quasi-2D perovskite of(BA)2(MA)x-1PbxBr3x+1presents higher luminous efficiency and better environmental stability than that of traditional 3D perovskites,which is mainly due to the dimensionality-reduced perovskite has higher exciton binding energy and formation energy.Under the optimal MA:BA ratio of 1:1,the quasi-2D perovskite exhibits about four times luminescence efficiency(PLQY=49.44%)higher than that of pristine MAPbBr3meanwhile emits stable luminescence in an environment with 80%humidity for a long period.Most importantly,carbon quantum dots(CQDs)doping has also been applied in this work,which effectively passivates the defects of(BA)2(MA)x-1PbxBr3x+1via H-bond interaction,further improving the stability of perovskite in water.Inspired by the superior performances of the proposed quasi-2D nanomaterial,a novel colorimetric method based on halide ions exchange has been developed for H2O2detection,which also demonstrates that PQDs shows significant potential in the field of environmental monitoring.(3)Highly stable uncoated 2D perovskite by 3-aminophthalhydrazide(lum)-dopingIn our pervious works,we have noticed that the perovskites quantum dots(PQDs)exhibit excellent luminescence performance,however,due to their large specific surface area,the PQDs can easily adsorb water or oxygen molecules,thus causing the materials to be destroyed.Fortunately,the low-dimensional perovskites with a novel bulk-material luminescent characteristic can effectively avoiding the defect of large specific surface area of quantum dots,which due to their good environmental inertia and intrinsic quantum confinement effect.As a proof of concept,a new3-aminophthalhydrazide(lum)doped 2D butylammonium lead bromide perovskite(lum-BA2PbBr4)is successfully synthesized,which exhibits ideal water stability.The electrostatic and hydrogen bond interaction between lum and BA2PbBr4greatly improve the structural stability of this perovskite.In addition,lum and BA cations present large steric hindrances,which effectively prevents lum-BA2PbBr4from being destroyed by water,resulting in a significant enhancement stability of the proposed material in water.Compared with the quasi-2D perovskite quantum dots in our previous work,the prepared lum-BA2PbBr4displays an extremely high water-stability in aqueous solution for over a month,which lays a foundation for the preparation of non-coated water-stable perovskite materials.(4)Strong white emission halide perovskite with superior water stabilityIn our previous work,the unencapsulate lum-BA2PbBr4perovskite exhibits excellent environmental stability,which can stably emit blue-light in water for one month.However,the luminescence performance of this blue light perovskite is not ideal,the fluorescence quantum yield of which is only 10%.In order to further improve the luminous efficiency of the material,here,an organic molecule of trans-2,5-dimethylpiperazine(TDMP)has been introduced into lum-BA2PbBr4to prepare a white light perovskite composite of lum-(BA/TDMP)-PbBr,which exhibits excellent stability and excellent luminescence performance.We have characterized the structure,fluorescence properties and stability of this white-light perovskite.Experimental results show that the main structure of this material is a 0D structure,the fluorescence quantum yield which is about 55%,and the material could remain stable in water for a long period. |
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