Synthesis,Properties,and White Led Applications Of Porous Material-Encapsulated CsPbBr₃ Nanocrystal Phosphors

All-inorganic CsPbX₃（X=Cl,Br,I）perovskite nanocrystals（NCs）have great application prospects in optoelectronic devices due to their excellent optoelectronic properties.However,the inherent ionic nature,low formation energy,and large specific surface area of CsPbX₃ NCs make them highly sensitive to polar solvents and external factors such as light,oxygen,and heat,resulting in poor environmental stability.When CsPbX₃ NCs with different halogen components are mixed,rapid ion exchange will occur between NCs,which results in a large shift in emission spectra,and ultimately the luminous efficiency and color stability of optoelectronic devices will decline.In addition,CsPbX₃ NCs often experience severe fluorescence quenching due to solid-state aggregation when they transform from solution to solid state,which greatly limits their commercial applications.It has been reported that CsPbX₃ NCs can be effectively protected from erosion by polar solvents,environmental atmospheres,and high temperatures when they are encapsulated by an additional porous matrix material.Simultaneously,the porous matrix material acts as a framework to prevent aggregation between NCs.As a result,the excellent luminescent performances of NCs are well maintained even in the solid-state form.This encapsulation strategy is considered an effective solution to solve all the problems mentioned above in perovskite NCs.Based on it,this paper aims to optimize the optical performances of solid-state CsPbBr₃ NCs,reduce or eliminate solid-state aggregation fluorescence quenching,and enhance their environmental stability.To achieve this goal,a series of porous framework materials with different pore sizes and compositions were selected to encapsulate CsPbBr₃ NCs.As a result,CsPbBr₃@porous material NC phosphors with excellent photoluminescent（PL）performances and high stability were successfully prepared.The growing dynamics process,existence form,size,and morphology of NCs in porous framework materials and the combination between them were systematically investigated by regulating the encapsulation process,characterizing morphology and optical properties in combination with theoretical calculation.The internal mechanisms for improving the optical properties and stability of NC phosphors were revealed.Finally,as-prepared CsPbBr₃@porous material NC phosphors were successfully applied in wide-color gamut white LED devices.The main research contents are described as follows:1.The porous MIL-53 MOFs with excellent hydrophobic properties were selected as the encapsulation matrix.CsPbBr₃ NCs were grown in situ within the pores of MIL-53 by hot-injection process.CsPbBr₃@MIL-53 NC phosphors with excellent PL properties were successfully prepared.MIL-53 chelates with CsPbBr₃ through the contained benzene ring and organic ligands.NCs were securely anchored within the pores.This encapsulation strategy not only protects the CsPbBr₃ NCs from direct contact with the external environment but also effectively prevents their aggregation,thereby avoiding solid-state aggregation fluorescence quenching.Furthermore,the COO^-functional groups within MIL-53 passivate the surface vacancy defects of CsPbBr₃ NCs through bonding with unpaired Pb²⁺ions,thereby suppressing non-radiative recombination between charge carriers.Combined with the excellent hydrophobic properties of MIL-53,the optical properties and water-resistance stability of CsPbBr₃@MIL-53 NC phosphors prepared by the synergistic action of several factors are significantly improved.The PL quantum yield（PLQY）reached 75.4%,which is 2.3 times（33.2%）of pure solid-state CsPbBr₃ phosphors.After immersing CsPbBr₃@MIL-53 in water for 10 h,PL intensity can still maintain 75%of its initial value.In contrast,the optical performances of pure solid-state CsPbBr₃ powders almost disappeared after only immersion in water for 1.5 h.2.Monodisperse CsPbBr₃ NCs with excellent optical properties and enhanced thermal stability were synthesized by using KIT-6,an inorganic mesoporous material with good thermal stability and uniform pore size,as the encapsulation matrix,in combination with in situ hot-injection process,named as H-CsPbBr₃@KIT-6.CsPbBr₃NCs are anchored within the pores of KIT-6 through strong chemical bonding.Organic ligands of oleic acid/oleylamine introduced in hot-injection together with the KIT-6matrix provide dual passivation and protection for NCs.The optimized H-CsPbBr₃@KIT-6 NC phosphors achieved a PLQY of as high as 81.7%and exhibited significantly improved thermal stability.H-CsPbBr₃@KIT-6 nanocrystal phosphors can retain 32.3%of their initial fluorescence intensity at 423 K,compared to CsPbBr₃@MIL-53,which can only retain 12.2%of its initial intensity at 373 K.However,due to the open pore structure of KIT-6,when NC phosphors were exposed to the external environment for a long time,water molecules still inevitably entered the inner pore to erode NCs.Furthermore,to address this issue,the NC phosphors were further modified by the hydrolysis of tetraethyl orthosilicate（TEOS）.By sealing the pore,the water stability of as-prepared H-CsPbBr₃@KIT-6@Si O₂ was further markedly enhanced.After immersing them in water for 10 h,the fluorescence intensity was maintained at 95.3%of its initial value.3.To address the issues of harsh reaction conditions,complicated reaction processes,and unfriendly organic solvents during the synthesis of CsPbBr₃NCs by hot-injection,CsPbBr₃ NCs were directly synthesized by a simple one-step high-temperature solid-state reaction sintering within the KIT-6 matrix.The obtained S-CsPbBr₃@KIT-6 NC phosphors not only maintained excellent optical performances but also exhibited comprehensive improvements in light,water,and thermal stability.Compared to the hot-injection process discussed in H-CsPbBr₃@KIT-6 NC,the high-temperature sintering process led to the direct melting and collapse of the KIT-6framework,and then,its open pores were completely sealed off.CsPbBr₃ NCs were fully encapsulated and isolated from the external environment.After S-CsPbBr₃@KIT-6 phosphors were completely immersed in water for 128 days,89.4%of their initial PL intensity was still maintained.The synthesis process is very simple and easy to operate,which lays a foundation for future large-scale industrial production.4.To further elucidate the growth kinetics mechanism of CsPbBr₃ NCs within porous materials and clarify the binding mode between CsPbBr₃ NCs and porous matrices,we selected Zeolite A（Na）,which has good a crystalline phase,low-cost,rich composition,and pore size less than 1 nm,as the encapsulation matrix.CsPbBr₃@Zeolite NC phosphors with excellent PL performances and stability were synthesized using a one-step high-temperature solid-state method.The formation kinetics,nucleation,and growth mechanism of CsPbBr₃ NCs in porous matrix materials at high temperatures were systematically investigated by combining experimental characterization and first-principles theoretical calculation.Under high temperatures,Pb Br₂ preferentially reacts with Zeolite A（Na）to form Zeolite A（Pb）compounds,which then react with Cs Br to generate CsPbBr₃ NCs.With the increase in reaction temperature,the phase transformation process from Cs Pb₂Br₅ to CsPbBr₃ and then to Cs₄Pb Br₆ occurred and was simultaneously accompanied by the nucleation and growth of NCs.Additionally,the changes in the structure and pore channels of Zeolite A were also observed.The environmental stability of as-obtained CsPbBr₃@Zeolite NC phosphors is comparable to that of S-CsPbBr₃@KIT-6.These experimental results provide new insights for the preparation of high-performance CsPbX₃ NC phosphors by adopting porous materials as encapsulation matrices.At the same time,it also provides a theoretical reference for clarifying the growth kinetic process of NCs in porous frame materials and the internal mechanism of optical properties and stability improvement of composite NC phosphors.