Study Of Pressure-induced Emission Toward A₂BX₄-Type Micro/nano Hybrid Halides Perovskites

Low dimensional hybrid halide perovskites were used as promising unit white light materials due to self-trapping excitons emission,which not only simplifies the fabrication process of light-emitting devices,but also overcomes the unstable chromaticity of traditional multi-component white light materials,and have gradually attracted wide attention from the scientific field.However,low-dimensional hybrid perovskites faced low emissive efficiency,which hinders their practical application(LED).As an important thermodynamic parameter and extreme conditions,high pressure can effectively reduce interatomic distance,increase electron cloud overlap and interatomic interaction,and then tune the crystal and electronic structure of materials.It is a powerful tool to study the relationship between structure and property as well as its potential mechanism.Tuning the distortion degree of the framework of perovskite or its derivatives using high pressure,resulted in enhanced recombination of self-trapping exciton.Pressure-induced emission was first found in non-emissive all-inorganic zero-dimensional perovskite Cs₄Pb Br₆ nanocrystals.Thereafter,this novel phenomenon was also discovered in one-dimensional hybrid halide perovskite C₄N₂H₁₄Sn Br₄ and two-dimensional halide perovskite(BA)₄Ag Bi Br₈.Numerous research achievements have attracted wide attention,which have potential promising application in the fields of pressure sensing,pressure switch and anti-counterfeiting.However,the reversibility of releasing pressure(that is,the high-pressure metastable phase with highly efficient emission cannot be stabilized to normal pressure)greatly hinds the practical application of these materials.Here,by introducing organic cations with complex configurations(C₅H₇N₂,4AMP)⁺and(C₁₁H₉NH₃,NAPH)⁺,we use pressure-treatment irreversible organic cations to build steric hindrance,thus improving the barrier of phase transition.Therefore,we achieved high-quality white light through retention of pressure-induced emission in the zero-dimensional hybrid halide perovskite(4AMP)₂Zn Br₄ microtubules and two-dimensional hybrid halide perovskite(NAPH)₂Pb Cl₄ nanoplates.It provides a new strategy for obtaining highly efficient unit emissive white light materials under ambient conditions.This work focuses on the key scientific issues how to"capture"pressure-induced emission related to high pressure,and the main innovative achievements are as follows:(1)Pressure-induced emission has been extensively studied in low dimensional hybrid halide perovskites.However,the reversibility of releasing pressure makes it difficult for the pressure-induced high-performance emission to be retained to ambient conditions,which largely hinders its practical application.Complex configurational rigid molecules used as organic components of hybrid halide perovskite to build steric barrier to improve the barrier of phase transition,prevented high-pressure metastable states from return to atmospheric pressure.Therefore,high quality emission related to to metastable states was retained to atmospheric pressure.We designed and synthesized(4AMP)₂Zn Br₄ microtubules by introducing 4-aminopyridine(4AMP)with complex configurational molecular.We also achieved pressure-induced emission at high pressures.It was found that before 3.14 GPa,the Zn Br₄^2-tetrahedron and the 4AMP⁺cations were gradually distorted,and the blue-light emission was slowly enhanced.After 3.14 GPa,a structural phase transition occurs,and(4AMP)₂Zn Br₄ undergoes an orthorhombic to monoclinic phase transition.The high-pressure phase featuring more severe distortion of the Zn Br₄^2-tetrahedron and the 4AMP⁺cations,resulted in a rapid increase in emission until 5.07 GPa,where the emission reached the highest value.Pressure-induced emission is derived from biexciton recombination consisting of self-trapping exciton and local exciton,which provides the possibility for the generation of white light.Theoretical calculations show that the enhancement of the transition dipole moment and the localization of the organic singlet exciton are main reposible for the enhancement of the emission probability.After releasing pressure,the pressure-induced high-performance emission was remained more than one order of magnitude,and the quantum yield reached 88.52%.The nature of emission retained resulted from the steric hindrance induced by 4AMP⁺cations,increased the barrier of phase transition.In addition,through pressure engineering,we also achieved effective tuning of color temperature from"sky blue"(9102 K)to"cold daylight"(6392 K),advancing its potential application in solid-state lighting.In the presented above work,we have qualitatively analyzed the steric hindrance effect toward harvesting high-pressure metastable state.Quantification of steric effect is of great significance for the design and synthesis of atmospheric materials under high pressure.In this work,we performed quantification of the steric hindrance effect.In order to verify our academic assumptions,we carried out high-pressure studies on two-dimensional quantum well perovskite(NAPH)₂Pb Cl₄ with a complex configuration of organic cation 1-(2-naphthalyl)methylamine(C₁₁H₉NH₃,NAPH)⁺.Hybrid halide perovskites(NAPH)₂Pb Cl₄ nanosheets were synthesized by ligand assisted precipitation method.In this type of naphthyl lead chloride quantum well perovskite system,due to the strong coupling between the excited states of the organic layer and the inorganic layer,the excitons formed in inorganic lattice is transferred to the organic chromophore,resulting in the radiative emission of the organic cation.Theoretical calculation shows that the band edge position of the system is provided by organic molecules,which further confirms that the emission of the system comes from organic molecules.When(NAPH)₂Pb Cl₄ nanosheets were pressurized in the low-pressure range(0?0.51 GPa),the enhanced organic-inorganic excited state coupling promoted the energy transfer,resulting in the pressure-induced emission enhancement.Synchrotron radiation X-ray diffraction experiment showed that the crystallinity of(NAPH)₂Pb Cl₄ nanosheets was destroyed and gradually changed to amorphous state with the increase of pressure.It is important to note that during the process of releasing pressure,the pressure-induced emission is retained at atmospheric pressure and emissive intensity is more than twice intense than the initial state.The narural reason for the interception of high emission properties is that(C₁₁H₉NH₃,NAPH)⁺cations has a very high steric hindrance factor(5.98),which increases the phase transition barrier and its metastable state was retained.In addition,we also achieved effective tuning of color temperature from"cold white light"(9453 K)to"warm white light"(5189 K)through pressure engineering.This study deepens the understanding of the relationship between pressure-induced emission qunched and steric hindrance,quantitatively gives the steric effect index of organic molecules with different chain lengths and configurations,and provides insights for the rational design and preparation of novel pressure-induced emission materials.