Pressure-Induced Structural Evolution And Optoelectric Properties Of Typical Inorganic Lead Halide Perovskite Nanocrystal

Metal halide perovskites?MHPs?have attracted increasing research attention given the excellent optical absorption and emission qualities.Especially in recent years,the success of organic-inorganic hybrid perovskite in photovoltaic devices has aroused people's interest in inorganic lead halide perovskite nanocrystals?NCs?.The research progress shows that the inorganic lead halide perovskite nanomaterials replace organic cations with inorganic cations,which show ultra-high photoluminescence quantum yield and better stability than organic-inorganic hybrid perovskite.However,effective strategies for engineering the band gap of MHPs to satisfy the requirements of practical applications are difficult to develop.Therefore,exploring the mechanism of the external environment on inorganic lead halide perovskite nanomaterials and looking for the relationship between their structure and optical properties can provide a scientific basis for the wide application of inorganic lead halide perovskite nanomaterials in optical devices.Firstly,we carried out a combination of in situ photoluminescence?PL?,absorption and angle dispersive synchrotron X-ray diffraction spectra to investigate the pressure-induced optical and structural changes of?-CsPbI₃ nanocrystals?NCs?.The?-CsPbI₃ NCs underwent a phase transition from cubic???to orthorhombic phase and subsequent amorphization upon further compression.First-principles calculations reveal that the band gap engineering is governed by orbital interactions within the inorganic Pb-I frame through the structural modification.The[PbI₆]^4-octahedral in the cubic?-CsPbI₃ underwent a contraction with the increase in pressure.The major Pb-I-Pb bond angle remained at nearly 180^o,but the Pb-I band length decreased,causing the red shift of the band gap with pressure.Meanwhile,the blue shift in band gap is caused by lattice distortions.When the phase transition occurred,the[PbI₆]^4-octahedra underwent a stark distortion and the averaged Pb-I-Pb bond angle markedly decreased in orthorhombic phase with increasing pressure.Subsequently,the high pressure behavior of CsPb_xMn_1-xCl₃ NCs was investigated.By analyzing in situ photoluminescence,we found that pressure-induced emission enhancement?PIEE?of CsPb_xMn_1-xCl₃ NCs occureed at 1.41 GPa.The third-order Birch-Murnaghan equation and angle dispersive synchrotron X-ray diffraction spectra indicated that,an isostructural phase transition occurred at 1.46GPa in CsPb_xMn_1-xCl₃ NCs.When the pressure reached 20.18 GPa,only a few broad diffraction peaks can be detected,proving that the crystallinity is getting worse and CsPb_xMn_1-xCl₃ NCs tends to become amorphous at higher pressures.The PIEE of CsPb_xMn_1-xCl₃ NCs was attributed to the increase of energy release from ⁴T₁ to ⁶A₁ of the Mn²⁺,caused by the suppression of radiation energy from CBM to VBM during the pressure-induced isostructural phase transition.Finally,the structure and optical properties of CsPbCl₃ NCs and CsPb_xMn_1-xCl₃NCs under high pressure were compared.In combination with absorption and angle dispersive synchrotron X-ray diffraction spectra,we found that CsPbCl₃ NCs underwent an isostructural phase transition at 1.40 GPa.When the pressure reached10.21 GPa,CsPbCl₃ NCs tends to become amorphous.In situ photoluminescence indicated that the As the pressure increases,the PL intensity of CsPbCl₃ NCs exhibited persistent reduction upon compression,until fluorescence was abruptly quenched at 1.42 GPa.Compared with CsPbCl₃ NCs,the PL pressure range of CsPb_xMn_1-xCl₃ NCs has been improved by an order of magnitude.Meanwhile the photoluminescence?PL?can exist until almost 20 GPa,suggesting CsPb_xMn_1-xCl₃NCs exhibited better environmental suitability and worked under high pressure.