Postsynthetic Doping of MnCl2 Molecules into Preformed CsPbBr3 Perovskite Nanocrystals via a Halide Exchange‐Driven Cation Exchange

Unlike widely used postsynthetic halide exchange for CsPbX₃ (X is halide) perovskite nanocrystals (NCs), cation exchange of Pb is of a great challenge due to the rigid nature of the Pb cationic sublattice. Actually, cation exchange has more potential for rendering NCs with peculiar properties. Herein, a novel halide exchange‐driven cation exchange (HEDCE) strategy is developed to prepare dually emitting Mn‐doped CsPb(Cl/Br)₃ NCs via postsynthetic replacement of partial Pb in preformed perovskite NCs. The basic idea for HEDCE is that the partial cation exchange of Pb by Mn has a large probability to occur as a concomitant result for opening the rigid halide octahedron structure around Pb during halide exchange. Compared to traditional ionic exchange, HEDCE is featured by proceeding of halide exchange and cation exchange at the same time and lattice site. The time and space requirements make only MnCl₂ molecules (rather than mixture of Mn and Cl ions) capable of doping into perovskite NCs. This special molecular doping nature results in a series of unusual phenomenon, including long reaction time, core–shell structured mid states with triple emission bands, and dopant molecules composition‐dependent doping process. As‐prepared dual‐emitting Mn‐doped CsPb(Cl/Br)₃ NCs are available for ratiometric temperature sensing.     

0D Cs3Cu2X5 (X = I,Br, and Cl) Nanocrystals: Colloidal Syntheses and Optical Properties

0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs₃Cu₂X₅ (X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs₃Cu₂X₅ NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs₃Cu₂Cl₅ NCs, while Cs₃Cu₂I₅ NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs₃Cu₂X₅ NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX₃ perovskite NCs.     

Nanocube Superlattices of Cesium Lead Bromide Perovskites and Pressure‐Induced Phase Transformations at Atomic and Mesoscale Levels

Lead halide perovskites are promising materials for a range of applications owing to their unique crystal structure and optoelectronic properties. Understanding the relationship between the atomic/mesostructures and the associated properties of perovskite materials is crucial to their application performances. Herein, the detailed pressure processing of CsPbBr₃ perovskite nanocube superlattices (NC‐SLs) is reported for the first time. By using in situ synchrotron‐based small/wide angle X‐ray scattering and photoluminescence (PL) probes, the NC‐SL structural transformations are correlated at both atomic and mesoscale levels with the band‐gap evolution through a pressure cycle of 0 ? 17.5 GPa. After the pressurization, the individual CsPbBr₃ NCs fuse into 2D nanoplatelets (NPLs) with a uniform thickness. The pressure‐synthesized perovskite NPLs exhibit a single cubic crystal structure, a 1.6‐fold enhanced photoluminescence quantum yield, and a longer emission lifetime than the starting NCs. This study demonstrates that pressure processing can serve as a novel approach for the rapid conversion of lead halide perovskites into structures with enhanced properties.     

Room‐Temperature Stimulated Emission and Lasing in Recrystallized Cesium Lead Bromide Perovskite Thin Films

Cesium lead halide perovskites are of interest for light‐emitting diodes and lasers. So far, thin‐films of CsPbX₃ have typically afforded very low photoluminescence quantum yields (PL‐QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX₃ nanoparticles (NPs). Here, thin films of cesium lead bromide, which show a high PL‐QY of 68% and low‐threshold ASE at RT, are presented. As‐deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin‐film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX₃ perovskites can only be achieved with NPs.     

A Strategy toward New Low‐Dimensional Hybrid Halide Perovskites with Anionic Spacers

The low‐dimensional halide perovskites have received enormous attention due to their unique photovoltaic and optoelectronic performances. Periodic spacers are used to inhibit the growth of 3D perovskite and fabricate a 2D counterpart with layered structure, mostly based on organic/inorganic cations. Herein, by introducing organic anions (e.g., pentanedioic acid (PDA) and hexanedioic acid (HDA) simultaneously), leaf‐shaped (Cs₃Pb₂Br₅)₂(PDA–HDA) microplates with low‐dimensional structure are synthesized. They also exhibit significant photoluminescence (PL) centered at 540 nm with a narrow emission peak. The synthesis of single crystals of Pb(PDA) and Pb(HDA) allows to further clarify the crystal structure of (Cs₃Pb₂Br₅)₂(PDA–HDA) perovskite and its structural evolution mechanism. Moreover, the cooperative introduction of dicarboxylic acid pairs with appropriate lengths is thermodynamically favored for the low‐dimensional perovskite crystallization. The temperature‐dependent PL indicates a V‐shaped Stokes shift with elevated temperature that could be associated with the localization of excitons in the inorganic layers between organic dicarboxylic acid molecules. This work demonstrates low‐dimensional halide perovskite with anionic spacers, which also opens up a new approach to the growth of low‐dimensional organic–inorganic hybrid perovskite crystals.     

Aqueous Phase Exfoliating Quasi‐2D CsPbBr3 Nanosheets with Ultrahigh Intrinsic Water Stability

All‐inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water‐stable all‐inorganic quasi‐2D CsPbBr₃ nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these unique quasi‐2D CsPbBr₃ nanosheets present an outstanding long‐term water stability with 87% photoluminescence (PL) intensity remaining after 168 h under water conditions. Moreover, the photoluminescence quantum yields (PLQY) of quasi‐2D CsPbBr₃ NSs is up to 82.3%, and these quasi‐2D CsPbBr₃ NSs also present good photostability of keeping 85% PL intensity after 2 h under 365 nm UV light. Evidently, such quasi‐2D perovskite NSs will open up a new way to investigate the intrinsic stability of all‐inorganic perovskites and further promote the commercial development of perovskite‐based optoelectronic and photovoltaic devices.     

Improving the Quality and Luminescence Performance of All‐Inorganic Perovskite Nanomaterials for Light‐Emitting Devices by Surface Engineering

Lead halide perovskites and their applications in the optoelectronic field have garnered intensive interest over the years. Inorganic perovskites (IHP), though a novel class of material, are considered as one of the most promising optoelectronic materials. These materials are widely used in detectors, solar cells, and other devices, owing to their excellent charge‐transport properties, high defect tolerance, composition‐ and size‐dependent luminescence, narrow emission, and high photoluminescence quantum yield. In recent years, numerous encouraging achievements have been realized, especially in the research of CsPbX₃ (X = Cl, Br, I) nanocrystals (NCs) and surface engineering. Therefore, it is necessary to summarize the principles and effects of these surface engineering optimization methods. It is also important to scientifically guide the applications and promote the development of perovskites more efficiently. Herein, the principles of surface ligands are reviewed, and various surface treatment methods used in CsPbX₃ NCs as well as quantum‐dot light‐emitting diodes are presented. Finally, a brief outlook on CsPbX₃ NC surface engineering is offered, illustrating the present challenges and the direction in which future investigations are intended to obtain high‐quality CsPbX₃ NCs that can be utilized in more applications.     

FA‐Assistant Iodide Coordination in Organic–Inorganic Wide‐Bandgap Perovskite with Mixed Halides

Mixed‐halide wide‐bandgap perovskites are key components for the development of high‐efficiency tandem structured devices. However, mixed‐halide perovskites usually suffer from phase‐impurity and high defect density issues, where the causes are still unclear. By using in situ photoluminescence (PL) spectroscopy, it is found that in methylammonium (MA⁺)‐based mixed‐halide perovskites, MAPb(I_0.6Br_0.4)₃, the halide composition of the spin‐coated perovskite films is preferentially dominated by the bromide ions (Br^?). Additional thermal energy is required to initiate the insertion of iodide ions (I^?) to achieve the stoichiometric balance. Notably, by incorporating a small amount of formamidinium ions (FA⁺) in the precursor solution, it can effectively facilitate the I^? coordination in the perovskite framework during the spin‐coating and improve the composition homogeneity of the initial small particles. The aggregation of these homogenous small particles is found to be essential to achieve uniform and high‐crystallinity perovskite film with high Br^? content. As a result, high‐quality MA_0.9FA_0.1Pb(I_0.6Br_0.4)₃ perovskite film with a bandgap (E_g) of 1.81 eV is achieved, along with an encouraging power‐conversion‐efficiency of 17.1% and open‐circuit voltage (V_oc) of 1.21 V. This work also demonstrates the in situ PL can provide a direct observation of the dynamic of ion coordination during the perovskite crystallization.     

From Nonluminescent to Blue‐Emitting Cs4PbBr6 Nanocrystals: Tailoring the Insulator Bandgap of 0D Perovskite through Sn Cation Doping

All‐inorganic cesium lead halide perovskite nanocrystals (NCs) with different dimensionalities have recently fascinated the research community due to their extraordinary optoelectronic performance such as tunable bandgaps over the entire visible spectral region. However, compared to well‐developed 3D CsPbX₃ perovskites (X = Cl, Br, and I), the bandgap tuning in 0D Cs₄PbX₆ perovskite NCs remains an arduous task. Herein, a simple but valid strategy is proposed to tailor the insulator bandgap (≈3.96 eV) of Cs₄PbBr₆ NCs to the blue spectral region by changing the local coordination environment of isolated [PbBr₆]^4? octahedra in the Cs₄PbBr₆ crystal through Sn cation doping. Benefitting from the unique Pb²⁺‐poor and Br^?‐rich reaction environment, the Sn cation is successfully introduced into the Cs₄PbBr₆ NCs, forming coexisting point defects comprising substitutional Sn_Pb and interstitial Br_i, thereby endowing these theoretically nonluminescent Cs₄PbBr₆ NCs with an ultranarrow blue emission at ≈437 nm (full width at half maximum, ≈12 nm). By combining the experimental results with first‐principles calculations, an unusual electronic dual‐bandgap structure, comprising the newly emerged semiconducting bandgap of ≈2.87 eV and original insulator bandgap of ≈3.96 eV, is found to be the underlying fundamental reason for the ultranarrow blue emission.     

Rare‐Earth‐Element‐Ytterbium‐Substituted Lead‐Free Inorganic Perovskite Nanocrystals for Optoelectronic Applications

Lead‐(Pb‐) halide perovskite nanocrystals (NCs) are interesting nanomaterials due to their excellent optical properties, such as narrow‐band emission, high photoluminescence (PL) efficiency, and wide color gamut. However, these NCs have several critical problems, such as the high toxicity of Pb, its tendency to accumulate in the human body, and phase instability. Although Pb‐free metal (Bi, Sn, etc.) halide perovskite NCs have recently been reported as possible alternatives, they exhibit poor optical and electrical properties as well as abundant intrinsic defect sites. For the first time, the synthesis and optical characterization of cesium ytterbium triiodide (CsYbI₃) cubic perovskite NCs with highly uniform size distribution and high crystallinity using a simple hot‐injection method are reported. Strong excitation‐independent emission and high quantum yields for the prepared NCs are verified using photoluminescence measurements. Furthermore, these CsYbI₃ NCs exhibit potential for use in organic–inorganic hybrid photodetectors as a photoactive layer. The as‐prepared samples exhibit clear on–off switching behavior as well as high photoresponsivity (2.4 × 10³ A W^?1) and external quantum efficiency (EQE, 5.8 × 10⁵%) due to effective exciton dissociation and charge transport. These results suggest that CsYbI₃ NCs offer tremendous opportunities in electronic and optoelectronic applications, such as chemical sensors, light emitting diodes (LEDs), and energy conversion and storage devices.     

Hydrochromic Perovskite System with Reversible Blue-Green Color for Advanced Anti-Counterfeiting

The intrinsic instability of halide perovskites toward to external stimulus, has created a competitive advantage for designing stimuli-responsive materials. However, the external environment tuning reversibly fluorescence emission of perovskite system is still limited. In this work, humidity is verified to act as a new option to modulate the emission properties of mixed-halide perovskite. The perovskite nanocrystals (PNCs) photoirradiated in dichloromethane are easily and stably redispersed in water, and emit bright fluorescence which is quite different from the original. Moreover, the perovskites confined on glass slide can reversibly switch their fluorescence between blue and green colors under moisture. It is demonstrated that the factors of different solubilities of CsCl and CsBr in water, the structural transformation of perovskites and the confine of glass matrix play key roles in the reversible transformation. Finally, the combination of hydrochromic CsPb(Br_xCl_y)₃ and water-resistant CsPb(Br_xCl_y)₃-polymethyl methacrylate have been applied in advanced anti-counterfeiting, which greatly improves the information security. This work not only give an insight into the effects of humidity on fluorescence and structures of PNCs, but also offer a new class of hydrochromic PNCs materials based on reversible emission transformation for potential application in sensors, anti-counterfeiting and information encryption.     

Control of Halogen Atom in Inorganic Metal-Halide Perovskites Enables Large Piezoelectricity for Electromechanical Energy Generation

Regulating the strain of inorganic perovskites has emerged as a critical approach to control their electronic and optical properties. Here, an alternative strategy to further control the piezoelectric properties by substituting the halogen atom (I/Br) in the CsPbX₃ perovskite (X = Cl, Br) structure is adopted. A series of piezoelectric materials with excellent piezoelectric coefficients (d₃₃) are unveiled. Iodine-incorporated CsPbBr₂I demonstrates the record intrinsic piezoelectric response (d₃₃ ≈47 pC N⁻¹) among all inorganic metal halide perovskites. This leads to an excellent electrical output power of ≈ 0.375 mW (24.8 µW cm⁻² N⁻¹) in the piezoelectric energy generator (PEG) which is higher than those of the pristine/mixed perovskite references with CsPbX₃ (X = I, Br, Cl). With its structural phase remaining unchanged, the strained CsPbBr₂I retains its superior piezoelectricity in both thin film and nanocrystal powder forms, further demonstrating its repeatability and versatility of applications. The origin of high piezoelectricity is found to be due to halogen-induced anisotropic lattice strain in the unit-cell along the c-axis, and octahedral distortion. This study reveals an avenue to design new piezoelectric materials by modifying their halide constituents and paves the way to design efficient PEGs for improved electromechanical energy conversion.     

Non-injection gram-scale synthesis of cesium lead halide perovskite quantum dots with controllable size and composition

Metal-halide perovskites are novel optoelectronic materials that are considered good candidates for solar harvesting and light emitting applications. In this study, we develop a reproducible and low-cost approach for synthesizing highquality cesium lead halide perovskite (CsPbX₃, X = Cl, Br, and I or Cl/Br and I/Br) nanocrystals (NCs) by direct heating of precursors in octadecene in air. Experimental results show that the particle size and composition of as-prepared CsPbX₃ nanocrystals can be successfully tuned by a simple variation of reaction temperature. The emission peak positions of the as-prepared nanocrystals can be conveniently tuned from the UV to the NIR (360–700 nm) region, and the quantum yield of the as-obtained samples (green and red emissions) can reach up to 87%. The structures and chemical compositions of the as-obtained NCs were characterized by transmission electron microscopy, X-ray diffraction, and elemental analysis. This proposed synthetic route can yield large amounts of high-quality NCs with a one-batch reaction, usually on the gram scale, and could pave the way for further applications of perovskite-based light-emitting and photovoltaic solar cells.

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Tunable Dual‐Emission in Monodispersed Sb3+/Mn2+ Codoped Cs2NaInCl6 Perovskite Nanocrystals through an Energy Transfer Process

Double halide perovskites are a class of promising semiconductors applied in photocatalysis, photovoltaic devices, and emitters to replace lead halide perovskites, owing to their nontoxicity and chemical stability. However, most double perovskites always exhibit low photoluminescence quantum efficiency (PLQE) due to the indirect bandgap structure or parity‐forbidden transition problem, limiting their further applications. Herein, the self‐trapped excitons emission of Cs₂NaInCl₆ by Sb‐doping, showing a blue emission with high PLQE of 84%, is improved. Further, Sb/Mn codoped Cs₂NaInCl₆ nanocrystals are successfully synthesized by the hot‐injection method, showing a tunable dual‐emission covering the white‐light spectrum. The studies of PL properties and dynamics reveal that an energy transfer process can occur between the self‐trapped excitons and dopants (Mn²⁺). The work provides a new perspective to design novel lead‐free double perovskites for realizing a unique white‐light emission.     

Lead-Free,Luminescent Perovskite Nanocrystals Obtained through Ambient Condition Synthesis

Heterovalently substituting toxic lead is an increasingly popular design strategy to obtain environmentally sustainable variants of the exciting material class of halide perovskites. Perovskite nanocrystals (NCs) obtained through solution-based methods exhibit exceedingly high optical quality. Unfortunately, most of these synthesis routes still require reaction under inert gas and at very high temperatures. Herein a novel synthesis routine for lead-free double perovskite (LFDP) NCs is presented. An approach based upon the hot injection and ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and ambient atmosphere-based synthesis for manganese-doped Cs₂NaBiCl₆ NCs is presented. Mn incorporation is critical for the otherwise non-emissive material, with a 9:1 Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and quantum yield (QY). Higher synthesis temperatures slightly increase the material's performance, yet NCs synthesized at room temperature are still emissive, highlighting the versatility of the synthetic approach. While the material's indirect bandgap limits its appeal for optoelectronics, this feature could benefit photocatalysis due to longer carrier lifetimes. Moreover, the developed synthesis is facile and can rapidly be adapted to other more viable material compositions and up-scaled to realize applications directly.     

Real‐Time Observation of Iodide Ion Migration in Methylammonium Lead Halide Perovskites

Organic–inorganic metal halide perovskites (e.g., CH₃NH₃PbI_3?x Cl_x ) emerge as a promising optoelectronic material. However, the Shockley–Queisser limit for the power conversion efficiency (PCE) of perovskite‐based photovoltaic devices is still not reached. Nonradiative recombination pathways may play a significant role and appear as photoluminescence (PL) inactive (or dark) areas on perovskite films. Although these observations are related to the presence of ions/defects, the underlying fundamental physics and detailed microscopic processes, concerning trap/defect status, ion migration, etc., still remain poorly understood. Here correlated wide‐field PL microscopy and impedance spectroscopy are utilized on perovskite films to in situ investigate both the spatial and the temporal evolution of these PL inactive areas under external electric fields. The formation of PL inactive domains is attributed to the migration and accumulation of iodide ions under external fields. Hence, we are able to characterize the kinetic processes and determine the drift velocities of these ions. In addition, it is shown that I₂ vapor directly affects the PL quenching of a perovskite film, which provides evidence that the migration/segregation of iodide ions plays an important role in the PL quenching and consequently limits the PCE of organometal halide‐based perovskite photovoltaic devices.     

A Highly Emissive Surface Layer in Mixed‐Halide Multication Perovskites

Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs_0.06MA_0.15FA_0.79)Pb(Br_0.4I_0.6)₃ perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI₂ material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.     

Morphology Engineering for High‐Performance and Multicolored Perovskite Light‐Emitting Diodes with Simple Device Structures

The film morphology is extremely significant for solution processed perovskite devices. Through fine morphology engineering without using any additives or further posttreatments, a full‐coverage and high quantum yield perovskite film has been achieved based on one‐step spin‐coating method. The morphologies and film characteristics of MAPbBr₃ with different MABr:PbBr₂ starting material ratios are in‐depth investigated by scanning electron microscopy, atomic force microscopy, X‐ray diffraction, photoluminescence, and time resolved photoluminescence. High performance organometal halide perovskite light‐emitting didoes (PeLEDs) based on simple device structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/perovskite/TPBi/Ca/Al are demonstrated. The green PeLED based on MAPbBr₃ shows a maximum luminance of 8794 cd m^?2 (at 7.3 V) and maximum current efficiency of 5.1 cd A^?1 (at 5.1 V). Furthermore, a class of hybrid PeLEDs by adjusting the halide ratios of methylammonium lead halide (MAPbX₃, where X is Cl, Br, or I) are also demonstrated at room temperature. These mix‐halogenated PeLEDs show bright luminance (above 100 cd m^?2) with narrow and clean emission bands over the wide color gamut.     

Europium and Acetate Co‐doping Strategy for Developing Stable and Efficient CsPbI2Br Perovskite Solar Cells

All‐inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed‐halide inorganic CsPbI₂Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI₂Br perovskites limit the open‐circuit voltage (V_oc < 1.2 V), short‐circuit current density (J_sc < 15 mA cm^?2), and fill factor (FF < 75%) of CsPbI₂Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI₂Br perovskite is doped by Eu(Ac)₃ to obtain a high‐quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable V_oc of 1.25 V, a reasonable J_sc of 15.44 mA cm^?2, and a high FF of 79.00% are realized for CsPbI₂Br solar cells. Moreover, the CsPbI₂Br solar cells with Eu(Ac)₃ doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35–40%) for 30 days.     

Two‐Photon Up‐Conversion Photoluminescence Realized through Spatially Extended Gap States in Quasi‐2D Perovskite Films

A new approach to generate a two‐photon up‐conversion photoluminescence (PL) by directly exciting the gap states with continuous‐wave (CW) infrared photoexcitation in solution‐processing quasi‐2D perovskite films [(PEA)₂(MA)₄Pb₅Br₁₆ with n = 5] is reported. Specifically, a visible PL peaked at 520 nm is observed with the quadratic power dependence by exciting the gap states with CW 980 nm laser excitation, indicating a two‐photon up‐conversion PL occurring in quasi‐2D perovskite films. Decreasing the gap states by reducing the n value leads to a dramatic decrease in the two‐photon up‐conversion PL signal. This confirms that the gap states are indeed responsible for generating the two‐photon up‐conversion PL in quasi‐2D perovskites. Furthermore, mechanical scratching indicates that the different‐n‐value nanoplates are essentially uniformly formed in the quasi‐2D perovskite films toward generating multi‐photon up‐conversion light emission. More importantly, the two‐photon up‐conversion PL is found to be sensitive to an external magnetic field, indicating that the gap states are essentially formed as spatially extended states ready for multi‐photon excitation. Polarization‐dependent up‐conversion PL studies reveal that the gap states experience the orbit–orbit interaction through Coulomb polarization to form spatially extended states toward developing multi‐photon up‐conversion light emission in quasi‐2D perovskites.