Heterostructural CsPbX3-PbS (X = Cl, Br, I) Quantum Dots with Tunable Vis-NIR Dual Emission

Nanocrystal Heterostructures Based on Halide Perovskites and Metal Sulfides

We report the synthesis of nanocrystal heterostructures composed of CsPbCl3 and PbS domains sharing an epitaxial interface. We were able to promote the growth of a PbS domain (in competition with the more commonly observed Pb4S3Cl2 one) on top of the CsPbCl3 domain by employing Mn2+ ions, the latter most likely acting as scavengers of Cl- ions. Complete suppression of the Pb4S3Cl2 domain growth was then achieved by additionally selecting an appropriate sulfur source (bis(trimethylsilyl)sulfide, which also acted as a scavenger of Cl- ions) and reaction temperature. In the heterostructures, emission from the perovskite domain was quenched, while emission from the PbS domain was observed, pointing to a type-I band alignment, as confirmed by calculations. These heterostructures, in turn, could be exploited to prepare second-generation heterostructures through selective ion exchange on the individual domains (halide ion exchange on CsPbCl3 and cation exchange on PbS). We demonstrate the cases of Cl- → Br- and Pb2+ → Cu+ exchanges, which deliver CsPbBr3-PbS and CsPbCl3-Cu2-xS epitaxial heterostructures, respectively.

Red-Emitting CsPbI3/ZnSe Colloidal Nanoheterostructures with Enhanced Optical Properties and Stability

Producing heterostructures of cesium lead halide perovskites and metal-chalcogenides in the form of colloidal nanocrystals can improve their optical features and stability, and also govern the recombination of charge carriers. Herein, the synthesis of red-emitting CsPbI3/ZnSe nanoheterostructures is reported via an in situ hot injection method, which provides the crystallization conditions for both components, subsequently leading to heteroepitaxial growth. Steady-state absorption and photoluminescence studies alongside X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy analysis evidence on a type-I band alignment for CsPbI3/ZnSe nanoheterostructures, which exhibit photoluminescence quantum yield of 96% due to the effective passivation of surface defects, and an enhancement in carrier lifetime. Furthermore, the heterostructure growth of ZnSe domains leads to significant improvement in the stability of the CsPbI3 nanocrystals under ambient conditions and against thermal and UV irradiation stress.

In situ fabrication of porous polymer films embedded with perovskite nanocrystals for flexible superhydrophobic piezoresistive sensors

The application of pressure sensors based on perovskite in high-humidity environments is limited by the effect of water on their stability. Endowing sensors with superhydrophobicity is an effective strategy to overcome the issue. In this work, MAPbBr3/Polyvinylidene Fluoride-TFSI composite was prepared by a one-step in-situ strategy to form a flexible superhydrophobic pressure sensor, which exhibited a contact angle of 150.25°. The obtained sensor exhibited a sensitivity of 0.916 in 1 kPa, a detection limit of 0.2 Pa, a precision of 0.1 Pa, and a response/recovery of ∼100 ms, along with good thermal stability. Through density functional theory calculations, it is revealed that the formation of the porosity is attributed to the interaction between the polymer and EMIM TFSI, which further leads to superhydrophobicity. And, the perovskite structure is easy to change under pressure, affecting the carrier transport and electrical signals output, which explains the sensing mechanism. In addition, the sensor performed well in monitoring facial expression, pulse, respiration, finger bending, and wind speed ranging from 1 m/s to 6 m/s. With both the Linear Regression and the Random Forest algorithm, the sensor can monitor the wind speed with an R2 greater than 0.977 in 60 tests.

Chiral Perovskite Heterostructure Films of CsPbBr3 Quantum Dots and 2D Chiral Perovskite with Circularly Polarized Luminescence Performance and Energy Transfer

This work reports the synthesis of chiral perovskite heterostructure films by combining a two-dimensional (2D) chiral (R-/S-MBA)2PbI4 perovskite with CsPbBr3 quantum dots (QDs). The as-synthesized chiral heterostructure films exhibit obvious circularly polarized luminescence (CPL) properties, even though pure 2D chiral perovskite cannot present photoluminescence. It indicates that the chirality of the excited state of the QDs originates from the 2D chiral perovskite. The circular polarization-resolved transient absorption (TA) spectra further demonstrate that the CPL response of heterostructure films originates from the energy transfer between the chiral perovskite layer and QDs layer and the suppression of spin relaxation, which induces the imbalance of the spin population of excited states in QDs layer. In addition, the photoluminescence (PL), circular dichroism (CD), and CPL spectra of these heterostructure films can be controlled by varying the thickness and component of the chiral perovskite layer, which demonstrates that the anion exchange between chiral perovskite and CsPbBr3 QDs can tune the chemical composition and optoelectronic properties due to the low bonding energy difference between them and decrease the strain within the QDs layer to reduce the radiative recombination lifetime. This work provides guidance for the synthesis of chiral perovskites with a strong CPL response and further provides insight into the origination of CPL.

Superoxide radicals mediated by high-spin Fe catalysis for organic wastewater treatment

Water resources are indispensable basic resources and important environmental carriers; the presence of organic contaminants in wastewater poses considerable risks to the health of both humans and ecosystems. Although the Fenton-like reactions using H2O2 as the oxidant to destroy organic pollutants are attractive, there are still challenges in improving reaction activity under neutral or even alkaline conditions. Herein, we designed a H2O2 activation pathway with O2•- as the main active species and elucidated that the spin interaction between Fe sites and coordinated O atoms effectively promotes the generation of the key intermediate Fe-*OOH. Furthermore, we successfully captured and analyzed the Fe-*OOH intermediate by in situ Raman spectroscopy. When applying FBOB to a continuous-flow reactor, CIP removal efficiency remained at around 90% within 600 min of continuous operation, achieving excellent efficiency, stability, and pH tolerance in removing pollutants.

Optimizations of luminescent materials for white light emitting diodes toward healthy lighting

White light emitting diodes (wLEDs) have been widely used as the green lighting sources. The commercial wLEDs devices are mainly achieved through the combination of blue emission chips and yellow phosphors, which offer advantages of high efficiency and long lifetime. However, the color rendering index (CRI) of traditional wLEDs is low due to the lack of red components. In recent years, with the improvement of the quality of life, a lot of efforts have been paid to improve the performance of wLEDs devices related to CRI, correlated color temperature, light uniformity, luminous flux, etc. In this article, we summarize the recent advances on the optimization of wLEDs toward healthy lighting. Brief introductions on the fundamentals of healthy effect of lighting are presented, followed by discussions of current methods to realize wLEDs devices. Special overviews on strategies for luminescent materials of wLEDs in recent years are presented. The opportunities and challenges in the future development of wLEDs lighting devices are also discussed.

Multifunctional Phosphor with High-Efficient Near-Infrared Emission Based on Antimony-Zinc Halides

Metal halide-based broadband near-infrared (NIR) luminescent materials face problems such as complicated preparation, high cost, low photoluminescence quantum yield, and high excitation energy. Here, incorporating Sb3+ and Br- into (C20H20P)2ZnCl4 crystals allowed for the achievement of efficient broadband near-infrared emission under 400 nm excitation while maintaining satisfactory environmental and thermal stability. The compounds exhibit a broad range of emission bands from 550 to 1050 nm, with a photoluminescence quantum yield of 93.57%. This is a groundbreaking achievement for organic-inorganic hybrid metal halide NIR luminescent materials. The near-infrared emission is suggested to originate from [SbX5]2-, as supported by the femtosecond transient absorption spectra and density-functional theory calculations. This phosphor-based NIR LEDs successfully demonstrate potential applications in night vision, medical imaging, information encryption, and anticounterfeiting.

Prevention of ion migration in lead halide perovskites upon plugging the anion vacancies with PbSe islands

To circumvent the issue of halide ion exchange in perovskites, we have decorated CsPbBr3 and CsPbI3 nanocrystals with different sized PbSe nanoparticles and demonstrated that it effectively prevents anion exchange reaction in CsPbBr3/CsPbI3 nanoheterostructures (NHSs) as a consequence of halide vacancy passivation by the more covalent selenide anion.

A luminescent Ag8(DPPY)6(PhCC)6 cluster with a triangular superatomic Ag8 core

We have synthesized single crystals of a highly stable Ag8 nanocluster protected by six ligands of diphenyl-2-phosphinic pyridine (DPPY) plus six ligands of phenylacetylene (PhCC). This Ag8(DPPY)6(PhCC)6 cluster bears a triangular superatomic Ag8 core, with the vertex and edge Ag atoms (quasi-triangle Ag6) being protected by both P and N bidentate coordination of the six DPPY ligands; meanwhile, the six PhCC ligands via μ3-C coordination form coordination on the two central Ag atoms capped on both sides of the triangle facet. Apart from the well-organized coordination of the two ligands pertaining to the balanced interactions with the Ag8 core, this Ag8 nanocluster exhibits superatomic stability with two delocalized valence electrons (1S2||1P0), assuming that the six PhCC ligands fix 6 localized electrons from the Ag atoms. Interestingly, the Ag8(DPPY)6(PhCC)6 NCs display temperature-dependent dual emissions at 330 and 535 nm under deep ultraviolet excitation. TD-DFT calculations reproduced the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in such a superatomic metal cluster.

Surface and Interface Engineering for Highly Stable CsPbBr3/ZnS Core/Shell Nanocrystals

Shelling with chalcogenides on the surface of lead halide perovskite (LHP) nanocrystals (NCs) is believed to be an effective approach to increase their stability under high-moisture/aqueous conditions, which is important for LHP NC-based optoelectronic devices. However, it is still a challenge to prepare high-quality LHP/chalcogenide core/shell NCs with moisture/aqueous stability. In this work, a surface-defect-induced strategy is carried out to facilitate the adsorption of Br- ions and subsequently Zn2+ ions to preform a bipolar surface, which reduces the energy barrier at the CsPbBr3/ZnS interface and promotes the epitaxial growth of the ZnS shell layer. The aqueous stability of the as-received NCs shows an increase of over 12 times compared to that of the original one. Likewise, Mn2+ ions are introduced to further reduce the geometric symmetry mismatch and defect density at the CsPbBr3/ZnS interface. Interestingly, aqueous stability characterizations illustrate negligible degradation even after 230 min of ultrasonication, suggesting their outstanding stability. This work proposes an effective approach to prepare high-quality LHP/chalcogenide core/shell NCs, which possess great potential in the fabrication of stable optoelectronic devices.

Recent Progress on Perovskite-Based Electrocatalysts for Efficient CO2 Reduction

An efficient carbon dioxide reduction reaction (CO2RR), which reduces CO2 to low-carbon fuels and high-value chemicals, is a promising approach for realizing the goal of carbon neutrality, for which effective but low-cost catalysts are critically important. Recently, many inorganic perovskite-based materials with tunable chemical compositions have been applied in the electrochemical CO2RR, which exhibited advanced catalytic performance. Therefore, a timely review of this progress, which has not been reported to date, is imperative. Herein, the physicochemical characteristics, fabrication methods and applications of inorganic perovskites and their derivatives in electrochemical CO2RR are systematically reviewed, with emphasis on the structural evolution and product selectivity of these electrocatalysts. What is more, the current challenges and future directions of perovskite-based materials regarding efficient CO2RR are proposed, to shed light on the further development of this prospective research area.

Recent Advances and Perspectives of Metal Halide Perovskite Heteronanocrystals

Heteronanocrystals that combine multiple semiconductors into a nanoscale heterostructure possess excellent optical performance and flexibility in property engineering compared with their single-component counterparts. The successes in fabricating lead halide perovskite-based heteronanocrystals (PHNCs) have drastically improved the stability and tunability of the optical and electrical properties. However, the epitaxial growth of semiconductor materials on perovskite nanocrystals remains a fundamental challenge because of the mismatch in their surface structure and crystal growth kinetics. Here, we review recent progress in the development of PHNCs with emphasis on their synthesis methods and surface chemistry that led to new insights and reaction protocols for the design and fabrication of PHNCs. In addition, the optical features of different types of PHNCs and nanocomposites and their application perspectives are summarized. Finally, we conclude with a discussion of the remaining issues, challenges, and opportunities in epitaxial growth of Janus and core-shell structure PHNCs.

Pt-CsPbBr3 Perovskite Nanocrystal Heterostructures: All Epitaxial

Designing heterostructures of soft ionic nanocrystals with metallic or covalent nanostructures having epitaxial junctions in solution poses several fundamental challenges. Hence, in spite of large successes in developing lead halide perovskite nanocrystals, the chemistry of formation of their facet-directive epitaxial growth of noble metals cannot be explored yet. To address this, herein, epitaxial heterostructures of orthorhombic CsPbBr3 and cubic Pt in multiple directional approaches are reported. Appropriate facets of perovskite nanocrystals and high-temperature reaction are the key parameters for obtaining such nanocrystal heterostructures. Interfacial planes at the junctions having ideal lattice matching helped in establishing the epitaxial relations of (110) of orthorhombic (space group Pbnm) CsPbBr3 with {020} of cubic Pt and again (011) of CsPbBr3 with {111} of Pt. These results provided strong fundamental insights that ionic halide perovskite nanostructures and materials having different crystal phases can be placed in a single building block with continuous sublattice structures.

In Situ Constructed Perovskite-Chalcogenide Heterojunction for Photocatalytic CO2 Reduction

Perovskite nanocrystals (PNCs) are promising candidates for solar-to-fuel conversions yet exhibit low photocatalytic activities mainly due to serious recombination of photogenerated charge carriers. Constructing heterojunction is regarded as an effective method to promote the separation of charge carriers in PNCs. However, the low interfacial quality and non-directional charge transfer in heterojunction lead to low charge transfer efficiency. Herein, a CsPbBr3 -CdZnS heterojunction is designed and prepared via an in situ hot-injection method for photocatalytic CO2 reduction. It is found that the high-quality interface in heterojunction and anisotropic charge transfer of CdZnS nanorods (NRs) enable efficient spatial separation of charge carriers in CsPbBr3 -CdZnS heterojunction. The CsPbBr3 -CdZnS heterojunction achieves a higher CO yield (55.8 µmol g-1  h-1 ) than that of the pristine CsPbBr3 NCs (13.9 µmol g-1  h-1 ). Furthermore, spectroscopic experiments and density functional theory (DFT) simulations further confirm that the suppressed recombination of charge carriers and lowered energy barrier for CO2 reduction contribute to the improved photocatalytic activity of the CsPbBr3 -CdZnS heterojunction. This work demonstrates a valid method to construct high-quality heterojunction with directional charge transfer for photocatalytic CO2 reduction. This study is expected to pave a new avenue to design perovskite-chalcogenide heterojunction.

Mitigating halide ion migration by resurfacing lead halide perovskite nanocrystals for stable light-emitting diodes

Lead halide perovskite nanocrystals are promising for next-generation high-definition displays, especially in light of their tunable bandgaps, high color purities, and high carrier mobility. Within the past few years, the external quantum efficiency of perovskite nanocrystal-based light-emitting diodes has progressed rapidly, reaching the standard for commercial applications. However, the low operational stability of these perovskite nanocrystal-based light-emitting diodes remains a crucial issue for their industrial development. Recent experimental evidence indicates that the migration of ionic species is the primary factor giving rise to the performance degradation of perovskite nanocrystal-based light-emitting diodes, and ion migration is closely related to the defects on the surface of perovskite nanocrystals and at the grain boundaries of their thin films. In this review, we focus on the central idea of surface reconstruction of perovskite nanocrystals, discuss the influence of surface defects on halide ion migration, and summarize recent advances in resurfacing perovskite nanocrystal strategies toward mitigating halide ion migration to improve the stability of the as-fabricated light-emitting diode devices. From the perspective of perovskite nanocrystal resurfacing, we set out a promising research direction for improving both the spectral and operational stability of perovskite nanocrystal-based light-emitting diodes.

Superexchange-induced Pt-O-Ti3+ site on single photocatalyst for efficient H2 production with organics degradation in wastewater

Efficient photocatalytic H2 production from wastewater instead of pure water is a dual solution to the environmental and energy crisis, but due to the rapid recombination of photoinduced charge in the photocatalyst and inevitable electron depletion caused by organic pollutants, a significant challenge of dual-functional photocatalysis (simultaneous oxidative and reductive reactions) in single catalyst is designing spatial separation path for photogenerated charges at atomic level. Here, we designed a Pt-doped BaTiO3 single catalyst with oxygen vacancies (BTPOv) that features Pt-O-Ti3+ short charge separation site, which enables excellent H2 production performance (1519 μmol·g-1·h-1) while oxidizing moxifloxacin (k = 0.048 min-1), almost 43 and 98 times than that of pristine BaTiO3 (35 μmol·g-1·h-1 and k = 0.00049 min-1). The efficient charge separation path is demonstrated that the oxygen vacancies extract photoinduced charge from photocatalyst to catalytic surface, and the adjacent Ti3+ defects allow rapid migration of electrons to Pt atoms through the superexchange effect for H* adsorption and reduction, while the holes will be confined in Ti3+ defects for oxidation of moxifloxacin. Impressively, the BTPOv shows an exceptional atomic economy and potential for practical applications, a best H2 production TOF (370.4 h-1) among the recent reported dual-functional photocatalysts and exhibiting excellent H2 production activity in multiple types of wastewaters.

Epitaxial CsPbBr3 /CdS Janus Nanocrystal Heterostructures for Efficient Charge Separation

Epitaxial heterostructures of colloidal lead halide perovskite nanocrystals (NCs) with other semiconductors, especially the technologically important metal chalcogenides, can offer an unprecedented level of control in wavefunction design and exciton/charge carrier engineering. These NC heterostructures are ideal material platforms for efficient optoelectronics and other applications. Existing methods, however, can only yield heterostructures with random connections and distributions of the two components. The lack of epitaxial relation and uniform geometry hinders the structure-function correlation and impedes the electronic coupling at the heterointerface. This work reports the synthesis of uniform, epitaxially grown CsPbBr₃ /CdS Janus NC heterostructures with ultrafast charge separation across the electronically coupled interface. Each Janus NC contains a CdS domain that grows exclusively on a single {220} facet of CsPbBr₃ NCs. Varying reaction parameters allows for precise control in the sizes of each domain and readily modulates the optical properties of Janus NCs. Transient absorption measurements and modeling results reveal a type II band alignment, where photoexcited electrons rapidly transfer (within ≈9 picoseconds) from CsPbBr₃ to CdS. The promoted charge separation and extraction in epitaxial Janus NCs leads to photoconductors with drastically improved (approximately three orders of magnitude) responsivity and detectivity, which is promising for ultrasensitive photodetection.

Efficient Near-Infrared Luminescence Based on Double Perovskite Cs2SnCl6

Cs₂SnCl₆ double perovskite has attracted wide attention as a promising optoelectronic material because of its better stability and lower toxicity than its lead counterparts. However, pure Cs₂SnCl₆ demonstrates quite poor optical properties, which usually calls for active element doping to realize efficient luminescence. Herein, a facile co-precipitation method was used to synthesize Te⁴⁺ and Er³⁺-co-doped Cs₂SnCl₆ microcrystals. The prepared microcrystals were polyhedral, with a size distribution around 1-3 μm. Highly efficient NIR emissions at 1540 nm and 1562 nm due to Er³⁺ were achieved in doped Cs₂SnCl₆ compounds for the first time. Moreover, the visible luminescence lifetimes of Te⁴⁺/Er³⁺-co-doped Cs₂SnCl₆ decreased with the increase in the Er³⁺ concentration due to the increasing energy transfer efficiency. The strong and multi-wavelength NIR luminescence of Te⁴⁺/Er³⁺-co-doped Cs₂SnCl₆ originates from the 4f→4f transition of Er³⁺, which was sensitized by the spin-orbital allowed ¹S₀→³P₁ transition of Te⁴⁺ through a self-trapped exciton (STE) state. The findings suggest that ns²-metal and lanthanide ion co-doping is a promising method to extend the emission range of Cs₂SnCl₆ materials to the NIR region.

Quantum dots are time bomb: Multiscale toxicological study

The use of quantum dots has spread widely into many applications. Works on the study of quantum dots on living organisms have had conflicting results on toxicity. There are no full-scale long-term toxicological studies with multiple administration of quantum dots. Understanding the toxicity of quantum dots is still limited. Here we present data on the effects of quantum dots on animals. In this work for the first time, it is shown that at a single administration of quantum dots in the body they have moderate species-specific toxicity, but repeated administration of quantum dots for 14 days even in the amount of 0.5 mg/kg leads to a delayed not completely irreversible hematotoxic effect, delayed irreversible disorders of barrier function of the liver, irreversible nephrotoxic effect, and to pathological changes in the thymus, kidneys and spleen. Administration of quantum dots in the amount of 2.5 mg/kg for 14 days leads to irreversible changes in the lungs, liver, spleen, kidneys and thyroid gland. This phenomenon is based on immunological reactions. On the one hand, these data confirm that quantum dots at a single administration can show relatively low toxicity. On the other hand, they cause to a delayed irreversible organ and tissue damage when repeatedly administered to the body even in small quantities. This study demonstrates that quantum dots are not as low in toxicity as previously thought to be and pose a serious risk when entering living organisms. Detecting and treating poisoning using standard methods of diagnosis and treatment of heavy metal poisoning may not be effective. This study demonstrates that toxic effects of quantum dots on a living body are quite complex and cannot be generalized based on previously reported assumptions.

Charge Transport Dynamics of Quasi-Type II Perovskite Janus Nanocrystals in High-Performance Photoconductors

CsPbBr₃-Pb₄S₃Br₂ Janus nanocrystals (NCs) are the only nanomaterial where the epitaxial structure of perovskite and chalcogenide materials has been realized at the nanoscale, but their exciton dynamics mechanism has not yet been thoroughly investigated or applied in photodetection applications. This work reports an attractive device performance of perovskite photoconductors based on epitaxial CsPbBr₃-Pb₄S₃Br₂ Janus NCs, as well as the carrier relaxation and transfer mechanism of the heterojunction. By a combination of transient optical absorption and quantum dynamics simulation, it is demonstrated that the photogenerated holes on CsPbBr₃ can be successfully extracted by Pb₄S₃Br₂, while the hole transfer proceeds about three times faster than energy loss and remains "hot" for about 300 fs. This feature has favorable effects on long-range charge separation and transport; therefore, the Janus NCs photoconductors exhibit an exceptional responsivity of 34.0 A W^-1 and specific detectivity of 1.26 × 10¹⁴ Jones.

Photoluminescence Sensing of Soluble Lead in Children's Crayons Using Perovskite Nanocrystal In Situ Growth on an Aluminum Hydroxide Layer

In this study, a fluorescence sensing approach for lead ion (Pb²⁺) was developed using in situ growth of methylamine lead bromine (MAPbBr₃) perovskite on an aluminum hydroxide (Al(OH)₃) thin layer. The Al(OH)₃ thin layer could be obtained on a glass slide by liquid phase deposition and is of a large specific surface area and insoluble in water. After sulfhydryl functionalization, the Al(OH)₃ thin layer reveals effective adsorption and excellent enrichment ability to Pb²⁺ and is additionally used as the substrate for the in situ growth of lead halogen perovskite. The fluorescence sensing of Pb²⁺ could be realized by the fluorescence intensity of lead halogen perovskite on the Al(OH)₃ layer. The linear relationship between the fluorescence intensity and the concentration of Pb²⁺ was found in the range from 80 to 1500 mg/kg. The detection limit of Pb²⁺ is found to be 40 mg/kg, which is lower than the maximum permission of lead residue in student products (90 mg/kg) stipulated by the National Standard of the People's Republic of China (GB21027-2020). After being grinded and pre-treated, soluble lead in watercolor paint and crayon samples can be extracted by the sulfhydryl functionalization Al(OH)₃ layer, then lead halogen perovskite can be generated in situ on the layer to achieve the fluorescence sensing for the determination of soluble lead in the samples.

Full-Color Circularly Polarized Luminescence of CsPbX3 Nanocrystals Triggered by Chiral Carbon Dots

Chiral carbon dots (Ch-CDs) trigger the full-color circularly polarized luminescence (CPL) of CsPbX₃  nanocrystals (NCs). Ch-CDs-CsPbBr₃  NCs are successfully synthesized via simple ligand-assisted coprecipitation of Ch-CDs and metal halides precursors at room temperature. Ch-CDs-CsPbBr₃  retains emission characteristics of the CsPbBr₃  with near-unity photoluminescence quantum yield, and meanwhile has special CPL, with a maximum luminescence dissymmetric factor (g_lum ) of -3.1 × 10^-3 , which is induced by Ch-CDs. This is the first report of chiral perovskite which is induced by other chiral nanomaterials. By anion exchange, CPL can cover almost the entire visible light band. Surprisingly, the chiral signal of Ch-CDs-CsPbBr₃  NCs is in-versed under excitation state, which can be induced by the charge transfers between Ch-CDs and perovskite NCs. The combination of perovskites and Ch-CDs pave away for the design of new chiral perovskite on multifunctional applications.

Interfacial Engineering of Semicoherent Interface at Purified CsPbBr3 Quantum Dots/2D-PbSe for Optimal CO2 Photoreduction Performance

Heterogeneous photocatalysts are extensively used to achieve interfacial electric fields for acceleration of oriented charge carrier transport and further promotion of photocatalytic redox reactions. Unfortunately, the incoherent interfaces are almost present in the heterostructures owing to large lattice mismatch accompanied by the interfacial defects and high density of gap states, acting as high energy barriers for charge migration. In this work, we report the atomic engineering of CsPbBr₃/PbSe heterogeneous interfaces and conversion from incoherent features to semicoherent characters via methyl acetate (MeOAc) purification of CsPbBr₃ quantum dots (QDs) before composited with two-dimensional (2D)-PbSe, which is confirmed by high-resolution transmission electron microscopy. The photocatalytic performances and theoretical calculations indicate that semicoherent interfaces are favorable for improving the activity and reactivity of the heterostructure, triggering 3 times enhanced photocatalytic CO₂ reduction rate with 91% selectivity and satisfactory stability. This study proposes a facile method for photocatalytic heterojunctions to transform incoherent interfaces to photocatalytically beneficial semicoherent boundaries, accompanying with a systematic analysis of the consequent chemical dynamics to demonstrate the mechanism of the semicoherent interface for supporting photocatalysis. The understandings gained from this work are valuable for rational interfacial lattice engineering of heterogeneous photocatalysts for efficient solar fuel production.

Facets-Directed Epitaxially Grown Lead Halide Perovskite-Sulfobromide Nanocrystal Heterostructures and Their Improved Photocatalytic Activity

Lead halide perovskite nanocrystal heterostructures have been extensively studied in the recent past for improving their photogenerated charge carriers mobility. However, most of such heterostructures are formed with random connections without having strong evidence of epitaxial relation. Perovskite-chalcohalides are the first in this category, where all-inorganic heterostructures are formed with epitaxial growth. Going beyond one facet, herein, different polyhedral nanocrystals of CsPbBr₃ are explored for facet-selective secondary epitaxial sulfobromide growths. Following a decoupled synthesis process, the heterojunctions are selectively established along {110} as well as {200} facets of 26-faceted rhombicuboctahedrons, the {110} facets of armed hexapods, and the {002} facets of 12-faceted dodecahedron nanocrystals of orthorhombic CsPbBr₃. Lattice matching induced these epitaxial growths, and their heterojunctions have been extensively studied with electron microscopic imaging. Unfortunately, these heterostructures did not retain the intense host emission because of their indirect band structures, but such combinations are found to be ideal for promoting photocatalytic CO₂ reduction. The pseudo-Type-II combination helped here in the successful movement of charge carriers and also improved the rate of catalysis. These results suggest that facet-selective all-inorganic perovskite heterostructures can be epitaxially grown and this could help in improving their catalytic activities.

Reversible Phase Segregation and Amorphization of Mixed-Halide Perovskite Nanocrystals in Glass Matrices

Mixed-halide perovskites have attracted great attention in applications of lighting and photovoltaic devices due to their excellent properties. Understanding the phase segregation mechanism of mixed-halide perovskite has significance for suppressing the performance degradation of optoelectronic devices. Herein, we investigate the mixed-halide perovskite nanocrystals (NCs) in isolation from the external factors (oxygen, moisture, and pressure) using glass encapsulation, which shows excellent photostability against phase segregation. By monitoring the structural evolution of the NCs in glass matrices, the coexisting phase segregation and amorphization of mixed-halide perovskites are observed in real-time. The results show that thermal-induced local temperature increase plays a dominant role in the phase segregation of mixed-halide perovskite NCs. The recovery process is driven by the spontaneous crystallization of the amorphous mixed-halide phase. The clarified dynamic equilibrium process between the compositional segregation (mixing) and structural disorder (order) gives us a better insight into the reversible phase segregation mechanism of mixed-halide perovskite.

How different are the surfaces of semiconductor Ag2Se quantum dots with various sizes?

The surface of nanocrystals plays a dominant role in many of their physical and chemical properties. However, controllability and tunability of nanocrystal surfaces remain unsolved. Herein, we report that the surface chemistry of nanocrystals, such as near-infrared Ag₂Se quantum dots (QDs), is size-dependent and composition-tunable. The Ag₂Se QDs tend to form a stable metal complex on the surface to minimize the surface energy, and therefore the surface chemistry can be varied with particle size. Meanwhile, changes in surface inorganic composition lead to reorganization of the surface ligands, and the surface chemistry also varies with composition. Therefore, the surface chemistry of Ag₂Se QDs, responsible for the photoluminescence (PL) quantum yield and photostability, can be tuned by changing their size or composition. Accordingly, we demonstrate that the PL intensity of the Ag₂Se QDs can be tuned reversely by adjusting the degree of surface Ag⁺ enrichment via light irradiation or the addition of AgNO₃. This work provides insight into the control of QD surface for desired PL properties.

Organic Amine-Bridged Quasi-2D Perovskite/PbS Colloidal Quantum Dots Composites for High-Gain Near-Infrared Photodetectors

Near-infrared (NIR) II detection at weak flux intensity is required in medical imaging and is especially urgent in light of the low quantum efficiency of NIR-II dyes. The low responsivity of traditional photodetectors in this region limits image quality. Here, we report a NIR-II photodetector with high gain based on perovskite coupled PbS colloidal quantum dots (CQDs). Tailoring the trap density of CQDs by designing surface ligands with dual functionality contributed to control over trap-induced charge-injection upon light illumination. As a result, a detector with high gain is realized, showing external quantum efficiency of 1260% at 1200 nm and achieving the lowest detectable light intensity, that is, as low as 0.67 pW cm^-2 with a linear dynamic range of 200 dB. Devices maintain over 90% of responsivity after 150 days of storage. We acquired images of a butterfly wing, showing the skeleton texture with a maximum spatial resolution of 3.9 lp/mm.

Controllable vapor growth of CsPbBr3/CdS 1D heterostructures with type-II band alignment for high-performance self-powered photodetector

The controllable growth of CsPbBr3/CdS heterostructures with a unique 1D morphology and type-II band alignment for a high-performance self-powered photodetector.

Encapsulation of lead halide perovskite nanocrystals (NCs) at the single-particle level: strategies and properties

Lead halide perovskite NCs (APbX₃, A = formamidinium (FA), methylammonium (MA) or Cs; X = Cl, Br, I or their mixture) have attracted unprecedented attention due to their excellent photophysical properties and wide application prospects. However, the inherent ionic structure of APbX₃ NCs makes them very sensitive to external conditions such as water and oxygen, resulting in poor stability. As a feasible strategy, encapsulation is considered to be effective in improving the stability. In this minireview, we focus on single-particle-level coating, which not only can improve the stability but also maintain the nano effect of the original NCs. This review summarizes the fundamental information on APbX₃ NCs and the necessity of single-particle-level coating. Subsequently, a variety of heterostructures at the single-particle level are introduced in detail. Then, their applications are summarized. Moreover, we discuss the challenges and prospects of the single-particle-level heterostructures based on APbX₃ NCs.

Upconversion Perovskite Nanocrystal Heterostructures with Enhanced Luminescence and Stability by Lattice Matching

Lead halide perovskite quantum dots (PQDs) exhibit excellent photoelectric and optical properties, but their poor stability and low multiphoton absorption efficiency greatly limit their biological applications. Efforts have been made to combine upconversion nanoparticles (UCNPs) with PQDs to produce a composite material that is NIR-excitable, upconverting, and emission-tunable due to the unique optical properties of UCNPs, which converts tissue-penetrating near-infrared light into visible light based on an upconversion multiphoton excitation process. However, it is challenging to make such a nanocrystal heterostructure and maintain good optical properties and stability of both UCNPs and PQDs because they have different crystal structures. Here, we report the synthesis of heterostructured UCNP-PQD nanocrystals to bring hexagonal-phase NaYF₄ UCNPs and cubic-phase CsPbBr₁X₂ PQDs in close proximity in a single nanocrystal, leading to efficient Förster resonance energy transfer (FRET) from the UCNP to the PQD under NIR excitation, as compared to their counterparts in solution. Moreover, by further improving the lattice matching between the UCNP and PQD using Gd to replace Y, heterostructured CsPbBr₃-NaGdF₄:Yb,Tm nanocrystals are successfully synthesized, with much enhanced luminescence and stability at high temperatures or in polar solvents or under continuous ultraviolet light excitation as compared to those of the CsPbBr₃-NaYF₄:Yb,Tm nanocrystals and pure PQDs.

One-Step Prepared Water-Resistant Organic-Inorganic-Hybrid Perovskite Quantum Dots with Zn-Oxygen Vacancies for Attempts at Nitrogen Fixation

Applying organic-inorganic hybrid perovskite quantum dots (PQDs) to photocatalytic nitrogen fixation is hindered long-term by the inherent instability in water and tedious preparations. Here, to realize PQD-catalyzed photocatalytic N₂ reduction reaction (NRR), water-resistant PQDs are simply prepared through one-step electrospray synthesis in microseconds. During the fast electrospray, PQDs of Zn/PbO-doped methylammonium lead bromide (Zn/PbO/PC-Zn/MAPbBr₃ , MA: CH₃ NH₃ ) are prepared and part-encapsulated by polycarbonate. The synthesis maintains good water resistance, whose restriction on charge transport is overcome skillfully. Simultaneously, substitution of Zn with Pb on water-resistant surface is also achieved, which fabricates new Zn-oxygen vacancies (Zn-OVs) with Zn/PbO-Zn/MAPbBr₃ type I heterojunction. This facilitates efficient electron transfer from internal heterojunction interface of Zn/MAPbBr₃ PQDs to the surface of Zn/PbO. Demonstrated by theoretical calculations, Zn-OVs promote chemisorption and polarization of N₂ . In addition, s-electrons in exposed Zn become active due to changes of electron filling of Zn orbitals under OVs' co-doping. Thus, photocatalytic N₂ reduction reaction catalyzed by organic-inorganic hybrid PQDs is first achieved in aqueous phase without sacrificial agents being added. This initiates possibilities for photocatalytic applications of organic-inorganic hybrid PQDs in aqueous phase.

Cs-Lattice Extension and Expansion for Inducing Secondary Growth of CsPbBr3 Perovskite Nanocrystals

The increase of the stability of perovskite nanocrystals with respect to exposure to polar media, layers growth, or shelling with different materials is in demand. While these are widely studied for metal chalcogenide nanocrystals, it has yet to be explored for perovskite nanocrystals. Even growth of a single monolayer on any facet or on the entire surface of these nanocrystals could not be established yet. To address this, herein, a secondary growth approach leading to creation of a secondary lattice with subsequent expansion on preformed CsPbBr₃ perovskite nanocrystals is reported. As direct layer growth by adding precursors was not successful, Cs-lattice extension to preformed CsPbBr₃ nanocrystals was performed by coupling CsBr to these nanocrystals. Opening both {110}/{002} and {200} facets of parent CsPbBr₃ nanocrystals, CsBr was observed to be connected with lattice matching to the {200} facets. Further with Pb(II) incorporation, the Cs-sublattices of CsBr were expanded to CsPbBr₃ and led to cube-couple nanocrystals. However, as cubes in these nanostructures were differently oriented, these showed lattice mismatch at their junctions. This lattice mismatch though restricted complete shelling but successfully favored the secondary growth on specific facets of parent CsPbBr₃ nanocrystals. Details of this secondary growth via lattice extension and expansion are microscopically analyzed and reported. These results further suggest that lead halide perovskite nanocrystals can be epitaxially grown under proper reaction design and more complex as well as heterostructures of these materials can be fabricated to meet the current demands.

One-Pot Synthesis and Structural Evolution of Colloidal Cesium Lead Halide-Lead Sulfide Heterostructure Nanocrystals for Optoelectronic Applications

Heterostructures, combining perovskite nanocrystals (PNC) and chalcogenide quantum dots, could pave a path to optoelectronic device applications by enabling absorption in the near-infrared region, tailorable electronic properties, and stable crystal structures. Ideally, the heterostructure host material requires a similar lattice constant as the guest which is also constrained by the synthesis protocol and materials selectivity. Herein, we present an efficient one-pot hot-injection method to synthesize colloidal all-inorganic cesium lead halide-lead sulfide (CsPbX₃ (X = Cl, Br, I)-PbS) heterostructure nanocrystals (HNCs) via the epitaxial growth of the perovskite onto the presynthesized PbS nanocrystals (NCs). Optical and structural characterization evidenced the formation of heterostructures. The embedding of PbS NCs into CsPbX₃ perovskite allows the tuning of the absorption and emission from 400 to 1100 nm by tuning the size and composition of perovskite HNCs. The CsPbI₃-PbS HNCs show enhanced stability in ambient conditions. The stability, tunable optical properties, and variable band alignments accessible in this system would have implications in the design of novel optoelectronic applications such as light-emitting diodes, photodetectors, photocatalysis, and photovoltaics.

Phase Engineering of Cesium Manganese Bromides Nanocrystals with Color-Tunable Emission

For display applications, it is highly desirable to obtain tunable red/green/blue emission. However, lead-free perovskite nanocrystals (NCs) generally exhibit broadband emission with poor color purity. Herein, we developed a unique phase transition strategy to engineer the emission color of lead-free cesium manganese bromides NCs and we can achieve a tunable red/green/blue emission with high color purity in these NCs. Such phase transition can be triggered by isopropanol: from one dimensional (1D) CsMnBr₃ NCs (red-color emission) to zero dimensional (0D) Cs₃ MnBr₅ NCs (green-color emission). Furthermore, in a humid environment both 1D CsMnBr₃ NCs and 0D Cs₃ MnBr₅ NCs can be transformed into 0D Cs₂ MnBr₄ ⋅2 H₂ O NCs (blue-color emission). Cs₂ MnBr₄ ⋅2 H₂ O NCs could inversely transform into the mixture of CsMnBr₃ and Cs₃ MnBr₅ phase during the thermal annealing dehydration step. Our work highlights the tunable optical properties in single component NCs via phase engineering and provides a new avenue for future endeavors in light-emitting devices.

CsPbX3 -ITO (X = Cl, Br, I) Nano-Heterojunctions: Voltage Tuned Positive to Negative Photoresponse

All-Inorganic perovskite CsPbX₃ (X = Cl, Br, I) quantum dots (QDs) have attracted tremendous attention in the past few years for their appealing performance in optoelectronic applications. Major properties of CsPbX₃ QDs include the positive photoconductivity (PPC) and the defect tolerance of the in-band trap states. Here it is reported that when hybridizing CsPbX₃ QDs with indium tin oxide (ITO) nanocrystals to form CsPbX₃ -ITO nano-heterojunctions (NHJs), a voltage tuned photoresponse-from PPC to negative photoconductivity (NPC) transform-is achieved in lateral drain-source structured ITO/CsPbX₃ -ITO-NHJs/ITO devices. A model combining exciton, charge separation, transport, and most critical the voltage driven electron filling of the in-band trap states with drain-source voltage (V_DS ) above a threshold, is proposed to understand this unusual PPC-NPC transform mechanism, which is different from that of any known nanomaterial system. This finding exhibits potentials for developing devices such as photodetectors, optoelectronic switches, and memories.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

Lead halide perovskite (LHP) nanocrystals (NCs) have recently garnered enhanced development efforts from research disciplines owing to their superior optical and optoelectronic properties. These materials, however, are unlike conventional quantum dots, because they possess strong ionic character, labile ligand coverage, and overall stability issues. As a result, the system as a whole is highly dynamic and can be affected by slight changes of particle surface environment. Specifically, the surface ligand shell of LHP NCs has proven to play imperative roles throughout the lifetime of a LHP NC. Recent advances in engineering and understanding the roles of surface ligand shells from initial synthesis, through postsynthetic processing and device integration, finally to application performances of colloidal LHP NCs are covered here.

Highly Stable Perovskite Quantum Dots Modified by Europium Complex for Dual-Responsive Optical Encoding

Inorganic perovskite quantum dots (QDs) have attracted great scientific attention in the field of luminescent materials, but the application has been limited by the inferior stability that results from highly dynamic capping ligands. In this work, we use a rare-earth complex to modify perovskite QDs with ligand exchange to realize perovskite functionalization; meanwhile, the stability of perovskite QDs is greatly improved. Density functional theory calculation results show that the adsorption energy of the europium complex to QDs is higher than that with traditional ligands, which provides a thermodynamic basis for stability improvement. Furthermore, the modified QDs exhibit attractive dual-response property, including temperature and pH response ascribed to QDs and europium complexes, respectively. The superior property can be applied to multi-stimuli-responsive optical encoding, which is further capable of enhancing the security of encrypted information. This study not only affords a strategy for the synthesis of highly stable perovskites but also provides a method for the functionalization of perovskites.

High-performance broadband photodetectors based on all-inorganic perovskite CsPb(Br/I)3 nanocrystal/CdS-microwire heterostructures

High-performance broadband photodetectors that can operate at UV, visible, and near-infrared wavelengths have been fabricated based on CsPb(Br/I)₃ nanocrystal (NC)/CdS-microwire (MW) heterostructures. Under an incident light illumination of 365, 530, and 660 nm, the CsPb(Br/I)₃-NC/CdS-MW-heterostructure-based photodetector exhibited a superior photosensitivity and broader spectral response than those of a bare-CdS-MW-based photodetector, which can be attributed to the light-trapping ability of the CsPb(Br/I)₃ NCs and charge-transfer efficiency at the CsPb(Br/I)₃-NC/CdS-MW-heterojunction interface. The photodetector based on the CsPb(Br/I)₃ NC/CdS-MW heterostructure also exhibited a good response to near-infrared light (760 and 810 nm) because the produced heterojunction facilitates the spatial separation of the photogenerated carriers, and the carriers are transferred from the CsPb(Br/I)₃ NC part to the CdS MW part through diffusion due to the relatively long diffusion length in the CsPb(Br/I)₃ layer. Therefore, the proposed photodetectors are promising for constructing high-performance broadband optoelectronic devices.

The high performance photodetector based on CsPb(Br/I)₃-NC/CdS-MW heterostructures showed broadband photodetection that covers UV-VIS-NIR range due to the charge transfer at the heterojunction interface and the absorption capability of CsPb(Br/I)₃.

Exploiting the Lability of Metal Halide Perovskites for Doping Semiconductor Nanocomposites

Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr₃ into Cs₄PbBr₆ in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded Cs₄PbBr₆ nanoprecipitates. We show that PbBr₂ is extracted from CsPbBr₃ and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 10¹⁹ and 10²⁰ cm^-3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors.

Halide Perovskite-Lead Chalcohalide Nanocrystal Heterostructures

We report the synthesis of colloidal CsPbX₃–Pb₄S₃Br₂ (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr₃–Pb₄S₃Br₂ nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr₃ clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Postsynthesis reaction with either Cl^– or I^– ions delivers the corresponding CsPbCl₃–Pb₄S₃Br₂ and CsPbI₃–Pb₄S₃Br₂ heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable γ phase (or “black” phase) of CsPbI₃ in the CsPbI₃–Pb₄S₃Br₂ heterostructure.

NIR-excitable heterostructured upconversion perovskite nanodots with improved stability

There is a great need to develop heterostructured nanocrystals which combine two or more different materials into single nanoparticles with combined advantages. Lead halide perovskite quantum dots (QDs) have attracted much attention due to their excellent optical properties but their biological applications have not been much explored due to their poor stability and short penetration depth of the UV excitation light in tissues. Combining perovskite QDs with upconversion nanoparticles (UCNP) to form hybrid nanocrystals that are stable, NIR excitable and emission tunable is important, however, this is challenging because hexagonal phase UCNP can not be epitaxially grown on cubic phase perovskite QDs directly or vice versa. In this work, one-pot synthesis of perovskite-UCNP hybrid nanocrystals consisting of cubic phase perovskite QDs and hexagonal phase UCNP is reported, to form a watermelon-like heterostructure using cubic phase UCNP as an intermediate transition phase. The nanocrystals are NIR-excitable with much improved stability.

Combining two or more different materials with different crystal structures into single nanoparticle with combined advantages is challenging. Here, the authors demonstrate one-pot synthesis of perovskite-upconversion hybrid nanocrystals consisting of cubic and hexagonal phases to form a watermelon-like heterostructure.

Deciphering the excited-state dynamics and multicarrier interactions in perovskite core-shell type hetero-nanocrystals

Deciphering and modulating the carrier dynamics of perovskite nanocrystals (Pe-NCs) is crucial for their optoelectronic applications, which remains elusive to date. Herein, we, for the first time, explore the ultrafast dynamics of perovskite core-shell type NCs using CsPbBr₃@ZnS as a model system. According to the transient spectroscopic characterization, a physical picture of the ultrafast dynamics in core-shell Pe-NCs is built. Specifically, we directly observed the "hot" hole transfer from CsPbBr₃ to ZnS and confirmed the formation of charge-transfer state in CsPbBr₃@ZnS NCs. Such ultrafast (<100 fs) hole rearrangement speeds up the carrier cooling and breaks the hot phonon bottleneck effect in Pe-NCs. Moreover, thanks to the charge separation in CsPbBr₃@ZnS NCs, the Auger recombination is largely suppressed and the Auger lifetime is increased nearly 5-fold compared to that of "pure" CsPbBr₃ NCs, which endows CsPbBr₃@ZnS NCs with unique optical gain properties. These results are informative for halide perovskite-based applications, such as photocatalysis, hot-carrier photovoltaics and lasers.

Facile Synthesis of a Color-Tunable Microcrystal Phosphor for Anti-Counterfeit Applications

Developing luminescent materials with tunable emission colors provides exciting opportunities for application in the display, anti-counterfeiting, and optical sensors. Here, we report a convenient, versatile approach to synthesize color-tunable, up/down-conversion luminescence in an inorganic host material. The emission color can be tuned by varying the excitation wavelength, allowing dynamic color tuning in the visible spectrum. We demonstrate that an unprecedented luminescence tunability from these phosphors can be achieved by tailoring the intensity ratio of different emission peaks. These findings provide valuable insights into controlling multiple emission color processes while offering the possibility for dynamic anti-counterfeiting and visual sensing of ultraviolet light in the range from 250 to 320 nm. These results open the opportunity for developing next-generation stimuli-responsive luminescent materials and smart devices.

Charge Transfer in the Heterostructure of CsPbBr3 Nanocrystals with Nitrogen-Doped Carbon Dots

Heterostructures of inorganic halide perovskites with mixed-dimensional inorganic nanomaterials have shown great potential not only in the field of optoelectronic energy devices and photocatalysis but also for improving our fundamental understanding of the charge transfer across the heterostructure interface. Herein, we present for the first time the heterostructure integration of the CsPbBr₃ nanocrystal with an N-doped carbon dot. We explore the photoluminescence (PL) and photoconductivity of the heterostructure of CsPbBr₃ nanocrystals and N-doped carbon dots. PL quenching of CsPbBr₃ nanocrystals with the addition of N-doped carbon dots was observed. The photoexcited electrons from the conduction band of CsPbBr₃ are trapped in the N-acceptor state of N-doped carbon dots, and the charge transfer occurs via quasi type II-like electronic band alignment. The charge transfer in the halide perovskite-based heterostructure should motivate further research into the new heterostructure synthesis with perovskites and the fundamental understanding of the mechanism of charge/energy transfer across the heterostructure interface.

Nano Ball-Milling Using Titania Nanoparticles to Anchor Cesium Lead Bromine Nanocrystals and Energy Transfer Characteristics in TiO2 @CsPbBr3 Architecture

Recently, all-inorganic halide perovskite (CsPbX₃ , (X = Cl, Br, and I)) nanocrystals (NCs) based hybrid architectures have attracted extensive attention owing to their distinct luminescence characteristics. However, due to stress and lattice mismatch, it is still a challenge to construct heterojunctions between perovskite NCs and the nanostructures with different lattice parameters and non-cubic contour. In this work, a room temperature mechanochemical method is presented to construct TiO₂ @CsPbBr₃ hybrid architectures, in which TiO₂ nanoparticles (NPs) with a hard lattice as nano "balls" mill off the angles and anchor to the CsPbBr₃ NCs with a soft lattice. On the contrary, to ball-mill without TiO₂ or with conventional ceramics balls replacing TiO₂ , CsPbBr₃ NCs still maintain cubic contour deriving from their cubic crystal structures. Moreover, the TiO₂ @CsPbBr₃ architectures display distinct improvement of photoluminescence quantum yields and more excellent thermal stability in contrast with pristine CsPbBr₃ owing to the passivation of surface defect, small surface area, and energy transfer from CsPbBr₃ to TiO₂ . Meanwhile, there is distinct luminous decay characteristic under the radiation of UV and visible light due to the "on" and "off" TiO₂ response. The method provides an alternative strategy to acquire other anchoring heterojunctions based on perovskite NCs for further regulating their luminescent characteristics.