Green-Emitting Lead-Free Cs4SnBr6 Zero-Dimensional Perovskite Nanocrystals with Improved Air Stability

Metal halide perovskite polymer composites for indirect X-ray detection

Metal halide perovskites (MHPs) have emerged as a promising class of materials for radiation detection due to their high atomic numbers and thus high radiation absorption, tunable and efficient luminescent properties and simple solution processability. Traditional MHP scintillators, however, suffer from environmental degradation, spurring interest in perovskite-polymer composites. This paper reviews recent developments in these composites tailored for scintillator applications. It discusses various synthesis methods, including solution-based and mechanochemical techniques, that enable the formation of composites with enhanced performance metrics such as light yield, detection limit, and environmental stability. The review also covers the remaining challenges and opportunities in fabrication techniques and performance metric evaluations of this class of materials. By offering a comprehensive overview of current research and future perspectives, this paper underscores the potential of perovskite-polymer composites to revolutionize the field of radiation detection.

Effect of CrF3 Addition on Photoluminescence Properties of Lead-Free Cs4SnBr6-xFx Zero-Dimensional Perovskite

Zero-dimensional (0D) tin halide perovskites, characterized by their broadband and adjustable emissions, high photoluminescence quantum yield, and absence of self-absorption, are crucial for the fabrication of high-efficiency optoelectronic devices, such as LEDs, solar cells, and sensors. Despite these attributes, boosting their emission efficiency and stability poses a significant challenge. In this work, Cr3+-doped Cs4SnBr6-xFx perovskites were synthesized using a water-assisted wet ball-milling method. The effect of CrF3 addition on photoluminescence properties of Cs4SnBr6-xFx Perovskites was investigated. We found that Cr3+-doped Cs4SnBr6-xFx Perovskites exhibit a broad emission band, a substantial Stokes shift, and an efficient green light emission centered at about 525 nm at ambient temperature. The derived photoluminescence quantum yield amounted to as high as 56.3%. In addition, these Cr3+-doped Cs4SnBr6-xFx perovskites outperform their undoped counterparts in terms of thermal stability. Through a comprehensive analysis of photoluminescence measurements, our findings suggested that the elevated photoluminescence quantum yield can be attributed to the enhanced exciton binding energy of self-trapped excitons (STEs) and the suitable electron-phonon coupling resulting from the substantial distortion of [SnBr6]4- octahedra instigated by the addition of CrF3.

Boosting the Self-Trapped Exciton Emission in Cs4SnBr6 Zero-Dimensional Perovskite via Rapid Heat Treatment

Zero-dimensional (0D) tin halide perovskites feature extraordinary properties, such as broadband emission, high photoluminescence quantum yield, and self-absorption-free characteristics. The innovation of synthesis approaches for high-quality 0D tin halide perovskites has facilitated the flourishing development of perovskite-based optoelectronic devices in recent years. However, discovering an effective strategy to further enhance their emission efficiency remains a considerable challenge. Herein, we report a unique strategy employing rapid heat treatment to attain efficient self-trapped exciton (STE) emission in Cs4SnBr6 zero-dimensional perovskite. Compared to the pristine Cs4SnBr6, rapid thermal treatment (RTT) at 200 °C for a duration of 120 s results in an augmented STE emission with the photoluminescence (PL) quantum yield rising from an initial 50.1% to a substantial 64.7%. Temperature-dependent PL spectra analysis, Raman spectra, and PL decay traces reveal that the PL improvement is attributed to the appropriate electron-phonon coupling as well as the increased binding energies of STEs induced by the RTT. Our findings open up a new avenue for efficient luminescent 0D tin-halide perovskites toward the development of efficient optoelectronic devices based on 0D perovskites.

Synthesis and Improved Photoluminescence of SnF2-Derived CsSnCl3-SnF2:Mn2+ Perovskites via Rapid Thermal Treatment

We report a rapid synthesis method for producing CsSnCl₃:Mn²⁺ perovskites, derived from SnF₂, and investigate the effects of rapid thermal treatment on their photoluminescence properties. Our study shows that the initial CsSnCl₃:Mn²⁺ samples exhibit a double luminescence peak structure with PL peaks at approximately 450 nm and 640 nm, respectively. These peaks originate from defect-related luminescent centers and the 4T¹→6A¹ transition of Mn²⁺. However, as a result of rapid thermal treatment, the blue emission is significantly reduced and the red emission intensity is increased nearly twofold compared to the pristine sample. Furthermore, the Mn²⁺-doped samples demonstrate excellent thermal stability after the rapid thermal treatment. We suggest that this improvement in photoluminescence results from enhanced excited-state density, energy transfer between defects and the Mn²⁺ state, as well as the reduction of nonradiative recombination centers. Our findings provide valuable insights into the luminescence dynamics of Mn²⁺-doped CsSnCl₃ and open up new possibilities for controlling and optimizing the emission of rare-earth-doped CsSnCl₃.

Lead-Free Metal Halide Perovskite Nanocrystals: From Fundamentals to Applications

Lead (Pb) halide perovskite nanocrystals, with the general formula APbX₃ , where A=CH₃ NH³⁺ , CH(NH₂ )²⁺ , or Cs⁺ and X=Cl^- , Br^- , or I^- , have emerged as a class of materials with promising properties due to their remarkable optical properties and solar cell performance. However, important issues still need to be addressed to enable practical applications of these materials, such as instability, mass production, and Pb toxicity. Recent studies have carried out the replacement of Pb by various less-toxic cations as Sn, Ge, Sb, and Bi. This variety of chemical compositions provide Pb-free perovskite and metal halide nanostructures with a wide spectral range, in addition to being considered less toxic, therefore having greater practical applicability. Highlighting the necessity to address and solve the toxicity problems related to Pb-containing perovskite, this review considers the prospects of the Pb-free perovskite, involving synthesis methods, and properties of them, including advantages, disadvantages, and applications.

Highly Stable and Efficient Mn2+ Doping Zero-Dimension Cs2ZnxPb1-xCl4 Alloyed Nanorods toward White Electroluminescent Light-Emitting Diodes

Zero-dimensional (0D) crystal structure perovskite NCs have reemerged as promising materials owing to their superior long-term stability; however, their poor conductivity leads to the inferior electrical performances and critically restricts the optoelectronic application of 0D perovskite materials. Herien, the alloyed 0D crystal structure Cs₂Zn_xPb_1-xCl₄ nanorods (NRs) have been synthesized by the modified hot-injection method, which emits bright blue-violet light at 408 nm, and the optimized photoluminescence quantum yield (PLQY) reaches 26%. The Cs₂Zn_0.88Pb_0.12Cl₄ NRs display more excellent air stability and an order of magnitude higher conductivity than CsPbCl₃ nanocube films. In addition, we dope Mn²⁺ ions into the Cs₂Zn_0.88Pb_0.12Cl₄ NRs, which accomplished the optimized PLQY of 40.3% and polarized emission with r = 0.19. The light-emitting diodes (LEDs) based on Mn²⁺ ion doped Cs₂Zn_0.88Pb_0.12Cl₄ NRs exhibit a chromaticity coordinate (CIE) of (0.36, 0.33), an EQE of 0.3%, and a maximum luminance of 98 cd m^-2. This work has enriched ideas for the production of white light perovskite LEDs.

The 3D-structure-mediated growth of zero-dimensional Cs4SnX6 nanocrystals

Innovations in approaches to synthesize high-quality lead perovskite nanocrystals have enabled the prosperous development of nanocrystal-based optoelectronic devices in recent years. However, the transfer of these approaches to tin perovskite nanocrystals, which are the most promising lead-free perovskite candidates, remains unsuccessful. Herein, based on a three-dimensional (3D)-structure-mediated approach, monodispersed and highly luminescent inorganic zero-dimensional (0D) tin perovskite nanocrystals (NCs) are synthesized. The crystal growth kinetics are revealed via tracking the intermediate structures and using theoretical simulations. The luminescence quantum yield of Cs₄SnBr₆ NCs is as high as 52%, which is the highest value for inorganic tin perovskite NCs. Cs₄SnI₆ NCs with a luminescence quantum yield of 27% are synthesized, which is 35 times higher than previous results. Based on the Cs₄SnBr₆ NCs, an ultraviolet-light-pumped white-light-emitting device (WLED) with an excellent color-rendering index of 92 is fabricated.

0D Perovskites: Unique Properties, Synthesis, and Their Applications

0D perovskites have gained much attention in recent years due to their fascinating properties derived from their peculiar structure with isolated metal halide octahedra or metal halide clusters. However, the systematic discussion on the crystal and electronic structure of 0D perovskites to further understand their photophysical characteristics and the comprehensive overview of 0D perovskites for their further applications are still lacking. In this review, the unique crystal and electronic structure of 0D perovskites and their diverse properties are comprehensively analyzed, including large bandgaps, high exciton binding energy, and largely Stokes-shifted broadband emissions from self-trapped excitons. Furthermore, the photoluminescence regulation are discussed. Then, the various synthetic methods for 0D perovskite single crystals, nanocrystals, and thin films are comprehensively summarized. Finally, the emerging applications of 0D perovskites to light-emitting diodes, solar cells, detectors, and some others are illustrated, and the outlook on future research in the field is also provided.

Quasi-Zero Dimensional Halide Perovskite Derivates: Synthesis, Status, and Opportunity

In recent decades, many technological advances have been enabled by nanoscale phenomena, giving rise to the field of nanotechnology. In particular, unique optical and electronic phenomena occur on length scales less than 10 nanometres, which enable novel applications. Halide perovskites have been the focus of intense research on their optoelectronic properties and have demonstrated impressive performance in photovoltaic devices and later in other optoelectronic technologies, such as lasers and light-emitting diodes. The most studied crystalline form is the three-dimensional one, but, recently, the exploration of the low-dimensional derivatives has enabled new sub-classes of halide perovskite materials to emerge with distinct properties. In these materials, low-dimensional metal halide structures responsible for the electronic properties are separated and partially insulated from one another by the (typically organic) cations. Confinement occurs on a crystal lattice level, enabling bulk or thin-film materials that retain a degree of low-dimensional character. In particular, quasi-zero dimensional perovskite derivatives are proving to have distinct electronic, absorption, and photoluminescence properties. They are being explored for various technologies beyond photovoltaics (e.g. thermoelectrics, lasing, photodetectors, memristors, capacitors, LEDs). This review brings together the recent literature on these zero-dimensional materials in an interdisciplinary way that can spur applications for these compounds. The synthesis methods, the electrical, optical, and chemical properties, the advances in applications, and the challenges that need to be overcome as candidates for future electronic devices have been covered.

Facile Fabrication of Highly Stable and Wavelength-Tunable Tin Based Perovskite Materials with Enhanced Quantum Yield via the Cation Transformation Reaction

Metal halide perovskites have attracted great attention for their superior light energy conversion applications. Herein, we demonstrated a facile synthesis of zero-dimensional Sn²⁺ perovskite Cs_4-xM_xSnBr₆(M = K⁺ and Rb⁺) material through the cation transformation reaction at room temperature. Cs₄SnBr₆ NCs was mixed with pure metal bromide salts (KBr and RbBr) via the mechanochemical process to successfully synthesize Cs_4-xM_xSnBr₆ perovskite where transformation of Cs to mixed Cs/Rb and mixed Cs/K was achieved. By substituting different cations, the bright fluorescence of the Cs_4-xM_xSnBr₆ was tuned from dim green to greenish-cyan while achieving the photoluminescence (PL) quantum yield of ∼39%. The crystal structure of Sn based perovskite with the substitution of K⁺ or Rb⁺ cations was determined by X-ray diffraction (XRD). Moreover, the Cs_4-xM_xSnBr₆ demonstrated superior air stability and exhibited a better photocatalytic activity for CO₂ reduction reaction (CO₂RR) with high selectivity of CH₄ gas with a higher yield rate compared to the pristine Cs₄SnBr₆ NCs.

Low Barrier for Exciton Self-Trapping Enables High Photoluminescence Quantum Yield in Cs3Cu2I5

The metal halide Cs₃Cu₂I₅ displays anomalous optical properties: an optical absorption onset in the ultraviolet region (∼ 330 nm) with highly efficient luminescence in the blue region (∼ 445 nm). Although self-trapped exciton formation has been proposed as the origin of giant Stokes shift, its connection to the photoluminescence quantum yield exceeding 90% remains unknown. Here, we explore the photochemistry of Cs₃Cu₂I₅ from first-principles and reveal a low energy barrier for exciton self-trapping associated with Cu-Cu dimerization. Kinetic analysis shows that the quantum yield of blue emission in Cs₃Cu₂I₅ is sensitive to the excited carrier density due to the competition between exciton self-trapping and band-to-band radiative recombination.

State of the Art and Prospects for Halide Perovskite Nanocrystals

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

Lead-Free Halide Perovskites for Light Emission: Recent Advances and Perspectives

Lead-based halide perovskites have received great attention in light-emitting applications due to their excellent properties, including high photoluminescence quantum yield (PLQY), tunable emission wavelength, and facile solution preparation. In spite of excellent characteristics, the presence of toxic element lead directly obstructs their further commercial development. Hence, exploiting lead-free halide perovskite materials with superior properties is urgent and necessary. In this review, the deep-seated reasons that benefit light emission for halide perovskites, which help to develop lead-free halide perovskites with excellent performance, are first emphasized. Recent advances in lead-free halide perovskite materials (single crystals, thin films, and nanocrystals with different dimensionalities) from synthesis, crystal structures, optical and optoelectronic properties to applications are then systematically summarized. In particular, phosphor-converted LEDs and electroluminescent LEDs using lead-free halide perovskites are fully examined. Ultimately, based on current development of lead-free halide perovskites, the future directions of lead-free halide perovskites in terms of materials and light-emitting devices are discussed.

Recent progress of zero-dimensional luminescent metal halides

This review provides in-depth insight into the structure–luminescence–application relationship of 0D all-inorganic/organic–inorganic hybrid metal halide luminescent materials.

Efficient Lone-Pair-Driven Luminescence: Structure-Property Relationships in Emissive 5s2 Metal Halides

Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides.