Surfactant-Free, One-Step Synthesis of Lead-Free Perovskite Hollow Nanospheres for Trace CO Detection

Colloidal Synthesis of Blue-Emitting Cs3TmCl6 Nanocrystals via Localized Excitonic Recombination for Down-Conversion White Light-Emitting Diodes

Lead-halide perovskite nanocrystals (NCs) have gained significant attention for their promising applications in lighting and display technologies. However, blue-emitting NCs have struggled to match the high efficiency of their red and green counterparts. Moreover, many reported blue-emitting perovskite NCs contain heavy metal lead (Pb), which poses risks to human health and the environment. In this study, we synthesized rare-earth-based Cs3TmCl6 NCs via the hot injection method, which exhibit a broadband blue emission at 440 nm. Combined experimental and theoretical studies indicate that the broadband emission in Cs3TmCl6 arises from self-trapped excitons due to the excited-state structural distortion of the [TmCl6]3- cluster. Furthermore, the ultrafast dynamics of charge carriers were analyzed using time-resolved photoluminescence and transient absorption measurements. Encouraged by the remarkable thermal, light, and water stabilities of Cs3TmCl6 NCs, as evidenced by experimental and theoretical results, a white light-emitting diode was further designed and fabricated using the Cs3TmCl6 NCs as the color converter. The device exhibits outstanding performance, achieving a long half-lifetime of 336 h and a large color-rendering index of 87.0. Combining eco-friendly features and a facile synthesis method, the rare-earth-based Cs3TmCl6 NCs mark a significant breakthrough as a reliable blue emitter, showcasing their future potential in lighting and display applications.

Recent progress of gas sensors based on perovskites

Gas sensors convert gas-related information into usable data by monitoring changes in conductivity and chemical reactions resulting from the adsorption of gas molecules. Recently, perovskites have emerged as promising candidate materials for gas sensors, owing to their polar reactivity, chemical responsiveness, and sensitivity. These characteristics enable the detection of the presence and concentration of various gases. This article provides a concise review of recent advancements in perovskite-based gas sensors. First, the chemical composition, structure, and preparation methods of perovskites, as well as the effects of their structure on gas sensing performance, are examined. The key performance parameters of the sensor and the sensing mechanism of the perovskite-based gas sensor are discussed. Then the development of gas sensors based on different structural types of perovskites, including single-component perovskites, mixed-component perovskites, and metal-oxide perovskites, is discussed. Finally, the challenges and opportunities for gas sensors based on perovskites are summarized and prospected.

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

High-Performance Optoelectronic Gas Sensing Based on All-Inorganic Mixed-Halide Perovskite Nanocrystals with Halide Engineering

Gas sensors are of great interest to portable and miniaturized sensing technologies with applications ranging from air quality monitoring to explosive detection and medical diagnostics, but the existing chemiresistive NO2 sensors still suffer from issues such as poor sensitivity, high operating temperature, and slow recovery. Herein, a high-performance NO2 sensors based on all-inorganic perovskite nanocrystals (PNCs) is reported, achieving room temperature operation with ultra-fast response and recovery time. After tailoring the halide composition, superior sensitivity of ≈67 at 8 ppm NO2 is obtained in CsPbI2 Br PNC sensors with a detection level down to 2 ppb, which outperforms other nanomaterial-based NO2 sensors. Furthermore, the remarkable optoelectronic properties of such PNCs enable dual-mode operation, i.e., chemiresistive and chemioptical sensing, presenting a new and versatile platform for advancing high-performance, point-of-care NO2 detection technologies.

Halide Perovskite glues activate two-dimensional covalent organic framework crystallites for selective NO2 sensing

Two-dimensional covalent organic frameworks (2D COFs) are promising for gas sensing owing to the large surface area, abundant active sites, and their semiconducting nature. However, 2D COFs are usually produced in the form of insoluble micro-crystallites. Their poor contacts between grain boundaries severely suppress the conductivity, which are too low for chemresistive gas sensing. Here, we demonstrate that halide perovskites can be employed as electric glues to bond 2D COF crystallites to improve their conductivity by two orders of magnitude, activating them to detect NO₂ with high selectivity and sensitivity. Resonant microcantilever, grand canonical Monte Carlo, density functional theory and sum-frequency generation analyses prove that 2D COFs can enrich and transfer electrons to NO₂ molecules, leading to increased device conductivity. This work provides a facile approach for improving the conductivity of polycrystalline 2D COF films and may expand their applications in semiconductor devices, such as sensors, resistors, memristors and field-emission transistors.

Moisture-Insensitive and Highly Selective Detection of NO2 by Ion-in-Conjugation Covalent Organic Frameworks

As a common toxic gas, nitrogen dioxide (NO₂) seriously threatens the environment and human respiratory system even at part per billion (ppb) level. Covalent organic frameworks (COFs) have gained widespread attention in sensing applications because of the benefits of designability, environmental stability, and a large number of active sites. However, the competitive adsorption of water molecules and the target gas molecules at room temperature as well as the weak interaction between COFs and gas molecules hinder their practical applications. Here, we introduce ion-in-conjugation (IIC) into a covalent organic framework (COF) by preparing a condensate of squaraine (SA) with 1,3,5-tris(4-aminophenyl)benzene (TAPB) to form a mesoporous macrocyclic material (SA-TAPB). Layers of SA-TAPB, drop cast onto interdigitated Ag-Pd alloy electrodes, show a statistically significant conductivity response to NO₂ at concentrations as low as 30 ppb and a theoretical detection limit of 10.9 ppb. The sensor displays a lower sensitivity to variations in humidity when operated at 80 °C compared to room temperature. The density functional theory (DFT) calculations indicated that the main adsorption site of NO₂ is dual hydrogen bonds formed between two amide hydrogen atoms of SA-TAPB and the NO₂ molecule. Gas adsorption experiments revealed that SA-TAPB has the largest adsorption capacity of NO₂ versus other interference gases, which were responsible for the excellent selectivity toward NO₂.

Eco-friendly MA3Bi2I9perovskite thin films based ammonia sensor

Organic-inorganic perovskite halides (OIPH) have emerged as a wonder material with growing interest in sensors detecting various toxic gases. However, lead toxicity represents a potential obstacle, and therefore finding lead-free cost-effective compatible materials for gas sensing applications is essential. In this work, methylammonium bismuth iodide i.e. (CH₃NH₃)₃Bi₂I₉(MABI) perovskite thin films-based ammonia (NH₃) sensor was synthesized using an antisolvent-assisted one-step spin coating method. The MABI sensor shows a linear relationship between the responsivity and concentration of NH₃with excellent reversibility, high gas responsivity, and humidity stability. The MABI thin-film sensor exhibits a maximum gas response of 24%, a short response/recovery time i.e. 0.14 s /8.15 s and good reversibility at 6 ppm of NH₃. It was observed that MABI thin films based sensors have excellent ambient stability over a couple of months. This work reveals that it is feasible to design high-performance gas sensors based on environmentally-friendly Bi-based OIPH materials.

Nanoscale Bimetallic AuPt-Functionalized Metal Oxide Chemiresistors: Ppb-Level and Selective Detection for Ozone and Acetone

As the most widely used gas sensors, metal oxide semiconductor (MOS)-based chemiresistors have been facing great challenges in achieving ppb-level and selective detection of the target gas. The rational design and employment of bimetallic nanocatalysts (NCs) are expected to address this issue. In this work, the well-shaped and monodispersed AuPt NCs (diameter ≈ 9 nm) were functionalized on one-dimensional (1D) In₂O₃ nanofibers (NFs) to construct efficient gas sensors. The sensor demonstrated dual-selective and ppb-level detection for ozone (O₃) and acetone (C₃H₆O) at different optimal working temperatures. For the possible application exploitation, a circuit was designed to monitor O₃ concentration and provide warnings when the concentration safety limit (50 ppb) was exceeded. Moreover, simulated exhaled breath measurements were also carried out to diagnose diabetes through C₃H₆O concentration. The selective detection for O₃ and C₃H₆O was further analyzed by principal component analysis (PCA). The drastically enhanced sensing performances were attributed to the synergistic catalytic effect of AuPt NCs. Both the "spillover effect" and the Schottky barrier at the interfaces of AuPt NCs and In₂O₃ NFs promoted the sensing processes of O₃ and C₃H₆O.

Cascading Photoelectric Detecting and Chemiresistive Gas-Sensing Properties of Pb5 S2 I6 Nanowire Mesh for Multi-Factor Accurate Fire Alarm

Accurate fire warning is very important for people's life and property safety. The most commonly used fire alarm is based on the detection of a single factor of gases, smoke particles, or temperature, which easily causes false alarm due to complex environmental conditions. A facile multi-factor route for fabricating an accurate analog fire alarm using a Pb₅ S₂ I₆ nanowire mesh based on its photoelectric and gas-sensing dual function is presented. The Pb₅ S₂ I₆ nanowire mesh presents excellent photoelectric detection capabilities and is sensitive to ppm-level NO₂ at room temperature. Under the "two-step verification" circuit of light and gas factors, the bimodal simulation fire alarm based on this Pb₅ S₂ I₆ nanowire mesh can resist the interference of complex environmental factors and effectively reduce the false alarm rate.

A multi-platform sensor for selective and sensitive H2S monitoring: Three-dimensional macroporous ZnO encapsulated by MOFs with small Pt nanoparticles

The high-selectivity and high-sensitivity determination of trace concentrations of toxic gases is a major challenge when using semiconductor metal oxide (SMO) gas sensors in complicated real-world environments. In this study, by strategically combining a three-dimensional inverse opal (3DIO) macroporous ZnO substrate and a ZIF-8 outer filter membrane, two series of sensors with Pt NPs loaded at different locations are developed. In the optimal 3DIO ZnO@ZIF-8/Pt sensor, the existence of small Pt NPs in ZIF-8 cavities can effectively accelerate the absorption of H₂S, capture electrons from the N site of ZIF-8, and donate the electron to the S site of H₂S, as indicated by density functional theory simulations, leading to a significantly increased response to H₂S. Together with the molecular-sieving effect that ZIF-8 exerts on gas molecules with larger kinetic diameters, the 3DIO ZnO@ZIF-8/Pt sensor exhibits a high response to H₂S (118-5.5 ppm), a detection limit of 40 ppb, and importantly, a 59-fold higher selectivity to H₂S against typical interference gases. In addition, the 3DIO ZnO@ZIF-8/Pt sensor is developed as a multi-platform sensor to evaluate trace concentrations of H₂S in meat quality assessment, halitosis diagnosis, and automobile exhaust assessment.

Anomalous NH3-Induced Resistance Enhancement in Halide Perovskite MAPbI3 Film and Gas Sensing Performance

Despite the growing interest in halide perovskite-based NH₃ sensors, the NH₃ sensing mechanism is still not well understood. Here, we report an anomalous behavior of resistance enhancement in CH₃NH₃PbI₃(MAPbI₃) perovskite films upon exposure to NH₃ gas, which is contrary to a resistance drop trend in previously reported perovskites. We propose a NH₃ sensing mechanism in which the anomalous resistance enhancement is dominated by grain boundaries of perovskites. It is demonstrated that NH₃ molecules can substitute MA⁺ cations of MAPbI₃ to form the insulating NH₄PbI₃·MA intermediate layers onto the surface of crystal grains, thereby resulting in an increase of resistance. Additionally, we construct the MAPbI₃-based sensor, and achieve a gas response of 472% toward 30 ppm of NH₃. This study suggests the potential of the perovskite-based NH₃ sensors, and also provides guidance for developing high-performance sensing perovskite materials.

All-inorganic lead-free metal halide perovskite quantum dots: progress and prospects

Lead halide perovskite quantum dots have drawn worldwide attention due to their quantum confinement effect and excellent optical gain properties. It is worth noting that due to the toxicity of lead ions and the inherent instability of organic groups, research on all-inorganic lead-free metal halide perovskite quantum dots (ILFHPQDs) has become a hot spot in recent years. This paper summarizes the latest research progress of ILFHPQDs, analyzes the sources and limitations affecting the performance of ILFHPQDs, and provides the improvement methods. Firstly, the typical synthesis strategies of ILFHPQDs are discussed, followed by a focus on the structural characteristics, optoelectronic properties and stability of each type of ILFHPQD. Next, the applications of ILFHPQDs in devices are investigated. Finally, the challenges, solutions and future application directions of ILFHPQDs are prospected.