Multifunctional Bismuth‐Doped Nanoporous Silica Glass: From Blue‐Green,Orange, Red,and White Light Sources to Ultra‐Broadband Infrared Amplifiers

Ultra‐broadband luminescent sources that emit light over an extremely wide wavelength range are of great interest in the fields of photonics, medical treatment, and precision measurement. Extensive research has been conducted on materials doped with rare‐earth and transition‐metal ions, but the goal of fabricating an ultra‐broadband emitter has not been attained. We present a facile method to realize this kind of novel light source by stabilizing “active” centers (bismuth) in a “tolerant” host (nanoporous silica glass). The obtained highly transparent materials, in which, unusually, multiple bismuth centers (Bi⁺, Bi²⁺, and Bi³⁺) can be stabilized, emit in an ultra‐broadband wavelength range from blue‐green, orange, red, and white to the near‐infrared region. This tunable luminescence covers the spectral range of the traditional three primary colors (RGB) and also the telecommunications windows.     

Enhanced luminescence of CaSb2O6:Bi3+ blue phosphors by efficient charge compensation

This paper reported an enhanced photoluminescence of CaSb₂O₆:Bi³⁺ by efficient charge compensation. Charge compensated CaSb₂O₆:Bi³⁺,M⁺ (M=Li, Na and K) phosphors were prepared using a co-precipitation technique followed by heat-treatment. The structure and morphology of the as-prepared CaSb₂O₆:Bi³⁺,M⁺ samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that the obtained CaSb₂O₆:Bi³⁺,M⁺ samples are hexagonal crystal structure and this structure was retained regardless of co-doping by Li⁺, Na⁺ or K⁺. All samples showed sphere-like shape with particle size of 40–80 nm. The optical properties of products were studied by UV–vis diffuse reflectivity, photoluminescence spectra and luminescence decay measurements. Under the excitation of 336 nm light, all of the samples exhibited a strong blue emission peaking around 437 nm, which is attributed to the ³P₁–¹S₀ transition of the Bi³⁺ ion. It was found that the charge compensation has significant effect on the photoluminescence properties of CaSb₂O₆:Bi³⁺ and the best luminescence properties have been achieved for CaSb₂O₆:0.75Bi³⁺,0.75 Na⁺. The mechanism for the enhancement of the blue emission has also been studied in detail. Our results suggested that the optical properties of oxide nanostructures can be tailored through co-doping with aliovalent ions and the favorable luminescence properties of CaSb₂O₆:Bi³⁺,Na⁺ make it potential for lighting and display applications.     

Progress of Lead-Free Halide Perovskites: From Material Synthesis to Photodetector Application

Lead halide perovskite (LHP) has been widely researched in the photovoltaic field due to its highly attractive optoelectronic properties. Among the LHP-based devices, the detectivity of the photodetector is as high as 10¹⁵ Jones. However, their practical application is limited by the toxicity of lead in perovskite and the inherent instability induced by the perovskite structure against moisture, heat, and light. To address these issues, tremendous efforts have been made to replace Pb²⁺ with other environmentally friendly metal cations such as Sn²⁺, Bi³⁺, Cu²⁺, Sb³⁺, and Ge²⁺. Thus, considerable breakthroughs in device performance and stability using lead-free metal halide perovskite (LFMHP) have been made in recent years. In this review, the synthesis methods and strategies are focused for enhancing the material quality and photoelectric properties of LFMHPs and the recent research progress of LFMHP-based photodetectors is summarized. This research provides some promising perspectives for high-performance LFMHP photodetectors to achieve a broader range of practical applications in the future.     

XBi4S7 (X = Mn,Fe): New Cost‐Efficient Layered n‐Type Thermoelectric Sulfides with Ultralow Thermal Conductivity

A new class of cost‐efficient n‐type thermoelectric sulfides with a layered structure is reported, namely MnBi₄S₇ and FeBi₄S₇. Theoretical calculations combined with synchrotron X‐ray/neutron diffraction analyses reveal the origin of their electronic and thermal properties. The complex low‐symmetry monoclinic crystal structure generates an electronic band structure with a mixture of heavy and light bands near the conduction band edge, as well as vibrational properties favorable for high thermoelectric performance. The low thermal conductivity can be attributed to the complex layered crystal structure and to the existence of the lone pair of electrons in Bi³⁺. This feature combined with the relatively high power factor lead to a figure of merit as high as 0.21 (700 K) in undoped MnBi₄S₇, making this material a promising n‐type candidate for low‐ and intermediate‐temperature thermoelectric applications.     

Bandgap Engineering of BiIns Nanowire for Wide-Spectrum,High-Responsivity,and Polarimetric-Sensitive Detection

Optical devices based on alloying semiconductors offer a plethora of new possibilities for detection across a broad spectrum. Among these devices, nanowire-based devices have gained much attention due to their remarkable specific surface area properties in terms of material synthesis, device structure, and performance. In this work, (Bi_xIn_1−x)₂S₃ nanowires are designed by controlling the ratio of Bi and In atoms. The atomic ratio directly affects the electronic band structure of the crystal, thereby further optimizing the performance of optoelectronic devices. According to the experimental results, Bi_1.28In_0.72S₃ nanowire-based photodetectors obtain the most excellent photoresponse performance. The typical device demonstrates a spectral response from deep ultraviolet (DUV 254 nm) to near-infrared (NIR 1064 nm) and achieves a maximum dichroic ratio of photoresponse of 1.5 under polarization-angle-sensitive detection in the 266–808 nm range. It also exhibits a photoresponse of 10.1 A W⁻¹ and a photodetectivity of 5.7 × 10¹⁰ Jones under 532 nm light irradiation. Additionally, the photodetector displays a fast response speed with a rise/fall time of 5/4.7 ms. Finally, “CSU” and puppy images produced by this device further demonstrate the effectiveness of alloying semiconductors in creating wide-spectrum, high-responsivity, fast-response, and polarimetric-sensitive photodetectors.     

Two novel Bi-based oxychloride photocatalysts: Synthesis,optical property and visible-light-responsive photocatalytic activity

Two novel visible-light-responsive bismuth oxychloride photocatalysts Bi₂EuO₄Cl and Bi₂NdO₄Cl have been successfully developed via a solid-state reaction route. Their crystal structures and optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), diffuse reflectance spectra (DRS), and photoluminescence (PL) spectra. Fascinatingly, both the compounds possess considerable optical absorption in a broad region ranging from UV light to visible light. The indirect-transition optical band gaps of Bi₂EuO₄Cl and Bi₂NdO₄Cl are estimated to be 2.21 and 1.89 eV, respectively. For the first time, their photocatalytic activities were determined by photodecomposition of methylene blue (MB) in aqueous solution under visible light (λ>420 nm). The results revealed that both Bi₂EuO₄Cl and Bi₂NdO₄Cl can be used as effective visible-light-driven photocatalysts. In addition, theoretical calculations on the electronic structure, orbital constitutions and optical absorption of Bi₂NdO₄Cl were also performed. These findings shed light on the exploration of new photocatalytic materials activated by visible light.     

Prospect for Bismuth/Antimony Chalcohalides-Based Solar Cells

Inorganic–organic hybrid lead halide perovskites are emerging optoelectronic materials for solar cell application. However, the toxicity concerns and poor stability largely hamper their practical applications. For these reasons, the search for “perovskite-inspired” alternatives, having the same advantages but overcoming the drawbacks of the lead-based one, has become an important sector in the field. Among the candidates, Bi³⁺ and Sb³⁺ containing materials are of great interest, due to their electronic structures resembling the Pb²⁺. Bismuth/antimony chalcohalides have been known for a long time as the potential absorber in photovoltaics, even if their performances are still low. Interestingly, pnictogen chalcohalides can be the stepping stone toward numerous quaternary compounds, including some perovskite structures. The understanding of the fundamental properties and the current limitations of both the starting ternary compounds and the final quaternary materials can allow the achievement of improved photovoltaic absorbers, stable, and efficient. In this review, the fundamental properties and device performances of many ternary pnictogen chalcohalides and the derived quaternary compounds are summarized, focusing on the different preparation strategies.     

Structural and optoelectronic properties of hybrid halide perovskites for solar cells

Trihalide perovskites are an emerging class of materials, which have shown excellent performance so far in solution-processed optoelectronic devices such as perovskite solar cells (PSCs) and light emitting diodes (LEDs). The energy band gap (E_gap) of this class of materials is tunable and can be varied from 1.5 eV to 2.3 eV by changing its chemical composition, exhibiting a promising character to design versatile optoelectronic devices. It is thus, imperative to understand the relation between structural and optoelectronic properties of the perovskite-based materials offering intrinsic complexity. Hence, different interactions, defects as well as structural disorder have a defining role in the material properties. The intrinsic properties have been shown to have a significant impact on the performance of these perovskite materials. These properties include high dielectric constants, ambipolar transport features of long range, low exciton binding energies, and ferroelectric polarizations. In the current review, we briefly explore the crystal structure of the perovskite materials at atomistic-level and draw a comparison of the basic optical and electrical properties originating from particular atomic compositions together with their arrangements therein, and moreover, their applications in future optoelectronic devices are elaborated upon.     

High-Performance Photodetector and Angular-Dependent Random Lasing from Long-Chain Organic Diammonium Sandwiched 2D Hybrid Perovskite Non-Linear Optical Single Crystal

3D organic-inorganic metal halide perovskites are excellent materials for optoelectronic applications due to their exceptional properties, solution processability, and cost-effectiveness. However, the lack of environmental stability highly restricts them from practical applications. Herein, a stable centimeter-long 2D hybrid perovskite (N-MPDA)[PbBr₄] single crystal using divalent N1-methylpropane-1,3-diammonium (N-MPDA) cation as an organic spacer, is reported. The as-grown single crystal exhibits stable optoelectronic performance, low threshold random lasing, and multi-photon luminescence/multi-harmonic generation. A photoconductive device fabricated using (N-MPDA)[PbBr₄] single crystal exhibits an excellent photoresponsivity (≈124 AW⁻¹ at 405 nm) that is ≈4 orders of magnitudes higher than that of monovalent organic spacer-assisted 2D perovskites, such as (BA)₂PbBr₄ and (PEA)₂PbBr₄, and large specific detectivity (≈10¹² Jones). As an optical gain media, the (N-MPDA)[PbBr₄] single crystal exhibits a low threshold random lasing (≈6.5 µJ cm⁻²) with angular dependent narrow linewidth (≈0.1 nm) and high-quality factor (Q ≈ 2673). Based on these results, the outstanding optoelectronic merits of (N-MPDA)[PbBr₄] single crystal will offer a high-performance device and act as a dynamic material to construct stable future electronics and optoelectronic-based applications.     

Enhanced Photoluminescence and Photoresponsiveness of Eu3+ Ions-Doped CsPbCl3 Perovskite Quantum Dots under High Pressure

Metal halide perovskite quantum dots (QDs) have garnered tremendous attention in optoelectronic devices owing to their excellent optical and electrical properties. However, these perovskite QDs are plagued by pressure-induced photoluminescence (PL) quenching, which greatly restricts their potential applications. Herein, the unique optical and electrical properties of Eu³⁺-doped CsPbCl₃ QDs under high pressure are reported. Intriguingly, the PL of Eu³⁺ ions displays an enhancement with pressure up to 10.1 GPa and still preserves a relatively high intensity at 22 GPa. The optical and structural analysis indicates that the sample experiences an isostructural phase transition at approximately 1.53 GPa, followed by an amorphous state evolution, which is simulated and confirmed through density functional theory calculations. The pressure-induced PL enhancement of Eu³⁺ ions can be associated with the enhanced energy transfer rate from excitonic state to Eu³⁺ ions. The photoelectric performance is enhanced by compression and can be preserved upon the release of pressure, which is attributed to the decreased defect density and increased carrier mobility induced by the high pressure. This work enriches the understanding of the high-pressure behavior of rare-earth-doped luminescent materials and proves that high pressure technique is a promising way to design and realize superior optoelectronic materials.     

Anisotropic Properties of Quasi-1D In4Se3: Mechanical Exfoliation,Electronic Transport,and Polarization-Dependent Photoresponse

Theoretical and experimental investigations of various exfoliated samples taken from layered In₄Se₃ crystals are performed. In spite of the ionic character of interlayer interactions in In₄Se₃ and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few-nanometer-thick flakes of In₄Se₃ by mechanical exfoliation of its bulk crystals. The In₄Se₃ flakes exfoliated on Si/SiO₂ have anisotropic electronic properties and exhibit field-effect electron mobilities of about 50 cm² V⁻¹ s⁻¹ at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS₂ and TiS₃. In₄Se₃ devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry-dependent band structure calculations for the most expected ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In₄Se₃ crystals is possible, while the fast anisotropic photoresponse makes In₄Se₃ a competitive electronic material, in the TMC family, for emerging optoelectronic device applications.     

Atomic‐Level Passivation of Individual Upconversion Nanocrystal for Single Particle Microscopic Imaging

Lanthanide‐doped upconversion nanoparticles (UCNPs) have significant applications for single‐molecule probes and high‐resolution display. However, one of their major hurdles is the weak luminescence, and this remains a grand challenge to achieve at the single‐particle level. Here, 484‐fold luminescence enhancement in LuF₃:Yb³⁺, Er³⁺ rhombic flake UCNPs is achieved, thanks to the Yb³⁺‐mediated local photothermal effect, and their original morphology, size, and good dispersibility are well preserved. These data show that the surface atomic structure of UCNPs as well as transfer from amorphous to ordered crystal structure is modulated by making use of the local photothermal conversion that is generated by the directional absorption of 980 nm light by Yb³⁺ ions. The confocal luminescence images obtained by super‐resolution stimulated emission depletion also show the great enhancement of individual LuF₃:Yb³⁺, Er³⁺ nanoparticles; the high signal‐to‐noise ratio images indicate that the laser treatment technology opens the door for single particle imaging and practical application.     

Dual Emission of Water‐Stable 2D Organic–Inorganic Halide Perovskites with Mn(II) Dopant

Moisture‐delicate and water‐unstable organic–inorganic halide perovskites (OI‐HPs) create huge challenges for the synthesis of highly efficient water‐stable light‐emitting materials for optoelectronic devices. Herein, a simple acid solution–assisted method to synthesize quantum confined 2D lead perovskites through Mn doping is reported. The efficient energy transfer between host and dopant ions in orange light‐emitting Mn²⁺‐doped OI‐HPs leads to the most efficient integrated luminescence with a photoluminescence quantum yield over 45%. The Mn²⁺ substitution of Pb²⁺ and passivation with low dielectric constant molecules such as phenethylamine, benzylamine, and butylamine enhance water resistivity, leading to water stability. The dual emission process of this water‐stable 2D Mn‐doped perovskite will help in developing highly efficient 2D water‐stable perovskites for practical applications.     

Defect Passivation in Air-Stable Tin(IV)-Halide Single Crystal for Emissive Self-Trapped Excitons

Tin(IV)-based metal halides are promising optoelectronic materials due to their robust structure and eco-friendly nature, but these materials exhibit poor photoluminescence (PL) properties and the underlying mechanisms are still elusive. Here, a novel air-stable hybrid Sn⁴⁺-halide material (C₈H₂₂N₂Cl)₂SnCl₆ that is resistant to moisture ( > 70% relative humidity) for > 1 year is reported. The inferior PL property of (C₈H₂₂N₂Cl)₂SnCl₆ is limited by the lattice defects and robust crystal structure, which however could be effectively improved by introducing Sb³⁺ ion with stereoactive 5s² lone pair. As a result, Sb³⁺-doped (C₈H₂₂N₂Cl)₂SnCl₆ exhibits a superbly stable room-temperature PL centered at 690 nm with an unprecedented quantum yield (QY) of 41.76% from self-trapped excitons, which is the highest PLQY of hybrid tin(IV)-based perovskite materials. The improved PL efficiency is attributed to the defect passivation and remarkable structure distortion induced by Sb³⁺ dopants. This dopant-induced defect passivation and exciton self-trapping approach offers an avenue to improve optoelectronic material performance.     

Colloidal Bi2S3 Nanocrystals: Quantum Size Effects and Midgap States

Among solution‐processed nanocrystals containing environmentally benign elements, bismuth sulfide (Bi₂S₃) is a very promising n‐type semiconductor for solar energy conversion. Despite the prompt success in the fabrication of optoelectronic devices deploying Bi₂S₃ nanocrystals, the limited understanding of electronic properties represents a hurdle for further materials developments. Here, two key materials science issues for light‐energy conversion are addressed: bandgap tunability via the quantum size effect, and photocarrier trapping. Nanocrystals are synthesized with controlled sizes varying from 3 to 30 nm. In this size range, bandgap tunability is found to be very small, a few tens of meV. First principles calculations show that a useful blueshift, in the range of hundreds of meV, is achieved in ultra‐small nanocrystals, below 1.5 nm in size. Similar conclusions are envisaged for the class of pnictide chalcogenides with a ribbon‐like structure [Pn₄Ch₆]_n (Pn = Bi, Sb; Ch = S, Se). Time‐resolved differential transmission spectroscopy demonstrates that only photoexcited holes are quickly captured by intragap states. Photoexcitation dynamics are consistent with the scenario emerging in other metal–chalcogenide nanocrystals: traps are created in metal‐rich nanocrystal surfaces by incomplete passivation by long fatty acid ligands. In large nanocrystals, a lower bound to surface trap density of one trap every sixteen Bi₂S₃ units is found.     

Fabrication of MAPbBr3 Single Crystal p‐n Photodiode and n‐p‐n Phototriode for Sensitive Light Detection Application

In this study, MAPbBr₃ single crystal (MSC) p‐n perovskite homojunction photodiode and n‐p‐n phototriode are successfully fabricated through controlled incorporation of Bi³⁺ ions in solution. Optoelectronic analysis reveals that the photodiode shows typical photovoltaic behavior and the best photovoltaic performance can be achieved when the n‐type MSC is grown in 0.3% Bi³⁺ feed solution. The as‐assembled p‐n MSC photovoltaic detector displays obvious sensitivity to 520 nm illumination, with a high responsivity of up to 0.62 A W^‐1 and a specific detectivity of 2.16 × 10¹² Jones, which surpass many those of MSC photodetectors previously reported. Further performance optimization can be realized by constructing an n‐p‐n phototriode using the same growth method. The photocurrent magnification rate of the as‐fabricated n‐p‐n phototriode can reach a maximum value of 2.9 × 10³. Meanwhile, a higher responsivity of 14.47 A W^‐1, specific detectivity of 4.67 × 10¹³ Jones, and an external quantum efficiency of up to 3.46 × 10³ are achieved under an emitter–collector bias of 8 V. These results confirm that the present p‐n and n‐p‐n MSC homojunctions are promising device configurations, which may find potential application in future optoelectronic devices and systems.     

Self-Recoverable Mechanically Induced Instant Luminescence from Cr3+-Doped LiGa5O8

Currently, most of the mechanoluminescence (ML) phosphors strongly depend on postirradiation stimulation using ultraviolet light (denoted as “UV exposure” from hereon) to show the ML. However, only a few transition metal cations are proven to be effective luminescence centers, which hinder the development of more ML phosphors. This study reports a self-recoverable deep-red-to-near-infrared ML using Cr³⁺-doped LiGa₅O₈ phosphor with fully recoverable ML performance. The ML performance can be further optimized by tuning the trap redistributions by codoping the phosphor with Al³⁺ and Cr³⁺ cations. Theoretical calculations reveal the important role of Cr dopants in the modulation of local electronic environments for achieving the ML. Owing to the induced interelectronic levels and shallow electron trap distributions, the electron recombination efficiency is enhanced both through direct tunneling and energy transfer toward the dopant levels. Moreover, the ML of Cr³⁺-doped LiGa₅O₈ can penetrate a 2-mm-thick pork slice, showing that it can have wide-ranging in vivo applications, including the optical imaging of intracorporal stress/strain distribution and dynamics. Therefore, this work fabricates a novel ML material with self-recoverable luminescence in an extended wavelength range, increasing the number of potential ML candidates and promoting the fundamental understanding and practical applications of ML materials.     

Versatile Crystal Structures and (Opto)electronic Applications of the 2D Metal Mono‐, Di‐, and Tri‐Chalcogenide Nanosheets

Emerging 2D metal chalcogenides present excellent performance for electronic and optoelectronic applications. In contrast to graphene and other 2D materials, 2D metal chalcogenides possess intrinsic bandgaps, versatile band structures, and superior atmospheric stability. The many categories of 2D metal chalcogenides ensure that they can be applied to various practical scenarios. 2D metal monochalcogenides, dichalcogenides, and trichalcogenides are the three main categories of these materials. They have distinct crystal structures resulting in different characteristics. Some basic device characteristics, such as the charge carrier characteristics, scattering mechanisms, interfacial contacts, and band alignments of heterojunctions, are vital factors for practical device applications that ensure that the desired properties can be achieved. Various electronic, optoelectronic, and photonic applications based on 2D metal chalcogenides have been extensively investigated. 2D metal chalcogenides are considered as competitive candidates for future electronic and optoelectronic applications.     

PdPSe: Component-Fusion-Based Topology Designer of Two-Dimensional Semiconductor

Novel 2D semiconductors play an increasingly important role in modern nanoelectronics and optoelectronics. Herein, a novel topology designer based on component fusion is introduced, featured by the submolecular component integration and properties inheritance. As expected, a new air-stable 2D semiconductor PdPSe with a tailored puckered structure is successfully designed and synthesized via this method. Notably, the monolayer of PdPSe is constructed by two sublayers via P P bonds, different from 2D typical transition metal materials with sandwich-structured monolayers. With the expected orthorhombic symmetry and intralayer puckering, PdPSe displays a strong Raman anisotropy. The field-effect transistors and photodetectors based on few-layer PdPSe demonstrate good electronic properties with high carrier mobility of ≈35 cm² V⁻¹ s⁻¹ and a high on/off ratio of 10⁶, as well as excellent optoelectronic performance, including high photoresponsivity, photogain, and detectivity with values up to 1.06 × 10⁵ A W⁻¹, 2.47 × 10⁷%, and 4.84 × 10¹⁰ Jones, respectively. These results make PdPSe a promising air-stable 2D semiconductor for various electronic and optoelectronic applications. This work suggests that the component-fusion-based topology designer is a novel approach to tailor 2D materials with expected structures and interesting properties.     

Enhanced On–Off Ratio Photodetectors Based on Lead‐Free Cs3Bi2I9 Single Crystal Thin Films

Hybrid organic–inorganic lead halide perovskite single crystal thin film (SCTF) recently has attracted enormous interest in the field of optoelectronic devices, since it efficiently resolves the trade‐off between thickness and carrier diffusion length. However, the toxicity of lead element and the instability induced by organic component still hinder its future developments. In this work, lead‐free all‐inorganic Cs₃Bi₂I₉ SCTF with a high orientation along (00h) has been in situ grown on indium tin oxide (ITO) glass via a space‐limited solvent evaporation crystallization method. The trap density of Cs₃Bi₂I₉ SCTF (5.7 × 10¹² cm^?3) is 263 folds lower than that of the polycrystalline thin film (PCTF) counterpart, together with a 5‐order‐of‐magnitude higher carrier mobility. These superior charge transfer properties enable a photoresponse on–off ratio as high as 11 000, which far surpasses that of the PCTF device by 460 folds, comparable to the lead halide perovskite. Furthermore, the Cs₃Bi₂I₉ SCTF photodetector exhibits outstanding stability even without any encapsulation, whose initial performance is well maintained after aging 1000 h in humid air of 50% RH or continuous on–off light illumination for 20 h. This work will pave the way to produce new families of high‐performance, stable, and nontoxic perovskite SCTF for future optoelectronic applications.