Jing Zhang

Nature Communications, Published online: 19 July 2022; doi:10.1038/s41467-022-31902-3

The authors fabricate a 3D achromatic diffractive metalens on the end face of a single-mode fiber, useful for endoscopic applications. They demonstrate achromatic and polarization insensitive focusing across the entire near-infrared telecommunication wavelength band ranging from 1.25 to 1.65 µm.

Nature Communications, Published online: 21 July 2022; doi:10.1038/s41467-022-31868-2

The formation of nanostructures with chiral symmetry often requires chiral directing agents at a smaller length scale. Here, the authors report the self-assembly of 2D chiral superlattices from achiral tetrahedron-shaped building blocks.

Nature, Published online: 20 July 2022; doi:10.1038/d41586-022-01941-3

Applying strain to a material that has a type of magnetism called antiferromagnetism allows its magnetization to be fully switched with an electric current — making it appealing for use in next-generation magnetic memory devices.

Primary luminescent thermometers based on the excitation and emission spectra of Ln(III) ions are proposed, implemented, and validated using an Eu(III)-β-diketonate complex as proof-of-concept. The temperature is predicted through many distinct thermometric parameters permitting to achieve an unprecedented very high accuracy of 0.2% in the physiological range.

Abstract

Remote sensing through ratiometric luminescence thermometry based on trivalent lanthanide ions (Ln(III)) has lately become a promising technique due to its numerous applications. Most available Ln(III)-based luminescent thermometers require a calibration process with a reference thermal probe (secondary thermometers) and recurrent calibrations are mandatory, particularly when the thermometers are used in different media. This is sometimes impractical and a medium-independent calibration relation is postulated, which is potentially inaccurate. Thus, the determination of the temperature based on well-grounded physical principles by primary thermometers is the only way to overcome these challenges. Despite being considered one of the most important developments in luminescence thermometry, primary luminescent thermometers are scarce. Primary thermometers requiring calibration are proposed, implemented, and validated at one known temperature (primary-T), which are also self-referencing, employing ratiometric data from the excitation spectrum of Ln(III). By combining with the emission spectrum, thermometers not requiring calibration (primary-S) are devised. An Eu(III)-β-diketonate complex is used as a proof-of-concept, but the approach is universal and other Ln(III)-based materials can be explored. Because many thermometric parameters are employed for temperature prediction an unprecedented very high accuracy of 0.2% in the physiological range is obtained.

All-inorganic Er³⁺-based double perovskites exhibit efficient multimode luminescence features. By introducing energy trapping centers (Yb³⁺ and Tm³⁺), the upconversion photoluminescence (UCPL) emission color can be customized and the UCPL emission intensity can be compared with commercial upconversion phosphors. This work opens up a new approach for the multiple anticounterfeiting and information security applications of rare-earth-based halide perovskites.

Abstract

Rare-earth ions doped halide double perovskites are considered as promising luminescent materials. However, the contradiction of fluorescence quenching at high concentrations and the lack of sufficient upconversion photoluminescence (UCPL) emitters remain a significant challenge. Here, a lead-free Er³⁺-based halide double perovskite Cs₂NaErCl₆ is reported, which exhibits bright orange and green UCPL emission under 980 and 808 nm laser excitation, respectively. Subsequently, the UCPL emission intensity is greatly enhanced and the emission color is tunable by introducing different energy trapping centers. Importantly, under 980 nm laser excitation, the facilely prepared Yb³⁺- and Tm³⁺-doped Cs₂NaErCl₆ perovskites exhibit remarkably efficient multicolor upconverting emission, which is comparable to or even outperformes the commercial UCPL phosphor prepared by the high-temperature solid-state method. Meanwhile, the UCPL mechanisms involved in the energy transfer upconversion and excited-state absorption are also explored, which can promote a better understanding of the UCPL processes. Moreover, these efficient multimode luminescence features show great potential in anticounterfeiting applications.

Lead-free Cs₃Bi₂Br₉/Cs₃BiBr₆ perovskite bulk heterojunction photodetectors are successfully fabricated and demonstrate self-powered dual-band photodetecting abilities. A high on/off ratio (18881), fast response speed (rise time 200 ns; decay time 1.09 µs) and high detectivity (1.2 × 10¹² Jones) are realized under the UV band at 0 V bias, showing great application prospsect in encrypted communication and imaging fields.

Abstract

Self-powered, dual-band photodetection of electromagnetic signals promises wide photoelectric applications in imaging, communication, environmental monitoring, and rescue. However, most reported dual-band photodetectors (PDs) based on various heterojunctions are realized by complex fabrication processes, which may introduce defects in the depletion layer. Here, first, a self-powered dual-band PD based on lead-free perovskite bulk heterojunction (Cs₃Bi₂Br₉/Cs₃BiBr₆) fabricated by a one-step spatial confinement method is demonstrated. Its two peaks of self-powered responsivities are 59.4 mA W⁻¹ at 360 nm and 3.09 mA W⁻¹ at 450 nm. A high on/off ratio (18881), fast response speed (rise time 200 ns; decay time 1.09 µs), high detectivity (1.2 × 10¹² Jones), and cycle stability are realized under UV band, which exceeds most reported state-of-the-art lead-free halide perovskite PDs. The dual-band PD is suitable for encrypted communication and image sensing. This research represents a new frontier in the search for novel dual-band high-performance PDs based on lead-free perovskite bulk heterojunction fabricated by low-cost and simple fabrication methods.

A vertical van der Waals double heterojunction (n-Ga₂O₃/p-WSe₂/n-Ge) photodiode is demonstrated. The ultrawide bandgap Ga₂O₃ layer with a high electron carrier density and negligible hole density functions as an electron reservoir, resulting in amplified photocurrent gains. The achieved superior performance and shortwave infrared imaging capability show that the carrier reservoir can be a strategy for multispectral imaging with enhanced responsivity.

Abstract

Co-integration of visible and infrared (IR) photodetection into a simple configuration is of essential importance for broadband multispectral imaging, and various heterostructures based on group IV, III–V, and recent 2D semiconductors have been studied in efforts to circumvent limits on photoresponsivity and response speed in IR ranges. In this work, a vertically stacked double heterojunction (DHJ) photodiode (PD) with ultrawide-bandgap gallium oxide (Ga₂O₃) is reported on, and the performance is compared with p-WSe₂/n-Ge PD. The fabricated n-Ga₂O₃/p-WSe₂/n-Ge PD responds to a broad spectral range from vis to shortwave IR (SWIR) (1550 nm) with a response time of ≈2.6 µs and responsivity of 17.2 A W⁻¹. The superior performance is attributed to amplified photocurrent gains, and the additional n-Ga₂O₃ has a high electron carrier density with negligible hole density at room temperature and thus, can play a role as an electron reservoir while being transparent to the spectral ranges. vScanning photocurrent microscopy analysis is performed to provide the mechanism. The demonstrated SWIR imaging shows that the proposed DHJ provides a potential pathway for high-speed multispectral vision applications.

This work proposes and demonstrates a novel optical encryption scheme based on single-sized nanostructures by introducing camouflage strategy into Malus metasurfaces design processes to store multiple meta-images in different encryption levels, which can ensure that even if the camouflage information is decrypted, the real information is still safe.

Abstract

The superior capability of light manipulation makes optical metasurfaces capable of high-quality multichannel displays, demonstrating great potential in high-security optical encryption. Different from the previous multichannel nanoprinting metasurfaces based on the sophisticated nanostructure design, Malus metasurface can obtain multichannel meta-images only by arranging the orientations of single-sized nanostructures and thus have gained great attention. Here, an optical encryption scheme based on single-sized nanostructures is proposed by introducing camouflage strategy into Malus metasurfaces design processes to store multiple meta-images in different encryption levels. Experimental results demonstrate that the preset camouflage meta-image can be decoded by inserting a filter and a polarizer in the incident light path, while the decryption of real meta-image requires not only the insertion of a filter and polarizer in the incident optical path, but also the insertion of an analyzer in the outgoing optical path and setting them to the specific polarization direction. This work eliminates the consistency of encryption level in conventional multi-channel Malus metasurface, builds the differences of preset camouflage information and real information in decryption difficulty, and easily merges with other works, thereby paving a new way toward a high-security optical encryption technology.

This review addresses current challenges for the adaptation of lanthanide-doped luminescent nanoparticles to aqueous environments. The particular properties of water as a solvent, and their effects on dispersibility, disintegration, luminescence quenching, light absorption and anomalous temperature-dependences are discussed. Promising strategies for the optimization of lanthanide-doped nanoparticles are critically reviewed, especially those fostering their use in nanomedicine.

Abstract

Optimization of lanthanide-doped luminescent nanoparticles for use in nanomedicine has encountered some difficulties due to the specific properties of water as a solvent. In this review, the current challenges for the adaptation of lanthanide-doped luminescent nanoparticles to aqueous environments, and promising strategies to optimize their colloidal dispersibility and stability in water and physiological buffers, are summarized. Moreover, the possible luminescence de-excitation paths caused by water molecule vibrations and how they can be prevented under different measurement conditions are discussed. This review also deals with the latest developments in lanthanide-doped luminescent nanoparticle design for nanomedicine, to increase the depth at which they can be monitored, which is mainly limited by the absorption bands of water. Furthermore, the anomalous temperature dependence of water and the different effects it has on lanthanide-doped luminescent nanoparticles in the physiological temperature range are commented on. Finally, a critical opinion on the possible next steps in this field is provided.

Two-color, highly nonlinear (S = 8–12) photon avalanche (PA) emission at 475 and 800 nm is observed in bulk single crystal, individual microcrystals, and ensembles of colloidal core and core–shell nanoparticles of LiYF₄ host doped with either 3 or 8% of thulium ions. Theoretical simulations and super-resolution imaging of individual PA nanoparticle support high applicative potential of PA phenomenon.

Abstract

Photon avalanche (PA) is a highly nonlinear mode of upconversion that is characterized by 100–1000-fold increase in luminescence intensity upon minute increments of pumping power. The practical realization of numerous possible nano-bio-technology applications utilizing the PA phenomenon will require information on its susceptibility to the material volume and surface. Here, these parameters are investigated via experimental and theoretical PA. The two-color, highly nonlinear PA emission at 475 and 800 nm is clearly observed in bulk single crystal, individual microcrystals, and ensembles of colloidal core and core–shell nanoparticles of LiYF₄ host doped with either 3 or 8% of thulium ions. The properties of PA emission, such as PA nonlinearity, PA gain, PA intensity, and luminescence kinetics in these materials show dependence on crystal volume and surface quenching. Theoretical simulations provide understanding of key physical processes that influence PA performance. Moreover, photon avalanche single beam super-resolution imaging is realized for the first time in 3% Tm³⁺ doped LiYF₄ core–shell nanoparticles. The obtained insights and predictions form a solid background for further development and applications of new optimized PA materials.

In this work, novel strategies and guidelines for designing high-sensitivity sensor materials are presented, by applying the 4f-5d transitions of Eu²⁺ and Sm²⁺ lanthanide ions for optical temperature and pressure sensing. The developed Eu²⁺/Sm²⁺-co-doped SrB₄O₇ optical sensors exhibit the highest relative sensitivity ever reported (up to 45.6% K⁻¹) for any luminescent thermometer.

Abstract

The concept of optical temperature sensing using band intensity ratio is considered as one of the most effective, self-reference, non-invasive, and rapid detection techniques for the local temperature in natural or engineered systems. In this work, for the first time a divalent lanthanide-co-doped dual-center system, i.e., SrB₄O₇:Eu²⁺/Sm²⁺ phosphors, working as a bifunctional ratiometric sensor of temperature and pressure is employed. With temperature alterations, the Eu²⁺/Sm²⁺ luminescence intensity ratio and the emission lifetime of Sm²⁺ are significantly changed, showing unprecedentedly high relative sensitivity of 45.6 and 3.17% K^-1, respectively. Moreover, in the pressure range from ≈10 to 40 GPa, the intensity ratio of the Eu²⁺/Sm²⁺ emissions shows strong pressure dependence and can be utilized for pressure monitoring, with high pressure relative sensitivity of ≈13.8% GPa^-1. The superior performance indicates that the developed dual-center Eu²⁺/Sm²⁺-co-doped SrB₄O₇ phosphors are promising candidates for supersensitive optical sensing applications. The findings open a new approach of designing optical temperature and pressure sensors.

Developing X-ray or UV-light charged storage and mechanoluminescence (ML) materials with high charge carrier storage capacity is challenging. Such materials have promising utilization in developing new applications, for example, in flexible X-ray imaging, stress sensing, or non-real-time recording. Herein, we report on such materials; Bi³⁺, Tb³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃ perovskite storage and ML phosphors with high charge carrier storage capacity.

Abstract

Developing X-ray or UV-light charged storage and mechanoluminescence (ML) materials with high charge carrier storage capacity is challenging. Such materials have promising utilization in developing new applications, for example, in flexible X-ray imaging, stress sensing, or non-real-time recording. Herein, the study reports on such materials; Bi³⁺, Tb³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃ perovskite storage and ML phosphors. Their photoluminescence, thermoluminescence (TL), and ML properties are studied. The charge carrier trapping and release processes in the Bi³⁺, Tb³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃ are explained by using the constructed vacuum referred binding energy diagram of LiTaO₃ including the energy level locations of unintended defects, Tb³⁺, Bi³⁺, and Bi²⁺. The ratio of the TL intensity after X-ray charging of the optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ga³⁺, or LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ge⁴⁺ to that of the state-of-the-art BaFBr(I):Eu²⁺ is ≈1.2 and 2.7, respectively. Force induced charge carrier storage phenomena is studied in the Tb³⁺, Bi³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃. Proof-of-concept compression force distribution sensing and X-ray imaging is demonstrated by using optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ga³⁺ dispersed in a hard epoxy resin disc and in a silicone gel film. Proof-of-concept color-tailorable ML for anti-counterfeiting is demonstrated by admixing commercial ZnS:Cu⁺,Mn²⁺ with optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ge⁴⁺ in an epoxy resin disc.

Alkyl substitutional chains are critical to the charge injection from metal electrodes to organic semiconductor crystals. By decreasing the alkyl chain length of C_n-DNTT molecular monolayer crystals, current injection efficiency is improved, achieving a high current density >19 µA µm^-1 (width-normalized) and >1 MA cm^-2 (area-normalized). Such a high density of current has not been achieved by planar organic transistors.

Abstract

Organic semiconductor materials are not recognized as a system for high current density applications due to the generally low mobility and high contact resistance. In this work, solution-processed organic molecular monolayer crystals (1L-crystals) as the active layers in field-effect transistors, demonstrating high current density application are utilized. The 1L-crystal-based devices exhibit high intrinsic mobility of 10.9 cm² V^–1 s^–1 and a contact resistance as low as 28 Ω cm, offering unprecedently high width-normalized current density up to 19 µA µm^–1 and 1.2 MA cm^–2 normalized by cross-section area. Joule heating effects in these high current devices are investigated. At a current density of 7 µA µm^–1, 1L-crystal-based transistor works stably within 1000 consecutive scans. Above this current density, thermal degradation in the current starts to occur and pulsed mode operation can restrict the degradation. The 1L-crystals exhibit superiority in high-current and potential high-frequency applications, which can expand the current boundary of organic semiconductor materials.

Neuromodulation

In article number 2200337, Cheol Seong Hwang, Kyung Min Kim, and co-workers demonstrate a stashing system that can increase the energy efficiency of a conventional spiking neural network, available on a chip that performs artificial intelligence. This system comes from brain neuromodulation, which is a technology that can efficiently handle mathematical operations for artificial intelligence by imitating the continuous changes in the topology of the neural network according to the situation.

Nature Materials, Published online: 14 July 2022; doi:10.1038/s41563-022-01303-4

Colour centre emission from hexagonal boron nitride (hBN) holds promise for quantum technologies but activation and tuning are challenging. Here, the authors show twist-angle emission brightness tuning and external voltage brightness modulation at the twisted interface of hBN flakes.

Nature Materials, Published online: 14 July 2022; doi:10.1038/s41563-022-01309-y

Single-molecule electronics provide the potential solution for high-density integration and low-power consumption in massive data-driven applications, but have yet to be explored. Here, the authors report low-power logic-in-memory operations, based on single electric dipole flipping in the two-terminal single-metallofullerene device at room temperature.

Nature Materials, Published online: 14 July 2022; doi:10.1038/s41563-022-01304-3

We show that an insulating bulk state and helical edge state coexist in Bi4Br4 and that this coexistence persists up to room temperature.

Nature Materials, Published online: 14 July 2022; doi:10.1038/s41563-022-01310-5

Individual fullerenes containing switchable electric dipoles have been demonstrated to function as single-molecule memory and logic at room temperature.

Nature, Published online: 13 July 2022; doi:10.1038/s41586-022-04821-y

Individually addressable ‘T centre’ photon-spin qubits are integrated in silicon photonic structures and their spin-dependent telecommunications-band optical transitions characterized, creating opportunities to construct silicon-integrated, telecommunications-band quantum information networks.

Anderson's theorem states that nonmagnetic impurities do not affect the isotropic order parameter in Bardeen–Cooper–Schrieffer (BCS) superconductors, whereas scattering on paramagnetic centers is very efficient in destroying the s-wave superconductivity. This work demonstrates that LaH₁₀, the best so far known superconductor, obeys Anderson's theorem, which makes it possible to adjust its critical temperature for a specific application.

Abstract

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications. On the other hand, a complete experimental study of the best so far known superconductor, lanthanum superhydride LaH₁₀, encounters a serious complication because of the large upper critical magnetic field H _C2(0), exceeding 120–160 T. It is found that partial replacement of La atoms by magnetic Nd atoms results in significant suppression of superconductivity in LaH₁₀: each at% of Nd causes a decrease in T _C by 10–11 K, helping to control the critical parameters of this compound. Strong pulsed magnetic fields up to 68 T are used to study the Hall effect, magnetoresistance, and the magnetic phase diagram of ternary metal polyhydrides for the first time. Surprisingly, (La,Nd)H₁₀ demonstrates completely linear H _C2(T) ∝ |T – T _C|, which calls into question the applicability of the Werthamer–Helfand–Hohenberg model for polyhydrides. The suppression of superconductivity in LaH₁₀ by magnetic Nd atoms and the robustness of T _C with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson's theorem gives new experimental evidence of the isotropic (s-wave) character of conventional electron–phonon pairing in lanthanum decahydride.

Nature Nanotechnology, Published online: 14 July 2022; doi:10.1038/s41565-022-01165-6

This Review elaborates on the recent developments and the future opportunities and challenges of fundamental research on semiconductor moiré materials, with a particular focus on transition metal dichalcogenides.

Nature Nanotechnology, Published online: 14 July 2022; doi:10.1038/s41565-022-01184-3

The recent advent of transition metal dichalcogenides moiré materials is a promising platform for studying correlated electron phenomena and moiré exciton physics.

Taking advantage of the ferroelectric-semiconducting coupling property of α-In₂Se₃ and the light-induced ferroelectric flipping effect, photodetectors with sensitivity approaching twenty photons and photoelectric memories with excellent endurance of more than 10⁶ cycles are achieved on the ferroelectric semiconductor phototransistors with a CMOS-compatible device architecture and operation voltage.

Abstract

Low-light-level photodetections are highly desired in the fields of astronomy and quantum information. However, the existing techniques suffer from high operation voltages and complexity of fabrication, which reduces its compatibility with complementary metal oxide semiconductors (CMOS) based read-out circuit and prevent the use of imaging. Here, a low-light-level phototransistor that employs a photo-induced ferroelectric reversal mechanism in a ferroelectric semiconductor channel: α-In₂Se₃ is demonstrated. It shows a record-low noise-equivalent power of 7.9 × 10⁻²² W Hz^−1/2, a record-high specific detectivity of 6.34 × 10¹⁷ Jones, and sensitivity approaching 20 photons in a photon-counting mode, and fast time response of 260 µs/50 ns in the rise/decay period. It also works as an optoelectronic memory with an on/off ratio of 2.9 × 10⁵, retention of longer than 10 years, and endurance of more than 10⁶ cycles. Due to its high performance, simple architecture, and small operation voltage, the phototransistor provides a feasible platform for new-generation low-light-level image sensors.