huangpanqi

Recently reported new methods to induce strain are summarized and discussed, and the latest developments on the modification of electrical, magnetic, and optical properties of 2D materials are updated by strain engineering (in particular properties such as the electrochemical, magnetic and superconducting characteristics, and their strain tuning have received little attention previously), and future perspectives are presented.

Abstract

Strain engineering is a promising way to tune the electrical, electrochemical, magnetic, and optical properties of 2D materials, with the potential to achieve high-performance 2D-material-based devices ultimately. This review discusses the experimental and theoretical results from recent advances in the strain engineering of 2D materials. Some novel methods to induce strain are summarized and then the tunable electrical and optical/optoelectronic properties of 2D materials via strain engineering are highlighted, including particularly the previously less-discussed strain tuning of superconducting, magnetic, and electrochemical properties. Also, future perspectives of strain engineering are given for its potential applications in functional devices. The state of the survey presents the ever-increasing advantages and popularity of strain engineering for tuning properties of 2D materials. Suggestions and insights for further research and applications in optical, electronic, and spintronic devices are provided.

Nature Nanotechnology, Published online: 16 August 2022; doi:10.1038/s41565-022-01192-3

Suspensions of 2D hexagonal boron nitride show an anomalously large specific Cotton–Mouton coefficient, enabling the fabrication of a magnetically tuneable and stable birefringent optical device. This device serves as a transmissive light modulator with wavelengths entering the ultraviolet (UV)-C region, representing a technological advance in deep-UV modulation.

Low-dimensional light-emitting materials have presented peculiar optical and optoelectronic properties, unlike their bulk form. The light–matter interaction of these emitters can be engineered by integrating with various planar optical cavities, which is a planar nano- and microstructure that tightly confines light. These integrations provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters.

Abstract

Low-dimensional light-emitting materials have been actively investigated due to their unprecedented optical and optoelectronic properties that are not observed in their bulk forms. However, the emission from low-dimensional light-emitting materials is generally weak and difficult to use in nanophotonic devices without being amplified and engineered by optical cavities. Along with studies on various planar optical cavities over the last decade, the physics of cavity–emitter interactions as well as various integration methods are investigated deeply. These integrations not only enhance the light–matter interaction of the emitters, but also provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters. In this review, the fundamentals, strengths and weaknesses of various planar optical resonators are first provided. Then, commonly used low-dimensional light-emitting materials such as 0D emitters (quantum dots and upconversion nanoparticles) and 2D emitters (transition-metal dichalcogenide and hexagonal boron nitride) are discussed. The integration of these emitters and cavities and the expect interplay between them are explained in the following chapters. Finally, a comprehensive discussion and outlook of nanoscale cavity-emitter integrated systems is provided.

Erbium-doped WS₂ hybrids with down- and up-conversion photoluminescence are integrated on silicon and are highly beneficial to 980-nm detection with a responsivity of 39.8 mA W⁻¹ at a weak power of 4.4 µW and a high detectivity of 2.79 × 10¹⁰ Jones, thus supporting the significance of rare-earth doping as a robust strategy for boosting the characteristics of 2D optoelectronic devices.

Abstract

The integration of 2D nanomaterials with silicon is expected to enrich the applications of 2D functional nanomaterials and pave the way for next-generation, nanoscale optoelectronics with enhanced performances. Herein, a strategy for rare earth element doping is utilized for the synthesis of 2D WS₂:Er nanosheets to achieve up-conversion and down-conversion emissions ranging from visible to near-infrared regions. Moreover, the potential integration of the synthesized 2D nanosheets in silicon platforms is demonstrated by the realization of an infrared photodetector based on a WS₂:Er/Si heterojunction. These devices operate at room temperature and show a high photoresponsivity of ≈39.8 mA W⁻¹ (at 980 nm) and a detectivity of 2.79 × 10¹⁰ cm Hz^1/2 W⁻¹. Moreover, the dark current and noise power density are suppressed effectively by van der Waals-assisted p–n heterojunction. This work fundamentally contributes to establishing infrared detection by rare element doping of 2D materials in heterojunctions with Si, at the forefront of infrared 2DMs-based photonics.

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.

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.

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.

Nature Photonics, Published online: 01 August 2022; doi:10.1038/s41566-022-01042-7

Lanthanide nanotransducers are developed to detect broadband incoherent mid-infrared radiation in the 4–11 μm spectral window by ratiometric luminescence measurements.

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01051-6

A tilted plasmonic nanocavity enables shortening of the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns. High quantum efficiency enhancement, chiral polarization and directional far-field emission are maintained.

Nature Communications, Published online: 12 August 2022; doi:10.1038/s41467-022-32498-4

Here, the authors report tunable luminescence from a single lanthanide ion upon changing excitation conditions through co-doping an energy-modulator ion, thus adjusting the photon transition process of the lanthanide activator ion. Optical encryption has also been demonstrated as an application of this universal strategy.

Light: Science & Applications, Published online: 13 July 2022; doi:10.1038/s41377-022-00871-z

This review presents a summary of diverse designs and applications of nanocomposites based on lanthanide-doped upconversion nanoparticles.

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.

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.