Quantum coherence and interference of a single moiré exciton in nano-fabricated twisted monolayer semiconductor heterobilayers.

The moiré potential serves as a periodic quantum confinement for optically generated excitons, creating spatially ordered zero-dimensional quantum systems. However, a broad emission spectrum resulting from inhomogeneity among moiré potentials hinders the investigation of their intrinsic properties. In this study, we demonstrated a method for the optical observation of quantum coherence and interference of a single moiré exciton in a twisted semiconducting heterobilayer beyond the diffraction limit of light. We observed a single and sharp photoluminescence peak from a single moiré exciton following nanofabrication. Our findings revealed the extended duration of quantum coherence in a single moiré exciton, persisting beyond 10 ps, and an accelerated decoherence process with increasing temperature and excitation power density. Moreover, quantum interference experiments revealed the coupling between moiré excitons in different moiré potential minima. The observed quantum coherence and interference of moiré exciton will facilitate potential applications of moiré quantum systems in quantum technologies.

Symmetry Engineering in Twisted Bilayer WTe2.

The fabrication of artificial structures using a twisted van der Waals assembly has been a key technique for recent advancements in the research of two-dimensional (2D) materials. To date, various exotic phenomena have been observed thanks to the modified electron correlation or moiré structure controlled by the twist angle. However, the twisted van der Waals assembly has further potential to modulate the physical properties by controlling the symmetry. In this study, we fabricated twisted bilayer WTe2 and demonstrated that the twist angle successfully controls the spatial inversion symmetry and hence the spin splitting in the band structure. Our results reveal the further potential of a twisted van der Waals assembly, suggesting the feasibility of pursuing new physical phenomena in 2D materials based on the control of symmetry.

High-throughput dry transfer and excitonic properties of twisted bilayers based on CVD-grown transition metal dichalcogenides.

van der Waals (vdW) layered materials have attracted much attention because their physical properties can be controlled by varying the twist angle and layer composition. However, such twisted vdW assemblies are often prepared using mechanically exfoliated monolayer flakes with unintended shapes through a time-consuming search for such materials. Here, we report the rapid and dry fabrication of twisted multilayers using chemical vapor deposition (CVD) grown transition metal chalcogenide (TMDC) monolayers. By improving the adhesion of an acrylic resin stamp to the monolayers, the single crystals of various TMDC monolayers with desired grain size and density on a SiO2/Si substrate can be efficiently picked up. The present dry transfer process demonstrates the one-step fabrication of more than 100 twisted bilayers and the sequential stacking of a twisted 10-layer MoS2 single crystal. Furthermore, we also fabricated hBN-encapsulated TMDC monolayers and various twisted bilayers including MoSe2/MoS2, MoSe2/WSe2, and MoSe2/WS2. The interlayer interaction and quality of dry-transferred, CVD-grown TMDCs were characterized by using photoluminescence (PL), cathodoluminescence (CL) spectroscopy, and cross-sectional electron microscopy. The prominent PL peaks of interlayer excitons can be observed for MoSe2/MoS2 and MoSe2/WSe2 with small twist angles at room temperature. We also found that the optical spectra were locally modulated due to nanosized bubbles, which are formed by the presence of interface carbon impurities. The present findings indicate the widely applicable potential of the present method and enable an efficient search of the emergent optical and electrical properties of TMDC-based vdW heterostructures.

Dynamics of Moiré Trion and Its Valley Polarization in a Microfabricated WSe2/MoSe2 Heterobilayer.

The moiré potential, induced by stacking two monolayer semiconductors with slightly different lattice mismatches, acts as periodic quantum confinement for optically generated excitons, resulting in spatially ordered zero-dimensional quantum systems. However, there are limitations to exploring intrinsic optical properties of moiré excitons due to ensemble emissions and broadened emissions from many peaks caused by the inhomogeneity of the moiré potential. In this study, we proposed a microfabrication technique based on focused Ga+ ion beams, which enables us to control the number of peaks originating from the moiré potential and thus explore unknown moiré optical characteristics of WSe2/MoSe2 heterobilayer. By taking advantage of this approach, we reveal emissions from a single moiré exciton and charged moiré exciton (trion) under electrostatic doping conditions. We show the momentum dark moiré trion state above the bright trion state with a splitting energy of approximately 4 meV and clarify that the dynamics are determined by the initial trion population in the bright state. Furthermore, the degree of negative circularly polarized emissions and their valley dynamics of moiré trions are dominated by a very long valley relaxation process lasting ∼700 ns. Our findings on microfabricated heterobilayer could be viewed as an extension of our groundbreaking efforts in the field of quantum optics application using moiré superlattices.

Shift-Current Photovoltaics Based on a Non-Centrosymmetric Phase in In-Plane Ferroelectric SnS.

The shift-current photovoltaics of group-IV monochalcogenides has been predicted to be comparable to those of state-of-the-art Si-based solar cells. However, its exploration has been prevented from the centrosymmetric layer stacking in the thermodynamically stable bulk crystal. Herein, the non-centrosymmetric layer stacking of tin sulfide (SnS) is stabilized in the bottom regions of SnS crystals grown on a van der Waals substrate by physical vapor deposition and the shift current of SnS, by combining the polarization angle dependence and circular photogalvanic effect, is demonstrated. Furthermore, 180° ferroelectric domains in SnS are verified through both piezoresponse force microscopy and shift-current mapping techniques. Based on these results, an atomic model of the ferroelectric domain boundary is proposed. The direct observation of shift current and ferroelectric domains reported herein paves a new path for future studies on shift-current photovoltaics.

Valley Relaxation of the Moiré Excitons in a WSe2/MoSe2 Heterobilayer.

The moiré superlattice consisting of lattice- or angular-mismatched van der Waals heterostructures drastically changes the physical properties of constituent atomically thin materials by confinement of the exciton by the moiré potential, which is promising for next-generation quantum optics. The moiré superlattice also affects the valley degrees of freedom of the monolayer transition-metal dichalcogenides (TMDs) and the valley-dependent optical selection rule, which results in the characteristic circular polarized light emission of the moiré exciton. However, the valley relaxation process of excitons in the moiré superlattice remains to be understood. Here, we studied valley relaxation of moiré excitons in a twisted WSe2/MoSe2 heterobilayer by circularly polarized photoluminescence and photoluminescence excitation (PLE) spectroscopy. The experimentally observed circularly polarized emission strongly depends on the excitation power density, which contrasts with the case of two-dimensional monolayer TMDs. The excitation power-dependent circularly polarized emission suggests the characteristic valley relaxation of the moiré exciton with a small density of states in zero-dimensional systems. In addition, the resonant PLE measurement reveals the intravalley relaxation process from the triplet to singlet state of the moiré exciton via Γ5 phonon emission. Our findings clarified the valley relaxation of the moiré excitons, which would lead to the application of the circularly polarized quantum light emitter in twisted semiconducting heterobilayers.

Continuous Color-Tunable Light-Emitting Devices Based on Compositionally Graded Monolayer Transition Metal Dichalcogenide Alloys.

The diverse series of transition metal dichalcogenide (TMDC) materials has been employed in various optoelectronic applications, such as photodetectors, light-emitting diodes, and lasers. Typically, the detection or emission range of optoelectronic devices is unique to the bandgap of the active material. Therefore, to improve the capability of these devices, extensive efforts have been devoted to tune the bandgap, such as gating, strain, and dielectric engineering. However, the controllability of these methods is severely limited (typically ≈0.1 eV). In contrast, alloying TMDCs is an effective approach that yields a composition-dependent bandgap and enables light emissions over a wide range. In this study, a color-tunable light-emitting device using compositionally graded TMDC alloys is fabricated. The monolayer WS2 /WSe2 alloy grown by chemical vapor deposition shows a spatial gradient in the light-emission energy, which varies from 2.1 to 1.7 eV. This alloy is incorporated in an electrolyte-based light-emitting device structure that can tune the recombination zone laterally. Thus, a continuous and reversible color-tunable light-emitting device is successfully fabricated by controlling the light-emitting positions. The results provide a new approach for exploring monolayer semiconductor-based broadband optical applications.

Science of 2.5 dimensional materials: paradigm shift of materials science toward future social innovation.

The past decades of materials science discoveries are the basis of our present society - from the foundation of semiconductor devices to the recent development of internet of things (IoT) technologies. These materials science developments have depended mainly on control of rigid chemical bonds, such as covalent and ionic bonds, in organic molecules and polymers, inorganic crystals and thin films. The recent discovery of graphene and other two-dimensional (2D) materials offers a novel approach to synthesizing materials by controlling their weak out-of-plane van der Waals (vdW) interactions. Artificial stacks of different types of 2D materials are a novel concept in materials synthesis, with the stacks not limited by rigid chemical bonds nor by lattice constants. This offers plenty of opportunities to explore new physics, chemistry, and engineering. An often-overlooked characteristic of vdW stacks is the well-defined 2D nanospace between the layers, which provides unique physical phenomena and a rich field for synthesis of novel materials. Applying the science of intercalation compounds to 2D materials provides new insights and expectations about the use of the vdW nanospace. We call this nascent field of science '2.5 dimensional (2.5D) materials,' to acknowledge the important extra degree of freedom beyond 2D materials. 2.5D materials not only offer a new field of scientific research, but also contribute to the development of practical applications, and will lead to future social innovation. In this paper, we introduce the new scientific concept of this science of '2.5D materials' and review recent research developments based on this new scientific concept.

Analysis of senescence in gingival tissues and gingival fibroblast cultures.

OBJECTIVE: To determine senescence-associated changes in the gingival tissues of aged mice and gingival fibroblast cultures. MATERIALS AND METHODS: The production of senescence-associated ß-galactosidase (SA-ß-gal) and mRNA expression of p16, p21, interleukin (IL)-1ß, and tumor necrosis factor α (TNF-α) were evaluated in gingival tissues, gingival fibroblasts of 10- and 20-month-old C57BL/6NCrl mice, and multiple-passaged and hydrogen peroxide-stimulated human gingival fibroblasts (HGFs). Changes in molecular expression in HGF cultures due to senescent cell elimination by the senolytic drug ABT-263 (Navitoclax) were analyzed. RESULTS: Compared to 10-week-old mice, the 20-month-old mice had higher numbers of M1 macrophages. The proportion of cells expressing SA-ß-gal were also higher in 20- month-old mice than in 10-week-old-mice. Gingival fibroblasts in 20-month-old mice expressed less collagen 1a1, collagen 4a1, and collagen 4a2 mRNA than those in 10-week-old mice. Compared to control cells, H2O2 treated HGF cells expressed higher levels of SA-ß-gal and p16, p21, IL-1ß, and TNF-α. Furthermore, ABT-263 suppressed HGF cell expression of cytokines after senescence induction. CONCLUSIONS: Senescence-associated changes were observed in the gingival tissues of aged mice and HGF cultures. In addition, the potential of senolytic drugs to modify aging-related changes in the gingiva was shown.

Directional Exciton-Energy Transport in a Lateral Heteromonolayer of WSe2-MoSe2.

Controlling the direction of exciton-energy flow in two-dimensional (2D) semiconductors is crucial for developing future high-speed optoelectronic devices using excitons as the information carriers. However, intrinsic exciton diffusion in conventional 2D semiconductors is omnidirectional, and efficient exciton-energy transport in a specific direction is difficult to achieve. Here we demonstrate directional exciton-energy transport across the interface in tungsten diselenide (WSe2)-molybdenum diselenide (MoSe2) lateral heterostructures. Unidirectional transport is spontaneously driven by the built-in asymmetry of the exciton-energy landscape with respect to the heterojunction interface. At excitation positions close to the interface, the exciton photoluminescence (PL) intensity was substantially decreased in the WSe2 region and enhanced in the MoSe2 region. In PL excitation spectroscopy, it was confirmed that the observed phenomenon arises from lateral exciton-energy transport from WSe2 to MoSe2. This directional exciton-energy flow in lateral 2D heterostructures can be exploited in future optoelectronic devices.

Magnon-Coupled Intralayer Moiré Trion in Monolayer Semiconductor-Antiferromagnet Heterostructures.

Moiré fringe patterns created by stacking different 2D layered materials as artificial van der Waals (vdW) heterostructures have become a novel platform to study and engineer optically generated excitonic properties. The moiré patterns contribute to the formation of spatially ordered excitonic states (excitons and trions), which can be used in the quantum simulation of many-body systems and ensembles of coherent quantum light emitters. The intriguing moiré excitonic properties are affected by and controlled via the interaction with magnetic elements. Here, a moiré excitonic system interacting with the magnetic elementary excitation of antiferromagnetic orders in MoSe2 /MnPS3 vdW heterostructures is reported. The low-temperature photoluminescence spectra with additional fine spectral structures on the low-energy side, which are coupled magnon-trion peaks below the Néel temperature of MnPS3 , are carefully investigated. The fine spectral structures with long lifetime and coherence time are assigned to intralayer trion-magnon complexes trapped in the moiré potentials (moiré trion-magnon complexes). These findings highlight the emergence of moiré trion-magnon complexes and provide a new way to explore novel quantum phenomena in moiré excitonic systems with magnetic functionalities.

Tuning the Reactivity of a Substrate for SNAP-Tag Expands Its Application for Recognition-Driven DNA-Protein Conjugation.

Recognition-driven modification has been emerging as a novel approach to modifying biomolecular targets of interest site-specifically and efficiently. To this end, protein modular adaptors (MAs) are the ideal reaction model for recognition-driven modification of DNA as they consist of both a sequence-specific DNA-binding domain (DBD) and a self-ligating protein-tag. Coupling DNA recognition by DBD and the chemoselective reaction of the protein tag could provide a highly efficient sequence-specific reaction. However, combining an MA consisting of a reactive protein-tag and its substrate, for example, SNAP-tag and benzyl guanine (BG), revealed rather nonselective reaction with DNA. Therefore new substrates of SNAP-tag have been designed to realize sequence-selective rapid crosslinking reactions of MAs with SNAP-tag. The reactions of substrates with SNAP-tag were verified by kinetic analyses to enable the sequence-selective crosslinking reaction of MA. The new substrate enables the distinctive orthogonality of SNAP-tag against CLIP-tag to achieve orthogonal DNA-protein crosslinking by six unique MAs.

Analgesic Mechanisms of Steroid Ointment against Oral Ulcerative Mucositis in a Rat Model.

Despite the long history of use of steroid ointments for oral mucositis, the analgesic mechanism has not been fully elucidated. In this study, we examined the effects of triamcinolone acetonide (Tmc) on oral ulcerative mucositis-induced pain in conscious rats by our proprietary assay system. Based on evaluations of the physical properties and retention periods in the oral mucosa of human volunteers and rats, we selected TRAFUL® ointment as a long-lasting base. In oral ulcerative mucositis model rats, TRAFUL® with Tmc suppressed cyclooxygenase-dependent inflammatory responses with upregulations of glucocorticoid receptor-induced anti-inflammatory genes and inhibited spontaneous nociceptive behavior. When an ointment with a shorter residual period was used, the effects of Tmc were not elicited or were induced to a lesser extent. Importantly, TRAFUL® with Tmc also improved oral ulcerative mucositis-induced mechanical allodynia, which has been reported to be independent of cyclooxygenase. Ca2+ imaging in dissociated trigeminal ganglion neurons showed that long-term preincubation with Tmc inhibited the hypertonic stimulation-induced Ca2+ response. These results suggest that the representative steroid Tmc suppresses oral ulcerative mucositis-induced pain by general anti-inflammatory actions and inhibits mechanical sensitivity in peripheral nerves. For drug delivery, long-lasting ointments such as TRAFUL® are needed to sufficiently induce the therapeutic effects.

Resonant Coupling of a Moiré Exciton to a Phonon in a WSe2/MoSe2 Heterobilayer.

Moiré patterns with an angular mismatch in van der Waals heterostructures are a fascinating platform to engineer optically generated excitonic properties. The moiré pattern can give rise to spatially ordered exciton ensembles, which offer the possibility for coherent quantum emitters and quantum simulation of many-body physics. The intriguing moiré exciton properties are affected by their dynamics and exciton-phonon interaction. Here, we report the moiré exciton and phonon interaction in a twisted WSe2/MoSe2 heterobilayer. By tuning the excitation energy, we realized the selective excitation of the moiré exciton at phonon resonances and the otherwise negligible small absorption. Furthermore, we revealed the relaxation of moiré exciton ensembles between different potential minima via the resonant phonon scattering process. Our findings highlight resonant coupling of a moiré exciton to a phonon and could pave a new way for the exploration of novel quantum phenomena of the moiré exciton.

Room-Temperature Chiral Light-Emitting Diode Based on Strained Monolayer Semiconductors.

Room-temperature chiral light sources whose optical helicity can be electrically switched are one of the most important devices for future optical quantum information processing. The emerging valley degree of freedom in monolayer semiconductors allows generation of chiral luminescence via valley polarization. However, relevant valley-polarized light-emitting diodes (LEDs) have only been achieved at low temperatures (typically below 80 K). Here, a room-temperature chiral LED with strained transition metal dichalcogenide monolayers is realized. Spatially resolved polarization spectroscopy reveals that strain effects are crucial to yielding robust valley-polarized electroluminescence. The broken threefold rotational symmetry of strained monolayers induce inequivalent valley drifts at the K/K' valleys, resulting in different amounts of spin recombination driven by electric fields. Based on this scenario, ideally strained conditions are designed for LEDs on flexible substrates, in which the helicity of room-temperature valley-polarized electroluminescence is electrically tuned. The results provide a new pathway for practical chiral light sources based on monolayer semiconductors.

Ultralarge Photoluminescence Enhancement of Monolayer Molybdenum Disulfide by Spontaneous Superacid Nanolayer Formation.

Due to the direct band gap nature, extensive studies have been conducted to improve the optical behavior in monolayer transition metal dichalcogenides (TMDCs) with a formula of MX2 (M = Mo, W; X = S, Se, Te). One of the strongest modulating agents of optical behavior is a molecular superacid treatment; however, the chemical event has not been unveiled. Also, the engineering protocol for keeping the treatment is immature. In this work, we systematically study the superacid treatment procedures on monolayer molybdenum disulfide (MoS2) and propose that the interaction, a hydrophilic interaction, between the superacid molecule and MoS2 surface would be critical. As a result of the interaction, the superacid molecules spontaneously form an acidic layer with the thickness of several nanometers on the surface. The power-dependent photoluminescence (PL) measurement indicates the edge of MoS2 flake is more effective and electronically modulated by the treatment. By understanding the superacid nanolayer formation by the treatment, we succeeded in maintaining the ultrastrong PL in the superacid-treated MoS2 for more than 30 days in the ambient air by encapsulation with transparent organic polymers. This study advances the understanding and designing applications of strong luminescent properties in the superacid-treated TMDCs and paves the way toward engineering exciton dynamics and an experimental platform for treating multibody states.

Tranexamic Acid Improves Memory and Learning Abilities in Aging Mice.

PURPOSE: Although the onset mechanism of Alzheimer's disease, which co-occurs with aging, has been extensively studied, no effective methods that improve the decline in memory and learning abilities following aging have been developed. Tranexamic acid provided promising results for ameliorating photo-aging and extending the natural lifespan. However, it is unknown whether it affects the decline in memory and learning abilities due to aging. In this study, we examined the effect of tranexamic acid on memory and learning abilities of naturally aging mice. METHODS: ICR mice were orally administered with tranexamic acid (12 mg/kg/day) three times weekly for 2 years, and their memory and learning abilities were compared between the tranexamic acid-treated and non-treated groups. RESULTS: The decline in memory and learning abilities due to aging was ameliorated by tranexamic acid administration. The expression of plasmin and amyloid-ß decreased following the treatment with tranexamic acid. Furthermore, the number of M1-type brain macrophages diminished and that of M2 macrophages increased. In addition, administration of tranexamic acid decreased the concentrations of interleukin (IL)-1ß and tumor necrosis factor-α, while it increased the levels of IL-10 and transforming growth factor-α in the brain. CONCLUSION: These results indicated that tranexamic acid suppressed the secretion of the inflammatory cytokines aging M1-type macrophages, thereby improving age-related memory and learning abilities.

Controllable Magnetic Proximity Effect and Charge Transfer in 2D Semiconductor and Double-Layered Perovskite Manganese Oxide van der Waals Heterostructure.

Optically generated excitonic states (excitons and trions) in transition metal dichalcogenides are highly sensitive to the electronic and magnetic properties of the materials underneath. Modulation and control of the excitonic states in a novel van der Waals (vdW) heterostructure of monolayer MoSe2 on double-layered perovskite Mn oxide ((La0.8 Nd0.2 )1.2 Sr1.8 Mn2 O7 ) is demonstrated, wherein the Mn oxide transforms from a paramagnetic insulator to a ferromagnetic metal. A discontinuous change in the exciton photoluminescence intensity via dielectric screening is observed. Further, a relatively high trion intensity is discovered due to the charge transfer from metallic Mn oxide under the Curie temperature. Moreover, the vdW heterostructures with an ultrathin h-BN spacer layer demonstrate enhanced valley splitting and polarization of excitonic states due to the proximity effect of the ferromagnetic spins of Mn oxide. The controllable h-BN thickness in vdW heterostructures reveals a several-nanometer-long scale of charge transfer as well as a magnetic proximity effect. The vdW heterostructure allows modulation and control of the excitonic states via dielectric screening, charge carriers, and magnetic spins.

Carbon Nanotube Photoluminescence Modulation by Local Chemical and Supramolecular Chemical Functionalization.

ConspectusCarbon nanotubes (CNTs) have been central materials in nanoscience and nanotechnologies. Single-walled CNTs (SWCNTs) consisting of a cylindrical graphene show a metallic (met) or semiconducting (sc) property depending on their rolling up manner (chirality). The sc-SWCNTs show characteristic chirality-dependent optical properties of their absorption and photoluminescence (PL) in the near-infrared (NIR) region. These are derived from their highly π-conjugated structures having semiconducting crystalline sp2 carbon networks with defined nanoarchitectures that afford a strong quantum confinement and weak dielectric screening. Consequently, photoirradiation of the SWCNTs produces a stable and mobile exciton (excited electron-hole pair) even at room temperature, and the exciton properties dominate such optical phenomena in the SWCNTs. However, the mobile excitons decrease the PL efficiency due to nonradiative relaxation including collision with tube edges and relaxation to lower-lying dark states. A breakthrough regarding the efficient use of the mobile exciton for PL has recently been achieved by local chemical functionalization of the SWCNTs, in which the chemical reactions introduce local defects of oxygen and sp3 carbon atoms in the tube structures. The defect doping creates new emissive doped sites that have narrower band gaps and trap the mobile excitons, which provides locally functionalized SWCNTs (lf-SWCNTs). As a result, the localized exciton produces E11* PL with red-shifted wavelengths and enhanced PL quantum yields compared to the original E11 PL of the nonmodified SWCNTs.In this Account, we describe recently revealed fundamental properties of the lf-SWCNTs based on the analyses by photophysics, theoretical calculations, and electrochemistry combined with in situ PL spectroscopy. The new insight allows us to expand the wavelength regions of the NIR E11* PL derived from the localized exciton, in which upconversion generates a higher energy PL through thermal activation and proximal doped site formation using bis-aryldiazonium modifiers provides a much lower energy PL than typical E11* PL. Moreover, owing to the chemical reaction-dominant doping process, the molecular structure design of modifiers succeeds in producing functionalized lf-SWCNTs; namely, molecular functions are incorporated into the doped sites for their PL modulation. The wavelength changes/switching in the E11* PL selectively occurs by a supramolecular approach using molecular recognition and imine chemistry. Therefore, the local chemical functionalization of the SWCNTs is a key to designing the properties and creating their new functions of the lf-SWCNTs. Fundamental understanding of the doped site properties of the lf-SWCNTs and molecularly driven approaches for exciton and defect engineering would unveil the intrinsic natures of these materials, which is crucial for elevating the SWCNT-based nanotechnologies to the next stage. The resulting materials are of interest in the fields of high performance NIR-II imaging and sensing for bio/medical analyses and single-photon emitters in quantum information technology.

Photoactivation of Strong Photoluminescence in Superacid-Treated Monolayer Molybdenum Disulfide.

To advance the development of atomically thin optoelectronics using two-dimensional (2D) materials, engineering strong luminescence with a physicochemical basis is crucial. Semiconducting monolayer transition-metal dichalcogenides (TMDCs) are candidates for this, but their quantum yield (QY) is known to be poor. Recently, a molecular superacid treatment of bis(trifluoromethane)sulfonimide (TFSI) generated unambiguously bright monolayer TMDCs and a high QY. However, this method is highly dependent on the processing conditions and therefore has not been generalized. Here, we shed light on environmental factors to activate the photoluminescence (PL) intensity of the TFSI-treated monolayer MoS2, with a factor of more than 2 orders of magnitude greater than the original by photoactivation. The method is useful for both mechanically exfoliated and chemically deposited samples. The existence of photoirradiation larger than the band gap demonstrates enhancement of the PL of MoS2; on the other hand, activation by thermal annealing, as demonstrated in the previous report, is less effective for enhancing the PL intensity. The photoactivated monolayer MoS2 shows a long lifetime of ∼1.35 ns, more than a 30-fold improvement over the original as exfoliated. The consistent realization of the bright monolayer MoS2 reveals that air exposure is an essential factor in the process. TFSI treatment in a N2 environment was not effective for achieving a strong PL, even after the photoactivation. These findings can serve as a basis for engineering the bright atomically thin materials for 2D optoelectronics.