Solid-state quantum emitters play a critical role in the application of quantum information technology. Quantum emitters with high brightness at room temperature can be realized in hBN, and it has become a current research hotspot. However, much of the research up to now only produced quantum emitters at the edges and wrinkles of hBN, which tremendously limited the usage of the quantum emitters. In this work, heavy ions irradiation methods were employed to produce highquality quantum emitters in the middle region of the hBN sample. The quantum emitter production engineering via heavy ions irradiation was systematically investigated. The dependence of irradiated ion type, energy, and fluence, as well as the thickness of the hBN flakes, on the production efficiency of the hBN quantum emitters were analyzed in detail. The characteristics of luminescence of quantum emitters, such as second-order correlation function g (2) (τ), stability, polarization, and saturation, were all compared with different irradiation conditions. In addition, based on the wavelength statistical results of quantum emitters in hBN, the transition energies of various intrinsic point defects in hBN were studied through first-principles calculations to reveal the originations of luminescence. The calculation results indicated that the V N , V B , and B i point defects were possible candidates of the quantum emitter centers. Overall, in this study, according to experimental characterizations, heavy ion irradiation should be an efficient method to produce stable, ultrabright, highly linearly polarized quantum emitters in hBN flakes.

Massive magical phenomena in nature are closely related to quantum effects at the microscopic scale. However, the lack of straightforward methods to observe the quantum coherent dynamics in integrated biological systems limits the study of essential biological mechanisms. In this work, we developed a single-molecule coherent modulation (SMCM) microscopy by combining the superior features of single-molecule microscopy with ultrafast spectroscopy. By introducing the modem technology and defining the coherent visibility, we realized visualization and real-time observation of the decoherence process of a single molecule influenced by the microenvironment for the first time. In particular, we applied this technique to observe the quantum coherent properties of the entire chlorella cells and found the correlation between the coherent visibility and metabolic activities, which may have potential applications in molecular diagnostics and precision medicine.

Monolayer transition metal dichalcogenides (TMDs) are direct gap semiconductors emerging promising applications in diverse optoelectronic devices. To improve performance, recent investigations have been systematically focused on the tuning of their optical properties. However, an all-optical approach with the reversible feature is still a challenge. Here we demonstrate the tunability of the photoluminescence (PL)properties of monolayer WS2 via laser irradiation. The modulation of PL intensity, as well as the conversion between neutral exciton and charged trion have been readily and reversibly achieved by using different laser power densities. We attribute the reversible manipulation to the laser-assisted adsorption and desorption of gas molecules, which will deplete or release free electrons from the surface of WS2 and thus modify its PL properties. This all-optical manipulation, with advantages of reversibility, quantitative control, and high spatial resolution, suggests promising applications of TMDs monolayers in optoelectronic and nanophotonic applications, such as optical data storage, micropatterning, and display.

Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides are central to the functionality of devices based on them. Here, these properties in a large-size exfoliated high-quality monolayer MoSe 2 are addressed directly using heterodyned transient grating spectroscopy at room temperature. While the free exciton population is found to be long-lived (≈230 ps), an extremely fast intervalley scattering (≤170 fs) is observed, leading to a negligible valley polarization, consistent with steady state photoluminescence measurements and theoretical calculation. The exciton population decay shows an appreciable contribution from the exciton-exciton annihilation, with an annihilation rate of ≈0.01 cm 2 s −1. The annihilation process also leads to a significant distortion of the transient grating evolution. Taking this distortion into account, consistent exciton diffusion constants D ≈ 1.4 cm 2 s −1 are found by a model simulation in the excitation density range of 10 11-10 12 cm −2. The presented results highlight the importance of correctly considering the many-body annihilation processes to obtain a pronounced understanding of the excitonic properties of monolayer transition metal dichalcogenides.

Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides (TMDCs) are central to the functionality of devices based on them. In article number 2000029 by Jingyi Zhu, Paul H. M. van Loosdrecht, and co‐workers investigate exciton‐exciton annihilation dynamics and its effect in the distortion of the diffusion grating in an exfoliated monolayer TMDC, MoSe2.

van der Waals (vdW) heterostructures of transition metal dichalcogenides (TMDCs) provide an excellent paradigm for next-generation electronic and optoelectronic applications. However, the reproducible fabrications of vdW heterostructure devices and the boosting of practical applications are severely hindered by their unstable performance, due to the lack of criteria to assess the interlayer coupling in heterostructures. Here we propose a physical model involving ultrafast electron transfer in the heterostructures and provide two criteria, η (the ratio of the transferred electrons to the total excited electrons) and ζ (the relative photoluminescence variation), to evaluate the interlayer coupling by considering the electron transfer in TMDC heterostructures and numerically simulating the corresponding rate equations. We have proved the effectiveness and robustness of two criteria by measuring the pump–probe photoluminescence intensity of monolayer WS2 in the WS2/WSe2 heterostructures. During thermal annealing of WS2/WSe2, ζ varies from negative to positive values and η changes between 0 and 4.5 × 10–3 as the coupling strength enhanced; both of them can well characterize the tuning of interlayer coupling. We also design a scheme to image the interlayer coupling by performing PL imaging at two time delays. Our scheme offers powerful criteria to assess the interlayer coupling in TMDC heterostructures, offering opportunities for the implementation of vdW heterostructures for broadband and high-performance electronic and optoelectronic applications.

Atomically thin layer transition metal dichalcogenides have been intensively investigated for their rich optical properties and potential applications in nano-electronics. In this work, we study the incoherent optical phonon and exciton population dynamics in monolayer WS2 by timeresolved spontaneous Raman scattering spectroscopy. Upon excitation of the exciton transition, both the Stokes and anti-Stokes optical phonon scattering strength exhibit a large reduction. Based on the detailed balance, the optical phonon population is retrieved, which shows an instant buildup and a relaxation lifetime of ~4 ps at an exciton density ~10 12 cm -2 . The corresponding optical phonon temperature rises by 25 K, eventually, after some 10's of picoseconds, leading to a lattice heating by only ~3 K. The exciton relaxation dynamics extracted from the transient vibrational Raman response shows a strong excitation density dependence, signaling an important bimolecular contribution to the decay. The exciton relaxation rate is found to be ~ (70 ps) -1 and exciton-exciton annihilation rate ~0.1 cm 2 s -1 . These results provide valuable insight into the thermal dynamics after optical excitation and enhance the understanding of the fundamental exciton dynamics in two-dimensional transition metal materials.

Monolayer transition metal dichalcogenides have emerged as promising materials for optoelectronic and nanophotonic devices. However, the low photoluminescence (PL) quantum yield (QY) hinders their various potential applications. Here we engineer and enhance the PL intensity of monolayer WS2 by femtosecond laser irradiation. More than two orders of magnitude enhancement of PL intensity as compared to the asprepared sample is determined. Furthermore, the engineering time is shortened by three orders of magnitude as compared to the improvement of PL intensity by continuouswave laser irradiation. Based on the evolution of PL spectra, we attribute the giant PL enhancement to the conversion from trion emission to exciton, as well as the improvement of the QY when exciton and trion are localized to the new-formed defects.We have created microstructures on the monolayer WS2 based on the enhancement of PL intensity, where the engineered structures can be stably stored for more than three years. This flexible approach with the feature of excellent long-term storage stability is promising for applications in information storage, display technology, and optoelectronic devices.