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Quantum emitters are needed for a myriad of applications ranging from quantum sensing to quantum computing. Hexagonal boron nitride (hBN) quantum emitters are one of the most promising solid-state platforms to date due to their high brightness and stability and the possibility of a spin-photon interface. However, the understanding of the physical origins of the single-photon emitters (SPEs) is still limited. Here we report dense SPEs in hBN across the entire visible spectrum and present evidence that most of these SPEs can be well explained by donor-acceptor pairs (DAPs). On the basis of the DAP transition generation mechanism, we calculated their wavelength fingerprint, matching well with the experimentally observed photoluminescence spectrum. Our work serves as a step forward for the physical understanding of SPEs in hBN and their applications in quantum technologies. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version J.Z. acknowledges support from the National Basic Research Program of China (grant no. 2017YFA0303401, 2016YFA0301200), Beijing Natural Science Foundation (JQ18014), and Strategic Priority Research Program of Chinese Academy of Sciences (grant no. XDB28000000) and CAS Interdisciplinary Innovation team. W.G. acknowledges the Singapore National Research Foundation and DSO National Laboratories under the QEP grants NRF2021- QEP2-03-P01, 2019-0643 (QEP-P2), and 2019-1321 (QEPP3), CRP award nos. NRF-CRP21-2018-0007, NRF-CRP22- 2019-0004, and NRF-CRP23-2019-0002, and the Singapore Ministry of Education (MOE2016-T3-1-006 (S)). I.A. acknowledges the financial support from the Australian Research Council (via CE200100010).

Two-dimensional (2D) Janus materials with large exciton binding energies have attracted enormous attention for their novel photoelectric properties. Here, the quasiparticle (QP) band structures and...

Transition metal dichalcogenides (TMDCs) with different thickness can greatly influence the performance of photonic devices. However, how to accurately control the layers of TMDCs and realize the a...

Defect states and exciton of two-dimensional semiconductors play an important role in fundamental research and device applications. Here, we reported the defect emissions and exciton–lattice intera...

Current thermoelectric (TE) materials often have low performance or contain less abundant and/or toxic elements, thus limiting their large-scale applications. Therefore, new TE materials with high efficiency and low cost are strongly desirable. Here we demonstrate that SiS and SiSe monolayers made from nontoxic and earth-abundant elements intrinsically have low thermal conductivities arising from their low-frequency optical phonon branches with large overlaps with acoustic phonon modes, which is similar to the state-of-the-art experimentally demonstrated material SnSe with a layered structure. Together with high thermal power factors due to their two-dimensional nature, they show promising TE performances with large figure of merit (ZT) values exceeding 1 or 2 over a wide range of temperatures. We establish some basic understanding of identifying layered materials with low thermal conductivities, which can guide and stimulate the search and study of other layered materials for TE applications.

On the basis of the density functional theory (DFT) within local density approximations (LDA) approach, we calculate the band gaps for different size SnO2 quantum wires (QWs) and quantum dots (QDs). A model is proposed to passivate the surface atoms of SnO2 QWs and QDs. We find that the band gap increases between QWs and bulk evolve as ΔEgwire = 1.74/d1.20 as the effective diameter d decreases, while being ΔEgdot = 2.84/d1.26 for the QDs. Though the ∼d1.2 scale is significantly different from ∼d2 of the effective mass result, the ratio of band gap increases between SnO2 QWs and QDs is 0.609, very close to the effective mass prediction. We also confirm, although the LDA calculations underestimate the band gap, that they give the trend of band gap shift as much as that obtained by the hybrid functional (PBE0) with a rational mixing of 25% Fock exchange and 75% of the conventional Perdew−Burke−Ernzerhof (PBE) exchange functional for the SnO2 QWs and QDs. The relative deviation of the LDA calculated band gap ...