Photoluminescence imaging of single photon emitters within nanoscale strain profiles in monolayer WSe2

Local deformation of atomically thin van der Waals materials provides a powerful approach to create site-controlled chip-compatible single-photon emitters (SPEs). However, the microscopic mechanisms underlying the formation of such strain-induced SPEs are still not fully clear, which hinders further efforts in their deterministic integration with nanophotonic structures for developing practical on-chip sources of quantum light. Here we investigate SPEs with single-photon purity up to 98% created in monolayer WSe2 via nanoindentation. Using photoluminescence imaging in combination with atomic force microscopy, we locate single-photon emitting sites on a deep sub-wavelength spatial scale and reconstruct the details of the surrounding local strain potential. The obtained results suggest that the origin of the observed single-photon emission is likely related to strain-induced spectral shift of dark excitonic states and their hybridization with localized states of individual defects

New oxidovanadium(IV) complexes with 2,2′-bipyridine and 1,10-phenathroline ligands: Synthesis, structure and high catalytic activity in oxidations of alkanes and alcohols with peroxides

Reactions of [VCl 3 (thf) 3 ] or VBr 3 with 2,2′-bipyridine (bpy) or 1,10‐-phenanthroline (phen) in a 1:1 molar ratio in air under solventothermal conditions has afforded polymeric oxidovanadium(IV) four complexes 1‒4 of a general formula [VO(L)X 2 ] n (L = bpy, phen and X = Cl, Br). Monomeric complex [VO(DMF)(phen)Br 2 ] (4a) has been obtained by the treatment of compound 4 with DMF. The complexes were characterized by IR spectroscopy and elemental analysis. The crystal structures of 3 and 4a were determined by an X‐-ray diffraction (XRD) analysis. The {VOBr 2 (bpy)} fragments in 3 form infinite chains due to the V = O…V interactions. The vanadium atom has a distorted octahedral coordination environment. Complexes 1‒4 have been tested as catalysts in the homogeneous oxidation of alkanes (to produce corresponding alkyl hydroperoxides which can be easily reduced to alcohols by PPh 3 ) and alcohols (to corresponding ketones) with H 2 O 2 or tert‐-butyl hydroperoxide in MeCN. Compound 1 exhibited the highest activity. The mechanism of alkane oxidation was established using experimental selectivity and kinetic data and theoretical DFT calculations. The mechanism is of the Fenton type involving the generation of HO • radicals. © 2019 by the authors. Licensee MDPI, Basel, Switzerland