Quantum emitters in two-dimensional layered hexagonal boron nitride are quickly emerging as a highly promising platform for next-generation quantum technologies. However, precise identification and control of defects are key parameters to achieve the next step in their development. We conducted a comprehensive study by analyzing over 10,000 photoluminescence emission lines, revealing 11 distinct defect families within the 1.6 to 2.2 eV energy range, challenging the hypotheses of a random energy distribution. These findings provide valuable insights to decipher the microscopic origin of emitters in hBN. The spectral spacing between defect families could serve as a key parameter for theoretical investigations We also explored the influence of hBN host morphology on defect family formation, demonstrating its crucial impact. By tuning flake size and arrangement, we achieve selective control of defect types while maintaining high spatial density. This offers a scalable approach to defect emission control, diverging from costly engineering methods.
Group-VII transition metal dichalcogenides like ReS2 holds novel in-plane anisotropic excitons, owing to their reduced lattice symmetry. Despite their potential, the coherent dynamics of these anisotropic excitons remain unexplored yet. To address their coherent properties, here, we perform polarization sensitive, ultrafast non-linear optical measurements on ReS2. By implementing four-wave mixing spectroscopy along with spectral heterodyning detection at the microscopic limit, we measure the ultrafast coherence and population dynamics of the anisotropic excitonic system in layered ReS2. We attribute their dephasing times (T2) and radiative lifetime (T1) in a sub-picosecond range for both the anisotropic excitons. We observed the robustness of the homogeneous broadening with respect to the flake thickness, excitation powers, and temperatures. Such homogeneous broadening features suggest a low excitonic disorder level, setting a unique characteristic of ReS2 among two-dimensional semiconductor systems. Additionally, the layer-independent measured lifetime and exciton coherence times can be fundamental for understanding the exact electronic band structure of ReS2.
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