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      Ultra-narrow linewidth photo-emitters in polymorphic selenium nanoflakes

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      Author(s)
      Hussain, N.
      Ahmed, S.
      Tepe, H. U.
      Huang, K.
      Avishan, N.
      He, S.
      Rafique, M.
      Farooq, U.
      Kasirga, Talip Serkan
      Bek, A.
      Turan, R.
      Shehzad, K.
      Date
      2022-07-12
      Source Title
      Small
      Print ISSN
      1613-6810
      Electronic ISSN
      1613-6829
      Publisher
      Wiley
      Volume
      18
      Issue
      52
      Pages
      2204302-1 - 2204302-11
      Language
      English
      Type
      Article
      Item Usage Stats
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      Abstract
      Photoluminescence (PL) in state-of-the-art 2D materials suffers from narrow spectral coverage, relatively broad linewidths, and poor room-temperature (RT) functionality. The authors report ultra-narrow linewidth photo-emitters (ULPs) across the visible to near-infrared wavelength at RT in polymorphic selenium nanoflakes (SeNFs), synthesized via a hot-pressing strategy. Photo-emitters in NIR exhibit full width at half maximum (Γ) of 330 ± 90 µeV, an order of magnitude narrower than the reported ULPs in 2D materials at 300 K, and decrease to 82 ± 70 µeV at 100 K, with coherence time (τc) of 21.3 ps. The capping substrate enforced spatial confinement during thermal expansion at 250 °C is believed to trigger a localized crystal symmetry breaking in SeNFs, causing a polymorphic transition from the semiconducting trigonal (t) to quasi-metallic orthorhombic (orth) phase. Fine structure splitting in orth-Se causes degeneracy in defect-associated bright excitons, resulting in ultra-sharp emission. Combined theoretical and experimental findings, an optimal biaxial compressive strain of −0.45% cm−1 in t-Se is uncovered, induced by the coefficient of thermal expansion mismatch at the selenium/sapphire interface, resulting in bandgap widening from 1.74 to 2.23 ± 0.1 eV. This report underpins the underlying correlation between crystal symmetry breaking induced polymorphism and RT ULPs in SeNFs, and their phase change characteristics. © 2022 Wiley-VCH GmbH.
      Keywords
      2D materials
      Hot-pressing
      Polymorphic phase-transition
      Selenium nanoflakes
      Ultra-narrow linewidth photo-emitters
      Permalink
      http://hdl.handle.net/11693/111272
      Published Version (Please cite this version)
      https://www.doi.org/10.1002/smll.202204302
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      • Institute of Materials Science and Nanotechnology (UNAM) 2258
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