Blue‐Light Emissive Type II ZnO@5‐Amino‐2‐Naphthalene Sulfonic Acid Core–Shell Quantum Dots. Issue 4 (17th January 2022)

• Record Type: Journal Article
• Authors: Kim, Hong Hee; Park, Soohyung; Lee, Heebin; Kang, Jeung Ku; Choi, Won Kook
• Is Part Of: Advanced photonics research. Volume 3:Issue 4(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-17
• Subjects: blue-emissive quantum dots -- oxygen vacancy (VO+) -- spectral-dependent electron paramagnetic resonance -- zinc vacancy (VZn−) -- ZnO@5-amino-2-naphthalene sulfonic acid core–shell quantum dots; Photonics -- Periodicals; 621.36505
• DOI: 10.1002/adpr.202100315
• Languages: English
• ISSNs: 2699-9293

Abstract

Abstract : Blue‐light emissive type II ZnO@5‐amino‐2‐naphthalene sulfonic acid (ANSA) core–shell quantum dots (QDs) is first fabricated. Green luminescence (GL) of 2.25 eV of ZnO QDs disappears at the threshold excitation wavelengths ( λ ex ) > 400 nm due to the electronic transition from conduction band (CB) or shallow donor centers to VZn 2− at ≈0.9 eV above valence band (VB). Blue emissions from ZnO@ANSA QDs are well elucidated by the charge transfer from CB of ZnO QDs to lowest unoccupied molecular orbital (LUMO) of ANSA and from shallow donor Zn interstitial (Zni ) or extended Zni states to CO, CN, CS (π*)‐states, and then the electronic transitions to nonbonding CO, CN, CS (π) states of ANSA. Spectral‐dependent electron paramagnetic resonance (SDEPR) peak g = 1.96 of ZnO QDs emerges only with illumination of light shorter than 400 nm in wavelength and completely disappears in ZnO@ANSA QDs. Electrons trapped in CB or Zni 's are unveiled to participate in GL and the paramagnetic defect to derive electron paramagnetic resonance (EPR) peak g = 1.96 of ZnO. The estimated spin–spin relaxation time ( T 2 ) of ZnO QDs was about 32.5 ns, which is two orders of magnitude longer than known values for bulk or thin‐film ZnO. Abstract : ZnO QDs show green emission centered at 2.25 eV and electron paramagnetic resonance (EPR) peak g = 1.96, which disappear at the illumination of light longer than 400 nm. When ZnO QDs are hybridized with 5‐amino‐2‐naphthalene sulfonic acid (ANSA), only blue emission and EPR peak g = 2.006 from ZnO@ANSA core–shell QDs are observed irrespective of excitation wavelength.