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The Co-doped ZnO microwires (MWs) were grown using the optical furnace method. We used Scanning electron microscopy (SEM), polarized micro-Raman spectroscopy, photoluminescence (PL) and optical absorption spectroscopy to systematic investigation of the optical and structural properties of Co-doped ZnO MWs. The SEM analysis reveals that Co-doped ZnO MWs has hexagonal facets and cavity inside. The EDS results confirmed the presence and non-uniform distribution of Co impurities in the samples. Co doping of ZnO MWs leads to the decreased intensity, drastically broadening and high-energy shift of the NBE PL band. The red emission band at 1.85 eV originates from 2 E( 2 G) → 4 A 2 ( 4 F) intra-3d-transition of Co 2+ in the ZnO lattice has been observed. The intense structured absorption bands within the near infrared ranges 3800–4800 and 5500–9000 cm −1 are caused by electronic spin-allowed transitions 4 T 2 (F) ← 4 A 2 (F) and 4 T 1 (F) ← 4 A 2 (F) of the tetrahedrally coordinated Co 2+ (3 d 7 ) ions substituting Zn 2+ ions in Co-doped ZnO MWs. Micro-Raman studies of Co doped ZnO MWs show doping/disorder induced additional modes as compared to the undoped sample. The resonant enhancement of the additional local Co-related A 1 -symmetry Raman mode is observed in the parallel polarization geometry y ( z , z ) y ¯ . For the Co doped ZnO MWs, the enhancement of the additional Co-related local vibration mode with an increase in the excitation photon energy is also observed in the Raman spectra. [ABSTRACT FROM AUTHOR]

Abstract: The aging of the photoluminescence (PL) in bio-conjugated and non-conjugated CdSeTe–ZnS core–shell quantum dots (QDs) is studied by the micro-PL, micro-Raman and X-ray diffraction (XRD) in the samples of buffered QD solution dried on a crystalline Si wafer and stored in the atmospheric ambience for about 2years. The aging of the PL consists in a “blue” spectral shift of the PL band, an increase in PL band half-width and the decrease in the PL intensity. These changes are more pronounced in the conjugated QD samples. The XRD analysis of the aged samples revealed that the QD core diameter is reduced by ∼1.5nm in the conjugated QDs as compared to the non-conjugated ones. The possible mechanism of PL spectrum aging is the oxidation that decreases the QD core dimension. It is concluded that the bio-conjugation promotes QD oxidation and the mechanism of the effect is proposed. [Copyright &y& Elsevier]