Defect states of ZnO nanoparticles: Discrimination by time-resolved photoluminescence spectroscopy

Abstract

ZnO nanoparticles with different shapes and sizes were prepared by changing coordinating ligands. Hexagonal cones presented UV and green ͑ϳ500 nm͒ emissions, which originated from excitons and defects, respectively. Oxygen vacancies were found to be major defects in the hexagonal cones. Blue emission at ϳ440 nm was observed for hexagonal plates, and analyses of time-resolved photoluminescence spectra showed that two transitions were responsible for this blue emission, because transitions from Zn i to the valence band ͑430 nm͒ and from Zn i to V Zn ͑480 nm͒ were distinguished by emission wavelengths and lifetimes. The visible emissions from defects were related to the roles of coordinating ligands.

Observations of unusual temperature dependent photoluminescence anti-quenching in two-dimensional nanosheets of ZnS/ZnO composites and polarization dependent photoluminescence enhancement in fungi-like ZnO nanostructures

“…28 The other two components are attributed to the lifetime of free and bound excitons. [29][30][31][32] As shown in Figure S2 (see supplementary material), 21 instead of LTAQ, thermal quenching of PL emission has been observed for A6 sample with increasing temperature and is consistent with the previous reports of ZnO nanostructures and QDs. 32,33 For A6 sample, at 600 C annealing temperature, a complete oxidation of ZnS nanosheets occurs and as a result it has been converted into porous ZnO nanostructures as can be seen from the SEM images ( Fig.…”

Steady state and time resolved optical characterization studies of Zn2SnO4 nanowires for solar cell applications

“…We also see a much longer delay of about 68 ps for the rising edge of the 674 nm wavelength signal compared to the IRF signal. This rise time behavior is counter to what Han et al 16 observed in ZnO where they see no delay in PL rise time.…”

“…Thus the potential application of ZTO nanowires for use as a transparent conducting oxide (anode electrode) in sensitized solar cells 7,13,10 motivates the investigation of its optical and electronic properties. The primary goal of this work is to expand our understanding of ZTO nanowires through analysis of their steady state and time resolved emission spectra, and to use this data to develop a model describing the charge carrier dynamics in these nanowires 16 .…”

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

“…The enhancement of the UV luminescence is attributed to the elimination of the competing routes to the UV light emission due to defects. [33] 0.28 eV below CB [35] 0.15 eV below CBM (þ2/þ1) [36] 170 K [37] (0.57 eV) [38] O i Yellow 2.11 eV [39] 2.13 eV [40] 1.18 eV above VBM (-/2-) [41] 1.59 eV above VBM (-/2-) [38] 1.09 eV above the VB [35,42] 440 K [38,43] (1.1 eV) [38] Fig. 6.…”