Tunable Fluorescence Properties Due to Carbon Incorporation in Zinc Oxide Nanowires

Abstract

It is shown experimentally that carbon incorporation into zinc oxide (ZnO) nanowires (NWs) plays a crucial role in determining the NWs' fluorescence and photoluminescence properties. Through intentional adjustment of chemical vapor deposition growth parameters to allow for carbon incorporation, the ZnO NWs' fluorescence under ultraviolet excitation can be varied controllably from green to orange‐red. X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, and transmission electron microscopy correlate carbon incorporation to a systematic shifting of ZnO NWs' fluorescence toward higher wavelengths. This is consistent with a previous theoretical prediction of orange‐red fluorescence arising from a carbon‐related defect within ZnO. In the present work, further computational results from simulation of high carbon content within the ZnO lattice yield additional carbon‐related defect species as possible origins of orange‐red fluorescence. Furthermore, the extent of simulated band gap energies can help explain the broad visible fluorescence spectrum from carbon incorporated ZnO. Additional experiments involving plasma etching and oxygen annealing agree with the inferences of carbon‐related defects as a source of variable visible‐light emissions.

Fluorescence Invigoration in Carbon-Incorporated Zinc Oxide Nanowires from Passage of Field Emission Electrons

“…Following the growth technique as described previously 8 , ZnO NWs that emit different fluorescence colours under UV excitation are first grown by varying the growth parameters 8 . The NWs grown at 900 °C emit green fluorescence under UV excitation whereas the NWs grown with the zinc oxide/carbon source temperature at 850 °C emit orange-red fluorescence under UV excitation.…”

“…The green fluorescence is often attributed to oxygen vacancies in ZnO. Sample II NWs are considered to be C-ZnO NWs resulting from the off equilibrium growth with carbon incorporation in the ZnO NWs 8 .…”

“…Elucidation of the NWs’ work functions in both samples can help pinpoint the nature of defects within the NWs. Possible carbon-related defects with inter-band defect energy levels that can give rise to the respective emissions (green and orange-red) in C- ZnO have been formerly elucidated via density functional calculations 8,23 . Their highest occupied defect energy levels are illustrated in Fig.…”

“…While the fluorescence of ZnO has been widely studied and many of the defect-associated emissions have been documented, there are still some under investigation 4 . Some of the reported values for the various peaks and their respective origins are ~530 nm ‘green’ peak due to oxygen vacancies or zinc vacancies 3,5–7 , ~630 nm ‘orange’ peak due to interstitial oxygen, 730 nm ‘red-orange’ peak due to carbon incorporation in ZnO etc 8 .…”

“…The carbon-enriched ZnO NWs used in this work are grown by a chemical vapour deposition (CVD) process following the method (Fig. A1) described previously 8,16 . Samples undergoing field emission are placed in a typical parallel-plate configuration field emission setup as shown in Supplementary Information (Fig.…”