Wide spectrum multi-sub-band modulation of excitons and defect state emission simultaneously in surface oxidized CdS micro/nano-wires

Strong optical confinement and light–matter interaction within semiconductor nanostructures are crucial to modulate the emission property. A fundamental understanding of these interesting phenomena is important to scientific and industrial communities. In this paper, we synthesized the surface oxidized CdS micro/nano-wires by post-oxidation of CdS micro/nano-wires at 475 °C and investigated systematically their novel emission properties. Scanning electron microscopy, energy dispersive x-ray spectrometry, and Raman spectroscopy confirmed the formation of the oxidized surface without changing the structure and morphology of CdS micro/nano-wires greatly. In situ micro-photoluminescence showed the continuous modulation of multi-sub-band emission of both near bandgap and defect state simultaneously with an ultra-broad spectrum range from 490 nm to 750 nm. According to the excitation wavelength-, excitation power-, and temperature-dependent PL spectra, the sub-band near bandgap emission originated from strong light–matter interaction such as photon–exciton coupling, while the whispering gallery mode (WGM) micro-cavity played an important role in the sub-band emission of the defect state. The spatial-resolved mapping of emission modes confirmed the sub-band near bandgap and defect WGM micro-cavity emission from the core and oxidized surface of CdS micro-wires, respectively. The multi-exponential lifetime dynamics further indicated the complex recombination process of both near bandgap and defect state emission. These results are different from the one-step synthesized CdS@CdO core/shell micro-wires and reveal an interesting exciton–photon coupling with enhanced optical cavity confinement in the post-treated CdS micro/nano-wires, representing the rational tailoring of surface/interface relevant properties to control the light emission for application in nanophotonic devices.

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