Abstract
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.
Highlights
Oxygen can decorate and passivate the surface structure of CdS micro/nano-wires and tune the electron structure and energy band to result in an interesting emission property
The Raman spectra of individual oxidized CdS micro/nano-wires are measured at different temperatures from 300 K to 80 K
Surface oxidized CdS micro/nano-wires with high crystal quality are synthesized by the two-step CVD method and show an interesting PL spectrum with ultra-broad sub-band modulation emission wavelength ranging from 480 nm to 750 nm, different from the previously reported pure or doped CdS micro/nano-structures
Summary
Light–matter interactions, such as electron–phonon, photon–phonon, and photon–exciton coupling, are important to tune the optoelectronic properties of novel photonic and quantum devices. Notably, the exciton–polariton, a boson quasi-particle resulting from the strong coupling of an exciton and photon, exhibits half-light, half-matter nature and ultra-small effective mass (four orders smaller than that of a free electron). The exciton–polariton is crucial to many exciting phenomena, such as Bose–Einstein condensation, Fano resonance, ultralow threshold lasing, and light-emitting devices. The coupling strength of the exciton and photon in the optical micro-cavity can be expressed using the measurable Rabi splitting energy g (g ∝ n × f /Vm), where n is the number of oscillators, f is the corresponding oscillator strength, and Vm is the mode volume. the coupling. The PL spectra demonstrated continuous modulation of light emission with an ultra-broad spectrum range from 490 nm to 750 nm These results are different from those of the previous one-step synthesized CdS@CdO core/shell micro-wires and represent an interesting exciton–photon coupling with enhanced optical cavity confinement in the posttreated CdS micro/nano-wires, demonstrating the important role of the surface/interface in the performance modulation of semiconductor nanostructures. This simple while effective surface posttreatment of CdS micro/nanostructures can push their application into multi-functional integration of nano-photonic devices, such as multi-color lasers/LEDs and wide spectrum photodetectors
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