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Wide-band gap semiconductor nanoparticles has been the focus of interest recently, due to their validity for energy creations, decomposition of harmful substances, boosting useful chemical reactions etc. In this work, we will evaluate optical characteristics of a single semiconductor nanoparticle via broadband-UV Rayleigh scattering spectroscopy and photoluminescence (PL) spectroscopy. Rayleigh scattering spectroscopy reveal the bandgap energies while PL spectroscopy provide the information on exciton generation efficiencies as well as existence of surface defects.
In our microscopy setup, a broadband white light source (LDLS) was collimated and obliquely illuminated on the sample to realize dark-field illumination to distinguish the position of individual particles in the microscopic image. Scattering from a single nanocrystal was collected by an reflection-type objective lens (NA0.5) and introduced to a spectrometer and detected by an EMCCD camera. The spectrometer was designed specifically for UV-DUV broadband spectroscopy and imaging. For photoluminescence (PL) measurements, we introduce 320 nm (CW) laser for excitation. The sample is enclosed in a temperature-controlled cell ranging from room temperature to 77K.
We especially focus on titanium dioxide (TiO2), a typical photocatalyst, and tangusten trioxide (WO3) which is one of the candidate for decomposition of water into oxygen and hydrogen by a visible or longer wavelength light. The band structure of nano-particles is changed when the size is smaller than several tens of nanometers, due to crystallinity and quantum size effects. PL of single zinc oxide (ZnO) nanoparticles were also measured together with the temperature effects. The spectra obtained from a single nanoparticle is different from aggregates both for exciton PL and defects PL.
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