NSTI Nanotech 2009

Tunable photoluminescence spectrum of brightly luminescent silicon quantum dots

A. Gupta, M.T. Swihart, H. Wiggers
University of Duisburg-Essen, DE

Keywords: surface functionalization, FTIR spectroscopy, photoluminescence


Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, we have developed a novel approach of producing luminescent silicon nanoparticles (Si-NPs). We synthesize single crystalline Si-NPs via pyrolysis of silane (SiH4) in a microwave plasma reactor at very high production rates (0.1-10 g h-1) [1]. The emission wavelength of the Si-NPs is controlled by etching them in a mixture of hydrofluoric acid (HF) and nitric acid (HNO3). Emission across the entire visible spectrum is obtained by varying the etching time [Fig. 1]. We observed that the air oxidation of etched Si-NPs profoundly affects their optical properties, causing their emission to blue-shift and diminish in intensity with time [Fig 2a]. Extensive studies have been carried out in stabilizing the PL of Si-NPs via surface functionalization [2,3,4]. We observed that surface functionalization causes a shift in the emission spectrum of etched Si-NPs. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si-NPs. Additionally, the amount of shift depends on the type of organic ligands on the silicon surface [Fig. 2b] and the UV exposure time. The surface modification of Si-NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si-NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way toward their commercialization.
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