15 November 2002 Spectroscopy, dynamics, and electron transfer in GaSe nanoparticles
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Abstract
The synthesis, characterization and spectroscopy of GaSe nanoparticles are described in this paper. The particles are synthesized from the reaction of trioctylphosphine selenium with trimethylgallium in a solution of trioctylphosphine and trioctylphosphine oxide at 280 °C. TEM images show that this synthesis produces GaSe nanoparticles in the size range of 2 - 6 nm. These particles may be size segregated by column chromatography or size selective precipitation and relatively monodisperse nanoparticles are obtained. Electron diffraction results indicate that these particles have a two-dimensional single tetra-layer type structure. The particles have absorption onsets in the 360 to 450 nm region, with the smallest particles absorbing furthest to the blue. The particles are emissive, with emission quantum yields of about 10 - 15%. Following 400 nm excitation, these particles exhibit a static emission maximum at 480 nm. This emission is polarized and the anisotropy is largest on the blue edge of the emission spectrum. Both the total (unpolarized) emission kinetics and the emission anisotropy kinetics are obtained. Static emission spectra along with wavelength dependent kinetic results permit the reconstruction of time dependent spectra. The kinetic results are interpreted in terms of an energetic model that is based on the relative energetics of the band edge and trap states in bulk GaSe. The emission kinetics show an 80 ps decay component in the total emission, but not in the anisotropy decay kinetics. There is a ca. 270 cm-1 shift in the emission maximum during this decay. This transient is assigned to direct to indirect band edge relaxation. This is followed by 400 ps and 2.4 ns decay components in both the total emission and the anisotropy kinetics. These transients are assigned to trapping of holes in shallow, followed by deeper acceptor levels. As the 480 nm emission decays, it is replaced by a much weaker, long-lived, unpolarized 520 nm emission. Transient absorption results show a broad absorption in the 500 to 650 nm region, which is assigned to a hoole intraband transition. This band exhibits a 20 ps rise time, indicative of relaxation of holes to the valance band edge.
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Viktor Chikan, David F. Kelley, "Spectroscopy, dynamics, and electron transfer in GaSe nanoparticles", Proc. SPIE 4807, Physical Chemistry of Interfaces and Nanomaterials, (15 November 2002); doi: 10.1117/12.451233; https://doi.org/10.1117/12.451233
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