Abstract
Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.
Highlights
Ge QDs show tunable PL in the infrared region with a QY of ~8%24 where values typical for ‘bare’ Ge QDs are generally around 1%
Even though several steps are performed to remove any unreacted bromine from the samples, our energy dispersive X-ray (EDX) analysis reveals a majority of residual Br nanoparticles
According to Fourier Transform Infrared Spectroscopy (FTIR) analysis performed on n-butyl-terminated Si nanoparticles prepared in n-octane[45], CH2 and CH3 groups are present on their surface protecting the Si core against oxidation because the Si-O bond is weak in comparison
Summary
Ge QDs show tunable PL in the infrared region with a QY of ~8%24 where values typical for ‘bare’ Ge QDs are generally around 1%. Much research focused on explaining the origin of the PL and absorption mechanism in alkyl-terminated Si and Ge QDs38 and in GQDs39,40, comparative studies on these materials are lacking. In this respect, we investigate the optical properties of butyl-terminated Si (C-Si) and Ge QDs (C-Ge) and compare them to those of GQDs. The C-Si and C-Ge QDs were synthesized via a wet chemical method[26,27,41,42,43] adapted from Kauzlarich et al[44]. All QDs used in this study were dispersed in UV-grade ethanol
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