Brightly Luminescent Organically Capped Silicon Nanocrystals Fabricated at Room Temperature and Atmospheric Pressure

Abstract

Silicon nanocrystals are an extensively studied light-emitting material due to their inherent biocompatibility and compatibility with silicon-based technology. Although they might seem to fall behind their rival, namely, direct band gap based semiconductor nanocrystals, when it comes to the emission of light, room for improvement still lies in the exploitation of various surface passivations. In this paper, we report on an original way, taking place at room temperature and ambient pressure, to replace the silicon oxide shell of luminescent Si nanocrystals with capping involving organic residues. The modification of surface passivation is evidenced by both Fourier transform infrared spectroscopy and nuclear magnetic resonance measurements. In addition, single-nanocrystal spectroscopy reveals the occurrence of a systematic fine structure in the emission single spectra, which is connected with an intrinsic property of small nanocrystals since a very similar structure has recently been observed in specially passivated semiconductor CdZnSe nanoparticles. The organic capping also dramatically changes optical properties of Si nanocrystals (resulting ensemble photoluminescence quantum efficiency 20%, does not deteriorate, radiative lifetime 10 ns at 550 nm at room temperature). Optically clear colloidal dispersion of these nanocrystals thus exhibits properties fully comparable with direct band gap semiconductor nanoparticles.

Bright trions in direct-bandgap silicon nanocrystals revealed by low-temperature single-nanocrystal spectroscopy

“…At RT, the relaxation rate amounts to ,10 11 s 21 , which translates into the relaxation "decay time" of ,10 ps. This is a very fast process compared with the photoluminescence (PL) decay time in the SiNCs under study 5,24 (2 ns), which implies that the high-energy wing should not be observed. However, as a result of the strong size dependence, the relaxation time can change by several orders of magnitude with only a 10% change in size and can reach values as high as nanoseconds 32,33 .…”

“…Details of the preparation procedure and the investigation of the direct-bandgap switch-over in this material were published elsewhere 5,24,29 . The strain-engineered direct-bandgap SiNCs under study are characterized by short radiative lifetime 5,24 of 10 ns and a mean SiNC diameter of 2.523 nm 24,30 . Room-temperature single-NC spectroscopy of the oxidized precursor was also performed, but no signs of spectral structure appeared 20 (see also Supplementary Fig.…”

“…In contrast to the phonon-based explanation, our group noted not only the similarities of the spectral structures observed in SiNCs prepared by various methods but also the similarity of the spectral structures observed in SiNCs and II-VI NCs 13 . Therefore, we argued 24 that this structure is more closely connected to the core of the NC rather than to its surface.…”

“…With respect to single-NC spectroscopy in SiNCs, several types of samples have already been probed by different groups 3,4,6,[18][19][20][21][22][23][24][25][26][27] . The most commonly observed spectral shape was a mixture of broader unstructured spectra and structured spectra with peaks approximately 150 meV apart.…”

The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots

“…While crystalline Si (c‐Si) QDs have been extensively studied within the last decade,14, 15, 16, 17, 18, 19 investigation of amorphous Si (a‐Si) QDs properties has been very limited. One of the reasons for this limited effort is represented by the synthesis difficulties: during synthesis, it is challenging to preserve both the individuality of the QDs and their amorphous nature as QDs tend to aggregate with consequent loss of the quantum‐confined state.…”