Temperature Dependent Photoluminescence of Size-Purified Silicon Nanocrystals

Abstract

The photoluminescence (PL) of size-purified silicon nanocrystals is measured as a function of temperature and nanoparticle size for pure nanocrystal films and polydimethylsiloxane (PDMS) nanocomposites. The temperature dependence of the bandgap is the same for both sample types, being measurably different from that of bulk silicon because of quantum confinement. Our results also suggest weaker interparticle and environmental coupling in the nanocomposites, with enhanced PL and an unexpected dependence of lifetime on size for the pure nanocrystal films at low temperatures. We interpret these results through differences in the low-temperature size dependence of the ensemble nonradiative equilibrium constants. The response of the PDMS nanocomposites provides a consistent measure of local temperature through intensity, lifetime, and wavelength in a polymer-dispersed morphology suitable for biomedical applications, and we exploit this to fabricate a small-footprint fiber-optic cryothermometer. A comparison of the two sample types offers fundamental insight into the photoluminescent behavior of silicon nanocrystal ensembles.

Low Temperature Colloidal Synthesis of Silicon Nanorods from Isotetrasilane, Neopentasilane, and Cyclohexasilane

“…The PL emission quantum yield of these nanorods dispersed in toluene at room temperature was 2%. Generally, the absorbance and emission 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 spectra of these Si nanorods are similar to alkene-passivated Si nanocrystals [22][23][24][25] and Si nanorods made at higher temperature with trisilane and Sn seeds particles. 3 Figure 4d shows the timedependent PL decay.…”

Interaction of polymer-coated silicon nanocrystals with lipid bilayers and surfactant interfaces

“…Like the AP material, PEGylated SiNCs exhibit both 'fast' and 'slow' PL relaxation (Fig. 1b), where the fast (ns) relaxation has been linked to surface states [64] while the PL quantum yield is dominated by the slow (µs) mode [65,66]. Here, the fast decay is around 4 ns independent of sample, with a slow decay of around 10 µs.…”

“…Stretched-exponential relaxation is common in condensed-matter systems with disorder. Here, it reflect the combined effects of size polydispersity [65] and PL spectral linewidth, which is broadened by electron-phonon coupling in an indirect band-gap semiconductor [66]. The drop in PL lifetime after an extended time in water reflects a gradual decrease in quantum yield [67].…”

“…The cluster-size distribution based on TEM (Fig. 1c) is To assess the stability of the PL quantum yield, the slow component of PL relaxation was fit to a stretched exponential of the form [65,66] …”

UV‐Blocking Photoluminescent Silicon Nanocrystal/Polydimethylsiloxane Composites

“…The observed spherical aggregations are due to the phase separation phenomenon. [27] Obviously, the extent of aggregation of ncSi-decyl in the ncSi-decyl/PDMS composites is much smaller than that of …”