9 meV/K obtained in the current work. Furthermore, this deviation is decreasing with the nanoparticle diameter. As our nanoparticle has an average diameter of 7 nm, our results differ from those of the reference [28]. The main difference may lie in the fact that the size distribution is a little scattered which can be at the origin of the important red shift observed when increasing temperature. Figure 4 Temperature dependence and band gap variation.
Temperature dependence of the PL peak position of Si NPs VS-4718 clinical trial in squalane (blue curve) and in octadecene (red curve), and band gap variation of the bulk Si following the Varshni model (black curve) in the temperature range from 303 to 383 K. The Brownian motion of the NPs in the suspension increases with temperature; at the same time, their mobility also increases as the viscosity of the NPL strongly decreases. This leads to an enhanced GDC-0994 in vitro probability of energy transfer between NPs in close vicinity. The Förster resonant energy transfer (FRET)
of NPs with different BX-795 supplier sizes strongly depends on the distance D between two particles (approximately D −6) [29]. When the dynamic viscosity of the liquid decreases, it leads to high FRET probability for small NPs (approximately 4 nm in diameter) with larger band gaps toward big NPs (approximately 9 nm in diameter) having smaller band gaps. Thus, the small NPs are optically inactive from the photo-stimulated emission point of view. Therefore, the probability of the radiative recombination of the photo-excited charge carriers in the smaller NPs is considerably reduced. Consequently, large NPs become optically active and give their contribution in the PL spectrum, resulting in the observed red shift. This mechanism explains the high PL peak variation found in squalane (−0.91 meV/K). Indeed, from 303 to 383 K, the dynamic viscosity of squalane decreases
by a 7.5 factor, from 22.6 to 3 mPa.s. In order to assess this mechanism, we have measured the PL peak position as a function of liquid viscosity. Gemcitabine purchase Alkyl-capped Si NPs dispersed in five different liquids (decene, octadecene, SII_1 (mixture of octadecene and squalane with volume ratio of 0.45 and 0.55, respectively), SIII_1 (mixture of octadecene and squalane with volume ratio of 0.26 and 0.74, respectively), and squalane) with a concentration of 1 mg/mL were prepared. The dynamic viscosities of the liquids are respectively 0.73, 4, 12.3, 17.5, and 31.2 mPa.s at 25°C. Figure 5 shows the evolution of the PL peak position as a function of the dynamic viscosity of the liquids at 300 K. We clearly observe an almost linear red shift of 60 meV from squalane to decene. Figure 5 PL peak position evolution as a function of dynamic viscosity for different liquids at 300 K.
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