Size-Dependent Photothermal Performance of Silicon Quantum Dots

Silicon quantum dots (Si QDs) have recently attracted attention in clinical imaging technology owing to their nontoxicity to living cells and tissues. Here, we investigate the size-dependent photothermal effect of hydrogen-terminated Si QDs, which provides a common surface for further functionalization of biocompatibility. Three samples of QDs with diameters of 2.2, 3.8, and 4.7 nm were prepared by a thermal disproportionation reaction of triethoxysilane hydrolyzed at pH 3 and subsequent hydrofluoric etching. The photothermal responses, which occur through the sequential absorption of photons under photoexcited conditions, are measured at increasing laser power using Raman spectroscopy. The photothermal effect, which is quantified by the Raman spectroscopic study, is size-dependent and enhanced for larger QDs. Hence, the photothermal heat released from the QDs might be controlled between room temperature and 275 degrees C. To investigate their practical use, we prepared QDs terminated with undecanoic acid monolayers, giving the solubility in water. As expected, we observed the size dependence of thermal conductivity properties on warming 2.5 mL water under light illumination. The temperature dependence of the photoluminescence spectra reveals the important role of nonradiative channels in the photothermal performance controlled by the QD size.

Automated summary

Silicon quantum dots have demonstrated size-dependent photothermal effect and their photothermal responses are quantified using Raman spectroscopy. The study reveals that larger quantum dots exhibit enhanced photothermal effect and the temperature range of photothermal heat released from the quantum dots can be controlled between room temperature and 275 degrees Celsius. Additionally, surface modification of the quantum dots allows for solubility in water and the role of nonradiative channels in photothermal performance is highlighted.