Conversion from Red to Blue Photoluminescence in Alcohol Dispersions of Alkyl-Capped Silicon Nanoparticles: Insight into the Origins of Visible Photoluminescence in Colloidal Nanocrystalline Silicon

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The Journal of Physical Chemistry

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Nanoparticles -- research


Visibly emissive silicon nanoparticles (Si NPs) were obtained via annealing of (HSiO1.5)n polymer, followed by chemical etching. The hydride-terminated Si NPs (H-Si NPs) were surface-functionalized via thermal hydrosilylation with 1-decene and were dispersed in straight chain alcohols varying in carbon chain length (C1–C10). The initial red photoluminescence (PL) (λmax,em ∼580 nm) observed from hexane dispersions of the decane-terminated Si NPs (dec-Si NPs) became weaker upon exposure to alcohols smaller than a minimum chain length, commensurate with appearance of strong, blue PL (λmax,em ∼450 nm). A suite of spectroscopic and microscopic techniques was employed to study and correlate the change in Si NP PL with composition and/or size changes to the Si NPs. The results of these studies support that the conversion from red to blue PL originates from dangling bond defect passivation by small alcohol molecules, resulting in an enhanced blue/red PL ratio. The dangling bond defect (Si•) is supported by reactivity studies of H-Si NPs with the stable radical (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) and with n-alkanes. We discuss these experimental results in light of current hypotheses about the origins of Si NP visible light emission, which we demonstrate is markedly influenced by the Si NP surface chemistry. An energy level diagram is proposed to account for the spectral and dynamic features observed, in which the role of surface states is highlighted.


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