Excited-State Relaxation Dynamics of 3-Vinylthiophene-Terminated Silicon Quantum Dots

Abstract

In theory, silicon quantum dots (SiQDs) emit enhanced photoluminescence with a size-tunable spectrum in the visible range. In practice, surface states originating from oxide defect structures or organic ligands are strongly involved in exciton relaxation dynamics because the amplitudes of hole and electron wave functions are nonzero at the SiQD surface. In this study, SiQDs with well-defined surface properties were obtained through a wet-chemistry procedure providing SiQDs with adjustable sizes and oxide-free, 3-vinylthiophene-terminated surfaces. The 3-vinylthiophene-terminated SiQDs have a crystalline spherical 2 nm core and were observed to exhibit blue photoluminescence (∼460 nm) with a quantum yield and lifetime of ca. 23% and 1.3 ns, respectively. The interplay between electronically excited molecular states and conduction band states was examined upon direct monitoring of photoexcited carrier dynamics with femtosecond transient absorption spectroscopy. The 3-vinylthiophene ligands were found to act as surface-bound antennae that mediate ultrafast electron transfer or excitation energy transfer across the SiQD interface.

Femtosecond Ligand/Core Dynamics of Microwave-Assisted Synthesized Silicon Quantum Dots in Aqueous Solution

“…Only three compartments were required to fully describe the silica-encapsulated Si QDs data (3.7 ps, 72 ps, and ~12 ns) (Figures 5A, B) with the induced absorption ascribed to trapped charges based on the observed relaxation time constants. 31,32 Similar kinetics and spectra were observed in octyne-capped Si QD dynamics, demonstrating that the SiO 2 passivates surface traps of the Si QD equally well as long-chained alkanes. 31 The faster decay kinetics (72 ps) observed on the blue edge vs. the red edge (12 ns) is a signature of excited-state inhomogeneity and is similar to the photoluminescence signals resolved in alkane-terminated Si QDs by Klimov et al that were ascribed to core and surface trapped excitations, respectively.…”

“…32 The signals presented above are one-photon initiated with a linear dependence on excitation power.…”

Functionalized silicon quantum dots by N-vinylcarbazole: synthesis and spectroscopic properties

“…In addition to the surface protection, optoelectronic functional molecules as ligands of Si QDs are attracting increasing interest in recent years for the crucial role of the ligands to the interfacial related process in optoelectronic or light-harvesting devices. Kryschi and co-workers showed that 3-vinylthiophene ligands may act as surface-bound antennae that mediate ultrafast electron transfer or excitation energy transfer across the Si QD interface via high-energy two-photon excitation [ 37 , 38 ]. They also reported that for 2- and 4-vinylpyridine-terminated Si QDs, ultrafast excitation relaxation dynamics involving decay and rise dynamics faster than 1 ps were ascribed to electronic excitation energy transfer from an initially photoexcited ligand state to Si QD conduction band states [ 39 ].…”

Desarrollo de nanomateriales basados en silicio semiconductor

“…Existen en bibliografía muchos estudios cuidadosos sobre el efecto de distintos ligandos y reacciones superficiales sobre las propiedades de luminiscencia, incluyendo halógenos vía halogenación [90], alquenos y alquinos vía hidrosililación [86], [96] o por reacciones de adición nucleofílica [59], [97], silanización u oxidaciones usando procesos suaves [15], [62]. Sin embargo, aunque haya gran cantidad de datos en bibliografía (tabla 1.1), la evidencia experimental es ciertamente divergente y hace difícil la propuesta de un modelo único.…”