Abrupt Size Partitioning of Multimodal Photoluminescence Relaxation in Monodisperse Silicon Nanocrystals

Abstract

Intrinsic constraints on efficient photoluminescence (PL) from smaller alkene-capped silicon nanocrystals (SiNCs) put limits on potential applications, but the root cause of such effects remains elusive. Here, plasma-synthesized colloidal SiNCs separated into monodisperse fractions reveal an abrupt size-dependent partitioning of multilevel PL relaxation, which we study as a function of temperature. Guided by theory and simulation, we explore the potential role of resonant phonon interactions with "minigaps" that emerge in the electronic density of states (DOS) under strong quantum confinement. Such higher-order structures can be very sensitive to SiNC surface chemistry, which we suggest might explain the common implication of surface effects in both the emergence of multimodal PL relaxation and the loss of quantum yield with decreasing nanocrystal size. Our results have potentially profound implications for optimizing the radiative recombination kinetics and quantum yield of smaller ligand-passivated SiNCs.

Spectral Dependencies of the Stretched Exponential Dispersion Factor and Photoluminescence Quantum Yield as a Common Feature of Nanocrystalline Si

“…Although we do not want to belittle the surface role, we think that its responsibility might be slightly exaggerated. A similar conclusion was recently made by Brown et al…”

Size‐Controlled Si Nanocrystals Fabricated by Electron Beam Evaporation

“…In particular, the stretched exponential behavior exhibited by both low‐ (850 nm) and high‐energy (650 nm) contributions [see Figure (a) and (b), respectively] already gives relevant information about the emission centers that yield the observed luminescence. The stretched exponential function has typically been ascribed to i) a dispersion in excitonic recombination times originated by a broad NC size distribution, each NC size population exhibiting different characteristic decay times; ii) the interaction between neighboring NCs that induce effects related to electron‐phonon coupling; or iii) the degree of dispersion from the electron and hole motion due to disorder within the material . In these three different but correlated frames, the stretching parameter β can be interpreted as a dispersion from the ideal case ( β = 1) of size mono‐population of non‐interacting (i.e., separated enough) Si NCs.…”

Влияние Лигандов И Растворителя На Безызлучательные Переходы В Полупроводниковых Квантовых Точках (Обзор)

“…Было установлено, что во всех этих случаях положение спектра люминесценции не определяется размером частиц, а определяется поверхностными уровнями, на которые влияют пассивирующие лиганды. В работе Брауна и соавторов [98,99] исследовано влияние растворителей на выходы PL кремниевых квантовых точек, люминесцирующих в красной области спектра с длительностью в десятки микросекунд. Было показано, что выход и длительность PL уменьшаются с увеличением донорной силы растворителя.…”