Distributed luminescence from alkyl-capped silicon quantum dots

Abstract

Orange luminescence attributable to a core of silicon atoms in alkyl-capped crystalline quantum dots excited at λa=355 and 405 nm is investigated as a function of applied intensity and time. The intensity of luminescence displays a linear power dependence on the intensity of the applied field, from which an exponent n=0.94±0.02 commensurate with single-photon absorption is derived. The dependence of luminescence on time is observed to be strongly nonexponential and is optimally accounted for by a probability density function which describes a continuous distribution of two decay times: the behavior is characteristic of a pair of elementary steps connected with light emission within a distribution of local environments, or a single rate process supported by two environments. Nonlinear least-squares fits to the time dependent luminescence formulated on this basis with a Gaussian, Lorentzian, or log-normal distribution of rates return most probable lifetimes T¯1=21±1 μs and T¯2=3.7±0.8 μs. The widths of the distributions vary between σ1=0.01–0.03 μs−1 and σ2=0.14–1.1 μs−1 associated with 1/T¯1 and 1/T¯2, respectively.

Photoluminescence of silicon quantum dots in nanospheres

“…28 On the other hand, the PL properties of SiQDs could also be tailored through surface modication (or functionalization) by poly(acrylic acid), allylamine, alkynes, propionic acid, surfactant and so on. 17,[29][30][31][32][33] Surface modication can change the internal electronic structure and remove structural defects of Si, which play important roles in tuning the emission wavelength and determining solubility and stability. 34 It should be further pointed out that based on the long radiative decay time of the electron-hole pairs, Si can exhibit nonlinear effects, which can lead to PL photodegradation, optically induced polarization anisotropy, and PL up-conversion in porous Si.…”

Femtosecond luminescence spectroscopy of core states in silicon nanocrystals

“…Characterization of Si NCs prepared by this method by means of FTIR spectroscopy, x-ray scattering, absorption (XAS), diffraction (XRD), emission (XES) and photoelectron spectroscopy (XPS) as well as atomic force (AFM) and scanning tunneling microscopy (STEM) can be found in Ref [18,19]. Optical properties of the alkylated Si NCs have been investigated in detail [17,20] together with possible application of the alkylated NCs as fluorescent labels [4] Another sample, hereafter denominated "OXS" (oxidized sample), was prepared via a long (120 minutes) etching by applying a low current density (1.6 mA/cm 2 ). The electrolyte comprised 50% HF(aq) in 4:10 volume ratio with ethanol.…”

“…The samples were excited by 355 nm nanosecond pulses to create e-h pairs energetically high above the bandgap. The time integration window (0-1 μs) was chosen to be long enough compared to excitation pulse length and at the same time short enough compared to typical lifetimes of the long-lived PL (21 μs for ALS [20], 5-10 μs for OXS [21]).…”

Endocytosis and Lack of Cytotoxicity of Alkyl-Capped Silicon Quantum Dots Prepared from Porous Silicon

“…The obvious disadvantages of this preparation method are the low quantity of material produced, typically 200 μg from a 1 cm2 Si chip, and the hazardous nature of the aqueous hydrogen fluoride (HF) etch. The major advantages are that the process starts from pure Si wafer and these alkyl SiQDs have been extensively characterized in our laboratories with respect to size, structure [15], chemical stability [16], photophysics [17,18,19] and their fluorescence intensity provides a quantitative measure of concentration [16]. Figure 1B illustrates the structure and dimensions of these alkyl SiQDs, which are used throughout this report.…”