Understanding the Parameters Affecting the Photoluminescence of Silicon Nanoparticles

Abstract

Silicon nanoparticles of 1–5 nm size (SiNPs) were synthesized by a bottom-up (BU) approach involving a chemical wet method. The contribution of different emitters to the overall excitation–emission matrix was analyzed on the assumption that pure substances existing in a unique form show an excitation wavelength-invariant emission spectrum. The occurrence of emitters differing in size and aggregation was supported by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), time-resolved single photon counting, and time-resolved anisotropy experiments. The effect on photoluminescence (PL) of the particle surface oxidation as a result of aging is studied and compared to that of surface oxidized particles obtained by a top-down (TD) approach following an electrochemical method with HF etching. Surface oxidation to SiO x seems to introduce two different effects on the SiNP PL. An emission originated in surface states associated to SiO x was identified and observed for SiNPs synthesized by both BU and TD approaches. Blue-shifted excitation–emission spectra associated to a silicon core in embedded SiO x nanostructures were also identified. Theoretical studies were carried out to help understand the observed results.

White-blue electroluminescence from a Si quantum dot hybrid light-emitting diode

“…33 As for the oxygen passivation observed by the IR analysis, 21 it would be most probably a negligible role for the present luminescence. This is because the luminescence due oxygen-related surface states has been reported as the independence of the excitation wavelength, 25,[31][32][33] whereas the present PL data shows the dependence of excitation wavelength, as displayed in Fig. 1(c).…”

“…Blue-green PLs (2.4-3.4 eV) of Si nanostructured materials have been extensively investigated by experimental and theoretical approaches and ascribed to an intrinsic interband transition of Si core by quantum confinement effect or an extrinsic transition due to defective surface. [27][28][29][30][31][32] For the case of the present system, Figure 1(c) shows the PL-peak shifted by the excitation wavelength, whose phenomena have been attributed to various band-gap energies with a size distribution of QDs. [26][27][28][29][32][33][34] The present PL band of 3.1 eV is in good agreement with the energy of direct transition calculated at the U-point of Si nanocluster.…”

“…[27][28][29][30][31][32] For the case of the present system, Figure 1(c) shows the PL-peak shifted by the excitation wavelength, whose phenomena have been attributed to various band-gap energies with a size distribution of QDs. [26][27][28][29][32][33][34] The present PL band of 3.1 eV is in good agreement with the energy of direct transition calculated at the U-point of Si nanocluster. 35 In addition, we observed the band-gap energy of 3.1 eV as the direct transition, according to the analysis of the electronic absorption spectrum of Si QD solution, as shown in Figure S4.…”

Colloidal silicon quantum dots: from preparation to the modification of self-assembled monolayers (SAMs) for bio-applications

“…Despite the enormous efforts dedicated to methods of preparing and surface modifying silicon nanocrystals, much fewer studies have been focused on the relationship between the optical response and surface chemistries. 42,[189][190][191][192] There has been general agreement that quantum confinement, or particle size in this context, is a critical factor affecting wavelength of emission for all quantum dots. Surprisingly, silicon nanocrystals fabricated via etching methods usually emit in the red end of the visible spectrum, 38,167 whereas those prepared by solution reduction methods often emitted blue or green colour which appeared to be independent of particle size.…”

Size Controlled Synthesis of Silicon Nanocrystals within Inverse Micelles

“…Research interest in the preparation of oxide-free Si NCs has been steadily increasing, because the momentum requirements due to the indirect band gap structure of bulk Si are relaxed in the 1−5 nm size range as a result of quantum confinement effects. [1][2] This allows for their excellent photophysical properties, such as size-tunable and narrow luminescence and high quantum yields, to be combined with the richness of silicon surface chemistry. A large variety of both physical and chemical methods have been reported for the preparation of Si NCs, including physical and chemical vapor deposition, thermal annealing, laser induced-heating of gaseous precursors, electrochemical etching of crystalline silicon wafers, thermal decomposition of silane precursors and the reduction of silicon halides by various reducing agents.…”