Origin of blue photoluminescence from colloidal silicon nanocrystals fabricated by femtosecond laser ablation in solution

Abstract

We present a detailed investigation into the origin of blue emission from colloidal silicon (Si) nanocrystals (NCs) fabricated by femtosecond laser ablation of Si powder in 1-hexene. High resolution transmission electron microscopy and Raman spectroscopy observations confirm that Si NCs with average size 2.7 nm are produced and well dispersed in 1-hexene. Fourier transform infrared spectrum and x-ray photoelectron spectra have been employed to reveal the passivation of Si NCs surfaces with organic molecules. On the basis of the structural characterization, UV-visible absorption, temperature-dependent photoluminescence (PL), time-resolved PL, and PL excitation spectra investigations, we deduce that room-temperature blue luminescence from colloidal Si NCs originates from the following two processes: (i) under illumination, excitons first form within colloidal Si NCs by direct transition at the X or Γ (Γ25 → Γ'2) point; (ii) and then some trapped excitons migrate to the surfaces of colloidal Si NCs and further recombine via the surface states associated with the Si-C or Si-C-H2 bonds.

Optical absorption and photoluminescence properties of Cucurbita maxima dye adsorption on TiO2 nanoparticles

“…Figure 4(c) shows that the photoluminescence peak at 726 nm disappeared. The disappearance of this photoluminescence peak may improve the optoelectronic performance of the solar cells [37][38][39].…”

Femtosecond laser-induced size reduction and emission quantum yield enhancement of colloidal silicon nanocrystals: effect of laser ablation time

“…Very recently, we successfully fabricated stable blueemitting colloidal Si NCs in 1-hexene through a femtosecond (fs) LAL technique and demonstrated that the surfaces of the colloidal Si NCs have been well passivated by carbon chains as confirmed by Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopy (XPS) spectra. The blue luminescence from colloidal Si NCs is attributed to the radiative recombination of the excitons formed at X or Γ (Γ 25→ Γ′ 2 ) point via the surface states associated with the Si-C or Si-C-H 2 bonds [14]. Then, we carried out investigation on the effect of laser fluence on the structure and optical properties of colloidal Si NCs fabricated in 1-octadecence using fs laser ablation under different laser fluences.…”

“…The preparation procedure of colloidal Si NC solution was described in detail in our previous works [14,15]. In brief, the laser ablation experiments were carried out by using a Ti:sapphire fs laser system operated at 800 nm, with a pulse duration, laser fluence and frequency of 100 fs, 1.0 mJ cm −2 and 80 MHz, respectively.…”

“…Figure 4(a) (left) displays the FTIR spectra for all the samples, which can firsthand reveal the surface chemical bonding configuration of the Si NCs. The absorption bands at 1364, 2850, 2925 and 2960 cm −1 are attributed to the symmetric C-H 3 stretching, symmetric C-H 2 stretching, asymmetric C-H 2 stretching and asymmetric C-H 3 stretching mode, respectively [14,22]. The absorption peaks at 670, 880, 1100 and 1460 cm −1 correspond to Si-C asymmetric vibration, Si-C symmetric vibration, Si-O-Si vibration and Si-CH 2 bending vibration, respectively [8,23].…”

“…The clear Si-C asymmetric stretching vibration centered at ∼670 cm −1 can be seen in figure 4(a) (right). The presence of Si-C bonds suggests that the surfaces of the Si NCs have been successfully passivated by carbon chains [14,23]. The appearance of Si-O-Si bonds suggests that the surfaces of the Si NCs have been partly oxidized by oxygen dissolved in solution [24].…”