Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N 2 Gas Mixtures

Molecules. 2020 Jan 21;25(3):440. doi: 10.3390/molecules25030440.

Abstract

Using methods of pulsed laser ablation from a silicon target in helium (He)-nitrogen (N2) gas mixtures maintained at reduced pressures (0.5-5 Torr), we fabricated substrate-supported silicon (Si) nanocrystal-based films exhibiting a strong photoluminescence (PL) emission, which depended on the He/N2 ratio. We show that, in the case of ablation in pure He gas, Si nanocrystals exhibit PL bands centered in the "red - near infrared" (maximum at 760 nm) and "green" (centered at 550 nm) spectral regions, which can be attributed to quantum-confined excitonic states in small Si nanocrystals and to local electronic states in amorphous silicon suboxide (a-SiOx) coating, respectively, while the addition of N2 leads to the generation of an intense "green-yellow" PL band centered at 580 nm. The origin of the latter band is attributed to a radiative recombination in amorphous oxynitride (a-SiNxOy) coating of Si nanocrystals. PL transients of Si nanocrystals with SiOx and a-SiNxOy coatings demonstrate nonexponential decays in the micro- and submicrosecond time scales with rates depending on nitrogen content in the mixture. After milling by ultrasound and dispersing in water, Si nanocrystals can be used as efficient non-toxic markers for bioimaging, while the observed spectral tailoring effect makes possible an adjustment of the PL emission of such markers to a concrete bioimaging task.

Keywords: bioimaging; photoluminescence; pulsed laser ablation in gases; pulsed laser deposition; quantum confinement; silicon nanoparticles; silicon oxynitride; silicon quantum dots.

MeSH terms

  • Helium / chemistry*
  • Lasers*
  • Luminescent Measurements*
  • Nanoparticles / chemistry*
  • Nanoparticles / ultrastructure
  • Nitrogen / chemistry*
  • Pressure
  • Silicon / chemistry*
  • Spectroscopy, Fourier Transform Infrared
  • Spectrum Analysis, Raman

Substances

  • Helium
  • Nitrogen
  • Silicon