Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N2 Gas Mixtures.

Anastasiya A Fronya,Andrei V Kabashin,Andrei V Muratov,Victor Yu Timoshenko,Alexander A Garmash,Yaroslava I Dombrovska,Sergey M Klimentov,Alexander Yu Kharin,Nikolay I Kargin,Sergey I Derzhavin,Sergey V Antonenko,Nikita V Karpov,Yury A Aleschenko

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.

Highlights

Nanostructured silicon (Si) has attracted a lot of attention for the last couple of decades due to a series of unique properties opening up avenues for diverse applications [1,2,3]
Porous silicon technology based on electrochemical etching of crystalline Si (c-Si) wafers in hydrofluoric acid solutions presents a straightforward way to form such quantum dots (QDs), while a hydroxyl-based passivation of the nanocrystals offered by the combination of hydrogenation and oxidation ensures a good dispersion of Si-QDs in aqueous solutions [2,4,5]
We demonstrated the possibility of the preparation of quantum dots for bioimaging on the basis of the as formed Si nanocrystals

Summary

Introduction

Nanostructured silicon (Si) has attracted a lot of attention for the last couple of decades due to a series of unique properties opening up avenues for diverse applications [1,2,3]. The bioimaging functionality of Si-NPs typically relies on photoluminescence (PL) of quantum-confined excitons in Si nanocrystals and/or defect-related states [4,15] that makes possible an efficient light emission in the region of relative transparency of biotissues (600–850 nm). To enable highly emissive Si-based quantum dots (QDs), one has to form high quality nanocrystals and properly passivate them in order to remove non-radiative centers [16,17]. Porous silicon technology based on electrochemical etching of crystalline Si (c-Si) wafers in hydrofluoric acid solutions presents a straightforward way to form such QDs, while a hydroxyl-based passivation of the nanocrystals offered by the combination of hydrogenation and oxidation (during synthesis and subsequent storage in air, respectively) ensures a good dispersion of Si-QDs in aqueous solutions [2,4,5]. Porous silicon structures can be contaminated by acid derivatives [18], which complicates biological prospects of such

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Results

Conclusion