Preparation from a revisited wet chemical route of phase-pure, monocrystalline and SHG-efficient BiFeO3 nanoparticles for harmonic bio-imaging

Gareth Clarke,Andrii Rogov,Yannick Mugnier,Sarah Mccarthy,Luigi Bonacina,Yuri Volkov,Adriele Prina-Mello,Christine Galez,Ronan Le Dantec,Yurii Gun’Ko

doi:10.1038/s41598-018-28557-w

Abstract

We present two new synthetic routes for bismuth ferrite harmonic nanoparticles (BiFeO3 HNPs). Both phase-pure and mixed phase BiFeO3 materials were produced after improvement of the solvent evaporation and sol-gel combustion routes. Metal nitrates with a series of dicarboxylic acids (tartronic, tartaric and mucic) were used to promote crystallization. We found that the longer the carbon backbone with a hydroxyl group attached to each carbon, the lower the annealing temperature. We also demonstrate that nanocrystals more readily formed at a given temperature by adding glycerol but to the detriment of phase purity, whereas addition of NaCl in excess with mucic acid promotes the formation of phase-pure, monocrystalline nanoparticles. This effect was possibly associated with a better dispersion of the primary amorphous precursors and formation of intermediate complexes. The nanoparticles have been characterized by XRD, TEM, ζ-potential, photon correlation spectroscopy, two-photon microscopy and Hyper-Rayleigh Scattering measurements. The improved crystallization leads to BiFeO3 HNPs without defect-induced luminescence and with a very high averaged second harmonic efficiency (220 pm/V), almost triple the efficiency previously reported. This development of simple, scalable synthesis routes which yield phase-pure and, crucially, monocrystalline BiFeO3 HNPs demonstrates a significant advance in engineering the properties of nanocrystals for bio-imaging and diagnostics applications.

Highlights

We present two new synthetic routes for bismuth ferrite harmonic nanoparticles (BiFeO3 Harmonic Nanoparticle (HNP))
Applications using BiFeO3 HNPs are still limited by the difficulty in determining a facile, scalable synthesis route which yields nanoscale, monodisperse and monocrystalline nanoparticles
Carboxyl groups are required for complexing the Bi3+ and Fe3+ metal ions to obtain a homogeneous polyester precursor whereas hydroxyl groups are necessary for the subsequent polyesterification of the carboxyl groups

Summary

Introduction

We present two new synthetic routes for bismuth ferrite harmonic nanoparticles (BiFeO3 HNPs). We demonstrate that nanocrystals more readily formed at a given temperature by adding glycerol but to the detriment of phase purity, whereas addition of NaCl in excess with mucic acid promotes the formation of phase-pure, monocrystalline nanoparticles. The improved crystallization leads to BiFeO3 HNPs without defect-induced luminescence and with a very high averaged second harmonic efficiency (220 pm/V), almost triple the efficiency previously reported This development of simple, scalable synthesis routes which yield phase-pure and, crucially, monocrystalline BiFeO3 HNPs demonstrates a significant advance in engineering the properties of nanocrystals for bio-imaging and diagnostics applications. Applications in the biomedical field include deep-tissue imaging with second and third harmonic, for instance, as an unmet clinical challenge[26,27,28] To this end, the appealing optical and magnetic properties of BiFeO3 HNPs combined with its low cytotoxicity[29] have motivated this work. The key influence of NaCl and extra hydroxyl groups on the final nanoparticle size, polydispersity and crystallinity is investigated through XRD, TEM, magnetic measurements and assessment of the functional SHG response

Methods

Results

Conclusion