Control of particle size in flame spray pyrolysis of Tb-doped Y₂O₃ for bio-imaging

Recently, the use of oxide-based nanomaterials for bio-imaging has received great attention owing to their remarkable stabilities as compared to those of conventional organic dyes. Therefore, the development of scalable methods for highly luminescent oxide materials with fine control of size has become crucial. In this study, we suggested modified flame spray pyrolysis (FSP) as a scalable method to produce a green-light emitting phosphor-Tb-doped Y₂O₃-in the nanometer size range. In our FSP method, an alkali salt (NaNO3) was found to be highly effective as a size-controlling agent when it is simply mixed with other metal nitrate precursors. The FSP of the mixture solution resulted in oxide composites of Y₂O₃:Tb³⁺ and Na_xO. However, the sodium by-product was easily removed by washing with water. This salt-assisted FSP produced nano-sized and well-dispersed Y₂O₃:Tb³⁺ nanoparticles; their crystallinity and luminescence were higher than those of the bulk product made without the addition of the alkali salt. The nanoparticle surface was further coated with silica for biocompatibility and functionalized with amino groups for the attachment of biological molecules.