Silica-coated upconversion lanthanide nanoparticles: The effect of crystal design on morphology, structure and optical properties.

Uliana Kostiv,Hana Engstová,Miroslav Šlouf,Petr Ježek,Hana Macková,Katarína Smolková,Daniel Horák,Alexander Zhigunov

doi:10.3762/bjnano.6.235

Abstract

NaYF4:Yb3+/Er3+ nanoparticles were synthesized by thermal decomposition of lanthanide trifluoroacetates using oleylamine (OM) as both solvent and surface binding ligand. The effect of reaction temperature and time on the properties of the particles was investigated. The nanoparticles were characterized by transmission electron microscopy (TEM), electron diffraction (ED), energy dispersive spectroscopy (EDX), dynamic light scattering (DLS), thermogravimetric analysis (TGA), elemental analysis and X-ray diffraction (XRD) to determine morphology, size, polydispersity, crystal structure and elemental composition of the nanocrystals. TEM microscopy revealed that the morphology of the nanoparticles could be fine-tuned by modifying of the synthetic conditions. A cubic-to-hexagonal phase transition of the NaYF4:Yb3+/Er3+ nanoparticles at temperatures above 300 °C was confirmed by both ED and XRD. Upconversion luminescence under excitation at 980 nm was observed in the luminescence spectra of OM–NaYF4:Yb3+/Er3+ nanoparticles. Finally, the OM–NaYF4:Yb3+/Er3+ nanoparticles were coated with a silica shell to enable further functionalization and increase biocompatibility and stability in aqueous media, preventing particle aggregation.

Highlights

Due to their unique physicochemical properties, nanometerscale materials are finding widespread applications as drug delivery systems in the diagnosis and treatment of various diseases [1,2]
To prepare NaYF4:Yb3+/Er3+ nanoparticles with a hexagonal unit cell, lanthanide trifluoroacetates were decomposed in OM, serving as both solvent and surface binding ligand [20]
Because the particle size plays a key role in biomedical applications, e.g., for internalization of nanoparticles by cells of the reticuloendothelial system [32], the effects of both reaction temperature and time were investigated to control morphology, particle size and crystallinity

Summary

Introduction

Due to their unique physicochemical properties, nanometerscale materials are finding widespread applications as drug delivery systems in the diagnosis and treatment of various diseases [1,2]. Upconversion particles are typically prepared in different morphologies, sizes and shapes with high surface areas to efficiently conjugate target ligands and drugs [23]. Dn: number-average diameter (TEM); PDI: polydispersity index (TEM); Dh: hydrodynamic diameter (DLS); PI: polydispersity (DLS); L: average crystallite size (XRD); C: carbon content; N: nitrogen content; TGA: thermogravimetric analysis; I545/I660: characteristic upconversion ratio.

Results

Conclusion