Probing the optical and magnetic modality of multi core-shell Fe3O4@SiO2@β-NaGdF4:RE3+ (RE = Ce, Tb, Dy) nanoparticles

Abstract

A robust yellowish-green emitting multi core-shell Fe3O4@SiO2@β-NaGdF4:RE3+ (RE = 5% Ce, 5% Tb, x% Dy; x = 1, 5 and 10 mol.%) nanoparticles (NPs) containing both magnetic and luminescence modalities, are synthesized using simple, fast and efficient microwave-assisted hydrothermal method. The Rietveld analysis of X-ray diffraction and high-resolution transmission electron microscopy provides an average crystallite size of ∼30 nm, confirming the successful coating of the β-NaGdF4 hexagonal phase over Fe3O4. The detailed photoluminescence investigation suggests a down-converting energy transfer process, Ce3+→Gd3+→Tb3+↔ Dy3+ in which Gd3+ ions play a significant intermediate role assisted by Tb3+. The excitation spectra consist of dominant broadband at ∼252 nm due to Ce3+ (4f–5d), two sharp lines at ∼ 271 nm, and ∼311 due to Gd3+ (8S7/2→6IJ and 6PJ), and frail f−f transitions due to Tb3+ and Dy3+ ions. The excitation at ∼252 nm fetches weak and sharp emission of Gd3+ ions at 310 nm, weak broad emission of Ce3+ (300–400 nm), and strong emission color lines of RE3+ (400–700 nm) due to characteristic transitions of Tb3+ (5D4→7FJ, J = 6–3), and Dy3+ (4F9/2–6H15/2, 6H13/2), respectively. The quenching phenomenon is observed due to concentration, and back transfer energy is proposed. The magnetic hysteresis loops display superparamagnetic behavior at 300 K and ferromagnetic ordering at 2 K with a remarkable difference in their magnetization values and confirming the blocking temperatures around physiological temperature ranges. The magneto-luminescence characteristics of the bifunctional system can be easily manipulated under an external magnetic field and suggest an efficient candidate for hybrid medical imaging such as MRI plus X-ray imaging and radiation detection.