Browsing by Author "Luo, Zhiping"

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    Probing the optical and magnetic modality of multi core-shell Fe3O4@SiO2@?-NaGdF4:RE3+ (RE = Ce, Tb, Dy) nanoparticles
    (Elsevier B.V., 2023-02-22T00:00:00) Shrivastava, Navadeep; Ospina, Carlos; Jacinto, Carlos; de Menezes, Alan S.; Muraca, Diego; Javed, Yasir; Knobel, Marcelo; Luo, Zhiping; Sharma, Surender Kumar
    A robust yellowish-green emitting multi core-shell Fe3O4@SiO2@?-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 ?-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. � 2023 Elsevier B.V.