Abstract
Microwave assisted solvothermal method has been employed to synthesize multifunctional upconverting β-NaGdF4:Ln3+ and magnetic-upconverting Fe3O4/γ-Fe2O3@NaGdF4:Ln3+ (Ln = Yb and Er) nanoparticles. The powder x-ray diffraction data confirms the hexagonal structure of NaGdF4:Ln3+ and high resolution transmission electron microscopy shows the formation of rod shaped NaGdF4:Ln3+ (∼ 20 nm) and ovoid shaped Fe3O4/γ-Fe2O3@NaGdF4:Ln3+ (∼ 15 nm) nanoparticles. The magnetic hysteresis at 300 K for β-NaGdF4:Ln3+ demonstrates paramagnetic features, whereas iron-oxide@β-NaGdF4:Ln3+ exhibits superparamagnetic behavior along with a linear component at large applied field due to paramagnetic NaGdF4 matrix. Both nanoparticle samples provide an excellent green emitting [(2H11/2, 4S3/2)→4I15/2 (∼ 540 nm)] upconversion luminescence emission under excitation at 980 nm. The energy migration between Yb and Er in NaGdF4 matrix has been explored from 300-800 nm. Intensity variation of blue, green and red lines and the observed luminescence quenching due to the presence of Fe3O4/γ-Fe2O3 in the composite has been proposed. These kinds of materials contain magnetic and luminescence characteristics into single nanoparticle open new possibility for bioimaging applications.
Highlights
INTRODUCTIONLanthanide (Ln3+) doped rare earth fluoride upconversion (UC) nanoparticles absorb near–
For the last two decades, scientific and industrial interest in developing materials has culminated multiple times especially in the preparation of quality materials with enhanced multifunctionality at nanoscale.[1,2,3,4] For instance, the nanocomposites containing luminescent and magnetic characteristics are trending in a wide range of applications, such as bioimaging, diagnostic, and therapeutics
A small application oriented work has been performed combining iron oxide with luminescent materials due to the so called quenching effect induced by semimetallic Fe3O4 during simultaneous optical excitation/emission with applied external magnetic field.[5,6,7]. These multifunctional nanoparticles can serve as luminescent markers; they can be controlled by an external magnetic field.[8]
Summary
Lanthanide (Ln3+) doped rare earth fluoride upconversion (UC) nanoparticles absorb near–. UC nanoparticles exhibit paramagnetism at room temperature and they can efficiently alter the spin– spin relaxation time of surrounding water protons because Gd possesses seven unpaired electrons.[13] Gd3+ containing rare earth fluoride UC luminescence nanomaterials have been developed as potential T1–weighted MR imaging contrast agents in biomedical applications and are being explored.[5,14]. We focus on the changes of the intensity of emission peaks with lifetime variation in these two bifunctional nanomaterials and provide direct evidence of quenching induced by magnetite/maghemite phase. XRD, HRTEM, photoluminescence and dc magnetization measurements. These investigating techniques suggest a comparative approach to understand two different templates of magnetic-luminescent nanoparticles
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