Heterogeneity in optical properties of near white-light emissive europium complex species revealed by spectroscopy of single nanoaggregates

Tailoring the Design of a Lanthanide Complex/Magnetic Ferrite Nanocomposite for Efficient Photoluminescence and Magnetic Hyperthermia Performance

In this work, we have designed a magnetoluminescent nanocomposite as a single platform for optical imaging and safe magnetic hyperthermia therapy by optimizing the composition of magnetic nanoparticles and controlling the conjugation strategy of the luminescent lanthanide complex. We have synthesized Co_xMn_1-xFe₂O₄ nanoferrites, with x = 0 to 1 in 0.25 steps, from soft (MnFe₂O₄) to hard (CoFe₂O₄) ferrites of size (∼20 nm) following a one-pot oxidative hydrolysis method. We have performed the induction heating study with an aqueous dispersion of nanoferrites using an alternating magnetic field (AMF) of 12 kAm^-1, 335 kHz. This shows an enhancement of heating efficiency with the increment of manganese content and attains the highest intrinsic loss power (ILP) of 6.47 nHm² kg^-1 for MnFe₂O₄ nanoparticles. We have then fabricated a magnetoluminescent nanocomposite employing MnFe₂O₄ nanoparticles as it shows outstanding heating performance within the threshold limit of AMF (≤5 × 10⁹ Am^-1 s^-1). A layer-by-layer coating strategy is followed, where a pure silica coating of thickness ∼10 nm on MnFe₂O₄ nanoparticles is achieved before encapsulation of the luminescent complex of europium(III), 2-thenoyltrifluoroacetone, and 1,10-phenanthroline in the second layer of silica. This is to ensure the optimal distance between the magnetic core and Eu(III)-complex to pertain significant luminescence in the composite (Eu-MnFe₂O₄). The photoluminescence spectra of an aqueous dispersion of Eu-MnFe₂O₄ by excitation in the UV region show a narrow and strong emission at 612 nm, which is stable even after 72 h. The induction heating study of an aqueous dispersion of Eu-MnFe₂O₄ in 12 kAm^-1, 335 kHz AMF shows an ILP as 4.02 nHm² kg^-1, which is remarkably higher than the hyperthermia efficiency of reported magnetoluminescent nanoparticles.