Spectroscopic evidence of preferential excitation of interfacial EuIII by interfacial energy transfer process on core@shell nanoparticles

The hierarchical core@shell nanostructure in upconversion nanoparticle (UCNP) has allowed high intensities of upconversion emission by interfacial energy transfer (IET) mechanism, which can also account for high down-shifting emission intensities observed for core@shell nanostructures. It is well accepted that the emission of active ions, sensitized by IET is originated from ions located into narrow core@shell interface, which has been shown by physically separation of donor and acceptor ions in the core@shell nanostructure. Herein we have spectroscopic proof of the preferential sensitization of the ions into the core@shell interface by IET. We have analyzed the excitation and emission spectra profiles of the Eu-III sensitized by Gd-III ions on hierarchically structured beta-NaYF4 nanoparticles. In this work, Eu-III emission occurs through a downshifting mechanism that is like the last step of the energy transfer pathway from Gd-III to active ions in nanostructured UCNPs as part of a known UC-IET processes. Photophysical results indicate that IET sensitizes mainly the Eu-III ions located at the core@shell interface, where these ions experience a variety of distorted chemical environments. Such a non-symmetrical electrical fields results in an inomogeneous broadening of D-5(0) -> F-7(2) transition emission band. The preferential, but not unique, sensitization of Eu-III ions by energy transfer from Gd-III ions located at distorted interface may shine light on the upconversion emission bands intensities observed in several works describing the IET in UCNPs and spectrocopically confirms that Gd-III-mediated emission occurs spatially in a narrow core@shell interfacial region.

Automated summary

The study analyzed the excitation and emission spectra profiles of Eu-III sensitized by Gd-III ions in hierarchical structured beta-NaYF4 nanoparticles, indicating preferential sensitization of Eu-III ions at the core@shell interface by IET. This preferential sensitization may help explain the upconversion emission bands intensities observed in UCNPs and confirms that Gd-III-mediated emission occurs spatially in a narrow core@shell interfacial region.