Realizing efficient upconversion and down-shifting dual-mode luminescence in lanthanide-doped NaGdF4 core–shell–shell nanoparticles through gadolinium sublattice-mediated energy migration

• NaGdF4:Yb/Tm@NaGdF4:Ce/Ln@NaYF4 multishell nanoparticles were prepared.
• Upconversion and down-shifting dual-model luminescence was observed.
• The mechanisms responsible for dual-model luminescence were proposed.

Monodisperse rod-like colloidal core–shell–shell NaGdF4:Yb/Tm@NaGdF4:Ce/Ln@NaYF4 (Ln = Tb, Eu, Dy and Sm) nanoparticles (25 nm in diameter and 37 nm in length) have been successfully synthesized through a facile wet chemical method. X-ray diffraction, transmission electron microscopy, upconversion and down-shifting photoluminescence were used to characterize the samples. The prepared nanoparticles exhibited both tunable upconversion and down-shifting emissions from Tb, Eu, Dy and Sm activators under 980 nm near-infrared and 254 nm ultraviolet excitation, respectively. The dual-model luminescence was achieved through gadolinium (Gd3+) sublattice-mediated energy migration: Yb3+ → Tm3+→n(Gd3+) → Ln3+ and Ce3+ → n(Gd3+)→Ln3+ energy-transfer process, respectively. The advances on these dual-mode luminescent nanoparticles offer exciting opportunities for developing multifunctional optical nanoprobes for biological applications.

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