Rare Earth Doping in Inorganic Material Nanostructures

Metal oxides, metal fluorides, metal oxofluorides, metal oxysulfides, metal oxysalts, and inorganic minerals can all serve as matrices for doping with rare earth elements.
Rare Earth Compounds: The physicochemical properties of lanthanide rare earth elements are very similar, making rare earth compounds ideal matrices for doping.
(1) Rare Earth Fluorides and Rare Earth Tetrafluorides: Rare earth fluorides are favored due to their mild synthesis conditions, good photostability, and low phonon energy. Early research on rare earth fluorides focused on the easily synthesized LaF3 and GdF3, followed by multicomponent fluorides such as NaxScF3+x, KSc2F7, BaYF5, BaGdF5, KYb2F7, K2GdF5, and NaLaF4. Currently, research has shifted towards tetrafluorides (LiLnF4, NaLnF4, KLnF4; Ln = Y, Gd, Lu), not only because of their well-established synthesis conditions but also due to their superior luminescent properties, particularly in upconversion luminescence. High-quality rare earth nanocrystals are typically synthesized in organic solvents at high temperatures (250-300 °C), using common solvents like 1-octadecene combined with oleic acid or oleylamine as synthesis ligands. The reaction involves the co-precipitation of metal oleate precursors with fluorides and the thermal decomposition of metal trifluoroacetates. Among these, the hexagonal crystal phase NaYF4 is regarded as the most efficient matrix for achieving upconversion luminescence upon doping. The doped matrix can effectively achieve the substitution of doping ions through ion exchange strategies, thereby altering luminescent properties. On the other hand, the core-shell structure strategy can effectively enhance the luminescent performance of nanocrystals by eliminating non-radiative transition-induced luminescence quenching at the surface of fluoride nanocrystals. For core-shell nanoparticles, the surface passivation efficiency is positively correlated with the thickness of the shell layer, and the luminescent intensity typically saturates at a critical shell thickness, where surface quenching is sufficiently suppressed.
(2) Rare Earth Oxofluorides: The excitation and energy transfer of doped rare earth ions are largely influenced by the matrix materials. In recent years, rare earth oxofluorides have also garnered widespread attention, such as EuOF, GdOF, Y6O5F8, Yb6O5F8, and Lu6O5F8.


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