A strategy to prepare highly redispersible and strongly luminescent α-NaYF4:Eu3+ hybrid nanostructures with multi-channel excitation

Abstract

Rare earth doped NaYF₄ nanocrystals have received intensive attention in recent years because of their unique luminescence properties as a result of their very low phonon energy. However, their luminescence is largely limited by the low optical absorption of rare earth ions. This paper presents a novel strategy to prepare highly dispersible and strongly luminescent Eu³⁺ doped α-NaYF₄ (α-NaYF₄:Eu³⁺) nanocrystals, which can be intensely excited via multi-channel optical absorption. Highly dispersible α-NaYF₄:Eu³⁺ nanocrystals are synthesized using a solvothermal method, and they are coated with a SiO₂ layer to form the α-NaYF₄:Eu³⁺@SiO₂ core–shell nanostructures. These α-NaYF₄:Eu³⁺@SiO₂ core–shell nanostructures are thermally annealed and the SiO₂ shell is then removed to obtain the annealed α-NaYF₄:Eu³⁺ nanocrystals with strong O²⁻→Eu³⁺ charge transfer excitation. Luminescence of the α-NaYF₄:Eu³⁺ nanocrystals is further enhanced by energy transfer of organic ligands after forming a type of inorganic–organic hybrid nanostructure. This strategy is also useful for developing other types of dispersible and strongly luminescent nanocrystals.