Colloidal lanthanide-doped NaLuF4:Ln3+ nanocrystals: Synthesis, energy transfer, and tunable luminescence properties

Colloidal NaLuF4:Ln3+ (Ln = Yb/Er, Yb/Gd/Tm, and Gd/Eu) nanocrystals were synthesized by a hydrothermal method. The effects of NaF/Ln(NO3)3 ratio on the phase compositions, morphologies, and luminescence properties of NaLuF4:Ln3+ nanocrystals were investigated in detail. The results indicated that larger NaF/Ln(NO3)3 ratio is benefit for the formation of hexagonal phase NaLuF4:Ln3+. Multicolor up-conversion luminescence tuning of NaLuF4:Ln3+ nanocrystals was successfully achieved by adjusting lanthanide-ion-doped content. Especially, the 6P7/2 → 8S7/2 (∼313 nm) transition from Gd3+ ions was observed in NaLuF4:Yb3+/Gd3+/Tm3+ nanorods under 980 nm excitation. Decay dynamics was performed to study the down-conversion luminescence properties of the NaLuF4:Gd3+/Eu3+ nanorods. All the decay curves can be well fitted with a second order exponential decay function.