The effect of surface ligand, solvent and Yb3+ co-doping on the luminescence properties of Er3+ in colloidal NaGdF4 nanocrystals

Abstract

The emission properties of NaGdF₄ nanoparticles (NPs) doped with Er³⁺ and/or Yb³⁺ ions and their colloidal dispersions in different solvents were investigated. The organic ligands present on the surface of the NPs decrease the decay time of Er³⁺ emission. In contrast, virtually no change in decay times was observed after dispersing the NPs in solvents. Both surface ligands and solvent molecules exert a pronounced effect on the intensity ratio of the ²H_11/2 + ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions. Co-doping with Yb³⁺ is revealed as another important factor influencing the relative intensities of Er³⁺ emission bands. The influence of surface ligands and solvent molecules on emission spectra upon NIR excitation at 980 nm was investigated. The decay times of Er³⁺ emission were longer for Yb³⁺ co-doped NPs than for analogous NPs single doped with Er³⁺. This is ascribed to a feedback energy transfer process between Yb³⁺ and Er³⁺.