Synthesis and luminescence properties of NaGdF4: Yb3+, Ce3+, and Ho3+ upconversion nanoparticles doped with Zn2+

Abstract

Improving luminescence intensities of rare-earth (RE)-doped upconversion nanoparticles (UCNPs) have aroused great attention recently. In this study, NaGdF₄: Yb³⁺, Ce³⁺, and Ho³⁺ UCNPs doped with varying concentrations of Zn²⁺ were synthesized in one step by high temperature pyrolysis using oleate chemicals. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ICP-MS (inductively coupled plasma-mass spectrometry), upconversion emission spectra and luminescence lifetimes were used to study the samples. It was found that as the concentration of Zn²⁺ increased from 0 to 15 mol%, the luminescence intensities of both red and green emissions first increased and then decreased, with the maximum value of Zn²⁺ doping at 10 mol%. We concluded that Zn²⁺ dopant and F⁻ vacancies accounted for the intensity changes. Our research can be beneficial for the structural design and applications of RE-doped UCNPs.