Surface ligand-mediated phase and upconversion luminescence tuning of multifunctional NaGdF4:Yb/Er materials with paramagnetic and cathodoluminescent characteristics

NaGdF4:18%Yb/2%Er phosphors with tunable upconversion (UC) photoluminescence (PL), cathodoluminescence (CL) and paramagnetic properties are synthesized by a facile and low temperature solvothermal method. Organic compounds of 3-mercaptopropionic acid (3MPA), polyethylene glycol (PEG) and polyethylenimine (PEI) have been used as capping agents to coordinate the growth of NaGdF4:18%Yb/2%Er phosphors. The results reveal that a novel simultaneous control of crystal phases and UC emission colors can be readily realized by using 3MPA, PEG and PEI surface modifications. The red to green UC emission ratio is tuned from 7.323 (red) to 0.857 (green). The variation in the UC emission ratio is attributed to the presence of surface ligands, structural and morphological change. In addition, the as-synthesized phosphors present additional paramagnetic behavior with magnetic mass susceptibility of 8.36 × 10-5emu/g Oe and peak magnetization of 1.538 emu/g. Moreover, intense CL emission is detected under the irradiation of low voltage electron beam. Owing to the tunable UC luminescence colors, CL emission, and paramagnetic characteristics, the phosphors have high potential to be used in lightings, anti-fake labeling systems and field-emission displays.