The Effect of Nd³⁺ Concentration on Upconversion Luminescence in Yb³⁺/Tm³⁺/Nd³⁺ Tripledoped β-NaGdF₄ Nanocrystals

Nd³⁺-doped NaGdF₄: Yb, Tm nanocrystals were synthesized by an improved high-temperature thermal decomposition method, and the effects of doping concentrations on the crystal structure, phase composition, and upconverted fluorescence intensity were also investigated. The results reveal that the introduction of Nd³⁺ ions does not cause the transformation of the crystal phase, but induce the change of the unit cell parameters. Meanwhile, the fluorescence intensity of the synthesized nanocrystals when co-doped with 3 mol% Nd³⁺ is the strongest under the excitation of 980 nm laser, which is 3.9 times that of the Nd³⁺-free doped nanoparticles, and the average size is 62.9 nm. And it is located in the blue area of the CIE coordinate diagram, and the corresponding color purity is 91.81% under the same experimental conditions. The resulting nanocrystals show the potential as excellent fluorescence labeling and in vivo imaging probes.