Shape controllable synthesis and enhanced upconversion photoluminescence of β-NaGdF₄:Yb³⁺, Er³⁺ nanocrystals by introducing Mg²⁺

Different concentrations of Mg²⁺-doped hexagonal phase NaGdF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) were synthesized by a modified solvothermal method. Successful codoping of Mg²⁺ ions in upconversion nanoparticles (UCNPs) was supported by XRD, SEM, EDS, and PL analyses. The effects of Mg²⁺ doping on the morphology and the intensity of the upconversion (UC) emission were discussed in detail. It turned out that with the concentration of Mg²⁺ increasing, the morphology of the nanoparticles turn to change gradually and the UC emission was increasing gradually as well. Notably the UC fluorescence intensities of Er³⁺ were gradually improved owing to the codoped Mg²⁺ and then achieved a maximum level as the concentration of Mg²⁺ ions was 60 mol% from the amendment of the crystal structure of β -NaGdF₄:Yb³⁺, Er³⁺ nanoparticles. Moreover, the UC luminescence properties of the rare-earth (Yb³⁺, Er³⁺ ions codoped NaGdF4 nanocrystals were investigated in detail under 980-nm excitation.