Shape controllable synthesis and enhanced upconversion photoluminescence of ${{\beta }}$-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.