Hydrothermal Synthesis and Properties of Yb(3+)/Tm(3+) Doped Sr(2)LaF(7) Upconversion Nanoparticles

We report the procedure for hydrothermal synthesis of ultrasmall Yb(3+)/Tm(3+) co-doped Sr(2)LaF(7) (SLF) upconversion phosphors. These phosphors were synthesized by varying the concentrations of Yb(3+) (x = 10, 15, 20, and 25 mol%) and Tm(3+) (y = 0.75, 1, 2, and 3 mol%) with the aim to analyze their emissions in the near IR spectral range. According to the detailed structural analysis, Yb(3+) and Tm(3+) occupy the La(3+) sites in the SLF host. The addition of Yb(3+)/Tm(3+) ions has a huge impact on the lattice constant, particle size, and PL emission properties of the synthesized SLF nanophosphor. The results show that the optimal dopant concentrations for upconversion luminescence of Yb(3+)/Tm(3+) co-doped SLF are 20 mol% Yb(3+) and 1 mol% Tm(3+) with EDTA as the chelating agent. Under 980 nm light excitation, a strong upconversion emission of Tm(3+) ions around 800 nm was achieved. In addition, the experimental photoluminescence lifetime of Tm(3+) emission in the SLF host is reported. This study discovered that efficient near IR emission from ultrasmall Yb(3+)/Tm(3+) co-doped SLF phosphors may have potential applications in the fields of fluorescent labels in bioimaging and security applications.