Hydrothermal Synthesis and Properties of Yb/Tm Doped SrLaF Upconversion Nanoparticles.

We report the procedure for hydrothermal synthesis of ultrasmall Yb/Tm co-doped SrLaF (SLF) upconversion phosphors. These phosphors were synthesized by varying the concentrations of Yb (x = 10, 15, 20, and 25 mol%) and Tm (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 and Tm occupy the La sites in the SLF host. The addition of Yb/Tm 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/Tm co-doped SLF are 20 mol% Yb and 1 mol% Tm with EDTA as the chelating agent. Under 980 nm light excitation, a strong upconversion emission of Tm ions around 800 nm was achieved. In addition, the experimental photoluminescence lifetime of Tm emission in the SLF host is reported. This study discovered that efficient near IR emission from ultrasmall Yb/Tm co-doped SLF phosphors may have potential applications in the fields of fluorescent labels in bioimaging and security applications.