Towards pure near-infrared to near-infrared upconversion of multifunctional GdF_3:Yb^3+,Tm^3+ nanoparticles

Nearly pure near-infrared to near-infrared (NIR-to-NIR) upconversion in GdF(3) host with 23% Yb(3+) and 1% Tm(3+) under 980 nm excitation is firstly reported. The ratio of the intensity of the emission at 807 nm to that at 478 nm can reach to 105, and the intensity of the emission at 807 nm is preserved. Moreover, the excitation and the emission at 980 and 807 nm are away from the visible region. These are beneficial to deeper tissue penetration and reduced autofluorescence. Raman spectroscopy measurements suggest the high probability of NIR emission in GdF(3) host. Our results indicate that the reported multifunctional nanoparticles are promising in bio-imaging and bio-separation.