Light converting Yb3+/Er3+ doped YVO4 nanoparticles for biological applications

We have synthesized luminescent YVO4: Yb, Er nanoparticles (NPs) in the size range of 10-700 nm. A bright green luminescence of the dry NPs powder due to Er3+ ions emission centered at 526 and 550 nm was compared for upconverting and downconverting laser excitations at 980 nm and 257 nm, respectively. Moreover, the NPs exhibited bright luminescence in colloidal water solution upon 980 nm laser irradiation. All experiments showed very weak radiative 4F9/2→4I15/2 emission from Er3+ ions at 660 nm that indirectly indicates low efficiency of multiphonon intraionic transitions and insensitivity of the NPs to the luminescence quenchers in the water solution. A broad red band in the luminescence spectrum appearing under intense 257 nm laser excitation can be attributed to emission from crystal lattice defects in the NPs. Based on these facts we propose that YVO4: Yb, Er NPs are promising as efficient upconversion fluorescent nanoprobes for certain biological applications, like optogenetics.