Shortwave-infrared emitters for biological imaging based on Yb-Er-Tm and Yb-Er-Ho tridoped core-shell NaGdF4 nanoparticles

The use of shortwave-infrared radiation (1-2 μm spectral range) opened an opportunity for deep biotissue imaging due to low absorption and scattering in this range. The shortwave-infrared emitters based on Yb-Er-Tm and Yb-Er-Ho tridoped core-shell NaGdF4 nanoparticles were studied in this work. The ability to tune the luminescence intensity in 1000-1600 nm range by changing the rare-earth ions concentration ratio was shown. The energy transfer processes between rare-earth ions and their influence on each luminescence band and integral intensities were studied. Optimal rare-earth ions concentrations to obtain shortwave-infrared emitters with several intense luminescence bands were chosen. It was shown that coating of nanoparticles with passive shell effectively prevents the quenching of their luminescence in biological media.