Near infrared emission properties of Er doped cubic sesquioxides in the second/third biological windows

In the recent years, there is an extensive effort concentrated towards the development of nanoparticles with near-infrared emission within the so called second or third biological windows induced by excitation outside 800–1000 nm range corresponding to the traditional Nd (800 nm) and Yb (980 nm) sensitizers. Here, we present a first report on the near-infrared (900–1700 nm) emission of significant member of cubic sesquioxides, Er-Lu(2)O(3) nanoparticles, measured under both near-infrared up-conversion and low energy X-ray excitations. The nanoparticle compositions are optimized by varying Er concentration and Li addition. It is found that, under ca. 1500 nm up-conversion excitation, the emission is almost monochromatic (>93%) and centered at 980 nm while over 80% of the X-ray induced emission is concentrated around 1500 nm. The mechanisms responsible for the up-conversion emission of Er - Lu(2)O(3) are identified by help of the up-conversion emission and excitation spectra as well as emission decays considering multiple excitation/emission transitions across visible to near-infrared ranges. Comparison between the emission properties of Er-Lu(2)O(3) and Er-Y(2)O(3) induced by optical and X-ray excitation is also presented. Our results suggest that the further optimized Er-doped cubic sesquioxides represent promising candidates for bioimaging and photovoltaic applications.