Deep tumor imaging by upconversion nanoparticles Nataly Sholina, Polina Demina, Dmitry Khochenkov, Alla Generalova, Andrey Nechaev and Eugeny Khaydukov EPJ Web Conf., 190 (2018) 04020 Published online: 26 September 2018 DOI: 10.1051/epjconf/201819004020