SEARCH Articles Figures Tables Activators, upconversion Basic Principles of Upconversion Bioimaging upconversion nanoparticles Energy transfer upconversion Erbium upconversion Excited state absorption , upconversion Femtosecond fluorescence upconversion Femtosecond fluorescence upconversion measurements Fluorescence upconversion Fluorescence upconversion spectroscopy Fluorescence-upconversion experiments Frequency upconversion Lanthanide ions, upconversion Lanthanide upconversion nanomaterials Lanthanides materials, upconversion luminescence Lanthanides upconversion Light-energy upconversion Luminescent upconversion/downconversion Near-infrared emission upconversion Phosphor technology, upconversion Photoluminescence upconversion Photon upconversion Principles upconversion Rare Earth Nanophosphors with Upconversion Luminescence Sensitization upconversion Synthesis upconversion nanoparticles The Building Blocks of Upconversion Absorption and Energy Transfer The Fluorescence Upconversion Spectroscopy Transition metal-lanthanide upconversion Transitions upconversion Ultrafast fluorescence upconversion Upconversion Power Dependence Upconversion and Magnetic Resonance Imaging Upconversion in Doped Transition Metal Ion Systems Upconversion luminescence Upconversion luminescence, solids Upconversion method Upconversion nanocrystals Upconversion nanomaterial Upconversion nanoparticles Upconversion nanoparticles UCNPs) Upconversion nanoparticles energy transfer Upconversion nanoparticles excitation Upconversion nanoparticles excited Upconversion nanophosphors Upconversion particles Upconversion photonic Upconversion processes Upconversion wavelength sensitivity Ytterbium upconversion