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Abstract: We investigate the effects of heterovalent co – dopants on the structural and emission properties of 1% Er - CeO2 nanoparticles. The CeO2 oxide host was selected on the basis of its fairly well understood defect chemistry in either pure or doped state. As a luminescent activator, Er is acknowledged as an interesting one due to its rich luminescence and excitation properties spanning visible to near- infrared range. The optically inactive trivalent La and monovalent Li metal ions with concentration of up to 20 % were chosen to presumably generate a variable amount of defects into the Er - CeO2 lattice. It was found that La and Li co – dopants induced distinct changes related to size, lattice constant, bandgap energy, lattice and surface defects of Er - CeO2. As a result of these changes, a strong modulation of the luminescence intensity and shape was measured using a suite of excitation conditions (charge - transfer absorption band of CeO2, direct/up-conversion into Er absorptions and X-ray excitation modes). The use of Eu as a luminescent probe offered additional information concerning the effects of La/Li co – doping on the local structure surrounding the luminescent activator. A remarkably high percentages of 90 and 98% of the total emission of Er measured between 500 and 1000 nm is measured in the near – infrared at 980 nm under X - ray and up – conversion excitation at ~ 1500 nm, respectively. The optical properties suggest that Li, Er co - doped CeO2 has a good potential for therapy and biological imaging.
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