Abstract
This paper introduces a new synthesis procedure to form erbium-doped ceria nanoparticles (EDC NPs) that can act as an optical medium for both up-conversion and down-conversion in the same time. This synthesis process results qualitatively in a high concentration of Ce3+ ions required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, the synthesized EDC NPs can emit visible light when excited with either UV or IR photons. This opens new opportunities for applications where emission of light via both up- and down-conversions from a single nanomaterial is desired such as solar cells and bio-imaging.
Highlights
Optical nanostructures that emit visible light when excited by ultraviolet (UV) or infrared (IR) photons have been extensively studied for applications that include bioimaging [1,2], solar energy [3,4], and optical gas sensors [5,6]
The down-conversion process requires that the cerium ions are in the Ce3+ state and are associated with oxygen vacancies, which implies that ceria nanoparticles contain Ce2O3 is a direct semiconductor [11]
This weight ratio is selected after a study by the authors of erbium-doped ceria nanoparticles (EDC NPs), synthesized using the same process, in which it was found that optimal concentration of erbium in ceria for up-conversion is 5 wt.% which is close to the quenching ratio mentioned by another research group [13]
Summary
Optical nanostructures that emit visible light when excited by ultraviolet (UV) or infrared (IR) photons have been extensively studied for applications that include bioimaging [1,2], solar energy [3,4], and optical gas sensors [5,6]. Visible emission from either UV excitation (down-conversion) or IR excitation (up-conversion) can be obtained from ceria nanoparticles Both up- and down-conversion processes involve different physiochemical properties in ceria and optimization of each optical process via various nanoparticle synthesis and post-growth procedures tends to quench the efficiency of the other process. To obtain visible light via up-conversion, ceria nanoparticles must be doped with certain lanthanides, such as erbium, annealed at temperatures above 700°C [12]. Ceria is a low-phonon host for the erbium ions, which act as optical centers that convert the energy from absorbed IR photons into visible light [13]. To optimize the properties of ceria nanoparticles for the two optical conversion processes, it has been required two different nanoparticle synthesis and post-processing procedures
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