Abstract
Hollow and dense SiO2 microspheres doped with Er,Yb were characterized by extended X-ray absorption fine structure (EXAFS) on the Er,Yb LIII edges and photoluminescence (PL) measurements. The samples were synthesized by the sol–gel method and in situ Er,Yb doped, by introducing fluoride compounds (ErF3, YbF3) in the sol. Er,Yb doped transparent glass-ceramic, formed by NaYF4 nanocrystals dispersed in SiO2 matrix, was taken as the reference.The EXAFS results illustrate the Er,Yb local environment in all studied SiO2 matrices: in hollow-microspheres, crystalline Er,Yb fluoride was formed while in dense-microspheres, crystalline Er,Yb oxide developed.PL measurements of the Er3+ emission at 1.54μm were performed, on hollow and dense SiO2 microspheres, for different Er3+/Yb3+ ratios, ranging from 1:3 to 1:10mol%. Upconversion was observed in all samples, ordered by efficiency for the studied Er,Yb environments as: glass-ceramic (NaYF4 environment)≫hollow SiO2 microspheres (Er,Yb fluoride crystalline environment)>dense SiO2 microspheres (Er,Yb oxide crystalline environment). X-ray excited optical luminescence (XEOL) confirmed the Er green upconversion results.
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