Abstract: The structural and spectroscopic properties of (Eu1-xYbx)2O3 nanocrystals with cubic (C-type) and monoclinic (B-type) crystalline structures have been studied. NCs have been synthetized by the sol-gel Pechini method and characterized at room temperature by X-ray diffraction, transmission electron microscopy, diffuse reflectance, Raman spectroscopy and photoluminescence techniques. NIR emission from Yb3+ ions has been observed in both C- and B-type NCs upon excitation of Eu3+ ions at 532 nm, where Yb3+ ions do not absorb photons. This fact reveals that an efficient non-resonant energy transfer process from Eu3+ to Yb3+ takes place, allowing to obtain simultaneous visible and NIR emissions under visible excitation. The decay curves of the 5D0 ? 7F2 Eu3+ emission of C-type NCs corroborate this phenomenon since the Eu3+ lifetime has been found to decrease as the Yb3+ content increases. Finally, we discuss the use of the Eu3+ luminescence as a structural probe to distinguish between different RE2O3 polymorphs.

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