Comparative Investigation on Nanocrystal Structure and Luminescence Properties of Gadolinium Molybdates Codoped with Er3+/Yb3+

Abstract

This paper reports on the comparative investigation of nanocrystal structure and luminescence properties of Er(3+)/Yb(3+)-codoped gadolinium molybdate nanocrystals Gd(2)(MoO(4))(3) and Gd(2)MoO(6) synthesized by the Pechini method with citric acid and ethylene glycol. Their crystallization, structure transformation, and morphologies have been investigated by X-ray diffraction, thermogravimetric/differential scanning calorimetry, and transmission electron microscopy. It is noticed that Er(3+)/Yb(3+)-codoped monoclinic Gd(2)(MoO(4))(3) nanocrystals have shown an intense upconversion through a sintering of the organic complex precursor at 600 degrees C. Furthermore, it transforms to orthorhombic Gd(2)(MoO(4))(3) when the precursor is sintered at 900 degrees C. In counterpart of monoclinic Gd(2)MoO(6), however, the monoclinic structure remains unchanged when the precursor is sintered at a temperature ranging from 600 degrees C to 900 degrees C. Intense visible emissions of Er(3+) attributed to the transitions of (2)H(11/2), (4)S(3/2)-(4)I(15/2) at 520 and 550 nm, and (4)F(9/2)-(4)I(15/2) at 650 nm have been observed upon an excitation with a UV source and a 980 nm laser diode, and the involved mechanisms have been explained. It is quite interesting to observe obvious differences both in the excitation and the upconversion emission spectra of Er(3+)/Yb(3+)-codoped Gd(2)(MoO(4))(3) respectively with monoclinic and orthorhombic structure. The quadratic dependence of fluorescence on excitation laser power has confirmed that two-photons contribute to upconversion of the green-red emissions.