Flame synthesis and effects of host materials on Yb3+/Er3+ co-doped upconversion nanophosphors

The upconversion nanophosphors (UCNPs) of Yb3+/Er3+ co-doped into Y2O3, La2O3, and Gd2O3 were synthesized via the combustion method and characterized by powder X-ray diffractometer (XRD), scanning electron microscopy (SEM) and upconversion fluorescence spectroscopy. The characterization results showed that at the same flame temperature (2705 K) and precursor concentration (0.1 M), pure monoclinic and cubic-phase phosphors were achieved on Gd2O3 and Y2O3 hosted UCNPs, respectively; while the mixed phases were observed on La2O3 hosted UCNPs. Further annealing process at 850 degrees C produced pure cubic-phase La2O3:Yb3+,Er3+ UCNPs; while there was no phase transition observed on Gd2O3:Yb3+,Er3+ UCNPs. The dependence of upconversion luminescence on precursor concentrations and host materials was then examined. The La2O3 and Gd2O3 hosts were shown to be the promising alternates for the commonly used Y2O3 hosts for rare-earth doped phosphors. (C) 2009 Elsevier B.V. All rights reserved.