Effect of Yb3+ concentration on upconversion luminescence in Yb3+, Tm3+ co-doped Lu2O3 nanophosphors

Abstract

Lutetium oxide nanophosphors codoped with Yb3+ and Tm3+ ions were successfully synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitants. Effect of the Yb3+ molar concentration on the structural and upconversion luminescent properties of the Lu2O3 nanophosphors has been investigated. The XRD results show that all the prepared nanophosphors can be readily indexed to pure cubic phase of Lu2O3 and exhibit good crystallinity. The experimental results show that the optimum Yb3+ doped concentration is 4 mol% at fixed Tm3+ concentration of 0.2 mol%. The strong blue, weak red and near infrared emissions from the prepared nanophosphors were observed under 980 nm laser excitation, which are attributed to the 1G4 → 3H6,1G4 → 3F4 and 3H4 → 3H6 transitions of Tm3+ ion, respectively. Under strong power density (50 W/cm2) excitation, the upconversion blue intensity ratio (477 nm/490 nm) was dependent on the Yb3+ concentration, which was resulted from the thermal effect induced by laser irradiation. The upconversion mechanism was also discussed in detail.