Effect of Yb~(3+) concentration on upconversion luminescence in Yb~(3+) ,Tm~(3+) co-doped Lu_2O_3 nanophosphors

摘要

Lutetium oxide nanophosphors codoped with Yb~(3+) and Tm~(3+) ions were successfully synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitants. Effect of the Yb~(3+) molar concentration on the structural and upconversion luminescent properties of the Lu_2O_3 nanophosphors has been investigated. The XRD results show that all the prepared nanophosphors can be readily indexed to pure cubic phase of Lu_2O_3 and exhibit good crystalliniry. The experimental results show that the optimum Yb~(3+) doped concentration is 4 mol% at fixed Tm~(3+) 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 ~G_4 -> ~3H_6,~1G_4 -> ~3F_4 and ~3H_4 -> ~3H_6 transitions of Tm~(3+) ion, respectively. Under strong power density (50 W/cm~2) excitation, the upconversion blue intensity ratio (477 nm/490 nm) was dependent on the Yb~(3+) concentration, which was resulted from the thermal effect induced by laser irradiation. The upconversion mechanism was also discussed in detail.