Intense red up-conversion luminescence and dynamical processes observed in Sc2O3:Yb3+, Er3+ nanostructures

The intense red up-conversion luminescence in Sc2O3:Yb3+, Er3+ synthesized using a biphasic solvothermal (ST) method was observed upon laser diode pumping at 980 nm. Compared with that found in the bulk sample synthesized using a solid state (SS) reaction at the same sintering temperature (700 degrees C), the green and red up-conversion luminescence are enhanced by a factor of 19.7 and 23.4, respectively. The relative red intensity of the sample prepared using the ST method at 700 degrees C for 2 h was enhanced up to 6.6 times compared to that obtained by the SS reaction method at 1600 degrees C for 6 h. On analyzing the spectral distribution, power dependence and decay curves of Yb3+, we revealed that the red emission of the Er3+:F-4(9/2) level in Sc2O3:Yb3+, Er3+ was populated via three possible routes, i.e. excited-state absorption (ESA), two-step energy transfer up-conversion (ET) and non-multiphonon relaxation mechanism from the (H-2(11/2), S-4(3/2)) via cross-relaxation and energy back transfer (CRB). For the green up-conversion of the Er3+:(H-2(11/2), S-4(3/2)) level, a three-photon process described as Yb3+:F-2(5/2) + Er3+:F-4(9/2) -> Yb3+:F-2(7/2) + Er3+:H-2(9/2) occurs in the Sc2O3:Yb3+, Er3+ material. The results indicate that ST-Sc2O3:Yb3+, Er3+ can act as an efficient up-converting red light emitter and ST-Sc2O3 is an appropriate oxide host for up-conversion luminescence.