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 °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 °C for 2 h was enhanced up to 6.6 times compared to that obtained by the SS reaction method at 1600 °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⁺:⁴F_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 (²H_11/2, ⁴S_3/2) via cross-relaxation and energy back transfer (CRB). For the green up-conversion of the Er³⁺:(²H_11/2, ⁴S_3/2) level, a three-photon process described as Yb³⁺:²F_5/2 + Er³⁺:⁴F_9/2 → Yb³⁺:²F_7/2 + Er³⁺:²H_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.