Hydrothermal synthesis of Er-doped yttria nanorods with enhanced red emission via upconversion

(Y_0.95Er_0.05)₂O₃ single-crystalline nanorods with intense red emission via up-conversion are synthesized by a hydrothermal method under modest reaction conditions. Green and red emissions are observed for both as-synthesized sample and post-treated sample after excitation at 488 nm and with upconversion pumping (810 nm). The experimental results indicate that the stokes and up-conversion luminescence of the post-treated (500 °C for 2 h) Y₂O₃:Er nanorods is more efficient than those of as-prepared materials. The increase of the Stokes luminescence may result from the improved crystallization, smooth surface and uniform diameter distribution. The enhanced red emission via upconversion is due to removal of part of surface contaminants, such as CO₃²⁻ and OH⁻. It is believed that a new mechanism is responsible for populating the ⁴S_3/2 and ⁴F_9/2 levels.