Dominant red emission (4F9/2→4I15/2) via upconversion in YAG (Y3Al5O12):Yb3+ Er3+ nanopowders

YAG (Y3Al5O12):Yb3+,Er3+ pure phase nanopowders were prepared by a co-precipitation method in which ammonium hydrogen carbonate was adopted as precipitator. Upconversion emissions were investigated on the nanopowder compacts pumped by a 980 nm continuous wave diode laser, and red emission centered at 660 nm and green emission centered at 563 nm were observed. Energy transfer from Yb3+ to Er3+ ions and cooperative energy transfer between two nearby Er3+ ions were the main mechanisms of upconversion luminescence. Red emission relative to green emission (R/G) was strikingly enhanced with the increase of Yb3+ dopant concentration, and dominant red emission appeared when 20 at% Yb3+ ions were doped. On the other hand, the decrease of calcining temperature was beneficial to the red emission dominance. The reasons for the red emission enhancement were discussed based on the mechanisms of upconversion luminescence. (c) 2006 Elsevier B.V. All rights reserved.