Upconversion luminescence of Tm3+ and Yb3+-codoped lutetium oxide nanopowders

Lutetium oxide nanopowders codoped with Tm3+ and Yb3+ were synthesized by the co-precipitation method. Upconversion luminescence properties of the powder compacts have been investigated upon continuous wave excitation at 980 nm. Blue emission band was observed by naked eye, which was corresponded to the (1)G(4) -> H-3(6) transition of Tm3+ ions. However, upconversion spectra revealed that the strongest emission was centered at 809 nm, assigned to the H-3(4) -> H-3(6) transition. Weak red emission centered at 651.5 nm was attributed to the (1)G(4) -> H-3(4) transition while considerably weaker ultraviolet emission centered at 361 nm was ascribed to the D-1(2) -> H-3(6) transition. The dependence of the intensity of upconversion emissions on the pump power implies two-step and three-step excitation mechanisms of the H-3(4) and (1)G(4) levels, respectively. The possible upconversion schemes are discussed in this paper. Lutetium oxide powders can be sintered into transparent ceramics and high intensity of up-converted IR and blue emissions associated with the H-3(4) -> H-3(6) and (1)G(4) -> H-3(6) transitions of TM3+ in this matrix may offer lasers potential. (c) 2007 Elsevier B.V. All rights reserved.