Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes.

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er(3+)-Yb(3+) codoped NaYF(4) nanocubes synthesized with solvo-thermal route. Upon excitation with a 980 nm laser diode, the nanocube solution exhibited strong near-infrared emission by the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions due to energy transfer from Yb(3+) ions. We obtained the highest optical gain coefficient at 1550 nm of 0.58 cm(-1) for the solution with the pumping power of 200 mW. This colloidal solution might be a promising candidate as a liquid medium for optical amplifier and laser at the optical communication wavelength.