Optical gain at 1550 nm from colloidal solution of Er³⁺-Yb ³⁺ codoped NaYF₄ nanocubes

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er³⁺-Yb³⁺ 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 ⁴I_13/2 ⁴I_15/2 transition of Er³⁺ ions due to energy transfer from Yb³⁺ 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.