KGd(1-x-y)ErxYby(WO4)2 (x/y=0.024/0, 0.02/0.022 and 0.019/0.066) single crystals have been grown by the top seeded solution growth slow cooling method using K2W2O7 as solvent. Erbium concentration was selected at [Er]=1.2-1.5x1020 cm-3 in order to minimise Er-Er non-radiative losses and the ytterbium concentration was varied in the range [Yb]=0-4.2x1020 cm-3. The optical absorption in the 850-1100 nm spectral range is characterised by the overlap between ytterbium 2F5/2 and erbium 4I11/2 manifolds. At room temperature the green 4S3/2 Er3+ emission has been excited by energy transfer from the 2F5/2 (934.2, 953.2 and 980.8 nm) ytterbium multiplet. The up-converted emission is weakly polarised and within the concentration range studied its intensity increases with the Yb3+ concentration.