Yb sensitising of Er3+ up-conversion emission in KGd(WO4)2:Er:Yb single crystals

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]=1.2-1.5X10(20) cm(-3) in order to minimise Er-Er non-radiative losses and the ytterbium concentration was varied in the range [Yb]=0-4.2x10(20) cm-3. The optical absorption in the 850-1100 nm spectral range is characterised by the overlap between ytterbium F-2(5/2) and erbium I-4(11/2) manifolds. At room temperature the green S-4(3/2) Er3+ emission has been excited by energy transfer from the F-2(5/2) (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. (C) 2001 Elsevier Science B.V. All rights reserved.