Near vacuum ultraviolet luminescence of Gd3+ and Er3+ ions generated by super saturation upconversion processes

Near vacuum ultraviolet (UV) upconversion (UC) emissions with a spectral resolution of 1 nm, from the (6)G(J), D-6(J), I-6(J), P-6(J) levels of Gd3+ and the L-2(17/2), D-4(7/2), H-2(2)(9/2), D-2(5/2), (4)G(7/2), K-2(13/2), P-2(3/2) levels of Er3+, were observed under 974 nm laser excitation. Mechanism analyses illustrate that successive energy transfers (ETs) from Yb3+ to Er3+ generate UV UC radiations in Er3+, while two resonant ETs from Er3+ to Gd3+ lead to UV UC radiations in Gd3+. Power dependence analyses indicate that the expected inefficient four- and five-photon processes have been switched into efficient two-photon processes due to a super saturation UC phenomenon that employs consecutive saturations at the intermediate states. (C) 2009 Optical Society of America