Ultraviolet upconversion fluorescence from 6DJ of Gd3+ induced by 980 nm excitation

Ultraviolet upconversion emissions of 246.2 and 252.8 nm from D-6(J) levels of Gd3+ ions were observed in GdF3: 10% Y3+, 0.7% Tm3+ nanocrystals under 980 nm excitation from a laser diode. The D,, levels of Gd3+ ions can be efficiently populated by energy transfer processes of Yb -> Tin -> Gd and Yb -> Gd. A six-photon upconversion process was confirmed by the dependence of 252.8 nm emission intensity on the pumping power. The upconversion mechanism in the six-photon process was discussed based on excited state absorption of Gd3+ ions, cross relaxation energy transfer between two excited Gd3+ ions, and energy transfer between Gd3+ and Yb3+ or Tm3+ ions. (C) 2008 Optical Society of America