Sharp 2E upconversion luminescence of Cr3+ in Y3Ga5O12 codoped with Cr3+ and Yb3+ -: art. no. 125112

We report on upconversion luminescence in Y3Ga5O12 codoped with Cr3+ and Yb3+. This is, to our knowledge, the first upconversion process directly involving Cr3+. At low temperature excitation around 10 314 cm(-1) leads to relatively strong red luminescence in the title compound. The sharp upconversion luminescence around 14 300 cm(-1) is identified as the E-2-->(4)A(2) transition of Cr3+. The upconversion excitation spectrum follows the Yb3+ F-2(7/2)-->F-2(5/2) absorptions in the range 11 200-10 315 cm(-1). From transient measurements the upconversion mechanism is found to be dominated by an energy transfer step: Two excited Yb3+ ions simultaneously transfer their excitation energy to the Cr3+ ion. In Y3Ga5O12:2% Cr3+, 1% Yb3+ the efficiency of the process at 10 K and for 150 mW laser power is 6% and decreases with increasing temperature due to intrinsic loss mechanisms of the system.