Infrared-to-Visible Light Conversion in Er(3+) -Yb(3+) :Lu3 Ga5 O12 Nanogarnets

Er(3+) -Yb(3+) co-doped Lu3 Ga5 O12 nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb(3+) concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near-infrared light. The decay curves for the ((4) S3/2 , (2) H11/2 ) and (4) F9/2 levels of the Er(3+) ions exhibit a non-exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb(3+) concentration from 1.0 to 10.0 mol %. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole-quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red-to-green intensity ratio of Er(3+) ions was observed with an increase in Yb(3+) concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.