Abstract
Important for telecommunications, luminescence of trivalent erbium (Er) at 1.5 μm generally arises from a Stokes-shifted downconversion mechanism. We show that this luminescence following direct excitation of the state is generated by upconversion-mediated looping process in -codoped single crystal. Emissions at 1.0 and 1.5 μm from the and states display linear and quadratic dependences on the excitation density in two separated ranges with a threshold of . This observation correlates with two- and four-photon processes in green and red upconversion emissions. The mechanism described has implications in the improvement of the output of 1.5 μm luminescence.
©2012 Optical Society of America
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