Near-infrared→Visible light upconversion in a molecular trinuclear d-f-d complex

Giving the green light: The connection of two CrIII sensitizers around a central ErIII acceptor in a self-assembled cation provides high local metal concentrations that favor efficient nonlinear energy transfer upconversion luminescence (see picture). Upon selective low-energy near-infrared irradiation of CrIII-centered transitions, 1 displays an unprecedented molecular two-photon upconverted green ErIII-centered emission. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.