Near-infrared down-conversion in Mn2+-Yb3+ co-doped Zn2GeO4

We report on near-infrared (NIR) down-conversion by energy transfer between Mn2+ and Yb3+ in crystalline Zn-1.96 xGeO4+1/2x:Mn0.04Ybx. In the Zn2GeO4 lattice, intrinsic defect transitions and Mn2+ ions act as broadband spectral sensitizers by absorbing UV-Vis (280-500 nm) photons and transferring the absorbed energy to Yb3+ centers in a cooperative down-conversion process. The Yb3+ acceptor is then the source of NIR emission at a wavelength of similar to 1000 nm. Efficient energy transfer is reflected by a sharp decrease in the excited state lifetime and green photoluminescence (PL) from tetrahedrally coordinated Mn2+ with increasing Yb3+ concentration. PL-excitation spectra of NIR luminescence from Yb3+ are identical to those of from Mn-IV(2+). A maximal energy transfer efficiency (ETE) from Mn2+ to Yb3+ and a total theoretical quantum efficiency of 63.8% and 163.8%, respectively, are estimated.