Anomalous upconversion luminescence of SrMoO4:Yb3+/Er3+ nanocrystals by high excited state energy transfer

The SrMoO4:Yb3+/Er3+ nanocrystals (NCs) were synthesized by sol-gel method. The upconversion luminescence properties of SrMoO4:Yb3+/Er3+ NCs were studied in contrast to the identical dopants in Y2O3 NCs under the same experimental conditions. The results demonstrate that the green emission intensity of the former is much stronger than that of the latter, while the red emission intensity is reverse. Interestingly, the green-to-red intensity ratio of SrMoO4:Yb3+/Er3+ NCs increases with the increase of Yb3+ concentration at fixed Er3+ concentration. The anomalous luminescence properties of SrMoO4:Yb3+/Er3+ NCs are attributed to the high excited state energy transfer (HESET) from the vertical bar F-2(7/2), T-3(2)> state of the sensitizer Yb3+-MoO42- dimer to the F-4(7/2) level of the activator Er3+. The HESET process can partly decrease the lattice phonon quenching processes at lower energy levels of Er3+ and enhance the green emission dramatically. (C) 2015 Elsevier B.V. All rights reserved.