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

The SrMoO 4 :Yb 3+ /Er 3+ nanocrystals (NCs) were synthesized by sol–gel method. The upconversion luminescence properties of SrMoO 4 :Yb 3+ /Er 3+ NCs were studied in contrast to the identical dopants in Y 2 O 3 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 SrMoO 4 :Yb 3+ /Er 3+ NCs increases with the increase of Yb 3+ concentration at fixed Er 3+ concentration. The anomalous luminescence properties of SrMoO 4 :Yb 3+ /Er 3+ NCs are attributed to the high excited state energy transfer (HESET) from the | 2 F 7/2 , 3 T 2 > state of the sensitizer Yb 3+ – MoO 4 2 − dimer to the 4 F 7/2 level of the activator Er 3+ . The HESET process can partly decrease the lattice phonon quenching processes at lower energy levels of Er 3+ and enhance the green emission dramatically. [ABSTRACT FROM AUTHOR]