Anomalous upconversion emission of Eu3+–Yb3+–MoO6 in double perovskites induced by a laser
Abstract
The anomalous upconversion (UC) emission of Eu3+–Yb3+–MoO6 in Sr2Ca(Mo,W)O6 double perovskites is presented in detail and the proper theoretical interpretation is proposed. The relative intensity ratios of the magnetic dipole transition 5D0 → 7F1 at ∼594 nm to the electric dipole transition 5D0 → 7F2 at ∼615 nm of Eu3+ are changed for both A-site (Sr, C1 symmetry) and B-site (Ca, Ci symmetry) substitution by Eu3+ in Sr2Ca(Mo,W)O6 when comparing the UC emission spectra with the Stokes luminescence spectra, which may be due to the difference in energy transfer efficiency between Yb3+–Yb3+ to Eu3+ and (Mo,W)O6 to Eu3+. Another remarkable phenomenon is the emission peak at ∼700 nm, ascribed to the 5D0 → 7F4 transition, which is observed in the UC spectra for the samples with Mo while it is absent in the Stokes luminescence spectra. Furthermore, this peak almost disappears for those samples without Mo in the UC spectra. Theoretical analysis and