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 |²F₇/₂, ³T₂> state of the sensitizer Yb³⁺−MoO₄²⁻ dimer to the ⁴F₇/₂ 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.
- High excited state energy transfer