Hydrothermal synthesis, growth mechanism and down-shifting/upconversion photoluminescence of single crystal NaGd(MoO4)2 nanocubes doped with Eu3+, Tb3+ and Yb3+/Er3+

- Single crystal NaGd(MoO4)2 nanocubes are synthesized for the first time.
- Effect of Na2MoO4 contents on the formation of NaGd(MoO4)2 nanocubes is studied.
- Growth mechanism of NaGd(MoO4)2 nanocubes is investigated.
- Luminescence and upconversion mechanism of NaGd(MoO4)2: Ln3+ nanocubes are studied.

Uniform and well-crystallized tetragonal NaGd(MoO4)2 nanocrystals with the morphology of nanocubes were synthesized via a modified hydrothermal synthesis method with oleic acid as complexing agent. The as-synthesized NaGd(MoO4)2 nanocubes were characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction respectively. The side-length of the NaGd(MoO4)2 nanocubes is about 100-150 nm. The SAED pattern indicates highly crystalline nature of the NaGd(MoO4)2 nanocubes. The effect of Na2MoO4 contents on the formation of NaGd(MoO4)2 nanocrystals is investigated. A possible growth mechanism of NaGd(MoO4)2 nanocubes is deduced based on time-dependent morphology evolution and XRD analysis. Down-shifting/upconversion photoluminescence properties of NaGd(MoO4)2: Eu3+, Tb3+ and Yb3+/Er3+ nanocubes are investigated in detail. Furthermore, the energy transfer mechanism for upconversion luminescence in NaGd(MoO4)2: Yb3+/Er3+ nanocubes is investigated on the basis of energy level scheme and the excitation power dependence of upconversion luminescence intensities.