Synthesis of NaYF4, NaLuF4 and NaGdF4-Based Upconversion Nanocrystals with Hydro (Solvo) Thermal Methods

Serials of NaYF4, NaLuF4 and NaGdF4-based nanocrystals have been synthesized successfully by solvothermal and hydrothermal, respectively. The properties of the products were characterized and compared. The nanocrystals prepared by hydrothermal method exhibited uniform hexagonal phase and large size, while the nanocrystals prepared by solvothermal method displayed high upconversion luminescence (UCL) and small size. The UCL intensities of the nanocrystals prepared by solvothermal method were higher than that of nanocrystals from hydrothermal method. Whether using solvothermal or hydrothermal method, the UCL intensities of the nanocrystals were in the sequence (from strong to weak) of NaLuF4:Gd/Yb/Tm, NaLuF4:Yb/Tm, NaGdF4:Yb/Tm, NaYF4:Gd/Yb/Tm and NaYF4:Yb/Tm, respectively. This is the first time to systematically compare three kinds of host-based nanocrystals, which are prepared by two different approaches with various lanthanide ions doped. This work could provide new insight into fabrication of upconversion nanocrystals with intense UCL and controllable morphology and size via using suitable doping ions, host materials and efficient approaches.