Influence of SiO2 coating on morphology, phase and upconversion luminescence properties of NaYF4:Yb3+,Er3+ submicrocubes during annealing

Abstract NaYF 4 :Yb 3+ ,Er 3+ submicrocubes were synthesized by a facile method at room temperature, and they were coated with SiO 2 using a modified Stober procedure. Then bare NaYF 4 :Yb 3+ ,Er 3+ and NaYF 4 :Yb 3+ ,Er 3+ @SiO 2 submicrocubes were both annealed at 300 °C, 400 °C and 500 °C for 5 h under N 2 protection. The influence of SiO 2 shells on morphology, phase and upconversion luminescence properties of NaYF 4 :Yb 3+ ,Er 3+ submicrocubes during annealing was studied in detail. The results showed that silica shells can protect NaYF 4 :Yb 3+ ,Er 3+ cores from aggregating and growing up. Interestingly, SiO 2 shells can also prevent phase change of NaYF 4 :Yb 3+ ,Er 3+ submicrocubes from cubic (α-) to hexagonal (β-) phase during annealing, which provides a new way to control the phase of NaYF 4 nanocrystals. NaYF 4 :Yb 3+ ,Er 3+ cores became nanoporous after annealing, making them possess a feature of ‘cavity’ structure for the storage/delivery of therapeutic drugs. After annealing, NaYF 4 :Yb 3+ ,Er 3+ and NaYF 4 :Yb 3+ ,Er 3+ @SiO 2 submicrocubes both emit bright green light excited with a 980 nm laser source, and the upconversion luminescence properties were investigated in detail.