Preparation of Upconversion Luminescent NaYF_4 Co-doped with Yb~(3+)/Er~(3+) via Hydrothermal Synthesis

摘要

Hexagonal NaYF_4 crystals co-doped with different concentration of Yb~(3+) and Er~(3+) ions were synthesized via hydrothermal reaction route. The samples doped with 30mol% of Yb~(3+) and lmol% of Er~(3+) showed the highest upconversion efficiencies under 980nm excitation. Powder X-ray diffraction (XRD) analyses indicated that the samples were pure hexagonal phase. The morphology of the powder was observed by scanning electron microscopy (SEM). With the excitation of a 980mn diode laser, strong green emissions were obtained at 522, 530, 542 and 551 nm in addition to weak red emission at 654nm. The green and red emissions were attributed to the transitions of ~4S_(3/2),~2H_(11/2)→~4I_(15/2) and ~4F_(9/2)→~4i_(15/2) of Er ion, respectively. The additions of Yb~(3+) ion as sensitizer can notably enhance the upconversion efficiencies from infra-red to visible. The upconversion mechanism of the emission for the samples was also discussed.