Phase-selective Hydrothermal Preparation and Upconversion Luminescence of NaYF_4:Yb~(3+), Tm~(3+)

摘要

Upconversion luminescence materials have been proved to have a good efficiency on converting low energy light to high energy light. These materials have received considerable attentions for many applications such as bio-labels, sensors, using for developing solar cells and photocatalytic applications under sunlight. Among many inorganic host materials, NaYF_4 has been proved to be the best for doping lanthanide ions and have a good upconversion emission due to its low phonon energy, chemical stability, and transparency in the near infrared to ultraviolet range. In this study, NaYF4:Yb~(3+),Tm~(3+) upconversion luminescence materials were synthesized by hydrothermal method at temperature of 90 to 200°C for period between 1 to 24 hours. The synthesized NaYF4:Yb~(3+),Tm~(3+) were characterized by X-ray diffraction, scanning electron microscopy, and fluorescence spectroscopy. The hydrothermal temperature and reaction time have strongly influence on phases and upconversion emission of the synthesized NaYF4:Yb~(3+),Tm~(3+). At 90°C for 1 hour of reaction time, the pure cubic phase of NaYF4:Yb~(3+),Tm~(3+) was found. After increasing temperature and reaction time, the NaYF_4:Yb~(3+),Tm~(3+) converted from cubic phase to hexagonal phase. Under excitation of 980 nm diode laser, the hexagonal NaYF_4:Yb~(3+),Tm~(3+) exhibited the emission wavelength at about 656 nm (~3F_2→~3H_6), 469, 492, 552 nm (~1G_4→~3H_6), 537 nm (~1D_2→~3H_5), 450, 461 nm (~1D_2 →~3F_4), 362 nm (~1D_2→ ~3H_6) and 345 nm (~1I_6→ ~3F_4). The upconversion emission intensity of the hexagonal NaYF_4:Yb~(3+),Tm~(3+) was much stronger, compared with that of the cubic NaYF_4:Yb~(3+),Tm~(3+).