Abnormal Anti-Quenching and Controllable Multi-Transitions of Bi~(3+) Luminescence by Temperature in a Yellow-Emitting LuVO_4:Bi~(3+) Phosphor for UV-Converted White LEDs

摘要

Phosphors with an efficient yellow-emitting color play a crucial role in phosphor-converted white LEDs (pc- WLEDs), but popular yellow phosphors such as YAG:Ce or Eu~(2+)-doped (oxy)nitrides cannot smoothly meet this seemingly simple requirement due to their strong absorptions in the visible range. Herein, we report a novel yellow-emitting LuVO_4:Bi~(3+) phosphor that can solve this shortcoming. The emission from LuVO_4:Bi~(3+) shows a peak at 576 nm with a quantum efficiency (QE) of up to 68, good resistance to thermal quenching (T_(50)=573 K), and no severe thermal degradation after heating-cooling cycles upon UV excitation. The yellow emission, as verified by X-ray photoelectron spectra (XPS), originates from the (~3P_0,~3P_1)→~1S_0 transitions of Bi~(3+). Increasing the temperature from 10 to 300 K produces a temperature- dependent energy-transfer process between VO_4~(3-) groups and Bi~(3+), and further heating of the samples to 573 K intensifies the emission. However, it subsequently weakens, accompanied by blueshifts of the emission peaks. This abnormal anti-thermal quenching can be ascribed to temperature-dependent energy transfer from VO_4~(3-) groups to Bi~(3+), a population redistribution between the excited states of ~3P_0 and ~3P_1 upon thermal stimulation, and discharge of electrons trapped in defects with a trap depth of 359 K. Device fabrication with the as-prepared phosphor LuVO_4:Bi~(3+) has proved that it can act as a good yellow phosphor for pc-WLEDs.