Ba5GeO4Br6:Bi3+, a promising cyan phosphor for high-quality full-spectrum white light illumination

Using efficient cyan phosphors to reduce the cyan gap in the white light-emitting diode spectrum plays an important role in realizing full-spectrum white light illumination. In this work, herein, we successfully prepared a cyan phosphor Ba5GeO4Br6:Bi3+ by high-temperature solid-state method to compensate for the cyan gap in the spectrum and studied its crystal structure, luminescent properties, and thermal quenching behavior. Meanwhile, the valence state of Bi ions in the phosphor was determined by XPS spectroscopy. The Ba5GeO4Br6:Bi3+ phosphor shows strong absorption in the range of 250–400 nm, which can be attributed to the 1S0→3P1 transition of Bi3+. When excited at UV light, Ba5GeO4Br6:Bi3+ gives a bright and broad cyan emission with a half width at half maximum (FWHM) of 138 nm, and the emission peak at 491 nm. In addition, as the temperature increases, the blue shift and broadening of the spectrum can be elucidated by the nonradiative transfer and the increase of the thermally active phonon density. Finally, a full-spectrum WLED lamp with a color rendering index of 93.4 was prepared by coating Ba5GeO4Br6:Bi3+ phosphor, commercial BaMgAl10O17:Eu2+ and (Ca,Sr)AlSiN3:Eu2+ phosphors on a 310 nm UV LED chip.