A New Red Aluminate Phosphor CaAl12O19 Activated by Bi2+ for White LEDs

Unusually, valent Bi2+ ions doped into solids can exhibit near ultraviolet or blue excitation and red emissions. Previously the ion has only been found stabilized in compounds such as borate, sulfate or phosphate, and has not yet been reported in other types of compounds. In this work, we found that Bi2+ can also survive in CaAl12O19. Time resolved emission spectra reveal that there are two types of Bi2+ ions in the compound due to the substitution of calcium lattice sites. Both types of Bi2+ ions show blue excitations and red emissions, with energy transfer occurring from the longer wavelength emission center to the shorter wavelength emission center. As bismuth content x increases, Bi2+ luminescence intensifies at first, but is then quenched afterwards when x exceeds 0.3 mol%. The dominant mechanism of quenching was found to be due to electric quadrupole-quadrupole rather than exchange interactions. This work suggests that CaAl12O19: Bi2+ is a potential red phosphor for application in white light LEDs (WLEDs).