Redefinition of Crystal Structure and Bi3+ Yellow Luminescence with Strong Near-Ultraviolet Excitation in La3BWO9:Bi3+ Phosphor for White Light-Emitting Diodes.

Bi3+-activated photonic materials have received increased interest recently because they can be excited effectively with near-ultraviolet (NUV) but not visible light, thereby avoiding the reabsorption among phosphors, which cannot be solved intrinsically by traditional rare earth (e.g., Eu2+, Ce3+) phosphors. Such unique property suggests their potential application in NUV chip-based WLEDs. However, few Bi3+ phosphors exhibit strong excitation peak in NUV, though the excitation tail of some can extend to NUV. Herein, we report a novel yellow-emitting La3BWO9:Bi3+ (LBW:Bi3+) phosphor with strong NUV excitation. The photoluminescence (PL) spectroscopy analysis indicates that there are two Bi3+ luminescent centers in LBW:Bi3+ phosphor, which is clearly in contradiction with the established hexagonal structure of La3BWO9 with P63 space group because only one La site in this structure can accommodate Bi3+ ions. Combining the luminescent properties of Bi3+ with Rietveld refinement, La3BWO9 was redefined as a trigonal structure with the lower space group of P3 in which there are two independent crystallographic La sites. In addition, the rationalization of P3 space group was further confirmed by the finding of the reflection (0001) according to the extinction rule. Therefore, the PL behavior of Bi3+ can act as a complementary tool to determinate the real crystal structure especially when it is hard to distinguish by conventional X-ray diffraction techniques.