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

Bi 3+ -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., Eu 2+, Ce 3+ ) phosphors. Such unique property suggests their potential application in NUV chip-based WLEDs. However, few Bi 3+ phosphors exhibit strong excitation peak in NUV, though the excitation tail of some can extend to NUV. Herein, we report a novel yellow-emitting La 3 BWO 9:Bi 3+ (LBW:Bi 3+ ) phosphor with strong NUV excitation. The photoluminescence (PL) spectroscopy analysis indicates that there are two Bi 3+ luminescent centers in LBW:Bi 3+ phosphor, which is clearly in contradiction with the established hexagonal structure of La 3 BWO 9 with P 6 3 space group because only one La site in this structure can accommodate Bi 3+ ions. Combining the luminescent properties of Bi 3+ with Rietveld refinement, La 3 BWO 9 was redefined as a trigonal structure with the lower space group of P 3 in which there are two independent crystallographic La sites. In addition, the rationalization of P 3 space group was further confirmed by the finding of the reflection (0001) according to the extinction rule. Therefore, the PL behavior of Bi 3+ 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.