Highly Luminous Ba(2)SiO(4−δ)N(2/3δ):Eu(2+) Phosphor for NUV-LEDs: Origin of PL-Enhancement by N(3−)-Substitution

Ba(2)SiO(4−δ)N(2/3δ):Eu(2+) (BSON:Eu(2+)) materials with different N(3−) contents were successfully prepared and characterized. Rietveld refinements showed that N(3−) ions were partially substituted for the O(2−) ions in the SiO(4)-tetrahedra because the bond lengths of Si‒(O,N) (average value = 1.689 Å) were slightly elongated compared with those of Si‒O (average value = 1.659 Å), which resulted in the minute compression of the Ba(2)‒O bond lengths from 2.832 to 2.810 Å. The average N(3−) contents of BSON:Eu(2+) phosphors were determined from 100 nm to 2000 nm depth of grain using a secondary ion mass spectrometry (SIMS): 0.064 (synthesized using 100% α-Si(3)N(4)), 0.035 (using 50% α-Si(3)N(4) and 50% SiO(2)), and 0.000 (using 100% SiO(2)). Infrared (IR) and X-ray photoelectron spectroscopy (XPS) measurements corroborated the Rietveld refinements: the new IR mode at 850 cm(−1) (Si‒N stretching vibration) and the binding energy at 98.6 eV (Si-2p) due to the N(3-) substitution. Furthermore, in UV-region, the absorbance of N(3−)-substituted BSON:Eu(2+) (synthesized using 100% α-Si(3)N(4)) phosphor was about two times higher than that of BSO:Eu(2+) (using 100% SiO(2)). Owing to the N(3−) substitution, surprisingly, the photoluminescence (PL) and LED-PL intensity of BSON:Eu(2+) (synthesized using 100% α-Si(3)N(4)) was about 5.0 times as high as that of BSO:Eu(2+) (using 100% SiO(2)). The compressive strain estimated by the Williamson−Hall (W−H) method, was slightly increased with the higher N(3−) content in the host-lattice of Ba(2)SiO(4,) which warranted that the N(3-) ion plays an important role in the highly enhanced PL intensity of BSON:Eu(2+) phosphor. These phosphor materials could be a bridgehead for developing new phosphors and application in white NUV-LEDs field.