Highly Luminous BaSiON:Eu Phosphor for NUV-LEDs: Origin of PL-Enhancement by N-Substitution.

BaSiON:Eu (BSON:Eu) materials with different N contents were successfully prepared and characterized. Rietveld refinements showed that N ions were partially substituted for the O ions in the SiO-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 contents of BSON:Eu 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-SiN), 0.035 (using 50% α-SiN and 50% SiO), and 0.000 (using 100% SiO). Infrared (IR) and X-ray photoelectron spectroscopy (XPS) measurements corroborated the Rietveld refinements: the new IR mode at 850 cm (Si‒N stretching vibration) and the binding energy at 98.6 eV (Si-2p) due to the N substitution. Furthermore, in UV-region, the absorbance of N-substituted BSON:Eu (synthesized using 100% α-SiN) phosphor was about two times higher than that of BSO:Eu (using 100% SiO). Owing to the N substitution, surprisingly, the photoluminescence (PL) and LED-PL intensity of BSON:Eu (synthesized using 100% α-SiN) was about 5.0 times as high as that of BSO:Eu (using 100% SiO). The compressive strain estimated by the Williamson-Hall (W-H) method, was slightly increased with the higher N content in the host-lattice of BaSiO which warranted that the N ion plays an important role in the highly enhanced PL intensity of BSON:Eu phosphor. These phosphor materials could be a bridgehead for developing new phosphors and application in white NUV-LEDs field.