Abstract
Ba2SiO4−δN2/3δ:Eu2+ (BSON:Eu2+) materials with different N3− contents were successfully prepared and characterized. Rietveld refinements showed that N3− ions were partially substituted for the O2− ions in the SiO4-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 N3− contents of BSON:Eu2+ 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-Si3N4), 0.035 (using 50% α-Si3N4 and 50% SiO2), and 0.000 (using 100% SiO2). 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 N3- substitution. Furthermore, in UV-region, the absorbance of N3−-substituted BSON:Eu2+ (synthesized using 100% α-Si3N4) phosphor was about two times higher than that of BSO:Eu2+ (using 100% SiO2). Owing to the N3− substitution, surprisingly, the photoluminescence (PL) and LED-PL intensity of BSON:Eu2+ (synthesized using 100% α-Si3N4) was about 5.0 times as high as that of BSO:Eu2+ (using 100% SiO2). The compressive strain estimated by the Williamson−Hall (W−H) method, was slightly increased with the higher N3− content in the host-lattice of Ba2SiO4, which warranted that the N3- ion plays an important role in the highly enhanced PL intensity of BSON:Eu2+ phosphor. These phosphor materials could be a bridgehead for developing new phosphors and application in white NUV-LEDs field.
Highlights
Light-emitting diodes (LEDs) have been rapidly developed as solid state lighting sources as well as components in flat-panel displays
The ionic radius of N3− ion (1.46 Å) is larger than that of O2− ion (1.38 Å) in coordination number (CN) = 4, the lattice parameters of BSON:Eu are slightly shortened by introducing the nitrogen atom, and the unit cell volume is slightly decreased from 444.65 to 443.96 Å3 by N ion doping
By comparison of the Si-2p binding energy between SiO2 and Si3 N4, it is evident that the lowest binding energy (98.6 eV) of Si-2p is ascribed to the bond character of Si-(O,N) formed by introduced N3− ions into the SiO2 matrix, which can be proved by the N-1s binding energy at 399 eV in BSON compound
Summary
Light-emitting diodes (LEDs) have been rapidly developed as solid state lighting sources as well as components in flat-panel displays. Commercial white LEDs were initially developed using the combination of blue-emitting InGaN chips and a YAG:Ce3+ phosphor, resulting in the white light-emission [1]. This LED exhibits high efficiency, the color rendering index is poor. Rare earth activated metal silicon-oxynitride phosphors have been considered as a breakthrough to improve the low color rendering index for white LED applications [2,3,4,5,6,7,8]. The origin of the remarkably enhanced luminescence for BSON:Eu2+ phosphor is verified using infrared (IR), X-ray photoelectron spectroscopy (XPS), UV/Visible absorbance, photoluminescence (PL) and LED-PL
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