Effects of Ca Content on Formation and Photoluminescence Properties of CaAlSiN3:Eu2+ Phosphor by Combustion Synthesis

Abstract

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN3:Eu2+ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu2O3, NaN3, NH4Cl and Si3N4 powders were used as the starting materials and they were mixed and pressed into a compact which was then wrapped up with an igniting agent (i.e., Mg + Fe3O4). The compact was ignited by electrical heating under a N2 pressure of ≤1.0 MPa. By keeping the molar ratios of Al and Si (including the Si powder and the Si in Si3N4 powder) both at 1.00 and that of Eu2O3 at 0.02, XRD (X-ray diffraction) coupled with TEM-EDS (transmission electron microscope equipped with an energy-dispersive X-ray spectroscope) and SAED (selected area electron diffraction) measurements show that AlN:Eu2+ and Ca-α-SiAlON:Eu2+ are formed as the major phosphor products when the Ca molar ratio (denoted by Y) is equal to 0.25 and AlN:Eu2+ and Ca-α-SiAlON:Eu2+ could not be detected at Y ≥ 0.75 and ≥1.00, respectively. CASIN (i.e., CaAlSiN3:Eu2+) becomes the only phosphor product as Y is increased to 1.00 and higher. The extent of formation of CASIN increases with increasing Y up to 1.50 and begins to decrease as Y is further increased to 1.68. While the excitation wavelength regions are similar at various Y, the emission wavelength regions vary significantly as Y is increased from 0.25 to 1.00 due to different combinations of phosphor phases formed at different Y. The emission intensity of CASIN was found to vary with Y in a similar trend to its extent of formation. The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures.

Effects of Variation in Al Content on the Emission of Eu Doped CaAlSiN3 Red Phosphor Synthesized by Combustion Synthesis Method for White LEDs

“…Another of the reasons is the morphology of the as-synthesized products transformed. Chung et al [ 2 ] reported that the three major types of morphology were observed for the synthesized products: plate-like crystals, bar-like crystals, and agglomerated fine particles. Among the three types of morphology of CASIN, the bar-like morphology seems to give a stronger emission than the other two.…”

“…After the evacuation, the reactor was backfilled with nitrogen to the desired pressures. The combustion reaction was ignited by heating the top surface of the compact for ~10 s by applying an electrical power of ~1 KW to the heating coil [ 1 , 2 ]. After combustion, the igniting agent was converted to MgO + Fe, which was loosely attached to the interior product.…”

“…The white light-emitting diode (LED) has drawn much more attention because of high efficiency, long lifetime, compactness, environmental friendliness, and designable features. Generally, white LED lighting devices are fabricated based on the combination of an InGaN-based blue-LED chip and a yellow-emitting phosphor, i.e., YAG:Ce 3+ [ 1 , 2 ]. One of the main problems of this type of LED lighting is the low color rendering index due to deficiency of red light.…”

Preparation of Red Phosphor Sr2Si5N8: Eu2+ by Pellet Method and Its Optical Characteristics

“…In particular, M 2 Si 5 N 8 : Eu 2+ (M = Ca, Sr, Ba) phosphors give a broad emission band from 570 to 680 nm due to the 5d−4f parity-allowed transition of Eu 2+ , when excited by blue or near-UV LED chips. This means that M 2 Si 5 N 8 : Eu 2+ (M = Ca, Sr, Ba) is a good candidate for red-emitting phosphor, which can convert the blue or near-UV light of LED chips into red light [11][12][13]. The most common synthesis technique for nitride phosphor is high-temperature reaction, where precursors (Ca 3 N 2 , Sr 3 N 2 and EuN) are very sensitive to air and moisture [1,9,14,15].…”