Effects of Ca content on formation and photoluminescence properties of CaAlSiN₃:Eu²⁺ phosphor by combustion synthesis

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.