The luminescence properties of Eu 2+ -activated alkaline-earth silicon-oxynitrides have been studied. In the BaO-SiO 2 -Si 3 N 4 system, a new BaSi 2 O 2 N 2 compound was obtained having the monoclinic structure with lattice parameters a ) 14.070(4) Å, b ) 7.276(2) Å, c ) 13.181(3) Å, β ) 107.74(6)°. All MSi 2 O 2-δ N 2+2/3δ :Eu 2+ (M ) Ca, Sr, Ba) materials can be efficiently excited in the UV to visible region (370-460 nm), making them attractive as conversion phosphors for LED applications. A blue-green emission at 490-500 is observed for BaSi 2 O 2 N 2 :Eu 2+ , yellow emission at 560 nm for CaSi 2 O 2-δ N 2+2/3δ : Eu 2+ (δ ≈ 0), and a green-yellow emission peaking from 530 to 570 nm for SrSi 2 O 2-δ N 2+2/3δ :Eu 2+ (δ ≈ 1), the position depending on the exact value of δ. BaSi 2 O 2 N 2 :Eu 2+ is the most promising conversion phosphor for white-light LEDs due to its high conversion efficiency for blue light from InGaN-based LEDs related to its very small Stokes shift.

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Undoped and Eu-doped MAl 2−x Si x O 4−x N x ͑M = Ca, Sr, Ba͒ were synthesized by a solid-state reaction method at 1300-1400°C under nitrogen-hydrogen atmosphere. The solubility of ͑SiN͒ + in MAl 2 O 4 was determined. Nitrogen can be incorporated into MAl 2 O 4 by replacement of ͑AlO͒ + by ͑SiN͒ + , whose amount of solubility depends on the M cation. The solubility of ͑SiN͒ + is very low in CaAl 2 O 4 and SrAl 2 O 4 lattices ͑x Ϸ 0.025 and 0.045, respectively͒, whereas a large amount of ͑SiN͒ + can be incorporated into BaAl 2 O 4 ͑x Ϸ 0.6͒. Incorporation of ͑SiN͒ + hardly modifies the luminescence properties of Eu 2+ -doped MAl 2 O 4 ͑M = Ca, Sr͒ because of limited solubility of ͑SiN͒ + , showing the blue and green emission at almost constant wavelength of 440 and 515 nm, respectively. Eu 2+ -doped BaAl 2−x Si x O 4−x N x exhibits a broad green emission band with a maximum in the range of 500-526 nm, depending on the concentration of ͑SiN͒ + and Eu 2+ . In addition, both excitation and emission bands of Eu 2+ show a significant red shift as nitrogen is incorporated. BaAl 2−x Si x O 4−x N x :Eu 2+ can be efficiently excited in the range of 390-440 nm radiation, which makes this material attractive as conversion phosphor for white light-emitting diode ͑LED͒ lighting applications. .As an important class of phosphors, Eu 2+ -doped MAl 2 O 4 ͑M = Ca, Sr, Ba͒, has been widely used as persistent luminescent materials because of their high efficiency, chemical stability, and long-lasting high-luminance afterglow characteristics. 1-3 These phosphors also have been proposed for plasma display panel ͑PDP͒ 4 and optoelectronic applications. 5 Under ultraviolet and cathode-ray excitation these phosphors show a strong blue ͑M = Ca͒, green ͑M = Sr͒, and blue-green ͑M = Ba͒ fluorescence.In MAl 2 O 4 ͑M = Ca, Sr, Ba͒, the three-dimensional framework is built-up by a motif of six rings formed by corner-sharing AlO 4 tetrahedra. The tetrahedral framework is isostructural, with the SiO 2 polymorph having the tridymite structure. 6-8 The various MAl 2 O 4 structures differ in the arrangement and number of crystallographic sites of the divalent cations within the channels formed by the AlO 4 rings. CaAl 2 O 4 has a monoclinic structure in space group P2 1 /n. In this structure there are three Ca sites: two of them are sixfold and the third is ninefold coordinated, with the oxygen atoms in a different channel. However, for the larger M cations, SrAl 2 O 4 and BaAl 2 O 4 crystallize in a monoclinic and a hexagonal system with the space group P2 1 and P6 3 , respectively. Both Sr and Ba ions occupy two crystallographic sites, which are located in the channels of the AlO 4 rings, each with ninefold coordination with the oxygen anions.Although extensive investigations have been done on Eu 2+ -doped alkaline earth aluminates MAl 2 O 4 ͑M = Ca, Sr, Ba͒, [9][10][11][12][13][14][15] in previous studies considerable attention has been paid to improve the performance of these phosphors by partial substitution of the M ion ͑for example, replacemen...

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