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.

Photoluminescence properties of novel red-emitting Mn 2+ -activated MZnOS (M ) Ca, Ba) phosphors were investigated. Mn 2+ -activated MZnOS phosphors show a single symmetric narrow red emission band in the wavelength range of 550-700 nm due to the 4 T 1 ( 4 G) f 6 A 1 ( 6 S) transition of Mn 2+ . Peak centers are at about 614 nm for M ) Ca and 634 nm for M ) Ba, regardless of the excitation wavelength and Mn 2+ doping concentration. A comparison is made between the luminescence properties of Mn 2+ in the Ca versus Ba compound. A similarity between them is that both Mn 2+ -activated CaZnOS and BaZnOS can be efficiently excited under host lattice excitation in the wavelength range of 250-350 nm due to efficient energy transfer between the host lattice (MZnOS) and activator (Mn 2+ ). An unexpected difference is that Mn 2+ -activated CaZnOS can also be efficiently excited under the excitation of Mn 2+ itself (d-d transitions) in the wavelength range of 350-500 nm. This difference is ascribed to different crystal structures, different coordination environments, and point symmetries for Mn in these two compounds. The potential applications of these phosphors are pointed out. Among them, Mn 2+ -activated CaZnOS shows great potential for application as an alternative red-emitting LED conversion phosphor due to its high absorption and strong excitation bands in the wavelength range of 350-500 nm.

No abstract

No abstract

No abstract