Yq Yuan Qiang Li

Luminescence of a new class of UV–blue-emitting phosphors MSi2O2−δN2+2/3δ:Ce3+(M = Ca, Sr, Ba)

The luminescence properties of Ce3+,Na+-codoped MSi2O2−δN2+2/3δ (M = Ca, Sr, Ba) are reported. The undoped and Ce3+,Na+-codoped MSi2O2−δN2+2/3δ powders were prepared by a solid-state reaction at temperatures between 1300–1400 °C under N2–H2 (10%) atmosphere in the system MO–SiO2–Si3N4 (M = Ca, Sr, Ba). MSi2O2−δN2+2/3δ (M = Ca, Sr, Ba) crystallizes in the monoclinic system with different crystal structures. For excitation in the 300–360 nm range, MSi2O2−δN2+2/3δ:Ce3+ shows typical broad emission bands peaking at about 392, 473 and 396 nm for M = Ca, Sr and Ba, respectively. In particular, CaSi2O2−δN2+2/3δ:Ce3+ shows an unusual short-wavelength emission (∼392 nm) with a very small Stokes shift of 2200 cm−1; BaSi2O2N2:Ce3+ shows an interesting white-light emission in the visible range 350–600 nm for excitation at 365 nm.

Luminescence properties of Eu2+-doped MAl2-xSixO4-xNx (M = Ca, Sr, Ba) conversion phosphor for white LED applications

Undoped and Eu-doped MAl 2-x Si x O 4-x N x (M = Ca, Sr, Ba) were synthesized by a solid-state reaction method at 1300-1400°C under nitrogen-hydrogen atmosphere. The solubility of (SiN) + in MAl 2 O 4 was determined. Nitrogen can be incorporated into MAl 2 O 4 by replacement of (AlO) + by (SiN) + , whose amount of solubility depends on the M cation. The solubility of (SiN) + is very low in CaAl 2 O 4 and SrAl 2 O 4 lattices (x ≈ 0.025 and 0.045, respectively), whereas a large amount of (SiN) + can be incorporated into BaAl 2 O 4 (x ≈ 0.6). Incorporation of (SiN) + hardly modifies the luminescence properties of Eu 2+ -doped MAl 2 O 4 (M = Ca, Sr) because of limited solubility of (SiN) + , 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 (SiN) + 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 (LED) lighting applications.

Crystal and electronic structure of the novel nitrides MYSi4N7(M = Sr, Ba) with peculiar NSi4 coordination

The new ternary nitrides MYSi4N7 (M = Sr, Ba) have been investigated using first-principles techniques and experimental methods. The crystal structure data predicted are in good agreement with our measurements on prepared powder samples. Calculations also show that the electronic structure is strongly dependent on the local chemical bonding. The top of the valence bands is dominated by the 2p states of the N atoms coordinated to two Si atoms (NSi2), while the 2p states of the N atoms coordinated to four Si atoms (NSi4) lie about 1.0 eV below the top. The bottom of the conduction band is dominated by the Y 4d states. Both MYSi4N7 compounds are calculated to be wide band-gap semiconductors, with a band gap of about 2.9 eV, in reasonable agreement with the experimentally determined values (4.0 to 4.5 eV).