Crystal Structure of Scheelite-type LiTb(WO_4)_2 and Multi-color Emitting Properties Doped by Eu~(3+)

Single crystal of lithium terbium tungstate LiTb(WO4)2 has been grown by the flux method. The crystal structure was refined from single-crystal X-ray data. It crystallizes in tetragonal system, space group I41/a with a = 5.1749(9), c = 11.1953(19) ?, V = 299.81(12) ?~3, Z = 2, Mr = 661.56, Dc = 7.328 g/cm^3, F(000) = 560, μ(MoKα) = 49.94 mm^-1, R(F^2 > 2σ(F^2)) = 0.026 and wR(F^2) = 0.070. It features a typical scheelite-type structure composed of two-direction packing of isolated WO4 tetrahedra. Li and Tb atoms in the structure occupy the same crystallographic site. Moreover, a series of solid solution phosphors LiTb(1-x)Eux(WO4)2(x = 0.004~0.1) were synthesized by high temperature solid-state reactions. The phosphors could be effectively excited by a wavelength range from 379 to 487 nm, which matches well with the UV and near-UV LED chip. The emission color of the phosphor can be tuned from green, through yellow to red by simply adjusting the relative Eu³⁺ and Tb³⁺ concentration due to the Tb³⁺ to Eu³⁺ energy transfer.     

Energy Transfer and Green Emitting Properties of Solid Solution PbGd_(1-x)Tb_xB_7O_(13)(x = 0～1)

A series of Tb-doped solid solutions PbGd_(1-x)Tb_xB_7O_(13)(x = 0~1) were synthesized by high-temperature solid state reaction method. The luminescence properties were investigated under UV(274 nm) and near-UV(372 nm) excitation. The emission spectrum by 274 nm exciting reveals a charge-transfer between Gd~(3+) and Tb~(3+) ions. Under near-UV light(372 nm) excitation, PbGd_(1-x)Tb_xB_7O_(13):x Tb~(~(3+)) exhibits intense green emission centered at 543 nm due to the ~5D_4→~7F_5 transition of Tb~(3+) activator. The optimum doping concentrations were found to be x = 0.8 with the quantum efficiency of 35%. One may expect that PbGd_(1-x)Tb_xB_7O_(13) has the potential to be used as a green phosphor activated by near near-UV light.     

Crystal Structure and Luminescent Properties of a New Rare-earth Borate K_3Pr_3(BO_3)_4

A new borate K_3Pr_3(BO_3)_4 has been prepared using a high temperature flux method and structurally characterized by single-crystal X-ray diffraction analyses.It crystallizes in triclinic system,space group ■ with a=9.0814(10),b=10.8052(12),c=14.0885(16)?,α=69.800(1)°,β=89.922(1)o,γ=89.892(1)°,V=1297.4(3)?~3,Z=4,M_r=775.27,D_c=3.969 g/cm~3,F(000)=1400,μ(Mo Kα)=12.11 mm~(-1),R(F~22σ(F~2))=0.028 and wR(F~2)=0.054.Interestingly,the crystal of K_3Pr_3(BO_3)_4 was twinned by pseudo-merohedry that is mimic monoclinic space group P2/c.The structure of K_3Pr_3(BO_3)_4 exhibits a three-dimensional(3D)network based on isolated anionic(BO_3)~(3-)units that are further bridged by K~+and Pr~(3+)ions.Furthermore,X-ray diffraction(XRD),IRspectrum and photoluminescence(PL)properties were studied.     

分级燃烧稳定性的数值计算

发展低NOx燃烧技术,一个主要方法是通过分级燃烧组合燃烧过程来满足工况下的低污染排放要求.实现该技术的一个关键技术是如何在运行中避免或控制非稳定振荡燃烧.通过对分级燃烧系统的非稳态数值模拟,可以看列燃烧系统动态特性不仅与每个进口的安排有关,也和频率密切相关.通过构建火焰传递函数,可以定量分析火焰动态变化的大小和它们之间的相位关系.这些结果可以帮助我们在设计和运行分级燃烧系统时,防止可能出现的振荡燃烧,实现燃烧系统在全工况下安全、高效运行.