Doping effects of Nb5+ on red long afterglow phosphor CaTiO3:Pr3+

A series of Nb5+ codoped red long afterglow phosphors CaTi1 xNbxO3:Pr03.+002 (0 ≤ x ≤ 0.05) is prepared by a solid state reaction method. Their photoluminescence, phosphorescence and thermoluminescence are investigated. The results indicate that codoping Nb5+ can improve the photoluminescence and phosphorescence property of CaTiO3:Pr3+ significantly. When 3-mol% Nb5+ is codoped, the emission intensity of CaTiO3:Pr3+ is enhanced twice, while the afterglow time is extended from 10 min to about 40 min. Thermoluminescence results reveal that the trapping level of CaTiO3:Pr3+ is reduced from 0.82 eV to 0.62 eV by codoping Nb5+. The effect of Nb5+ doping on enhancing the photoluminescence intensity and afterglow time of CaTiO3:Pr3+ is discussed.     

Luminescence properties of Tm co-doped Sr2Si5N8:Eu red phosphor

The Sr₂Si₅N₈:Eu²⁺ phosphors, both undoped and doped with Tm³⁺, were synthesized by high temperature solid-state method. The XRD pattern shows that only Sr₂Si₅N₈ phase is formed whatever Tm³⁺ was doped or not. The peak positions of both phosphors are centered at 612 nm which is assigned to the 4f⁶5d→4f⁷ transition of Eu²⁺. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after the phosphor is doped with Tm³⁺. The afterglow time is about 10 min after Tm³⁺ ion is introduced into the phosphor. The concentration of Tm³⁺ has little influence on the afterglow time of the phosphor. The depths of trap energy level of the two phosphors were calculated based on the TL spectra. The depths of Sr₂Si₅N₈:Eu²⁺ and Sr₂Si₅N₈:Eu²⁺, Tm³⁺ are 1.75 and 1.01 eV, respectively.     

尿素用量对燃烧法合成CaAl_2O_4∶Eu~(2+),Nd~(3+)长余辉材料发光性能的影响

利用金属硝酸盐和尿素的氧化还原反应,通过燃烧法在600℃的炉温下合成了蓝紫色长余辉发光材料CaA l2O4∶Eu2 ,Nd3 。在金属硝酸盐溶液浓度不变的条件下,通过改变尿素与硝酸根的量的比,合成了多组长余辉材料样品。当尿素用量较少时,Eu3 不能完全被还原为Eu2 ;随尿素用量增加,样品的Eu3 特征发射减弱,余辉初始亮度和持续时间均得到改善;当尿素的用量达到理论用量的5倍时,样品余辉特性最好,继续增加尿素用量,余辉亮度和持续时间反而下降。将燃烧法制备的各组样品用活性炭密封,在1 000℃条件下反应2 h,使Eu3 完全被还原为Eu2 ,同时除去燃烧法反应不完全的杂质,可以一定程度提高材料的余辉发光性能。     

Influence of Tester Geometry,Speed and Procedure on the Results from a Ring Shear Tester

Automated ring shear testers have gained widespread acceptance in the chemical industry. In this paper, comparative measurements with different shear testers are described and possible factors influencing the measurement of flowability, are discussed. The measurement results presented show a dependency on the bulk solid investigated. No significant influence of the shear tester was measured for easy flowing bulk solids. An influence of the shear tester is observed for poor flowing, compressible bulk solids. Experiments have shown that test procedure and shear cell design (tester geometry) affect the measurements considerably.     

Metal Halide Regulated Photophysical Tuning of Zero-Dimensional Organic Metal Halide Hybrids: From Efficient Phosphorescence to Ultralong Afterglow

The photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP₂MX_n (MX_n=SbCl₅, MnCl₄, ZnCl₄, ZnCl₂Br₂, ZnBr₄), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP⁺ cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl₅²⁻ and MnCl₄²⁻, but significantly enhanced for the hybrids containing wide band gap non-emissive ZnCl₄²⁻. Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π–π stacking and intermolecular electronic coupling between TPP⁺ cations in TPP₂ZnCl₄ than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP₂ZnX₄ can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.     

Photoluminescence and thermoluminescence of Ce and Eu in Ca2Al2SiO7 matrix

The Ca₂Al₂SiO₇ samples doped with Ce³⁺ and Eu²⁺ are synthesized via a high temperature solid-state reaction. Ca₂Al₂SiO₇: Ce³⁺ emits a strong UV-violet emission while Ca₂Al₂SiO₇: Eu²⁺ emits a blue-green emission. The Stokes shift of the latter is greater due to a stronger crystal repulsion from ligands to Eu²⁺ ions. Ca₂Al₂SiO₇: Ce³⁺ exhibits a stronger initial intensity and longer duration of afterglow due to the higher liberated probability of the trapped carriers. The thermoluminescence curves reveal that at least three traps exist in the phosphors. Ca²⁺ vacancies may enhance the electron trapping and then lead to a stronger afterglow. A possible explanation will be provided.     

SrAl2O4∶Eu2+,Dy3+长余辉发光材料的喷雾热解制备及其表征

采用喷雾热解两段法制备了SrAl₂O₄∶Eu²⁺ ,Dy³⁺长余辉发光材料,并利用XRD、SEM、荧光长余辉亮度测试等方法分析了不同制备工艺条件下SrAl₂O₄∶Eu²⁺ ,Dy³⁺发光材料的结构、形貌以及发光性能的变化。结果表明:采用喷雾热解两段法可制备出球形SrAl₂O₄∶Eu²⁺ ,Dy³⁺长余辉发光材料,SrAl₂O₄∶Eu²⁺ ,Dy³⁺的晶体结构与α-SrAl₂O₄磷石英晶体结构相同。热解温度、还原温度、添加剂对产物的形貌、粒度分布、发光性能有较大影响。较之高温固相法,喷雾热解法制备的SrAl₂O₄∶Eu²⁺ ,Dy³⁺具有发光性能好、形貌好、粒度分布窄等优点。     

SrO/Al2O3比率对Sr2AlO4:Eu,Dy发光性能的影响

采用高温固相法合成稀土离子掺杂碱土铝酸盐发光粉,通过改变原料配比分别合成出富Sr和富Al的Sr2AlO4：Eu,Dy发光粉样品。XRD分析结果表明,SrO／Al2O3比率的微小变化不会影响样品的晶相组成。样品的发光性能和长余辉特性测试结果表明,富Al的Sr2AlO4：Eu,Dy发光粉具有较高的荧光强度及较长的余辉时间,说明Sr2AlO4晶格中SrO／Al2O3比率对Sr2AlO4：Eu,Dy发光性能和长余辉特性有很大的影响。激发与发射光谱、发射峰余辉衰减以及热释光谱分析表明,SrO／Al2O3比率的微小变化,导致晶格中发光中心Eu^2 浓度和陷阱的深度与密度发生改变。在富Sr体系中,稀土掺杂离子Eu^2 ,Dy^3 较难进入Sr^2 的晶格位置,晶格中发光中心Eu^2 浓度和陷阱密度都较低,使得粉体发光强度较低,余辉时间较短。     

Y2O2S:Eu3+,Mg2+,Ti4+红色材料的制备和长余辉性能

用高温固相法制备了Y2O2S：Eu^3 ,Mg^2 ,Ti^4 红色长余辉材料,余辉时间达到1h以上,X射线衍射测量表明材料的晶体结构为Y2O2S。发射光谱对应了Eu^3 离子^5DJ(J=0,1,2,3)→^7FJ(J=0,1,2,3,4))的特征发射;激发光谱主峰位于345nm,另外在260,396,468,540nm等处也存在激发峰。对比测量了Y2O2S：Eu^3 ,Mg^2 ,Ti^4 和Y2O2S:Eu^3 的热释发光曲线,Y2O2S:Eu^3 的热释发光曲线可以拟合成3个热释发光峰的叠加：237,226,301K;而Y2O2S：Eu^3 ,Mg^2 ,Ti^4 的热释发光曲线可以拟合成5个热释发光峰的叠加：149,215,262,287,334K,并计算了相应的陷阱能级。Ti^4 是引起较深陷阱能级的主要原因,Mg^2 起电荷补偿的作用。     

关于物理潜蚀作用及其概念模型的讨论

在对国内外物理潜蚀作用相关文献进行调研的基础上回顾了潜蚀作用的研究历史,对目前物理潜蚀作用研究中存在的问题进行了总结。指出潜蚀工程地质问题在各类工程建设活动中已经变得越来越突出,但由于潜蚀作用发生环境的多样性、作用方式的复杂性、发生过程的随机性等原因,造成实际应用中将各种潜蚀作用尤其是物理潜蚀作用过程的概念经常混淆。对"管涌"、"渗透压密"、"接触管涌"、"接触冲刷"、"流土"、"突涌"、"接触流土"、"流砂"、"流滑"等物理潜蚀作用的发生机理进行了深入细致的分析,在此基础上对目前一些界定不严格的物理潜蚀相关概念进行了辨析和澄清,初步建立了清晰的物理潜蚀作用概念模型,为潜蚀工程地质进一步研究奠定了基础。