Spectroscopic Properties of Ce：YAP Scintillation Crystal Grown by Temperature Gradient Technique

Spectroscopic properties of Ce-doped yttrium orthoaluminate （Ce：YA1O3 or Ce：YAP） crystals gown by temperature gradient technique （TGT） were investigated, and the effects of the growth conditions on the properties were analyzed. Methods of optical absorption （OA）, photoluminescence （PL）, photoluminescence decay （PLD）, X-my excited luminescence （XL） and cathodeluminescence （CL） were used in these investigations. The results showed that the absorption band peak at 202,394 and 532 nm originated from F and F^＋ color center induced by the weak reducing growth atmosphere, green emission band near 500 nm derived from Ce3^＋ -Ce^3＋ pairs and band at 650 - 850 nm from some unintentional impurity in crystals.     

Influence of the chromium and ytterbium co-doping on the photoluminescence of zinc selenide crystals

The luminescent properties of ZnSe, ZnSe：Cr（0.05 at.% Cr）, ZnSe：Yb（0.03 at.% Yb） and ZnSe：Cr：Yb（0.05 at.% Cr, 0.05 at.% Yb） crystals, doped during the growth process by the chemical vapor transport method, were studied within the temperature interval of 6–300 K. At the 6 K temperature in the visible spectral range 2 bands were observed： a band in the excitonic spectral region and a band of self-activated luminescence. It was shown that co-doping of zinc selenide crystals with the chromium and ytterbium led to the combination of the impurities influence on the photoluminescent properties. At the liquid helium temperature in the middle infrared range of the spectra of the ytterbium and chromium co-doped crystal a band with the maximum localized at 1.7μm was observed, which was overlapped with a complex band in the middle-IR spectral range, characteristic for the chromium doped ZnSe crystals. On the basis of obtained data an interaction mechanism of the chromium and ytterbium co-doping impurities was proposed. Guided by the existent model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made. It was assumed that the resonant energy transfer from one chromium ion to another,which led to the concentration quenching of the IR emission in the ZnSe：Cr PL spectra, would lead to the broadening of the IR emission in the spectra of ytterbium and chromium co-doped zinc selenide crystals.g     

Growth and Characterization of Perovskite K1-yLiyTa1-xNbxO3∶Ce

The grown Ce doped potassium lithium tantalite niobate (KLTN) crystals and characterize their physical properties were reported. The top seeded solution growth method was described. The specifics of a particular KLTN∶Ce growth were presented. X-ray diffraction spectra of paraelectric and ferroelectric KLTN crystals were illustrated. Dielectric and absorption studies on KLTN∶Ce were carried out compared with pure KLTN.     

Hydrothermal synthesis of Ce: LuzSiO5 scintillator powders

The synthesis of cerium-doped lutetium oxyorthosilicate (LSO) polycrystalline powders was investigated by a hydrothermal proc-ess. The precursor was obtained by the hydrothermal reaction of Lu(NO3)3 with Na2SiO3 at 200 ℃ for 10 h by using urea as precipitator, fol-lowed by a calcination uader proper temperatures. The results of XRD indicated that the precursor was crystallized into A-type LSO phase at 1000 ℃, and transfetrred to B-type LSO phase when temperature was raised above 1050 ℃. After being heated at 1250 ℃ for 2 h, single phase of B-type LSO powder was synthesized with homogeneous distribution of particle size ranging from 200 to 300 nm. The photolumi-nescence spectrum of as-synthesized LSO: Ce powders showed a typical broad emission peak centered at 404 nm, corresponding to the 5d1-4f transition of Ce3+.     

The association of different detergents with the photosynthetic reaction center protein of Rhodobacter sphaeroides R26 and the effects on its photochemistry

Detergent-free reaction centers from Rhodobacter sphaeroides R26 were used to study the solubilization of reaction centers in various detergents and their effects on reaction center photochemistry. 500 +/- 100 n-octyl-beta-D-glucopyranoside or 51 +/- 5 Triton X-100 molecules were associated with one reaction center. For N.N-alkylamine N-oxide detergents with chain lengths in the range from 8-13 carbon atoms, the number of detergent molecules associated with the reaction centers increased with decreasing chain length. The amount of detergent molecules associated with the reaction centers decreased almost tenfold if the pH was increased from pH 6 to pH 10. The addition of 5% 1,2,3-heptanetriol to various detergents lowered the detergent/reaction center ratio by a factor of two compared to that for the pure detergent. The detergent concentration at which solubilization of the reaction center occurs was close to the critical micelle concentration for all detergents studied. The absorption band at 865 nm of the primary donor in the reaction center shifts to 846 nm when detergent was removed from the reaction center; upon resolubilization with various detergents, this band shifts back to 865 nm. In 80-90% of the detergent-free reaction centers, the secondary electron transfer from QA to QB was inhibited: this electron transfer was restored after re-addition of detergent.     

Photorefractive Properties of Potassium Lithium Niobate Crystals with CeO2 and Nd2O3

KLN and Ce：Nd：KLN crystals were gown by Czochralski method and polarized into single ferroelectrics domain along c-axis. The properties of KLN and Ce：Nd：KLN crystals, such as Curie temperature, Raman spectra, exponential gain coefficient （Г） and thin crystal sheet effect, were measured. The results showed that the two spectra resembling Ce：Nd：KLN crystal were of tetragonal tungsten bronze structure, the exponential gain coefficient of Ce：Nd：KLN crystal was higher than that of KLN crystals and Ce：Nd：KLN crystal had thin crystal sheet effect, for its exponential gain coefficient increasing with crystal sheet thinning. The thin crystal sheet effect of Ce：Nd：KLN crystal was also discussed.     

Radiation induced color centers in cerium-doped and cerium-free multicomponent silicate glasses

The effect of doped cerium on the radiation-resistance behavior of silicate glass was investigated in our work. The ultraviolet-visible absorption spectra and electron paramagnetic resonance（EPR） spectra were obtained after the cerium-rich and cerium-free multicomponent silicate glasses（K509 and K9） were irradiated by gamma rays with a dose range from 10 to 1000 kGy. The results showed that E’ center, oxygen deficient center（ODC） and non-bridging oxygen hole center（HC1 and HC2） were induced in K9 and K509 glasses after radiation. The concentrations of all color centers presented an exponential growth with the increase of the gamma dose. Moreover, the concentration of HC1 and HC2 in cerium-doped K509 glass was much lower than that in cerium-free K9 glass at the same dose of radiation, which could be attributed to the following mechanism： Ce3＋ ions capturing holes then forming Ce3＋＋ centers inhibited the formation of hole trapped color centers（HC1 and HC2） and Ce4＋ ions capturing electrons to form Ce3＋ centers suppressed the formation of electron trapped color centers like E’ center.     

Improved photoluminescence of green-emitting phosphor Ca3Sc2Si3O12:Ce3+ for white light emitting diodes

Ca3Sc2Si3O12:Ce3+ phosphors with single-phase were successfully synthesized by a gel-combustion method.Annealing atmosphere greatly affected the luminescent properties of the phosphor.The intensity of absorption band at 450 nm was greatly increased with a reducing atmosphere,which was very suitable as a color converter in white LED.The absorption at 243 and 311 nm was gradually enhanced with a stronger reducing atmosphere and a new absorption peak at 362 nm appeared in N2+H2 mixing gas.The emission intensit...     

New Green Phosphors Ba（1-x）SrxZr（BO3）2 Doped with Tb^3＋ for PDP Applications

Thephosphorsusedinplasmadisplaypanel(PDP)deviceshouldemitvisiblelightundervacuum ultraviolet(VUV)excitationof147nmand or172nm fromXe Hegasplasma[1].Recentlylotsoftraditional lampphosphorshavebeenusedascommercialphos phorsforPDP.However,thesematerialsstill…     

Effects of aluminum co-doping on photoluminescence properties of Ce³⁺-doped SiO₂ glasses

SiO2 glasses co-doped with Al3+ ions were prepared by a sol-gel method by holding 0.5% of Ce3+ ions constant and varying the Al3+ ions concentrations.Thermal stability,the structural,chemical and the optical properties of the samples were studied by using differential scanning calorimetric(DSC),thermo gravimetric analysis(TGA),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),UV-vis spectroscopy and photoluminescence spectroscopy(PL).The DSC and TGA of samples depicted that the presence of dopant and co-dopant decreased the endothermic peak temperature and the yield respectively.SEM images showed that the particles were in the nano-range and spherical in shape.The XRD showed that all the samples were amorphous.The UV absorption measurements indicated that the presence of Al3+ ions significantly reduced the SiO2 absorption band,increased the absorbance intensity of SiO2 and decreased the transmittance as compared to the presence of the Ce3+ ions alone.The photoluminescence results displayed an optimum increase in luminescence intensity when the ratio of Al:Ce was 10:1 and further increase in aluminum content quenched the luminous intensity.     

Fast growth of cerium-doped lutetium yttrium orthosilicate single crystals and their scintillation properties

The growth of high-quality and large-size cerium-doped lutetium yttrium orthosilicate (Ce:(LuY)₂SiO₅, Ce:LYSO) crystals with lower cost has great influence on their applications in various physical devices. According to the chemical bonding theory of single crystal growth, the fast thermodynamic growth direction of Ce:LYSO is [010] direction. In this work, the maximum pulling rate of 3.5 mm/h is obtained along [010] direction of Ce:LYSO via the Czochralski (Cz) method. Finally, Ce:LYSO bulk single crystals with diameter of 64 mm and length of 220 mm and mass of 4.2 kg are grown. The luminescence performance of low-doped Ce:LYSO for nuclear irradiation (²²Na) detector device was studied. Light yield of 26193 ph/MeV and decay time of 38 ns are obtained. The present work provides a promising fast growth approach to achieving large size functional bulk crystal via both thermodynamic and kinetic controls.     

水解-红外吸收光谱法测定精四氯化钛中总油

精四氯化钛是海绵钛及钛生产的关键原材料,提高海绵钛及钛质量的关键在于控制精四氯化钛中杂质含量。由于生产工艺原因,精四氯化钛中含碳杂质主要为油类杂质,因此测定精四氯化钛中油类杂质含量,对精四氯化钛中碳杂质的分析具有重要意义。总油以碳为主要成分,具有红外吸收带,因此能够利用红外吸收光谱法实现测定。而四氯化钛与水气接触极易发生水解反应,生成的氯化氢同样具有红外吸收峰,且氯化氢与油类的吸收峰波数较接近,致使氯化氢干扰红外吸收光谱法测定四氯化钛原样中总油含量。实验建立水解-红外吸收光谱法测定精四氯化钛中总油含量的方法,将四氯化钛样品与水按体积比1∶25水解平衡后,采用四氯乙烯萃取水解溶液中的总油,通过外标定量分析精四氯化钛中总油含量。校准曲线中总油的线性范围为0～80 mg/L,相关系数r为0.999 9;总油的检出限为2.5 mg/kg。方法用于测定3个精四氯化钛样品中总油,结果的相对标准偏差(RSD,n=6)为3.5%～4.1%;加标回收率为96%～109%。     

水解-红外吸收光谱法测定精四氯化钛中总油

精四氯化钛是海绵钛及钛生产的关键原材料,提高海绵钛及钛质量的关键在于控制精四氯化钛中杂质含量。由于生产工艺原因,精四氯化钛中含碳杂质主要为油类杂质,因此测定精四氯化钛中油类杂质含量,对精四氯化钛中碳杂质的分析具有重要意义。总油以碳为主要成分,具有红外吸收带,因此能够利用红外吸收光谱法实现测定。而四氯化钛与水气接触极易发生水解反应,生成的氯化氢同样具有红外吸收峰,且氯化氢与油类的吸收峰波数较接近,致使氯化氢干扰红外吸收光谱法测定四氯化钛原样中总油含量。实验建立水解-红外吸收光谱法测定精四氯化钛中总油含量的方法,将四氯化钛样品与水按体积比1∶25水解平衡后,采用四氯乙烯萃取水解溶液中的总油,通过外标定量分析精四氯化钛中总油含量。校准曲线中总油的线性范围为0～80 mg/L,相关系数r为0.999 9;总油的检出限为2.5 mg/kg。方法用于测定3个精四氯化钛样品中总油,结果的相对标准偏差(RSD,n=6)为3.5%～4.1%;加标回收率为96%～109%。     

Fabrication of Ce-doped(Gd_2Y)Al_5O_(12)/Y_3Al_5O_(12) composite-phase scintillation ceramic

In this paper, a novel Ce(Gd_2 Y)Al_5O_(12)/Ce:Y_3Al_5O_(12)(Ce:GYAG/Ce:YAG) composite scintillation ceramic was designed and fabricated by a solid-state reaction method. The phase, luminescence and scintillation properties were investigated. The Ce:GYAG/Ce:YAG composite ceramic consisting of two-phase has a broad emission band ranging from 500 to 750 nm. The total mass attenuation coefficient of Ce:GYAG/Ce:YAG is 0.3864 cm~(-1), in between those of Ce:YAG and Ce:GYAG ceramics. In addition, the composite ceramic had a high light yield of 20430 ph/MeV. By controlling the ratio of GYAG and YAG, the composite ceramic can realize a spectrum design and total mass attenuation coefficient control to meet the requirements for wide-X-ray-energy-range detectors.     

Exploring the energy transfer processes in Lu2(1–x)Y2xSiO5:Ce crystals

A systematical exploration of energy transfer processes in Lu_(2(1-x)Y_2 xSiO_5:Ce(LYSO) crystals under vacuum ultraviolet-ultraviolet(VUV-UV) excitation was implemented. The relationship between energy transfer and scintillation properties was established. It is revealed that there are mainly three energy transfer types in the crystal i.e. host → Ce1/Ce2/STEs, Ce1 →Ce2 and STEs → Ce1/Ce2. The influence of Y content of the LYSO crystals on the energy transfer efficiency of the above processes was carefully analyzed. Besides, we find a special component of the crystal i.e. Y content = 45 at% at which the energy resolution and light output of the crystal perform the worst.     

电感耦合等离子体原子发射光谱法测定La、Ce、Yb基体中痕量稀土杂质的多元光谱拟合校正限度

考察了La、Ce和Yb等基体元素对稀土杂质元素测定的光谱干扰。在杂质元素谱线窗口内,La、Ce和Yb所产生的干扰线总数量比文献报导的少,且当基体元素浓度增大时,在杂质元素谱线窗口内出现一些未曾报道过的谱线。经多元光谱拟合（MSF）法校正,基体元素的光谱干扰得到有效消除,杂质元素的检出限明显降低,但仍达不到没有La、Ce和Yb时的水平。当测定质量浓度为0100 μg/mL杂质元素时允许质量浓度为1 000～2 000 μg/mL基体元素存在,当被测的杂质浓度进一步降低时允许基体元素的最高浓度也随之降低。建立MSF模型时,应使建模溶液中杂质元素浓度是这些元素检出限的100倍,基体元素浓度接近实际样品中基体的存在量,MSF建模数据与样品测定数据还须在同一实验条件下完成。     

Characterization of the reaction center bound tetraheme cytochrome of Rhodocyclus tenuis

Properties of the tetrahemic reaction center bound cytochrome have been investigated by different techniques. The mid-point potentials of the four hemes were determined by redox titration. The best fit of the data was obtained with a (n = 1) Nernst curve by using the following values of the redox parameters: Em = +420 mV for the two high-potential hemes and Em = +110 and +60 mV for the two low-potential hemes. The mid-point potentials of the two high-potential hemes are the highest reported so far. The spectral properties of the four hemes in the alpha-band have been determined by absorption spectroscopy and measurements of light-induced difference spectra in membranes of Rhodocyclus tenuis. The two high potential hemes present very similar spectra centered at 557 nm. The absorption spectra of the two low-potential hemes are very similar, and their alpha-band centered around 551 nm. Spectral properties at 100 K and the linear dichroism of optical transitions allow the determination of the relative orientations of the hemes with respect to the membrane plane. The orientation patterns thus obtained corresponds to none of the arrangements described so far for reaction center bound cytochromes.     

The active site of the bacterial nitric oxide reductase is a dinuclear iron center

A novel, improved method for purification of nitric oxide reductase (NOR) from membranes of Paracoccus denitrificans has been developed. The purified enzyme is a cytochrome bc complex which, according to protein chemical and hydrodynamic data, contains two subunits in a 1:1 stoichiometry. The purified NorBC complex binds 0.87 g of dodecyl maltoside/g of protein and forms a dimer in solution. Similarly, it is dimeric in two-dimensional crystals. Images of these crystals have been processed at 8 A resolution in projection to the membrane. The NorB subunit is homologous to the main catalytic subunit of cytochrome oxidase and is predicted to contain the active bimetallic center in which two NO molecules are turned over to N2O. Metal analysis and heme composition implies that it binds two B-type hemes and a nonheme iron but no copper. NorC is a membrane-anchored cytochrome c. Fourier transform infrared spectroscopy shows that carbon monoxide dissociates from the reduced heme in light and associates with another metal center which is distinct from the copper site of heme/copper oxidases. Electron paramagnetic resonance spectroscopy reveals that NO binds to the reduced enzyme under turnover conditions giving rise to signals near g = 2 and g = 4. The former represents a typical nitrosyl-ferroheme signal whereas the latter is a fingerprint of a nonheme iron/NO adduct. We conclude that the active site of NOR is a dinuclear iron center.     

Ab Initio Calculation of 4f→5d Transition Energy and Electronic Structure of Ce3+ Doped in LiYF4 Crystal

The electronic structures of LiYF4:Ce3 and LiYF4 crystals simulated by an embedded (in a microcrystal containing 1938 ions) cluster CeY4Li8F24, and Y5Li8F24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa(discrete variational Xa) method. The ground-state calculation showed that only the lowest 5d level Ed of Ce3 ion lies around the BCB (bottom of the conduction band) while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4p of Y mixed with 5d of Ce, even for the wavefunctions (WFS) of Ed under BCB there are still 24% of Y-4p and 9% of F-2p as components. Furthermore, transition state (TS) calculation was performed in this work to obtain the 4f→5d transition energies Efd, to improve the calculation of Ref.[6] in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare directly with the observed 4f→5d transition energies. The ionic radius of Ce3 is larger than that of Y3 , for modeling approximately the lattice relaxation, we simply let the eight fluorine ions of the nearest-neighbor and next-nearest-neighbor move out radially and simultaneously. As results, the CeY4Li8F24 cluster with 4.56% outward relaxation of the eight fluorines has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the calculated ground-state Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure (including zero-phonon line) of the lowest 5d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is somehow around 4.56%～7.36% outward, not as large as 10%.     

Crystallographic Analysis of Tapering of ADP Crystallites

On the basis of crystallographic characteristics of ADP (ammonium dihydrogen phosphate) crystals and the selected growth conditions, the growth habit of ADP crystals was studied. In comparison with pyramidal planes, the growth rate of prismatic faces is slower and more sensitive to the additives and impurities for ADP crystals. When the supersaturation is low, the advance of growth steps on prismatic face can be blocked by ethanol or impurities, the crystal morphology is changed from the tetragonal prism to shuttle (i.e., the tapered shape). The tapering formation of ADP crystallites was structurally studied in a novel view.