Near-infrared to visible up-conversion emissions of Er^3＋ doped Al2O3 powders derived from the sol-gel method

The Er3 doped Al2O3 powders were prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3.5H2O]. The different phase structure, including three crystalline types of (Al,Er)2O3 phases, γ, θ, α, and two Er-Al-O phases, ErAlO3 and Al10Er6O24, was obtained with the 1 mol% Er3 doped Al2O3 powders at the different sintering temperatures of 600―1200℃. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3 , were detected by a 978 nm semiconductor laser diodes excitation. The phase structure and OH content had evident influence on the up-conversion emissions intensity. The maximum intensities of both the green and red emissions were obtained respectively for the Er3 doped Al2O3 powders sintered at 1200 ℃, which was composed mainly of α-(Al,Er)2O3, less of ErAlO3 and Al10Er6O24 phases, and with the least OH content. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er3 doped Al2O3 powders.     

Effects of Yb^3＋ codoping on visible and near infrared emissions of Er^3＋-Yb^3＋ codoped Al2O3 powders by the sol-gel method

The 0.1 mol% Er^3＋ and 0-2 mol% Yb^3＋ codoped Al2O3 powders were prepared by the sol-gel method, and the phase structure, including only two crystalline types of doped Al2O3 phase, γ-（Al,Er, Yb）2O3 and θ-（Al,Er, Yb）2O3, was detected at the sintering temperature of 1000℃. The visible and near infrared emissions properties depended strongly on the Yb^3＋ codoping, and the corresponding maximal peak intensities centered at about 523, 545, 660 and 1533 nm were obtained respectively for the 0.1 mol% Er^3＋ and 0.5 mol% Yb^3＋ codoped Al2O3 powders, which were composed of θ-（Al,Er,Yb）2O3 and a small amount of γ-（Al,Er, Yb）2O3 phases. The two-photon absorption process was responsible for the visible up-conversion emissions, and the one-photon absorption process was involved in the near infrared emissions of the Er^3＋-yb^3＋ codoped Al2O3 powders.     

Preparation of Zn-doped TiO2 nanotubes electrode and its application in pentachlorophenol photoelectrocatalytic degradation

Zn-doped titanium oxide （TiO2） nanotubes electrode was prepared on a titanium plate by direct anodic oxidation and immersing method in sequence. Field emission scanning electron microscopy （FESEM） showed that the Zn-doped TiO2 nanotubes were well aligned and organized into high density uniform arrays with diameter ranging from 50 to 90 nm. The length and the thickness were about 200 and 15 nm respectively. TiO2 anatase phase was identified by X-ray diffraction （XRD）. X-ray photoelectronspectroscopy （XPS） indicated that Zn ions were mainly located on the surface of TiO2 nanotubes in form of ZnO clusters. Compared with TiO2 nanotubes electrode, about 20 nm red shift in the spectrum of UV-vis absorption was observed. The degradation of pentachlorophenol （PCP） in aqueous solution under the same condition （initial concentration of PCP： 20 mg/L; concentration of Na2SO4：0.01 mol/L and pH： 7.03） was carried out using Zn-doped TiO2 nanotubes electrode and TiO2 nanotubes electrode. The degradation rates of PCP using Zn-doped TiO2 nanotubes electrode were found to be twice and 5.8 times as high as that using TiO2 nanotubes electrode by UV radiation （400 μw/cm^2） and visible light radiation （4500 μw/cm^2）, respectively. 73.5% of PCP was removed using Zn-doped TiO2 nanotubes electrode against 45.5% removed using TiO2 nanotubes electrode in 120 min under UV radiation. While under visible light radiation, the degradation efficiency of PCP was 18.4% using Zn-doped TiO2 nanotubes electrode against 3.2% using TiO2 nanotubes electrode in 120 min. The optimum concentration of Zn doping was found to be 0.909%. The PCP degradation efficiencies of the 10 repeated experiments by Zn-doped TiO2 nanotubes electrode were rather stable with the deviation within 3.0%.     

Effects of Yb～(3 ) codoping on visible and near infrared emissions of Er～(3 )-Yb～(3 ) codoped Al_2O_3 powders by the sol-gel method

The 0.1 mol% Er3 and 0―2 mol% Yb3 codoped Al2O3 powders were prepared by the sol-gel method,and the phase structure,including only two crystalline types of doped Al2O3 phase,γ-(Al,Er,Yb)2O3 and θ-(Al,Er,Yb)2O3,was detected at the sintering temperature of 1000℃. The visible and near infrared emissions properties depended strongly on the Yb3 codoping,and the corresponding maximal peak intensities centered at about 523,545,660 and 1533 nm were obtained respectively for the 0.1 mol% Er3 and 0.5 mol% Yb3 codoped Al2O3 powders,which were composed of θ-(Al,Er,Yb)2O3 and a small amount of γ-(Al,Er,Yb)2O3 phases. The two-photon absorption process was responsible for the visible up-conversion emissions,and the one-photon absorption process was involved in the near infrared emissions of the Er3 -Yb3 codoped Al2O3 powders.     

Preparation, characterization and photodegradation of methylene blue based on TiO2 microparticles modified with thiophene substituents

The new microparticles,2-formylthiophene(FT)/TiO2 and(E)-1,2-bis(5-formyl-2-thienyl) ethylene(EBFTE)/TiO2 were synthesized with a silane coupling agent.The prepared TiO2 composites were characterized using Ultraviolet-Vis absorption(UV-Vis),X-ray diffraction(XRD),scanning electron microscope(SEM) and thermogravimetric analyzer(TGA).Methylene blue was used as a model material to examine the photocatalytic activities of the prepared catalysts under both Ultraviolet-Vis(UV) and visible(Vis) light.The enhanced photocatalytic activities were observed in the presence of(FT)/TiO2 and EBFTE/TiO2 under Vis light.It suggests that FT or EBFTE plays a block or active role in the photodegradation mechanisms under UV and Vis light irradiation,respectively.     

Investigation of the electronic structure and photoluminescence properties of Eu3＋ in Sr2Mgl_xZnxSi207 （0 〈x 〈 1）

Undoped and Eu 3+-doped Sr 2 Mg 1-x Zn x Si 2 O 7 (0≤x≤1) powder crystals were obtained by conventional solid-state reaction.X-ray diffraction,inductively coupled plasma analysis,and Fourier transform infrared spectroscopy results implied that a complete solid-solution formed between Sr 2 MgSi 2 O 7 and Sr 2 ZnSi 2 O 7 as well as local structural adjustment.Excitation spectra exhibited O 2-Eu 3+ charge transfer (CT) bands centered at 250 nm for Sr 2 MgSi 2 O 7:Eu 3+ and 258 nm for Sr 2 ZnSi 2 O 7:Eu 3+.Emission spectra exhibited a major band around 616 nm,which showed the environment around Eu 3+ was non-centrosymmetric in both Sr 2 MgSi 2 O 7:Eu 3+ and Sr 2 ZnSi 2 O 7:Eu 3+.In addition,first principles calculations within the local density approximation (LDA) of density functional theory (DFT) were used to calculate the electronic structure of Sr 2 MgSi 2 O 7 and Sr 2 ZnSi 2 O 7.Calculated results were correlated with experimental UV-vis reflection spectra and the observed shift of the O 2-Eu 3+ CT band.     

Photocatalytic oxidation of gaseous benzene over nanosized TiO2 prepared by solvothermal method

Nanosized TiO2 particles were prepared by solvothermal method using tetrabutyl titanate as precursor,ethanol and water as solvents,and a facile immobilization method of nanosized TiO2 particles on woven glass fabric was developed. The samples obtained under various preparation conditions were charac-terized by means of thermo gravimetric analysis(TG) and differential scanning calorimetry(DSC) ,X-ray diffraction(XRD) ,transmission electron microscopy(TEM) ,high resolution-transmission electron mi-croscopy(HR-TEM) ,and Brunauer-Emmett-Teller(BET) . The results show that the cube-shape of TiO2 prepared by solvothermal method has good crystallinity of(101) surface,higher thermal stability and large specific surface area. Scanning electron microscopy(SEM) images confirmed that the immobi-lized TiO2 film was uniformly distributed and clung to the substrate firmly. The photocatalytic activity of the catalysts was tested using photocatalytic oxidation of gaseous benzene. The results show that the TiO2 calcined after solvothermal treatment suffers from lower specific surface area,and hence de-creases its photocatalytic activity. The photocatalytic activities of the TiO2 by solvothermal treatment with or without calcination in degradation 400 mg/m3 benzene are 3.7 and 4.1 times as high as catalyst without solvothermal treatment,respectively.     

Preparation and performance of dye-sensitized solar cells based on ZnO-modified TiO_2 electrodes

The ZnO-modified TiO 2 electrode was prepared by adding Zn(CH 3 COO) 2 ·2H 2 O to the TiO 2 colloid during the sol-gel production process,and was used in dye-sensitized solar cells (DSCs).The open circuit voltage (V OC) and fill factor (ff) of the cells were improved significantly.The performances of the ZnO-modified TiO 2 electrode such as dark current,transient photocurrent,impedance,absorption spectra,and flat band potential (V fb) were investigated.It is found that the interface charge recombination impedance increases and V fb shifts about 200 mV toward the cathodic potential.The effect mechanism of ZnO modification on the performance of DSCs may be that ZnO occupies the surface states of the TiO 2 film.     

Preparation,Characterization and Solar Photocatalytic Activity of P-YFeO_3-N-TiO_2 Nanojunctions

1 Results YFeO3-TiO2 composite photocatalysts with p-n heterojunction have been prepared by physical amalgamation.The physical and photophysical properties of the composites were characterized by XRD,TEM,UV-vis/DRS,XPS.Effects of calcination temperature and constitute content on structure and surface characterization were also investigated.Results show that the presence of p-n junction not only has visible light harvesting but potential force for hole-electron pair separation.A preliminary investigation of photocatalytic activity on orange II showed that YFeO3-TiO2 heterojunctions could be activated under visible light irradiation.The optimum photocatalytic junction is w(TiO2) =90% in the composites after calcining at 600 ℃.The improved photocatalytic activity,comparing with that of pure TiO2 and pure YFeO3,might attribute to the p-n heterojunction composed of p-type YFeO3 and n-type TiO2.Study of the process of electron and hole migratation will facilitate the exploitation of novel,highly efficient,visible-light-driven photocatalyst.     

Selective catalytic reduction of NO x by hydrogen over modified Pd/TiO2-Al2O3 catalyst under lean-burn conditions

A series of Ni, Sn and Ca modified Pd/TiO2-Al2O3 catalysts were prepared by the incipient wetness impregnation method and their catalytic performance for the selective catalytic reduction of NOx by H2 was evaluated. The results showed that the NOx conversion and N2 selectivity were improved over Pd-Sn/TiO2-Al2O3 and Pd-Ni/TiO2- Al2O3 catalysts above 200 ℃. More importantly, the N2 selectivity and high-temperature activity of Pd-Sn/TiO2- Al2O3 catalyst was far superior to the single Pd/TiO2-Al2O3 catalyst. The optimal Sn loading was 2 wt.%. X-ray diffrac- tion （XRD） results showed that the interaction between Pd and Sn promotes the dispersion of Pd over TiO2-Al2O3. Temper- ature-programmed reduction （Ha-TPR） results demonstrated that the addition of Sn contributes to the formation of PdO and improving the redox property of Pd/TiOz-Al2O3. The addi- tives of Ni and Sn also facilitated the absorption of NOx and the oxidation of NO to NOa, which play important roles in the selective catalytic reduction of NOx by hydrogen.     

Cr3+掺杂的TiO2纳米复合微粒的合成及表征

利用酸催化的溶胶-凝胶法合成了一系列不同Cr3 掺杂量的TiO2纳米复合微粒.用XRD,TEM,UV-Vis等技术进行了结构表征.结果表明利用该法所合成的Cr3 /TiO2纳米复合微粒尺寸小(约10 nm),粒度分布范围窄;在所研究的掺杂量范围内(x:0～0.1000),该纳米复合粒子的粒径随Cr3 掺杂量的增加呈减小的趋势,但幅度不大.从XRD中,没有发现Cr2O3相的偏析和TiO2由锐钛矿向金红石的相转变;TiO2的衍射峰随Cr3 掺杂量的增加有宽化和强度减弱的现象.UV-Vis光谱结果显示:由于Cr3 的加入,该纳米复合微粒对光的吸收拓展到了可见区,同时随着Cr3 掺杂量的增加,对可见光的吸收强度显著增强.     

Y2O3：Er纳米透明陶瓷的制备及其显微结构研究

以甘氨酸为燃烧剂,采用低温燃烧法制备了Y2O3：Er纳米前驱体粉末,采用XRD和TEM对纳米粉末的物相结构及其形貌进行了表征,结果表明前驱纳米粉末为分散均匀、轻微硬团聚、粒径均一、Y2O3立方晶相。前驱纳米粉末经研磨、高压钢模成型和1570℃真空烧结6h得到Y2O3：Er透明陶瓷。通过光学显微镜对陶瓷表面及断裂面观察和分析,定性讨论了低温燃烧法制备的纳米粉体的特性对陶瓷透光性的影响。     

低温合成TiO2/Fe3O4磁载光催化剂的光催化性能研究

采用化学共沉淀法合成的磁性纳米Fe₃O₄为磁核,以钛酸四丁酯为原料,通过溶胶-凝胶法,在较低温度下合成了TiO₂/Fe₃O₄磁性光催化剂。利用XRD、TEM、SEM-EDX等分析方法对合成催化剂的相组成、形貌、粒度、元素分布等进行了表征;研究了不同焙烧温度及TiO₂/Fe₃O₄比例对降解罗丹明B光催化活性及磁分离回收性能的影响。结果表明,在100、300和450 ℃焙烧温度下磁性光催化剂的催化活性依次降低,较低温度(100 ℃)制备的催化剂具备较高的催化活性;当TiO₂质量分数处于67.3%～73.0%时,催化剂既具有较高的光催化降解活性也具有较好的磁分离回收性能;光催化剂TiO₂/Fe₃O₄（100 ℃,TiO₂质量分数70%）在循环使用5次后,在降解75 min时仍能达到对罗丹明B 99%的脱色率和90%的回收率。     

水热法合成Y2O3 ∶ Yb3+,Er3+上转换材料及发光特性

以Y2O3,Yb2O3和Er2O3为原料,利用水热法制备Y2O3,Yb3+,Er3+纳米上转换材料.通过X射线粉末衍射、扫描电镜和透射电镜对材料的晶型、成分、粒径及表面形貌进行分析.实验结果表明:所得粉体的晶型为立方晶系,晶粒为圆球形,平均粒径为20 nm.在波长为980 nm半导体激光器激发下产生绿色和红色的上转换荧光;改变Yb3+,Er3+的掺杂比例,激发产生的绿光和红光的荧光强度随Yb3+,Er3+掺杂比例的改变而发生变化.     

复合催化剂AgI-Ag3PO4/TiO2纳米带的制备及其光催化性能研究

通过化学沉淀法在TiO₂纳米带上首先制备了Ag₃PO₄/TiO₂,然后利用离子交换法成功将AgI负载到Ag₃PO₄上,制备了具有优异催化活性的复合催化剂AgI-Ag₃PO₄/TiO₂。利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X-射线衍射仪（XRD）、X-射线光电子能谱（XPS）等分析方法对复合催化剂的形貌、晶型结构、元素组成等进行了表征,结果表明：TiO₂纳米带形貌规整,宽度在50~400 nm之间,AgI-Ag₃PO₄纳米颗粒均匀地负载于TiO₂纳米带表面;TiO₂纳米带晶型为典型锐钛矿相,AgI为六方晶相的β-AgI,Ag₃PO₄为立方晶相;AgI-Ag₃PO₄/TiO₂中Ag元素以+1价态存在于催化剂中,没有Ag单质析出,表明复合催化剂结构稳定。以罗丹明B作为复合光催化剂的模型反应物,评估了不同批次、AgI/Ag₃PO₄不同比例催化剂的光催化性能,结果显示：AgI-Ag₃PO₄/TiO₂系列催化剂的催化活性均高于单独的TiO₂、Ag₃PO₄和AgI;当AgI与Ag₃PO₄物质的量比为3∶5时,AgI-Ag₃PO₄/TiO₂具有最高的光催化效率,该催化剂在30 min后对罗丹明B的降解率可达到98.7%,并且在多次重复实验后仍然保持较高的催化活性。     

Preparation and luminescence characteristics of Sr3SiO5：Eu^2＋ phosphor for white LED

The Sr3SiO5：Eu^2＋ phosphor was synthesized by high temperature solid-state reaction. The emission spectrum of Sr3SiO5：Eu^2＋ shows two bands centered at 487 and 575 nm, which well agree with the theoretic values of emission spectrum. The excitation spectrum for 575 nm emission center has several excitation bands at 365, 418, 458 and 473 nm. And the results show that the emission spectrum of Sr3SiO5：Eu^2＋ is influenced by the Eu^2＋ concentration. The relative emission spectra of the white-emitting InGaN-based YAG：Ce^3＋ LED and Sr3SiO5：Eu^2＋ LED were investigated. The results show that the color development of InGaN-based Sr3SiO5：Eu^2＋ is better than that of InGaN-based YAG：Ce^3＋, and the CIE chromaticity of InGaN-based Sr3SiO5：Eu^2＋ is （x=0.348, y=0.326）.     

Er3+/Y3+/Yb3+共掺杂氧化铝光致发光增强研究

采用sol-gel法制备了不同摩尔比例的Er3+/Y3+/Yb3+共掺杂Al2O3粉末.X射线衍射(XRD)结果表明各样品均以δ-Al2O3为主相.利用荧光光谱仪测试各样品的光致发光(PL)谱,结果表明Y3+的共掺杂明显的提高了Er3+的PL强度.Er3+/Y3+/Yb3+共掺杂Al2O3粉末的PL强度随着Yb3+浓度呈先增大后减小的变化,Er3+∶Y3+∶Yb3+的摩尔比例为1∶20∶10时,样品的PL强度在Y3+共掺杂的Er3+∶Al2O3粉末的PL强度提高了7倍的基础上进一步提高了近4倍,说明Er3+/Y3+/Yb3+的共掺杂能够更有效地提高Er3+的PL强度.