Upconversion Luminescence Properties of Ho^(3+),Tm^(3+),Yb^(3+) Co-Doped Nanocrystal NaYF_4 Synthesized by Hydrothermal Method

Nanocrystal of upconversion （UC） phosphor Ho^3＋, Tm^3＋ , and Yb^3＋ co-doped NaYF4 was prepared by the hydrothermal method in the presence of the complexing agent EDTA. Under 980 nm diode laser excitation, the impact of different concentrations of Ho^3＋ ion on the UC luminescence intensity was discussed. The law of luminescence intensity versus pump power shows that the 474 nm blue emission, 538 nm green emission, and 642 nm red emission are all due to the two-photon process, while the 450 nm blue emission is a three-photon process. The UC mechanism and processes were also analyzed. The sample was characterized by transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The result shows that Ho^3＋ ,Tm^3＋ , and Yb^3＋ co-doped NaYF4 prepared by the hydrothermal method exhibits a hexagonal nanocrystal.

Gain properties of germanate glasses singly doped with Tm^(3+) and Ho^(3+) ions

Two kinds of germanate glasses singly doped with the ion concentration of 2.0mol.%Tm3＋ and 2.0mol.%Ho3＋, respectively, were prepared.According to McCumber theory, the absorption and stimulated emission cross-sections corresponding to the 3H6←→3F4 transitions of Tm3＋（at 1.8 μm） and the 5I8←→5I7 transitions of Ho3＋（at 2.0 μm） were obtained, and respective gain cross-section spectra were also computed as a function of population inversion according to absorption and emission cross-sections and the ion concentrations.For Tm3＋-doped germanate glasses, the maximum of the absorption, emission, and gain cross-sections reached a value higher than those reported for fluorozirconate, fluoride, and oxyfluoride glasses.For Ho3＋-doped germanate glasses, the maximum of absorption, emission, and gain cross-sections reached a value higher than that reported for fluorozircoaluminate glasses.Hence, these Tm3＋-doped and Ho3＋-doped germanate glasses exhibited an advantage for application in mid-infrared lasers at about 1.8 and 2.0 μm wavelength.

The effects of Er^(3+) ion concentration on 2.0-μm emission performance in Ho^(3+)/Tm^(3+) co-doped Na_(5)Y_(9)F_(32) single crystal under 800-nm excitation

Na_(5)Y_(9)F_(32) single crystals doped with ~0.8-mol% Ho^(3+),~1-mol% Tm^(3+),and various Er^(3+) ion concentrations were prepared by a modified Bridgman method.The effects of Er^(3+)ion concentration on 2.0-μm emission excited by an800-nm laser diode were investigated with the help of their spectroscopic properties.The intensity of 2.0-μm emission reached to maximum when the Er^(3+) ion concentration was ~1 mol%.The energy transfer mechanisms between Er^(3+),Ho^(3+),and Tm^(3+) ions were identified from the change of the absorption spectra,the emission spectra,and the measured decay curves.The maximum 2.0-μm emission cross section of the Er^(3+)/Ho^(3+)/Tm^(3+)tri-doped Na_(5)Y_(9)F_(32) single crystal reached 5.26 × 10^(-21) cm^(2).The gain cross section spectra were calculated according to the absorption and emission cross section spectra.The cross section for ~2.0-μm emission became a positive gain once the inversion level of population was reached 30%.The energy transfer efficiency was further increased by 11.81% through the incorporation of Er^(3+) ion into Ho^(3+)/Tm^(3+) system estimated from the measured lifetimes of Ho^(3+)/Tm^(3+)-and Er^(3+)/Ho^(3+)/Tm^(3+)-doped Na_(5)Y_(9)F_(32)single crystals.The present results illustrated that the Er^(3+)/Ho^(3+)/Tm^(3+)tri-doped Na_(5)Y_(9)F_(32) single crystals can be used as promising candidate for 2.0-μm laser.

Effect of Er substituting sites on upconversion luminescence of Er^(3+)-doped BaTiO_3 films

Erbium-doped BaTiO3 films on LaNiO3/Si substrates were fabricated by sol-gel method. The crystalline structure, morphologies and upconversion （UC） luminescence properties of films were respectively investigated by X-ray diffraction （XRD）, atomic force microcopy （AFM） and photoluminescence （PL）. The results indicate that both of the microstructure and luminescence are found to be dependent on Er^3＋ substituting sites. The samples with A-site substitution have smaller lattice constants, larger grains and smoother surface than those with B-site substitution. The photoluminescence spectra show that both of the samples have two stronger green emission bands centered at 528 and 548 nm and a weak red emission band centered at 673 nm, which correspond to the relaxation of Er^3＋ from ^2H11/2, ^4S3/2, and ^4F9/2 levels to the ground level ^4I15/2, respectively. Compared with B-site doped films, A-site doped films have a stronger integrated intensity of green emissions and a weaker relative intensity of red emissions. The differences could be explained by the crystalline quality and cross relaxation （CR） process.

亲水性CIT-NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子的制备及其发光性能研究

采用溶剂热法制备了油溶性稀土掺杂上转换纳米粒子NaYF_(4)∶Yb^(3+),Ho^(3+),并利用TEM、XRD、IR、荧光光谱法等考察了反应温度、反应时间、掺杂比等反应条件对纳米粒子形貌、结构、发光性能的影响。结果表明,在反应温度为300℃、反应时间为50 min、稀土离子掺杂比为NaYF_(4)∶20%Yb^(3+),2%Ho^(3+)条件下,制备出的油溶性NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子呈标准六方晶型,尺寸均一、单分散性好,平均粒径为31.55 nm。通过表面配体交换法成功将柠檬酸修饰在其表面,转为亲水性CIT-NaYF_(4)∶Yb^(3+),Ho^(3+)纳米粒子。

Preparation of Zr-doped CaTiO_3 with enhanced charge separation efficiency and photocatalytic activity

A series of Zr-doped CaTiO3 powders were prepared with the mild co-precipitation method and calcined at 850℃ for 3 h. The as-prepared Zr-doped CaTiO3 samples were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, UV-Vis diffuse reflectance spectra （DRS） and X-ray photoelectron spectra （XPS）. XRD result revealed the presence of single perovskite phase of CaTiO3. UV-Vis diffusive reflection spectra of Zr-doped CaTiO3 indicated that the absorbance obviously increased in the visible light irradiation. XPS analysis showed that two types of oxygen existed on the photocatalyst surface, including lattice oxygen and absorbed oxygen. Their photocatalytic activity in the case of the degradation of methyl orange in water and photoelectrochemical activity were also tested. The 5%Zr-doped （mole fraction） CaTiO3 sample showed the highest photocatalytic activity. The enhanced photocatalytic activity was ascribed to the change of the lattice structure, existence of oxygen vacancies and increase of the photogenerated charge separation efficiency.

Lu^(3+)掺杂Na_(5)Y_(9)F_(32)∶Ho^(3+)/Yb^(3+)/Ce^(3+)单晶体的增强红色上转换发光与光学温度传感性能

采用密封的坩埚下降法技术生长了一系列Lu^(3+)(摩尔分数0、0.6%、1.2%、1.8%)掺杂Na_(5)Y_(9)F_(32)∶Ho^(3+)/Yb^(3+)/Ce^(3+)单晶体。在980 nm LD激发下,观察到单晶体的绿光543 nm(^(5)S_(2)/^(5)F_(4)→^(5)I_(8))、红光656 nm(^(5)F_(5)→^(5)I_(8))以及近红外750 nm(^(5)S_(2)/^(5)F4→^(5)I_(7))上转换发光。从上转换发光强度随激发光强度的变化情况,确定了543 nm、656 nm与750 nm的发光为双光子跃迁过程。研究了Lu^(3+)离子掺杂浓度对其发光强度与荧光寿命的影响情况,随着Lu^(3+)掺杂浓度从0增加到1.8%,单晶体中的656 nm红光逐步增强,543 nm绿光与750 nm近红外光随之减弱,红绿光强度比从0.01增加到了1.55,而543 nm荧光寿命从1.29 ms降低至0.99 ms。Lu^(3+)离子的掺入取代Y^(3+)晶格位,改变了单晶体的局域场环境,导致上转换发光强度的变化。基于随温度变化的上转换红光656 nm(^(5)F5→^(5)I8)与绿光543 nm(^(5)S_(2)/^(5)F4→^(5)I8)的发光强度变化,研究了1.8%Lu^(3+)掺杂Na_(5)Y_(9)F_(32)∶Ho^(3+)/Yb^(3+)/Ce^(3+)单晶体在298~448 K范围内的绝对灵敏度和相对灵敏度最大值分别为0.242%·K^(-1)和0.217%·K^(-1)。

Preparation and Characterization of Fe^(3+)-doped Nanometer TiO_2 Photocatalysts

Fe^3＋ -doped nanometer TiO2 photocatalysts were prepared by sol-gel technique. TiO2 powders with different Fe^3＋ / Ti^4 ＋ molar ratios ranging from 0. 05% to 25% were synthesized by calcinating the gels in the temperature range of 200-600 ℃ . The effects of the content of iron ions and calcination temperature on the physical properties of the powders and their photocatalytic activities were examined by the photodecorapositon of methyl orange in sunlight. The results show that Fe dopant can decrease the temperature of nanatase-ratile transformation. The ideal photocatalytic property was achieved when the sample with an Fe^3＋ / Ti^4＋ ratio of 20 at% was calcined at about 300 ℃ for an hour, which is superior to that of commercial Degussa P-25. The optimum microstructure of the Fe-doped TiO2 for a high photocatalytic activity in sunlight is consisted of nanatase and ratile.

GdVO_(4):Yb^(3+),Ho^(3+)和GdPO_(4):Yb^(3+),Ho^(3+)荧光粉的上转换发光特性研究

为了探究Yb^(3+),Ho^(3+)分别共掺杂在GdVO_(4)和GdPO_(4)两种基质材料的发光差异性,采用高温固相法制备GdVO_(4):Yb^(3+),Ho^(3+)和GdPO_(4):Yb^(3+),Ho^(3+)上转换发光材料。并采用X射线衍射仪(X-ray diffraction,XRD)、拉曼光谱(Raman spectroscopy,Raman)、扫描电子显微镜(scanning electron microscopy,SEM)和荧光光谱对材料的结构、组成、形貌和上转换发光性能进行测试分析。结果表明,合成样品均是纯相,GdVO_(4):Yb^(3+),Ho^(3+)样品形状为不规则块状;GdPO_(4):Yb^(3+),Ho^(3+)样品为米粒状。在980 nm激发下,两种样品都存在绿光和红光发射。与掺杂相同浓度的GdVO_(4):Yb^(3+),Ho^(3+)相比,GdPO_(4):Yb^(3+),Ho^(3+)样品的红绿比较大,色度坐标更接近红光,在生物成像领域具有更大的应用潜力。

Structure and Luminescence Properties of Eu^(3+) Doped SiO_2 Glass Synthesized by Sol-Gel Process

Under different annealing temperatures, Eu 3+ doped SiO 2 gel and glass were prepared by sol gel method, and the structure and luminescent properties were studied with excitation spectra, emission spectra, IR and DTA TG. The results show that the fluorescent intensity tends to get stable when concentration of Eu 3+ doped is above 1 86 % (mass fraction) most water absorbed by the gel was removed at 300 ℃, and that the emission spectrum of Eu 3+ , with peaks at 614, 588, 577 nm, is due to 5D 0→ 7F 2, 5D 0→ 7F 1, 5D 0→ 7F 0 transitions, and the excitation peaks at 318, 362, 380, 393, 412 and 462 nm were observed. These results illustrate that the temperature range of 300～500 ℃ is critical for the structure conversion from gel to glass, and the fluorescence is strongly quenched by water.

A comparison study of alkali metal-doped g-C_3N_4 for visible-light photocatalytic hydrogen evolution

Photocatalytic hydrogen production based on semiconductor photocatalysts has been considered as one of the most promising strategies to resolve the global energy shortage.Graphitic carbon nitride(g‐C3N4)has been a star visible‐light photocatalyst in this field due to its various advantages.However,pristine g‐C3N4usually exhibits limited activity.Herein,to enhance the performance of g‐C3N4,alkali metal ion(Li+,Na+,or K+)‐doped g‐C3N4are prepared via facile high‐temperature treatment.The prepared samples are characterized and analyzed using the technique of XRD,ICP‐AES,SEM,UV‐vis DRS,BET,XPS,PL,TRPL,photoelectrochemical measurements,photocatalytic tests,etc.The resultant doped photocatalysts show enhanced visible‐light photocatalytic activities for hydrogen production,benefiting from the increased specific surface areas(which provide more active sites),decreased band gaps for extended visible‐light absorption,and improved electronic structures for efficient charge transfer.In particular,because of the optimal tuning of both microstructure and electronic structure,the Na‐doped g‐C3N4shows the most effective utilization of photogenerated electrons during the water reduction process.As a result,the highest photocatalytic performance is achieved over the Na‐doped g‐C3N4photocatalyst(18.7?mol/h),3.7times that of pristine g‐C3N4(5.0?mol/h).This work gives a systematic study for the understanding of doping effect of alkali metals in semiconductor photocatalysis.

Electric characteristics of Nd_2O_3 doped BaTiO_3 ceramics

Nd2O3 doped BaTiO3ceramics（the additive content was respectively 0.001, 0.002, 0.003, 0.005, 0.01 molar ratio）were prepared by Sol-Gel method to study their dielectric characteristics and electric conductivities through X-ray photoelectron spectrum （XPS）. The results showed that the dielectric characteristics of Nd2O3 doped BaTiO3 ceramics were improved by doping. When Nd2O3 content was 0.003 mol, the results were even better, the dielectric constant was increased, the dielectric loss was decreased, the Curie-temperature （Tc） was 110 ℃, and the frequency characteristic was also good. The resistivity of Nd2O3 doped BaTiO3 ceramics was lower than that of pure BaTiO3 ceramics, when Nd2O3 content was 0.001 mol,the resistivity was （2.364×）108 Ω·m, the smallest. The grain resistance of Nd2O3 doped BaTiO3 ceramics exhibited NTC effect, but the grain boundary resistance showed PTC effect, and the grain boundary resistance was larger than that of the grain resistance, so the PTC effect originated from the grain boundary. The analysis of the element binding energy through X-ray photoelectron spectrum were indicated that the quantivalence of Ba2+and Ti4+in Nd2O3 doped BaTiO3 ceramics was variable, and resulted in the improvement of the conductibility of BaTiO3 ceramics.

Synthesis and Luminescence Properties of Pr^(3+) Doped Ca_xBa_(1-x)TiO_3 (0.3≤x<1) Fine Particles

CaxBa1-xTiO3 （CBT） fine particles doped with red luminescence center of Pr3＋ ions （Pr： CBT） were successfully synthesized by salt assisted spray pyrolysis （SASP） process. Scanning electronic microscope （SEM） and laser scattering analysis demonstrate that salt can be removed from the surface of particles by washing with Milli-Q water and the particles can be further separated by ball-milling to get well-dispersed Pr^3＋ ions doped CBT fine particles. The luminescence properties, such as photoluminescence （PL） and mechanoluminescence （ML）, of as-synthesized Pr： CBT particles were investigated. For Pr： CBT fine particles with different Ca molar ratios, all the samples show one emission at 612 nm, with increasing Ca molar ratio, PL intensity of Pr： CBT fine particles become stronger and stronger. When pressure was loaded on the Pr： CBT pellet, mechanoluminescence（ML） emission was measured. The results show that the ML intensity is proportional to the applied pressure.

Doped Organic Electroluminescence from a Novel Rare Earth Complex Tb(3-metho)_3phen

A novel rare earth complex Tb(3 metho) 3phen was synthesized and characterized. The complex was doped into PVK to improve the conductivity and film forming property of Tb(3 metho) 3phen. A device with a structure of ITO/PVK∶Tb(3 metho) 3phen /Al was fabricated to study the electroluminescent properties of Tb(3 metho) 3phen. And the optoluminescent and AFM properties of this device were also studied, which proved the existence of energy transfer from PVK to Tb(3 metho) 3phen. As a result, a pure green emission with sharp spectral band at 547.5 nm was observed.

Upconversion Properties of LiNbO_3 Single Crystals Co-doped with Ho and Yb

The IR-to-visible upconversion fluorescent crystals, Yb：Ho：LiN-bO3, with a constant Ho^3＋ concentration （0.1 mol%） and different doping concentrations of Yb^3＋ （0.5, 1.5, 2.0, 2.5, 3.0 tool%） are synthesized by Czochralski method in air atmosphere. X-ray diffraction shows that the obtained crystal is a single phase of LiNbO3 and the rare-earth ions occupied the Li^＋ or Nb^5＋ sites instead of the interstitial sites. Under 980 nm excitation, green and red emission bands due to the Ho^3＋ （^5S2, ^5F4）/^5I8 and Ho^3＋ ^5F5/^5I8 energy transitions are observed in these samples, respectively. Power dependence studies on these samples with different Yb^3＋ dopant concentrations indicate that the red and green emissions are based on a two-photon process. The intensities of the red and green upconversion fluorescence increase with Yb3＋ ions of 0-2.0 mol% because of an increased Yb^3＋ sensitization, but decrease at higher concentrations owing to the back-energy transfer between the Yb^3＋ and Ho^3＋ ions.

Photoelectrocatalytic activity of immobilized Yb doped WO3 photocatalyst for degradation of methyl orange dye

Pure WOand Yb:WOthin films have been synthesized by spray pyrolysis technique. Effect of Yb doping concentration on photoelectrochemical, structural, morphological and optical properties of thin films are studied. X-ray diffraction analysis shows that all thin films are polycrystalline nature and exhibit monoclinic crystal structure. The 3 at% Yb:WOfilm shows superior photoelectrochemical（PEC） performance than that of pure WOfilm and it shows maximum photocurrent density（Iph= 1090 μA/cm） having onset potentials around +0.3 V/SCE in 0.01 M HClO. The photoelectrocatalytic process is more effective than that of the photocatalytic process for degradation of methyl orange（MO） dye. Yb doping in WOphotocatalyst is greatly effective to degrade MO dye. The enhancement in photoelectrocatalytic activity is mainly due to the suppressing the recombination rate of photogenerated electron-hole pairs. The mineralization of MO dye in aqueous solution is studied by measuring chemical oxygen demand（COD） values.

Preparation and characterization of Eu^(3+)-doped CaCO_3 phosphor by microwave synthesis

A Eu^3＋-doped CaCO3 phosphor with red emission was prepared by microwave synthesis. The scanning electron microscopy （SEM） image and laser particle size analysis show that the CaCO3：Eu^3＋ particles are needle-like in the length range of 5.0-10.0 μm. The results of X-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FT-IR）, and Raman spectroscopy indicate that pure aragonite CaCO3：Eu^3＋ is prepared using microwave irradiation and the Eu^3＋ ion as a luminescence center inhabits the site of Ca^2＋. The photoluminescence excitation （PLE） spectrum shows that the strong broad band at around 270 nm and weak sharp lines in 300-550 nm are assigned to the charge transfer band of Eu^3＋-O^2- and intra-configurational 4f-4f transitions of Eu^3＋, respectively. The photoluminescence （PL） spectrum implies that the red luminescence can be attributed to the transitions from the ^5D0 excited level to the ^7FJ （J = 0, 1, 2, 3, 4） levels of Eu^3＋ ions with the mainly electric dipole transition ^5D0 → ^7F2 （614 and 620 nm）, and the Eu^3＋ ions prefer to occupy the low symmetric site in the crystal lattice.

Aluminum and phosphorus codoped “superaerophobic” Co3O4 microspheres for highly efficient electrochemical water splitting and Zn-air batteries

Multifunctional non-precious catalysts for hydrogen/oxygen evolution reaction(HER/OER) and oxygen reduction reaction(ORR) constitute the bottleneck in the applications in electrochemical overall water splitting(OWS) and Zn-air batteries. Herein, a trifunctional electrocatalyst of urchin-like Al,P-codoped Co3O4 microspheres supported on Ni foam(denoted as AP-CONPs/NF) was fabricated via a hydrothermal process and subsequent low-temperature annealing and phosphorization, exhibiting enhanced OER, HER and ORR activities compared with single-doped and undoped samples. Their surface self-organized microstructure and excellent "superaerophobic" feature make a high bubble repellency, which boost diffusion of reactants and electrolyte-electrode intimate contact. The codoping of Al and P elements into Co3O4 betters right the balance among surface chemical state, the increased oxygen vacancies and the promoted charge transfer. Encouraged by these synergistic advantages, the AP-CONPs/NF was further employed as excellent bifunctional electrodes for the OWS(low cell voltage of 1.57 V at 10 mA cm-2) and as air cathode for rechargeable Zn-air batteries(high power density of 89.1 mW cm-2), which demonstrates a great feasibility for practical applications.

Oxygen vacancy defects engineering on Cu-doped Co_(3)O_(4) for promoting effective COS hydrolysis

The activation of H_(2)O is a key step of the COS hydrolysis,which may be tuned by oxygen vacancy defects in the catalysts.Herein,we have introduced Cu into Co_(3)O_(4) to regulate the oxygen vacancy defect content of the catalysts.In situ DRIFTS and XPS spectra reveal that COS and H_(2)O are adsorbed and activated by oxygen vacancy.The 10 at%Cu doped Co_(3)O_(4) sample(10Cu-Co_(3)O_(4))exhibits the optimal activity,100%of COS conversion at 70℃.The improved oxygen vacancies of CueCo_(3)O_(4) accelerate the activation of H_(2)O to form active -OH.COS binds with hydroxyl to form the intermediate HSCO^(-)_(2),and then the activated-OH on the oxygen vacancy reacts with HSCO^(-)_(2) to form HCO^(-)_(3).Meanwhile,the catalyst exhibits high catalytic stability because copper species(Cu+/Cu^(2+))redox cycle mitigate the sulfation of Co_(3)O_(4)(Co^(2+)/Co^(3+)).Our work offers a promising approach for the rational design of cobalt-related catalysts in the highly efficient hydrolysis COS process.

Rare earth doped CaCu_3Ti_4O_(12) electronic ceramics for high frequency applications

Ca1-xRxCu3Ti4O12(R=La,Y,Gd;x=0,0.1,0.2,0.3) electronic ceramics were fabricated by conventional solid-state reaction method.The microstructure and dielectric properties as well as impedance behavior were carefully investigated.XRD results showed that the secondary phases with the general formula R2Ti2O7 existed at grain boundaries of rare earth doped ceramics,which inhibited abnormal grain growth.The dielectric constant decreased from 4×105 in pure CaCu3Ti4O12(CCTO) ceramics to 2×103 with rare earth doping....