Strong visible up-conversion emissions and thermometric applications of Er<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> codoped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> prepared by the sol–gel method

The Er³⁺–Yb³⁺ codoped Al₂O₃ has been 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] and ytterbium nitrate [Yb(NO₃)₃ · 5H₂O]. The phase structure, including only two crystalline types of doped Al₂O₃ phases, θ and γ, was obtained for the 1 mol% Er³⁺ and 5 mol% Yb³⁺ codoped Al₂O₃ at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300–825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er³⁺–Yb³⁺ codoped Al₂O₃ plays an important role in the application of high temperature sensor.     

Opposite effect of Li<Superscript>+</Superscript> codoping on the upconversion emissions of Er<Superscript>3+</Superscript>-doped TiO<Subscript>2</Subscript> powders

The Er³⁺-Li⁺ codoped TiO₂ powders have been prepared by the non-aqueous sol–gel method. The green and red upconversion emissions centered at about 526, 550 and 663 nm were observed by the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. Li⁺ codoping has opposite effect on the upconversion emissions intensities for Er³⁺-doped TiO₂ at sintering temperatures of 1,073 and 1,273 K. At 1,073 K, the Er³⁺-doped TiO₂ phase transition from anatase to rutile was accelerated with increasing Li⁺ codoping concentration, leading to the increase of crystal field symmetry of Er³⁺, thus the upconversion emissions intensities decreased. At 1,273 K, Li⁺ codoping had no effect on the phase structure of Er³⁺-doped TiO₂ and only increased the Er–O bond length, it indicated that the upconversion emissions intensities greatly enhanced because of the decrease of crystal field symmetry of Er³⁺.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Enhancement of the Up-conversion Luminescence of 12CaO · 7Al2O3:Tm3+/Yb3+ Doped with Alkaline Earth Metal Ions

12CaO?·?7Al₂O₃ doped with lanthanide is characterized by remarkable and technologically important up-conversion emission. However, the low up-conversion efficiency still remains the main limitation for practical applications. To improve the efficiency, bivalent alkaline earth ions (Mg²⁺, Sr²⁺, Ba²⁺)-tridoped Tm³⁺/Yb³⁺/12CaO?·?7Al₂O₃ were synthesized through a high-temperature solid-state reaction. The up-conversion luminescence properties of the samples were investigated by X-ray diffraction, fluorescence spectral measurement pump power, and fluorescence decay curves. The luminescence intensity of samples was significantly enhanced by bivalent alkaline earth ions. 12CaO?·?7Al₂O₃ doped with Sr²⁺ ions has stronger effects on up-conversion enhancement, which is better than Mg²⁺ and Ba²⁺. The up-conversion emission intensity was enhanced by 318 times and the red emission intensity by 218 times with 10?mol% Sr²⁺ ion. Additionally, the blue and red up-conversion emission peaks at 475 and 650?nm corresponding to energy transitions of ¹G₄ → ³H₆ and ¹G₄ → ³F₄, ³F₂ → ³H₆ were characterized using steady-state rate equations.     

A new phosphor with flower-like structure and luminescent properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> long afterglow materials by sol–gel method

The flower-like phosphors of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ with high brightness and long afterglow were obtained by sol–gel method. X-ray diffraction pattern (XRD) shows that single-phased Sr₂MgSi₂O₇ phosphor is prepared by sol–gel method under 1250 °C. Scanning electron microscope (SEM) indicates that the phosphor consists of nano-sized whiskers which are detected for the first time in Eu²⁺ and Dy³⁺ co-doped long-lasting phosphorescence silicates. Furthermore, the investigation on the mechanism indicates that the internal structure and gas, liquid and solid phase effect play important roles in the formation of flower-like Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ nanostructure. Finally, the optical properties of flower-like Sr₂MgSi₂O₇ nanostructure have been characterized by photoluminescence (PL) spectra.     

Upconversion Luminescence Properties of a LiNb0.3Ta0.7O3:Er3+,Yb3+ Ceramic

A co-doped LiNb_0.3Ta_0.7O₃:Er³⁺,Yb³⁺ ceramic was prepared by a high temperature solid state procedure. Under the excitation of 980 nm laser radiation, intense 660 nm red light and 550 nm green light emissions corresponding to the ⁴F_9/2→⁴I_15/2 and ²H_11/2/⁴S_3/2→⁴I_15/2 transitions of Er³⁺ were observed. The change of Yb³⁺ concentration has a more significant influence on luminous intensity than the Er³⁺ concentration. The emission of red and green lights is attributed to a two-photon process. The upconversion luminescence mechanisms were analyzed in detail.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.     

Detection of up-conversion in nano-structure BaTiO<Subscript>3</Subscript> co-doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

Nano-structure pure barium titanate BaTiO₃ (BT) and (BT) co-doped with constant concentration of Er³⁺ ions and different concentrations of Yb³⁺ ions were prepared using sol–gel method. XRD results confirmed that the pure sample was found to crystallize in tetragonal phase by sintering at 750 °C for 1 h. All major peaks corresponding to perovskite BT phase appeared. Efficient infrared-to-visible up-conversion is reported in the doped samples. The conversion process and results in the generation of visible emissions are discussed. Up-conversion efficiency for red emission predominates in doped samples. Results illustrate the large potential of this class of materials for photonic applications in optoelectronics devices.     

Yb<Superscript>3+</Superscript> → Er<Superscript>3+</Superscript> energy transfer in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and temperature characteristic of near-infrared photoluminescence

For the Er³⁺–Yb³⁺ codoped Al₂O₃ powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb³⁺ to Er³⁺ was detected by a 978 nm laser diode excitation. Compared with that of Er³⁺ doped Al₂O₃ powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er³⁺–Yb³⁺ codoped Al₂O₃ powders at room temperature. The ET coefficient of 2.18 × 10⁻¹⁸ cm³ s⁻¹ from Yb³⁺ to Er³⁺ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation ⁴I_13/2 → ⁴I_15/2 dominated over thermally enhanced phonon-assisted ET in the Er³⁺–Yb³⁺ codoped Al₂O₃.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

Ho3+/Yb3+共掺ZnO-Al2O3-GeO2-SiO2玻璃陶瓷的制备和上转换发光性质

综合ZnO-Al_2O_3-SiO_2系和锗酸盐玻璃陶瓷的优点,采用熔融-晶化法首次制备了Ho~(3+)/Yb~(3+)共掺以ZnAl_2O_4为主晶相的ZnO-Al_2O_3-GeO_2-SiO_2系玻璃陶瓷。因[GeO_4]四面体和[SiO_4]四面体都是玻璃网络形成体,讨论了GeO_2取代SiO_2对玻璃陶瓷样品硬度及发光性能的影响,最终确定GeO_2的取代量为10.55%(w/w)时,玻璃陶瓷综合性能最佳。在980 nm泵浦光的激发下,发现强的绿色(546 nm)和弱的红色(650 nm)上转换发光,并研究了不同Ho~(3+)/Yb~(3+)掺杂比对样品上转换发光的影响,最终结果表明当Ho~(3+)/Yb~(3+)掺杂比为1∶11(n/n)时样品荧光强度最强,在绿色上转换发光材料方面具有潜在的应用。     

Theoretical study of the mechanism for C-H bond activation in spin-forbidden reaction between Ti<Superscript>+</Superscript> and C<Subscript>2</Subscript>H<Subscript>4</Subscript>

The mechanism of the spin-forbidden reaction Ti⁺(⁴F, 3d²4s¹) + C₂H₄→TiC₂H₂ ⁺ (²A₂) + H₂ on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing points between the potential energy surfaces and the possible spin inversion process are discussed by means of spin-orbit coupling (SOC) calculations. The strength of the SOC between the low-lying quartet state and the doublet state is 59.3 cm⁻¹ in the intermediate complex IM1-⁴B₂. Thus, the changes of its spin multiplicity may occur from the quartet to the doublet surface to form IM1-²A₁, leading to a sig-nificant decrease in the barrier height on the quartet PES. After the insertion intermediate IM2, two distinct reaction paths on the doublet PES have been found, i.e., a stepwise path and a concerted path. The latter is found to be the lowest energy path on the doublet PES to exothermic TiC₂H₂ ⁺(²A₂) + H₂ products, with the active barrier of 4.52 kcal/mol. In other words, this reaction proceeds in the following way: Ti⁺+C₂H₄→⁴IC→IM1-⁴B₂→^4,2ISC→IM1-²A₁→[²TS_ins]→IM2→[²TS_MCTS]→IM5→TiC₂H₂ ⁺(²A₂)+H₂. Supported by ‘Qinglan’ Talent Engineering Funds by Tianshui Normal University.     

Effect of Er<Subscript>2</Subscript>O<Subscript>3</Subscript> on thermal stability of oxyfluoride glass

Glasses have been synthesized in the system SiO₂–Al₂O₃–Na₂O–AlF₃–LaF₃–Er₂O₃. A base glass (in mol% 67SiO₂–9Al₂O₃–20Na₂O–Al₂F₆–3La₂F₆) was modified by 0.5, 0.75, 1, 1.25, 1.5, 2 and 5 mol% Er₂O₃, respectively. Glasses were prepared by conventional fusion method from 20 g batches. The glass transition temperature (T _g), the jump-like changes of the specific heat (ΔC _p) accompanying the glass transition and the enthalpy of crystallization (ΔH) were calculated. DTA measurements clearly reveal that the increase of the Er₂O₃ content in the glass changes the effects of crystallization and diminishes the thermal stability of the glassy network. In the same time the changes in the transition temperature are observed. The formation of NaLaF₄ and Na_1.45La_9.31(SiO₄)₆(F_0.9O_1.1) as a main phase was confirmed. The diminishing of the thermal stability was connected with erbium which incorporated into Na_1.45La_9.31(SiO₄)₆(F_0.9O_1.1) structure.     

Photoluminescence in Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped silica-titania inverse opal structures

Er³⁺ photoluminescence (PL) and Yb³⁺ → Er³⁺ energy transfer (ET) phenomena in the near infrared (NIR) have been studied in three-dimensional (3-D) inverse opal (IO) structures synthesized by a colloidal/sol–gel route, starting with the deposition of polystyrene microsphere (235 nm and 460 nm diameter) direct opal templates by convective self-assembly, followed by infiltration of the interstices with Er³⁺/Yb³⁺-doped silica, titania and silica-titania sols and heat-removal of the polymeric template material. The crystalline quality of the IOs has been optimized through suitable substrate treatments, plus the control of temperature and humidity during deposition of the templates. The structural and optical properties of the 3-D opal and IO structures have been studied by field emission scanning electron microscopy and visible-NIR reflection spectroscopy, in order to assess the relationship between microstructure and the photonic properties obtained. Photonic bandgaps have been evidenced by the corresponding stop bands in the reflection spectra. The shape and the intensity of the Er^{3+ 4}I_13/2 → ⁴I_15/2 transition at ~1.5 μm were modified in most IOs relatively to similar matrix deposits without a photonic crystal structure, particularly in the case of pure silica and titania IOs, where the PL peak narrowed and intensified. It was not possible at this stage to detect Yb³⁺ → Er³⁺ ET phenomena in the IOs structures.     

Osmotic Coefficients of the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=273.15 K

Osmotic coefficients and water activities for the Li₂B₄O₇+LiCl+H₂O system have been measured at T=273.15 K by the isopiestic method, using an improved apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined. φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq), and φ _E is based on equilibrium molalities from consideration of the equilibrium speciation into H₃BO₃,B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constants K _m for the aqueous speciation reactions were estimated. Two types of representations of the osmotic coefficients for the Li₂B₄O₇+LiCl+H₂O system are presented with ion-interaction models based on Pitzer’s equations with minor modifications: model (I) represents the φ _S data with six parameters based on considering the ion-interactions between three ionic species of Li⁺, Cl⁻, and B₄O₇²⁻, and model (II) for represents the φ _E data based on considering the equilibrium speciation. The parameters of models (I) and (II) are presented. The standard deviations for the two models are 0.0152 and 0.0298, respectively. Model (I) was more satisfactory than model (II) for representing the isopiestic data.     

Ho3+/Yb3+共掺ZnO-Al2O3-GeO2-SiO2玻璃陶瓷的制备和上转换发光性质

综合ZnO-Al₂O₃-SiO₂系和锗酸盐玻璃陶瓷的优点,采用熔融-晶化法首次制备了Ho³⁺/Yb³⁺共掺以ZnAl₂O₄为主晶相的ZnO-Al₂O₃-GeO₂-SiO₂系玻璃陶瓷。因[GeO₄]四面体和[SiO₄]四面体都是玻璃网络形成体,讨论了GeO₂取代SiO₂对玻璃陶瓷样品硬度及发光性能的影响,最终确定GeO₂的取代量为10.55%（w/w）时,玻璃陶瓷综合性能最佳。在980 nm泵浦光的激发下,发现强的绿色（546 nm）和弱的红色（650 nm）上转换发光,并研究了不同Ho³⁺/Yb³⁺掺杂比对样品上转换发光的影响,最终结果表明当Ho³⁺/Yb³⁺掺杂比为1：11（n/n）时样品荧光强度最强,在绿色上转换发光材料方面具有潜在的应用。     

Electrochemical properties of <Emphasis Type="Italic">n</Emphasis>-sulfonatothiacalyx[4]arene complexes with Fe<Superscript>3+</Superscript> and [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> ions

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H₄XNa₄) complexes with [Co(dipy)₃]³⁺ and Fe³⁺ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)₃]³⁺ bound extraspherically to the upper rim and Fe³⁺ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)₃]³⁺ · H₃X^5?, H₃X^5? · Fe³⁺, and ternary [Co(dipy)₃]³⁺ · H₃X^5? · Fe³⁺ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)₃]³⁺, ΔΔG ₀ = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe³⁺). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)₃]²⁺ outer ions.     

Formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> bilayer using atomic layer deposition and its application to dynamic random access memory

To enhance film conformality together with electrical property suitable for dynamic random access memory (DRAM) capacitor dielectric, the effects of oxidant and post heat treatment were investigated on aluminum and titanium oxide (Al₂O₃–TiO₂) bilayer (ATO) thin film formed by atomic layer deposition method. For the conformal deposition of Al₂O₃ thin film, the O₃ oxidant required a higher deposition temperature, more than 450 °C, while H₂O or combined oxygen sources (H₂O+O₃) needed a wide range of deposition temperatures ranging from 250 to 450 °C. Conformal deposition of the TiO₂ thin film was achieved at around 325 °C regardless of the oxidants. The charge storage capacitance, measured from the ATO bilayer (4 nm Al₂O₃ and 2 nm TiO₂) deposited at 450 °C for Al₂O₃ and 325 °C for TiO₂ with O₃ oxidant on the phosphine-doped poly silicon trench, showed about 15% higher value than that of 5 nm Al₂O₃ single layer thin film without any increase of leakage current. To maintain the improved electrical property of the ATO bilayer for DRAM application, such as enhanced charge capacitance without increase of leakage current, upper electrode materials and post heat treatments after electrode formation must be selected carefully. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

GdAlO_3:Er~(3+),Yb~(3+)荧光粉的制备与上转换发光性能

采用共沉淀、溶胶-凝胶和固相反应法制备了GdAlO3:Er3+,Yb3+荧光粉.借助X射线衍射、扫描电子显微镜、傅里叶变换红外光谱、N2-吸附、吸收光谱和荧光光谱等手段研究了不同方法制备的GdAlO3:Er3+,Yb3+荧光粉结构、形貌、表面基团和光吸收及上转换发光性能.结果表明:用共沉淀法比固相反应法和溶胶-凝胶法可以在更温和的条件下制得纯相GdAlO3:Er3+,Yb3+荧光粉,用共沉淀法和溶胶-凝胶法制备的GdAlO3:Er3+,Yb3+荧光粉颗粒都在纳米尺寸,溶胶-凝胶法制得的样品存在相对严重的颗粒团聚现象,而用固相反应法制备的荧光粉为微米级颗粒.GdAlO3:Er3+,Yb3+荧光粉在980 nm激发的上转换发射光谱包含波长为524和546 nm的绿光与659 nm的红光,且三种方法制备的样品绿光发射强度都显著高于红光.不同方法制备的荧光粉上转换发光强度和红光/绿光强度比相差较大,共沉淀法制备的样品上转换发光强度要显著高于固相法以及溶胶-凝胶法制备的样品,而溶胶-凝胶法制备的样品发光中红光/绿光相对强度比最高.红外光谱显示,不同方法制备的GdAlO3:Er3+,Yb3+荧光粉表面OH-、CO32-及CO2官能团含量不同,溶胶-凝胶法制备的样品要明显高些.基于红外光谱、不同Er3+和Yb3+离子掺杂浓度及不同激光功率上转换发光的结果,对Er3+和Yb3+之间的能量传递过程及不同方法制备荧光粉的上转换发光性能进行了讨论.     

Enthalpy of formation of BaCe<Subscript>0.9</Subscript>In<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>(s)

Enthalpy of formation of the perovskite-related oxide BaCe_0.9In_0.1O_2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl₂, CeCl₃, InCl₃ in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe_0.9In_0.1O_2.95 has been calculated as −1611.7±2.6 kJ mol⁻¹. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δ_ox H ⁰ (298.15 K)=−36.2±3.4 kJ mol⁻¹.