Investigation of the energy transfer mechanism in OLEDs based on a new terbium β-diketonate complex

This study is focused on the contribution of radiative and non-radiative processes to the electroluminescence emission of OLEDs based on a new terbium(III) complex: {Tris(acetylacetonate)[1,2,5]thiadiazole[3,4-f][1,10]phenanthroline}terbium(III) or [Tb(ACAC)₃TDZP]. The effects of the energy transfer mechanism are discussed based on photoluminescence and electroluminescence measurements. The terbium complex showed an intense photoluminescence with high color purity in the green region, characteristics of the Tb(III) ion narrow line transitions. However, when used in a double-layer OLED its electroluminescence showed an orange broad band emission which can be attributed to the electrophosphorescence of the ligands and to an inefficient energy transfer from the organic ligand to the Tb(III) ion. Alternatively, devices with a Tb(III) complex acting as a dopant (7.6%) in a matrix of CBP used as the active layer showed an improvement in the energy transfer process, resulting in the appearance of the characteristic emission lines of the Tb(III) ion.     

A tris β-diketonate europium(III) complex based OLED fabricated by thermal evaporation method displaying efficient bright red emission

A new tris β-diketonate europium(III) complex [Eu(btfa)₃Py-Im] (Eu-1) (4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfa) and 2-(2-pyridyl)benzimidazole (Py-Im)] has been synthesized and structurally characterized. A single crystal X-ray diffraction analysis shows that Eu-1 is octacoordinated and the coordination sphere is composed of a EuO₆N₂ core with a trigonal dodecahedral (D_2d) geometry. The photophysical properties of Eu-1 were analysed in detail and with the help of the experimental PL data and theoretical modelling, energy transfer rates were calculated, and an energy transfer mechanism is proposed for Eu-1. The complex has been used as the emitting layer (EML) to fabricate organic light emitting diodes (OLEDs). Eight OLEDs, of which four single-EML and four double-EML with varying doping concentration, were fabricated via a thermal evaporation method using Eu-1 as the EML. Under the optimum conditions a highly monochromatic bright red emission (CIE_x,y = 0.640, 0.311) with brightness (B) = 896 cd/m², current efficiency (η_c) = 2.26 cd/A, power efficiency (η_p) = 1.92 lm/W and external quantum efficiency (EQE) = 1.6% at very low V_turn-on = 3.4 V was obtained.     

Organic light-emitting devices based on new rare earth complex Tb（p-CIBA）3phen

A new rare earth complex Tb（p-CIBA）3phen was synthesized and introduced into organic tight emitting devices （OLEDs） as emitting material. The Tb（p-CIBA）3phen was doped into PVK to improve the filmforming and hole-transporting property. Two kinds of devices were fabricated. The device structure is as the following. Single-layer device： ITO/PVK： Tb （p-CIBA） 3 phen /LiF/Al; double-layer device： ITO/PVK： Tb（p-CIBA）3phen/AIQ/LiF/AI. The performances of both devices were investigated carefully. We found that the emission of PVK was completely restrained,and only the green emission was observed from the electroluminescence. The full width at half maximum （FWHM） was less than 10 nm. The highest EL brighthess of the single-layer device is 25.4 cd/cm^2 at a fixed bias of 18 V,and the highest EL brightness of the double-layer device reaches 234.8 cd/cm^2 at a voltage of 20 V.     

Organic light-emitting devices based on new rare earth complex Tb(p-ClBA)_3phen

Since Tang and Vanslyke[1]reportedtheir doublelay-er device in 1987 ,the organic light emitting devices(OLEDs) have attracted more and more attention all o-ver the world because of their potential applications infull color flat panel displays .However ,th…     

Zn3(BO3)(PO4)∶Ce3+/Tb3+中的发光特性及其能量传递

采用高温固相法合成了一系列Ce3＋、Tb 3＋及Ce3＋/Tb3＋掺杂的Zn₃(BO₃)(PO₄)荧光粉, 研 究了材料的发光性能。结果显示,在Ce3＋、Tb3＋在Zn₃(BO₃)(PO₄)中,分别发射蓝和绿色光, 同时,Ce3＋的发射光谱和Tb3＋的激发光谱有明显的重叠,通过分析Ce 3＋、Tb3＋共掺时,材料 的荧光寿命曲线,发现在Zn₃(BO₃)(PO₄):Ce3＋/Tb3＋中 ,Ce3＋对 Tb3＋有明显的能量传递,在实验范围内,能量传递效率可以达 到68%。     

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.     

掺Eu3+, Sm3+, Tb3+的TTFA配合物敏化发光效应的实验研究

为了研究稀土离子的α-噻吩甲酰三氟丙酮(α-thienyltrifluoroacetone,TTFA)配合物中敏化发光效应,对自行制备出的稀土离子Eu3+,Sm3+和Tb3+单掺TTFA配合物Eu(TTFA)3,Tb(TTFA)3,Sm(TTFA)3及3种稀土离子两两共掺的配合物的荧光光谱进行了分析,得出了稀土离子Eu3+,Sm3+,Tb3+与配体TTFA的敏化特性以及稀土离子Eu3+,Sm3+和Tb3+之间的敏化特性。Eu(TTFA)3,Tb(TTFA)3,Sm(TTFA)3及3种稀土离子共掺的配合物中,稀土离子Eu3+,Sm3+,Tb3+与配体TTFA及Eu3+,Sm3+,Tb3+之间有明显的敏化效应。结果表明,将其用于聚合物光纤放大器具有良好的发展前景。     

Combustion Synthesis and Optical Properties of Eu3+-Doped BaGd2ZnO5 f–f Transition Nanophosphor for White LED

An Eu³⁺-doped BaGd_2(1?x)ZnO₅ nanophosphor has been synthesized by means of a single-step, urea-assisted, solution-combustion process. The structural, morphological, and optical properties of the nanophosphor were studied by x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The XRD results showed that the pure orthorhombic BaGd₂ZnO₅ structure with space group Pbnm was obtained at 900°C. The intense red luminescence at 628 nm on near-UV (396 nm) excitation is because of the hypersensitive ⁵D₀ → ⁷F₂ transition of luminescent activator Eu³⁺ ions, located at a site with no inversion symmetry in the BaGd₂ZnO₅ crystal lattice. The optimum doping concentration and decay time of Eu³⁺-doped BaGd_2(1?x)ZnO₅ nanophosphor were also determined. The emission could be effectively tuned from blue to the white and red regions by varying the concentration of europium ions. Decay curve analysis revealed that cross-relaxation is primarily responsible for the concentration quenching. High luminescent intensity, low-cost, easy synthesis, uniform shape, and controlled color tunability suggest use of BaGd₂ZnO₅:Eu³⁺ as an efficient red-emitting nanophosphor for near-UV-based LED solid-state lighting applications.     

Photoelectrochemical cells based on ternary compounds CuIn2n + 1Se3n + 2 (n = 3–6)

Semiconductors - Single crystals of ternary CuIn2n + 1Se3n + 2 semiconductors with the composition index n = 3, 5, 6 were grown for the first time using the direct crystallization method. It was...     

Ca3(PO4)2:RE3+ (RE=Eu,Dy,Ce,Tb) 荧光粉的制备及其发光特性

采用高温固相法合成了Ca3(PO4)2:RE3+(RE = Eu, Dy, Ce, Tb)系列发光材料,研究了其发光性质。研究表明Ca3(PO4)2: RE3+ 在紫外区域均能有效被激发,有很强的荧光发射,且发光范围覆盖蓝到红光波段,是一类可以紫外激发实现白光LED用的潜在荧光粉。在0.005到0.03 mol 浓度范围内,Eu,Dy和Ce掺杂的荧光粉的发光都发生了浓度淬灭,分别对应于0.025,0.025和0.02 mol,而Tb3+掺杂的样品的表现出高的发光淬灭浓度。     

YPO4:Ln3+(Ln=Eu,Tb)球形荧光粉的合成及其发光性能优化

采用水热法结合高温退火处理制备了YPO₄:Ln³⁺(Ln=Eu,T b)荧光粉。通过X射线 粉末衍射(XRD)、扫描电镜(SEM)和荧光光谱(PL)对样品的结构、形貌和发光性能进行 表征。结果 表明:在水热条件下合成了含结晶水六角相结构的YPO₄·0.8H₂O :Eu³⁺和YPO₄·0.8H₂O:Tb³⁺前躯体;经过 800 ℃高温烧结2h后,前躯体 失去结晶水后得到球形、尺寸均一、表面光滑、四方锆石结构的YPO₄:Eu³⁺和 YPO₄:Tb³⁺荧光粉,颗粒平均粒径约为200 nm。在396 nm波长激发下,YPO₄:Eu³⁺荧光粉可以获得Eu³⁺离 子的跃迁能级⁵D₀→⁷FJ(J=1－4)特征发射,以磁偶极跃迁⁵D₀→⁷F₁(596 nm)的发光强度最强,观察到橙 红色发射,且Eu³⁺的最佳掺杂摩尔分数为11%。同时,YPO₄: Tb³⁺荧光粉在372 nm的光激发下,在548 nm 处的⁵D₄→⁷F₅跃迁具有最高的荧光强度,观察到绿光发 射,且Tb³⁺最佳掺杂摩尔分数为7%。     

Influence of Yb2O3 on the 1.53 μm spectroscopic properties in Er3+/Ce3+ co-doped TeO2-WO3-Na2O-Nb2O5 glasses

The Yb2O3 component was introduced into the Er3+/Ce3+ co-doped tellurite glasses with the composition of TeO2-WO3-Na2O-Nb2O5 to study the effect of Yb3+ on the 1.53 μm spectroscopic properties of Er3+. The X-ray diffraction (XRD) curve and Raman spectrum were measured to investigate the structure nature of synthesized tellurite glasses. The absorption spectrum, upconversion emission spectrum and fluorescence spectrum were measured to evaluate the improved effect of Yb3+ concentration on the 1.53 µm band fluorescence of Er3+. Results of the measured 1.53 µm band fluorescence intensity show a significant improvement with the increase of Yb3+ concentration, while the total quantum efficiency reveals a similar increasing trend. The results of the present work indicate that Er3+/Ce3+/Yb3+ tri-doped tellurite glass has good prospect as a promising gain medium applied for the 1.53 µm broadband amplifier.     

Effects of Disordered Atoms and Nanopores on Mechanical Properties of β-Zn4Sb3: a Molecular Dynamics Study

Effects of disordered Zn atoms and nanopores on mechanical properties of β-Zn₄Sb₃ are studied by using the molecular dynamics (MD) method. Due to the influence of disordered Zn atoms in β-Zn₄Sb₃, the elastic modulus decreases from 90.85 GPa to 68.17 GPa, a decrease of 24.96%. The ultimate tensile stress decreases from 18.25 GPa to 9.96 GPa, a decrease of 45.42%. The fracture strain decreases from 32.7% to 20.8%, a decrease of 36.39%. Due to the influence of nanopores, the elastic modulus decreases with growing porosity, and the relationship between the elastic modulus and porosity leads to a scaling law. It seems that the porous radius and porous distribution are also important factors influencing the ultimate tensile stress and fracture strain, in addition to the porosity. However, our simulation results demonstrate that disordered Zn atoms and nanopores reduce the structural stability, dramatically decreasing the mechanical properties of β-Zn₄Sb₃.     

Prospects of aβ-SiC based IMPATT oscillator for application in THz communication and growth of a β-SiC p-n junction on a Ge modified Si 《100》 substrate to realize THz IMPATTs

The prospects ofa p<'+>nn<'+> cubic silicon carbide (3C-SiC/β-SiC)based IMPATT diode as a potential solidstate terahertz source is studied for the first time through a modified generalized simulation scheme.The simulation predicts that the device is capable of generating an RF power output of 63.0 W at 0.33 THz with an efficiency of 13%.The effects of parasitic series resistance on the device performance and exploitable RF power level are further simulated.The studies clearly establish the potential of 3C-SiC as a base semiconductor material for a high-power THz IMPATT device.Based on the simulation results,an attempt has been made to fabricate β-SiC based IMPATT devices in the THz region.Single crystalline,epitaxial 3C-SiC films are deposited on silicon (Si)(100)substrates by rapid thermal chemical vapour deposition (RTPCVD)at a temperature as low as 800℃ using a single precursor methylsilane,which contains Si and C atoms in the same molecule.No initial surface carbonization step is required in this method.A p-n junction with an n-type doping concentration of 4×10<'24> m<'-3> (which is similar to the simulated design data)has been grown successfully and the characterization of the grown 3C-SiC film is reported in this paper.It is found that the inclusion of Go improves the crystal quality and reduces the surface roughness.     

Performance of a Thermoelectric Module Based on n-Type (La0.12Sr0.88)0.95TiO3−δ and p-Type Ca3Co4−xO9+δ

Here, we present the performance of a thermoelectric (TE) module consisting of n-type (La_0.12Sr_0.88)_0.95TiO₃ and p-type Ca₃Co_4?xO_9+δ materials. The main challenge in this investigation was operating the TE module in different atmospheric conditions, since n-type has optimum TE performance at reducing conditions, while p-type has optimum at oxidizing conditions. The TE module was exposed to two different atmospheres and demonstrated higher stability in N₂ atmosphere than in air. The maximum electrical power output decreased after 40 h when the hot side was exposed to N₂ at 600°C, while only 1 h at 400°C in ambient air was enough to oxidize (La_0.12Sr_0.88)_0.95TiO₃ followed by a reduced electrical power output. The module generated maximum electrical power of 0.9 mW (～?4.7 mW/cm²) at 600°C hot side and δT?～?570 K in N₂, and 0.15 mW (～?0.8 mW/cm²) at 400°C hot side and δT?～?370 K in air. A stability limit of Ca₃Co_3.93O_9+δ at ～?700°C in N₂ was determined by in situ high-temperature x-ray diffraction.

     

Photodeposition of silver at the interface of a heterojunction based on a solid electrolyte: The case of CdSe-As<Subscript>2</Subscript>S<Subscript>3</Subscript>:Ag<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis>=0.9–2.4) heterojunctions

The phenomenon of photodeposition of silver has been detected in CdSe-As₂S₃:Ag_x (x=0.9–2.4) heterojunctions. The mass transfer of silver ions to the interface is caused by an electric field arising due to separation of electron-hole pairs in the space-charge regions of the heterojunction upon photovoltage generation. The migration of ions is also stimulated by their entrainment by the electron flow. Recombination of electrons with ions at the interface causes photodeposition of clusters of a chemical element responsible for ionic conduction in the solid electrolyte. A new method is suggested for preparing materials for optical data storage. The method is based on the phenomenon of photostimulated transport of ions and photodeposition of a metal at the interfaces of heterojunctions based on solid electrolytes.