Luminescent properties of Sr2MgSi2O7 and Ca2MgSi2O7 long lasting phosphors activated by Eu, Dy

Long lasting afterglow phosphors Sr₂MgSi₂O₇:Eu,Dy and Ca₂MgSi₂O₇:Eu,Dy were prepared by solid-state reaction method. It is revealed by the results that both phosphors show two emission peaks that are caused by the different emitting centers Eu²⁺ held in the host lattice. Wavelength shift was observed due to the slight differences in the structure parameters of the two hosts. Investigation on afterglow property shows that Sr₂MgSi₂O₇:Eu,Dy phosphor held a better afterglow property than Ca₂MgSi₂O₇:Eu,Dy phosphor. Thermal simulated luminescence study indicates that the long afterglow is generated by a higher trap concentration formed by the co-doped rare earth ions within the host.     

Influence of ZrO2 particles on the optical properties of pc-LEDs

Experimental and modeling progress and results aiming to increase the color uniformity of hemisphere-type pcW-LEDs are proposed. By adding micrometric zirconia particles, the light scattering is enhanced, that induces a decrease of phosphor necessary to obtain a specific CCT. The optical model is able to determine the optical properties (CCT, angular CCT distribution, chromaticity and packaging efficiency) in a hemisphere LED for various amount of YAG-phosphor and ZrO₂-zirconia particles. Based on previous process, the work is in the first step to fit the effective radius and refractive index that will be implemented in the optical model. In the second step, the optical model is compared with the experimental measurement to determine the absorption coefficient and conversion efficiency of a package of silicone resin containing phosphor and zirconia. Finally, the model, confirmed by selected experimental results, allows determining the optical properties of any king of package that lead to a CCT emission ranging from 4500 K to 6500 K. The analysis of these data is interpreted by comparing, for a specific CCT, the phosphor loss, the packaging efficiency and the angular distribution of CCT. The results show that if the effort is targeted on one of the previous parameters, there is always a counterpart on the other ones. Increasing the color uniformity will induce to decrease the packaging efficiency.     

Low-temperature synthesis of nanocrystalline ZnGa2O4:Tb phosphors via the Pechini method

The synthesis of trivalent terbium doped ZnGa₂O₄ nanosized new phosphors by the Pechini method was reported. Well-crystallized ZnGa₂O₄:Tb³⁺ phosphors were obtained at low-temperature about 550 °C. The phosphors formed porous agglomerates which consist of spherical nanocrystallites with a uniform size at about 30 nm. The photoluminescence of the phosphors included both the luminescence of ZnGa₂O₄ host and characteristic emission of Tb³⁺, and the excitation spectra showed an energy transfer from the host lattice to the activator. The Tb³⁺ emission from the phosphors prepared by the Pechini process was more intensive than that of phosphors by solid-state reaction process.     

Energy transfer,superior thermal stability and multi-color emitting properties of langbeinite-type solid-solution phosphor K_2Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3

Langbeinite type compounds are a large kind of oxometallate with good flexibility structure.Herein,we synthesized a new langbeinite type compound K_2 Dy_(1.5)Ta_(0.5)(PO_4)_3,in which the Dy~(3+) and Ta~(5+) were blended to occupy the same crystallographic sites.Simultaneously,solid solutions of K_2 Dy_(1.5)_(-x)Eu_xTa_(0.5)(PO_4)_3(x=0-1.5) were prepared and their photoluminescence properties were investigated.Due to energy transfer from Dy~(3+) to Eu~(3+),both Dy~(3+) and Eu~(3+) characteristic emissions are observed under 393 nm light excitation.The emitting color of K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 turns from green through yellow to red by simply adjusting the Eu~(3+) concentration from 0 to 0.4.Moreover,K_2 Dy_(1.48)Eu_(0.02)Ta_(0.5)(PO_4)_3 phosphor possesses excellent fluorescence thermal stability and exhibits zero thermal quenching at 150 ℃.These results manifest that K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 solutions are promising multi-color emitting phosphors candidate for near-UV LED.     

Optimization of output and phosphor consumption for phosphor-converted white light-emitting diodes

Using ray-tracing simulation based on Monte Carlo method, the effects of phosphor concentration and thickness on light output and phosphor consumption of pcwLEDs were investigated in this work. The simulation was improved to comprehensively imitate the whole optical process of pc-wLEDs, including total produce of chip and phosphor light, losses in the propagation, and output.Experiments were conducted to verify the simulation.Results show that, light output changes non-monotonously over phosphor concentration and thickness, having maximum value. Experimental maximum light efficiency of158 lmáW-1was obtained at concentration of 16 wt%, 6 %higher than that of 11 wt% and 17 % higher than that of 33wt%. Phosphor consumption of pc-wLEDs increases linearly with the increase of phosphor concentration and the decrease of thickness. Experimental phosphor consumption of pc-wLEDs with concentration of 11 wt% is only 37 %of that of 33 wt%.     

TDS3000B系列数字示波器维修技术研究

本文通过对TDS3000B系列数字示波器几类常见故障现象的总结归纳，在系统研究仪器自身结构特点和电路组成的基础上，结合日常维修工作实践分析了各类故障具体成因，综合运用比对测量、电路功能性分割、在线追踪等故障测量分析方法，分析测量数据，逆向绘制出仪器局部电路原理图，研究并形成了具有针对性的故障诊断定位方法以及维修关键技术。     

Synthesis,photoluminescence properties and energy transfer behavior of color-tunable fluorapatite phosphor Sr9Gd(PO4)5(SiO4)F2:Tb3+/Sm3+

Tb³⁺-Sm³⁺ co-doped Sr₉Gd(PO₄)₅(SiO₄)F₂ (SGPSF) phosphors were prepared through a solid-state reaction, and their luminescence properties as well as energy transfer mechanism have been investigated in detail. The SGPSF:Tb³⁺, Sm³⁺ phosphors system could be efficiently excited at wavelengths ranging from 200 to 500 nm, which is well matched with the spectra of near ultraviolet chips. The emission of SGPSF:Tb³⁺, Sm³⁺ phosphor covers the entire visible region with sharp peaks in the blue, green, and red regions. The emission color of SGPSF:Tb³⁺, Sm³⁺ could be adjusted from green (0.275, 0.378) to red (0.519, 0.295) by controlling the doping content of Sm³⁺/Tb³⁺.     

Photoluminescence properties of Ce3+/Mn2+ doped calcium zirconium silicate phosphors with energy transfer for white LEDs

A series of Ce³⁺ doped and Ce³⁺/Mn²⁺ co-doped calcium zirconium silicate CaZrSi₂O₇ (CZS) phosphors have been synthesized via conventional high temperature solid state reactions. The luminescence properties, energy transfer between Ce³⁺ and Mn²⁺ have been investigated systematically. Under 320 nm excitation, the phosphor CZS: 0.05Ce³⁺ exhibit strong blue emission ranging from 330 nm to 500 nm, attributed to the spin-allowed 5d-4f transitions of Ce³⁺ ions. There are two different emission centers of Ce³⁺ ions, Ce³⁺(I) and Ce³⁺(II). The emission spectra of Ce³⁺, Mn²⁺ co-doped phosphors shows a broad emission around 550 nm corresponding to the ⁴T₁(⁴G)-⁶A₁(⁶S) spin-forbidden transition of Mn²⁺. The energy transfer between Ce³⁺ and Mn²⁺ is detected and the transfer efficiency of Ce³⁺(II) to Mn²⁺ is faster than that of Ce³⁺(I) to Mn²⁺. The resonant type is identified via dipole-dipole mechanism. Additionally, a blue-shift emission of Ce³⁺ and a red-shift emission of Mn²⁺ have been observed following the increase of Mn²⁺ content in relation to the energy transfer. Thermal quenching has been investigated and the emission spectra show a blue-shift with the temperature increases, which have been discussed in details. CZS: 0.05Ce³⁺, yMn²⁺ phosphors can be tuned from blue to white and even to yellow by adjusting the Mn²⁺ content. All the results indicate that CZS: Ce³⁺, Mn²⁺ phosphor have a potential application for near-UV LEDs.     

Tribological Properties of Phosphor Bronze and Nanocrystalline Nickel Coatings Under PAO + MoDTC and Ionic Liquid Lubricated Condition

The friction and wear properties of phosphor bronze and nanocrystalline nickel coatings were evaluated using a reciprocating ball-on-plates UMT-2MT sliding tester lubricated with ionic liquid and poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate, respectively. The morphologies of the worn surfaces for the phosphor bronze and nanocrystalline nickel coatings were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. Results show that the phosphor bronze and nanocrystalline nickel coatings exhibited quite different tribological behaviors under different lubricants. Phosphor bronze plate shows higher friction coefficient (0.14) and wear rate (3.2 × 10⁻⁵ mm³/Nm) than nanocrystalline nickel coatings (average friction coefficient is 0.097, wear rate is 1.75 × 10⁻⁶ mm³/Nm) under poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate lubricated conditions. The excellent tribological performance of nanocrystalline nickel coatings under above lubricant can be attributed to the formation of MoS₂ and MoO₃ on the sliding surface. a quite a number of C, O and F products on worn surface of phosphor bronze than NC nickel coatings can improve anti-wear properties while using ionic liquid as lubricant.     

薄膜电致发光材料的研究进展

薄膜电致发光(TFEL)显示是一种对材料有着严格要求的比较复杂的光电子器件.该多层结构通常包括2个电极,2个绝缘层和1个半导体发光层.在介绍了薄膜电致发光器件结构及工作原理的基础上,重点介绍了红色、绿色、蓝色和白色发光材料的研究现状,并讨论了薄膜电致发光材料的发展趋势.