The concentration quenching and crystallographic sites of Eu^(2+) in Ca_2BO_3Cl

A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.

Temperature modulation of concentration quenching in lanthanide-doped nanoparticles for enhanced upconversion luminescence

The doping concentration of lanthanide ions is important for manipulating the luminescence properties of upconversion nanoparticles （UCNPs）. However, the serious concentration quenching in highly doped UCNPs remains a vital restriction for further enhanced upconversion luminescence （UCL）. Herein, we examined the effect of temperature on the concentration quenching of rare-earth UCNPs, an issue that has been overlooked, and we show that it is significant for biomedical or optical applications of UCNPs. In this work, we prepared a series of UCNPs by doping Er3. luminescent centers at different concentrations in a NaLuF4：Yb3＋ matrix. At room temperature （298 K）, steady-state photoluminescence （PL） spectroscopy showed substantial concentration quenching of the Er~ emission with increasing doping concentrations. However, the concentration quenching effect was no longer effective at lower temperatures. Kinetic curves obtained from time-resolved PL spectroscopy further showed that the concen- tration quenching dynamics were vitally altered in the cryogenic temperature region, i.e., below 160 K. Our work on the temperature-switchable concentration quenching mechanism may shed light on improving UCL properties, promoting their practical applications.

Concentration quenching in transparent glass ceramics containing Er^(3+):NaYF_4 nanocrystals

In this work, we have studied the concentration quenching in transparent glass ceramics containing Er^3＋：NaYF4 nanocrystals. For different concentrations, the emission spectra and decay curves of the ^4I/3/2 → ^4I15/2 emission were measured. The Er-concentration dependence of integrated intensity and lifetime of ^4I13/2→^4I15/2 emission are showed. With the increase of the Er^3＋ doping concentration, the 1.5 μm fluorescence emission first increases, then decreases, and the lifetime falls gradually. With 980 nm excitation, the efficiency of the energy transfer from Er^3＋ to quenching centers reaches 73.73% for the sample with 4 mol% Er^3＋. Meanwhile, owing to the relation of fluorescence integrated intensity and Er-concentration, a dipole-dipole quenching mechanism in the framework of a limited diffusion regime has been proved. Using the limited diffusion case, the critical concentration for quenching has been determined from a fitting equation of the lifetime and Er-concentration. The fit- ting result shows the critical concentration for quenching is higher than the values obtained in Er-doped different glass by an order of magnitude.

Synergistic effect of crystal structure and concentration quenching on photoluminescence of Er^(3+) doped upconversion nanocrystals

YbF（2.357, YbF3, Ba2 YbF7, and Ba 2 upconversion nanocrystals doped with emitter Er^3＋ ion were synthesized in the same solvent system just with changing the molar ratio of Ba^2＋ to Yb^3＋ in the precursor, which corresponed to the crystal phases of rhombohedral, orthorhombic, tetragonal, and cubic, respectively. All the samples emitted both 660 nm red light and 543/523 nm green light which originated from Er^3＋-4f^n electronic transitions ~4F（9/2-~4I（15/2 and ~4S（3/2/~2H（11/2-~4I（15/2, respectively. It was worth mentioning that YbF 3：Er^3＋, Ba2 YbF7：Er^3＋, and BaF2：Er^3＋ could emit dazzlingly bright light even under the excitation of a 980 nm CW laser with output power of 0.1 W. Upconversion emission mechanism analysis indicated that the intensity ratio of red to green light highly depended on the synergistic effect of crystal structure, concentration quenching, and particle size, but were not sensitive to crystallinity as previously reported for NaL nF4（Ln=lanthanide.

Luminescence properties of Eu^(2+) -doped Ba_3Si_6O_12N_2 green phosphor: concentration quenching and thermal stability

The efficient Eu2＋ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 ℃ for 12h. Photoluminescence （PL） properties showed a broad emission band with a peak of 525 nm and the full width of half-emission maximums （FWHM） of 70 nm under 460 nm light irradiation. The X-ray diffraction patterns （XRD） and scanning electron microscope （SEM） images of the synthesized powder demonstrated its pure phase and excellent crystallization. Quenching concentration in this phosphor was found to be 0.3. The mechanisms of concentration quenching and redshift of emission peak with increasing concentration of Eu2＋ were studied. The temperature dependence measurement of this green phosphor revealed excellent thermal quenching property compared to silicate green phosphor. It is believed that Ba3 Si6O12N2 ：Eu2＋ is an excellent green phosphor for UV or blue chip based white LEDs.

Effect of concentration quenching on the spectroscopic properties of Er^(3+)/Yb^(3+) co-doped AlF_3-based glasses

A series of highly Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have been investigated in order to develop a microchip laser at 1.54 μm under 980 nm excitation. Measurements of absorption, emission and upconversion spectra have been performed to examine the effect of Er^(3+)/Yb^(3+) concentration quenching on spectroscopic properties. In the glasses with Er^(3+) concentrations below 10 mol%, concentration quenching is very low and the Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have stronger fluorescence of 1.54μm due to the ~4I_(13/2)→~4I_(15/2) transition than that of Er^(3+) singly-doped glasses. As Er^(3+) concentrations above 10 mol% in the Er^(3+)/Yb^(3+) co-doped samples, concentration quenching of 1.54μm does obviously occur as a result of the back energy transfer from Er^(3+) to Yb^(3+). To obtain the highest emission efficiency at 1.54μm, the optimum doping-concentration ratio of Er^(3+)/Yb^(3+) was found to be approximately 1:1 in mol fraction when the Er^(3+) concentration is less than 10 mol%.

The concentration quenching characteristics of ~5D_3-~7F_J and ~5D_4-~7F_J (J=0―6) transitions of Tb^(3+) in YBO_3:Tb^(3+) phosphor

The photoluminescence quenching behaviors of 5D3-7FJ and 5D4-7FJ (J = 0―6) transitions of Tb3+ in YBO3:Tb under 130―290 nm excitation were systematically investigated. The results revealed that the quenching concentrations of both 5D3-7FJ and 5D4-7FJ transitions of Tb3+ in YBO3:Tb were mainly de-pendent on excitation wavelength. Particularly,the quenching concentrations of 5D4-7FJ transitions of Tb3+ under 130―290 nm excitation were correlated with excitation bands of YBO3:Tb. The quenching concentrations of 5D3-7FJ transitions remained at low concentration (2%) under 186―290 nm excitation and then increased gradually with energy of incoming excitation photon when excited at 130―186 nm. This dependence should be involved in their excitation mechanisms and quenching pathway in particular excitation region.

Luminescence,Concentration Quenching and Thermal Stability of White Emitting Phosphor Ba_2Ca(BO_3)_2:Dy^(3+)

A white emitting phosphor Ba2Ca(BO3)2:Dy3+ was synthesized via a high temperature solid state reaction at 1000℃ for 5 h. The luminescence, mole fraction quenching and thermal stability of Ba2Ca(BO3)2:Dy3+ were investigated. According to the phase composition analyzed by X-ray powder diffraction, there is no crystalline phase except Ba2Ca(BO3)2 in the sample. Ba2Ca(BO3)2:Dy3+ can produce white emission under 348 nm excitation. The emission intensities of Ba2Ca(BO3)2:Dy3+ are affected by Dy3+ concentration. The concentration quenching effect was analyzed, and the concentration quenching mechanism was verified as dipole-dipole interaction. The critical distance(R c) obtained based on the crystal structure data is 2.911 nm. At 150℃, the emission intensity of Ba2Ca(BO3)2:Dy3+ is 68.0% of the initial value at room temperature. The activation energy for the thermal quenching calculated is 0.202 e V. Moreover, the CIE chromaticity coordinates of Ba2Ca(BO3)2:Dy3+ locate in the white region of(0.319, 0.356).

Luminescence, Energy Transfer and Concentration Quenching of Red Emitting Phosphor Ba_3Eu(PO_4)_3:Tb^(3+)

A red emitting phosphor of Ba_3Eu(PO_4)_3:Tb^(3+) was synthesized by a solid state method. The energy transfer from Tb^(3+) to Eu3+ in Ba_3Eu(PO_4)_3:Tb^(3+) was proved by the spectral properties and decay curves. The emission intensity of Ba_3Eu(PO_4)_3 is enhanced by doping Tb^(3+) as a sensitizer. For Ba_3Eu(PO_4)_3:Tb^(3+), the ~5D_3→~7F_J transition of Tb^(3+) occurs, and the corresponding emission intensities can be tuned when Tb^(3+) content increases, and the concentration quenching effect appears. However, for the ~5D_4→~7F_J transition of Tb^(3+), its intensity straight increases with increasing Tb^(3+) content. For Ba_3Eu(PO_4)_3:Tb^(3+), the values of CIE chromaticity coordinates are similar to those of commercial red phosphors of Sr_2Si_5N_8:Eu^(2+) and Y_2O_2S:Eu^(3+). The results indicate that this red emitting phosphor has a potential application for white LEDs.

Anneal and Concentration Effect on PL Properties of Sol-Gel Derived Eu^(3+) Doped SiO_2 Glass

Eu3+ doped SiO2 nano-crystalline glasses were prepared by sol-gel method. The broad peak of XRD pattern indicates an amorphous SiO2 matrix. The affection of anneal time and anneal temperatures on photoluminescence (PL) properties of SiO2 glass under different Eu doping concentration were studied systematically. It is found that the optimized anneal time is about 3 h. The excitation spectra of 2% Eu3+ doped SiO2 glass powder were measured under various anneal temperatures, and the optimized anneal temperature is observed around 700℃. The fluorescence-quenching effect can be observed in the emission spectra when the annealing temperature exceeds 700℃. The emission spectra of different molar ratio dopants were measured at an annealed temperature of 500℃, and the concentration-quenching phenomenon has also been observed in SiO2 glass powder when the molar ratio of Eu3+ ion exceeds 3% . The result shows that the PL intensity approaches its maximum when the molar ratio of Eu3+ ions in the sample is about 3% . In addition, a comparatively stronger emission spectrum at wavelength of 703 nm which is corresponding to the energy transition 5D0→7F4 of Eu ions is also obtained.

Quenching Phenomena Due to a Concentrated Nonlinear Source in an Infinitely Long Cylinder

This article studies a semilinear parabolic first initial-boundary value problem with a concentrated nonlinear source in an infinitely long cylinder. We study the effects of the strength of the source on quenching. Criteria for global existence of the solution and for quenching are investigated.

基于改进集中热容法的TC17钛合金淬火表面换热系数测算

表面换热系数是TC17钛合金淬火数值分析研究的重要边界条件,其准确性影响工件淬火温度与应力场的分布精度。基于深埋热电偶动态实测的温降曲线,采用改进后的集中热容法,计算求解TC17钛合金淬火表面换热系数,并通过数值模拟验证了结果的可靠性。结果表明,TC17钛合金水浴淬火过程中会经历3个主要阶段:蒸汽膜阶段、核沸腾阶段及对流冷却阶段。表面换热系数在蒸汽膜阶段、核沸腾阶段会快速增大,随后在对流冷却阶段会逐渐减小,在第50 s达到峰值1299 W/(m^(2)·℃),此时淬火面温度为355℃。将换热系数代入数值模型中进行温度场计算验证,计算结果与实测温降曲线吻合较好,平均相对误差仅为1.4%。

改善55钢零件高频感应淬火金相组织的措施

通过分析55钢制造减速器零件的高频感应淬火组织,并分别对零件的基体组织、感应加热功率、加热时间及淬火液浓度等影响淬火组织的各种因素进行试验验证,最后提出了改善55钢感应淬火金相组织的有效措施。

模压淬火工艺对渗碳轴承套圈畸变的影响

SAE5120钢制轴承套圈渗碳淬火后畸变较大,通过感应加热并模压淬火的方式可有效控制轴承套圈畸变。模具施加不同的压力、不同的加热工艺对套圈的畸变和理化性能有明显影响。阐述了不同模压淬火工艺方法,并通过统计分析,得出了模具压力与淬火冷却介质浓度对硬度、畸变和磨削余量的影响。

连接底开裂原因分析及改进措施

对失效连接底金相组织、化学成分、裂纹形态等进行理化检测,分析连接底裂纹产生的原因。结果表明:连接底裂纹为淬火裂纹;连接底中心圆柱部与底部过渡弧R角半径较小是主要原因,致使淬火过程中应力集中导致开裂;原材料中心部位组织疏松和冷却速度较快,进一步促进裂纹萌生;通过增大R角、调整热处理工艺来降低淬火应力,从而避免连接底淬火开裂的产生。

有机电致发光红色发光材料研究进展

本文总结了近年来有机金属配合物、分子内电荷转移化合物、稠环芳香类化合物以及齐聚物等几类有机电致发光红色发光材料的研究进展 ,详细介绍了它们在有机电致发光器件中的应用 ,并对有机电致发光红色发光材料未来的研究方向作了展望。

Fe^(3+)对KDP晶体生长影响的研究

金属离子对KDP晶体的影响是多方面的。本文采用不同的过饱和度,在不同的Fe3+掺杂浓度的生长溶液中生长KDP晶体,定量地研究了Fe3+对KDP晶体生长的影响。实验发现,无论是在高过饱和度还是在低过饱和度下生长KDP晶体,在一定的浓度范围内,Fe3+的掺入既可以增加生长溶液的稳定性,又可以有效抑制晶体柱面的扩展,而且晶体基本不楔化,同时,对晶体光学性能的影响也不大。

Y_2O_2S:Sm^(3+)发光材料在不同激发波长的浓度特征

研究了在不同激发波长下三价钐离子掺杂硫氧化钇的发光强度对浓度的依赖关系。研究发现磷光体的发光强度不仅跟激活离子的浓度有关,而且跟激发时所采用的不同激发波长有关。磷光体发光强度与激活剂掺杂量的变化曲线表明,在不同激发路径下磷光体具有不同的发光性质。采用Sm3+离子直接跃迁的413nm对样品进行激发时,发生猝灭的浓度低至约02mol%;当采用263nm高能紫外线激发时,浓度猝灭发生在较高浓度处(～2mol%),后者是前者的10倍。对Sm3+离子发射强度与浓度关系曲线进行了拟合计算,结果表明Sm3+在Y2O2S中浓度猝灭的原因主要是相邻中心的偶极四极相互作用引起的交叉弛豫。

橙红色荧光粉Ca_3Y_2(Si_3O_9)_2∶Sm^(3+)的制备及发光性能的表征

采用高温固相法合成了Ca3Y2-2x(Si3O9)2∶2xSm3+系列荧光粉,并表征了材料的发光特性.X射线衍射图谱表明:得到的样品为纯相Ca3Y2(Si3O9)2晶体;样品的激发光谱主要来源于Sm3+的特征激发;分别采用紫外、近紫外和蓝光作为激发源,样品均发射橙红光.在402nm近紫外光激发下,Ca3Y2(Si3O9)2∶Sm3+发射光谱主要由3个峰组成,发射峰值分别位于565nm、604nm和651nm,归属于Sm3+的4G5/2→6HJ/2(J=5,7,9)跃迁,其中发射主峰位于604nm处.通过时间分辨光谱测得Sm3+的4G5/2能级的荧光寿命.随着Sm3+摩尔浓度的增加,样品发光强度先增强后减弱,当x=0.02时发光强度达到最大,浓度猝灭机理为电偶极-电偶极相互作用.

Y_2O_2S纳米晶中Tb^(3+)发光的浓度猝灭

制备了Tb^(3+ )浓度不同而粒径相同的一系列纳米晶Y2 O2 S。由于表面态对发光的猝灭作用 ,Tb3 + 离子5D3发光的寿命与体材料比较明显缩短。研究了5D3和5D4 能级发光的浓度猝灭 ,发光强度与浓度的关系以及发光的衰减曲线都表明 :5D3的浓度猝灭是电偶极 电偶极相互作用引起的 ,而5D4 的浓度猝灭是交换相互作用引起的。