ZnSe(ZnS)纳米晶与MEH-PPV的共掺有机电致发光器件

采用水相法合成核壳结构ZnSe/ZnS 纳米晶,经X射线衍射(XRD)分析和透射电子显微镜(TEM)表征,证实所制备的样品为立方晶型闪锌矿结构ZnSe/ZnS量子点。按照一定的质量比将ZnSe/ZnS 纳米晶和有机聚合物MEH-PPV(poly ) 共掺并将其作为发光层,分别制备单层和多层有机电致发光器件,结构为ITO/MEH-PPV∶ZnSe(ZnS)(50 nm)/Al和 ITO/PEDOT∶PSS(70 nm)/ MEH-PPV∶ZnSe(ZnS)(50 nm)/BCP(15 nm)/Alq₃(12 nm) /LiF(0.5 nm)/Al。实验结果表明,多层发光器件的发光特性与单层器件不同,工作电压的增大使其发光峰发生了明显的蓝移。     

Influence of thickness of functional layer on performance of organic salt-doped OLED with ITO/PVK:PBD:TBAPF6/Al structure

The effect of thickness of functional layer on the electrical and electroluminescence (EL) properties of single-layer OLED with ITO/PVK:PBD:TBAPF₆/Al structure were investigated where indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule, tetrabutylammonium hexafluorophosphate (TBAPF₆) as organic salt dopant and aluminium (Al) as cathode. A unique transition phenomenon at high bias voltage in the devices was observed and the transition was reversible. The transition voltage and turn on voltage decreased with the decrease of functional layer thickness. The turn on voltage was approximately 5.5 V and 6.5 V for 55-nm-thick and 95-nm-thick devices, respectively. However, the current efficiency of 95-nm-thick device was higher than the 55-nm-thick device. More interestingly, the Commission Internationale d’Eclairage (C.I.E.) coordinates of EL spectra of 95-nm-thick device at bias voltage ranging from 7 V to 13 V located in the white light region even without any dye doping. The PL and EL spectra were found completely different. PBD electromer was proposed to dominate the EL spectrum, but the contribution from PVK–PBD electroplex cannot be completely ruled out.     

Improved photoluminescence of ZnS:Mn nanocrystals by microwave assisted growth of ZnS shell

The photoluminescence (PL) of ZnS:Mn nanocrystals was improved greatly by microwave assisted growth of ZnS shell. Under optimized conditions, the luminescence quantum yield of ZnS:Mn nanocrystals increased from 2.8% to 12.1% after the growth of the ZnS shell. Time-resolved fluorescence spectroscopic and electron paramagnetic resonance measurements indicate that the improvement of the dispersivity of the doped Mn ions is responsible for the PL enhancement. Growth of the ZnS shell not only facilitated the diffusion of Mn ions during microwave irradiation but also prohibited the segregation of Mn ions on the particle surface. As a result, more isolated Mn²⁺ ions were produced after the growth of the ZnS shell, and thus the orange luminescence of ZnS:Mn nanocrystals was enhanced greatly.     

The optical properties and energy transition process in nanocomposite of polyvinyl-pyrrolidone polymer and Mn-doped ZnS

This study has been carried out on the optical properties of polyvinyl-pyrrolidone (PVP), the energy transition process in nanocomposite of PVP capped ZnS:Mn nanocrystalline and the influence of the PVP concentration on the optical properties of the PVP capped ZnS:Mn nanocrystalline thin films synthesized by the wet chemical method. The microstructures of the samples were investigated by X-ray diffraction, the atomic absorption spectroscopy, and transmission electron microscopy. The results showed that the prepared samples belonged to the sphalerite structure with the average particle size of about 2–3 nm. The optical properties of samples are studied by measuring absorption, photoluminescence (PL) spectra and time-resolved PL spectra in the wavelength range from 200 to 700 nm at 300 K. From data of the absorption spectra, the absorption edge of PVP polymer was found about of 230 nm. The absorption edge of PVP capped ZnS:Mn nanoparticles shifted from 322 to 305 nm when the PVP concentration increases. The luminescence spectra of PVP showed a blue emission with peak maximum at 394 nm. The luminescence spectra of ZnS:Mn–PVP exhibits a blue emission with peak maximum at 437 nm and an orange–yellow emission of ion Mn²⁺ with peak maximum at 600 nm. While the PVP coating did not affect the microstructure of ZnS:Mn nanomaterial, the PL spectra of the PVP capped ZnS:Mn samples were found to be affected strongly by the PVP concentration.     

表面热透镜技术测量3.8μm和2.8μm激光薄膜的微弱吸收

 采用表面热透镜技术，对3.8μm和2.8μm激光辐照下镀制在Si基底上的单层ZnS，YbF₃和YBC薄膜及不同膜系的YbF₃/ ZnS多层分光膜和多层高反膜，以及镀制在CaF₂基底上的增透膜进行了吸收测量，并对3.8μm和2.8μm 激光的测量结果进行了比较分析。实验结果表明，2.8μm波长下的吸收比3.8μm的大得多，两者之间约相差一个量级，测得的多层高反膜YbF₃/ZnS薄膜在的3.8μm处的最低吸收为4.57×10^－4，测量系统的灵敏度约为10^-5。     

Combustion synthesis and photoluminescence of ZnS:Mn particles

An efficient process based on a solid-state combustion technique has been developed to produce high crystalline and micrometer sized particles of ZnS:Mn⁺² phosphor with sphalerite structure. The precursor mixture of 0.915Zn+S+0.05Mn+0.035ZnCl₂+kNaCl composition (where k is the mole number of NaCl) was combusted under the argon atmosphere followed by post-heat treatment procedure at 700 °C. It was shown that photoluminescence (PL) intensity of ZnS sample can be easily controlled through adjusting NaCl concentration. In the optimized reaction conditions ZnS samples have showed PL intensity almost comparable to that of a commercial one, despite the relatively low purity of precursor materials used. Many interesting phenomena such as high luminescent efficiency, pure cubic ZnS formation after the post-heat treatment and strong influence of Cl⁻ ion on PL intensity have been observed and discussed.     

High-contrast top-emitting organic light-emitting devices

In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer.The contrast-enhancement stack consists of a thin metal anode layer,a dielectric bilayer,and a thick metal underlayer.The resulting device,with the optimized contrast-enhancement stack thicknesses of Ni(30 nm)/MgF 2(62 nm)/ZnS(16 nm)/Ni(20 nm) and the 25-nm-thick ZnS anti-reflection layer,achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A(at 62.3 mA/cm 2) together with a very stable chromaticity.The contrast ratio reaches 561:1 at an on-state brightness of 1000 cd/m 2 under an ambient illumination of 140 lx.In addition,the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.     

Luminescence enhancement of Mn doped ZnS nanocrystals passivated with zinc hydroxide

Mn-doped ZnS nanocrystals prepared by solvothermal method have been successfully coated with different thicknesses of Zn(OH)₂ shells through precipitation reaction. The impact of Zn(OH)₂ shells on luminescent properties of the ZnS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the ZnS:Mn nanocrystals have cubic zinc blende structure. The morphology of nanocrystals is spherical shape measured by transmission electron microscopy (TEM). ZnS:Mn/Zn(OH)₂ core/shell nanocrystals exhibited much improved luminescent properties than those of unpassivated ZnS:Mn nanocrystals. The luminescence enhancement was observed with the Zn(OH)₂ shell thickening by photoluminescence (PL) spectra at room temperature and the luminescence lifetime of transition from ⁴T₁ to ⁶A₁ of Mn²⁺ ions was also prolonged. This result was led by the effective, robust passivation of ZnS surface states by the Zn(OH)₂ shells, which consequently suppressed nonradiative recombination transitions.     

核/壳结构的ZnS:Mn/SiO_2纳米粒子的制备及发光性质研究

采用溶剂热法制备了Mn离子掺杂的ZnS纳米粒子(ZnS∶Mn),然后利用正硅酸乙酯(TEOS)的水解反应对其进行了不同厚度的SiO2无机壳层包覆。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及荧光发射光谱(PL)对样品的结构及光学性质进行了表征和研究。包覆SiO2壳层后,粒子的粒径明显增大并且在ZnS∶Mn纳米粒子表面可以观察到明显的SiO2壳层。XPS测试印证了ZnS∶Mn/SiO2的核壳结构。随着SiO2壳层的增厚,ZnS∶Mn/SiO2的Mn离子的发光先增强后减弱,这是因为SiO2壳层同时具有表面修饰和降低发光中心浓度这两种相反的作用。当壳层厚度(壳与核的物质的量的比)达到5时,发光效果达到最好,其强度达到未包覆样品的7.5倍。     

与掺杂浓度相关的ZnS∶Mn纳米粒子的发光性质

采用溶胶法制备了Mn掺杂的ZnS纳米粒子,探讨了掺杂离子浓度对ZnS∶Mn纳米粒子的晶体结构和发光性质的影响。通过X射线衍射（XRD）对样品的结构进行了表征,结果表明：所制备的ZnS∶Mn纳米粒子为立方闪锌矿结构,其在Mn离子的掺杂浓度达到6%时不发生分相,但随着掺杂浓度的增加,纳米粒子的平均粒径会减小。光致发光光谱和荧光光谱的结果表明：通过改变掺杂离子的浓度可实现对ZnS∶Mn纳米粒子590 nm附近荧光发射波长的调节。此外,研究了温度对纳米粒子形貌和发光性质的影响。高分辨透射电子显微镜（HRTEM）观察发现,经过50℃陈化1 h后的ZnS∶Mn样品的平均粒径增大约为20 nm,且加热陈化有利于ZnS∶Mn纳米粒子中Mn2＋在590 nm处产生荧光。     

柠檬酸钾电子注入层对有机电致发光器件的影响

使用柠檬酸钾(C₆H₅K₃O₇)作为电子注入材料,制备了多层有机电致发光器件。当柠檬酸钾阴极修饰层厚度为0.5 nm时,得到3.6 cd/A 的发光效率,高于0.5 nm LiF作阴极修饰层时的发光效率(2.5 cd/A) 。器件的开启电压相比0.5 nm LiF作阴极修饰的器件降低了0.5 V。实验结果表明,柠檬酸钾(C₆H₅K₃O₇)是一种良好的电子注入材料。     

The characteristics of surface acoustic waves on AlN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO₃, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO₃ substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO₃ substrate. The TCF of a SAW on an AlN/LiNbO₃ device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO₃ substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO₃ substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V_p) of the SAW on an AlN/LiNbO₃ substrate was significantly increased by the increase of AlN thickness (h/λ). Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +886-7/525-4199, E-mail: ycc@ee.nsysu.edu.tw     

Fast two-step microwave-activated synthesis of Mn doped ZnS nanocrystals: Comparison of the luminescence and doping process with thermochemical approach

In this work we report a fast two-step microwave activated synthesis of the ZnS:Mn nanocrystals. Zn(NO₃)₂ and Na₂S₂O₃ were used as the precursors and Mn(NO₃)₂ was employed as the source of the impurity. The aqueous synthesis was based on the heat sensitivity of Na₂S₂O₃, which releases some S species on heating. Consequently, the reaction was well activated under microwave irradiation resulting in formation of ZnS:Mn nanocrystals. Thioglycerol (TG) was also used as the capping agent and the catalyst of the reaction. The synthesis process was done in two steps, i.e. 1 min irradiation without TG and then injection of TG and continuation of irradiation. ZnS:Mn nanocrystals were quickly formed in the solution and luminescence was emerged in a few minutes. Optical transmission spectroscopy and X-ray diffraction analysis demonstrated formation of ZnS:Mn nanocrystals with a cubic crystalline structure and 3.0 nm average size. Photoluminescence measurements also showed some spectra with a Mn related peak located at 585 nm. The mentioned peak corresponds to ⁴T₁→⁶A₁ transition in Mn impurities and revealed the effective incorporation of Mn ions inside the nanocrystals. Evolution of the PL was also investigated and showed an increase in longer irradiation times. A qualitative model is also used to justify the necessity of using a two-step method as well as the PL emergence and increase in longer irradiation times. The model is based on separation between the nucleation and growth steps and significant role of TG in these stages. Finally, we present a comparison between the results of microwave activated method and two-step thermochemical approach. Although the synthesis time in microwave activated method was considerably short (less than 5 min), the luminescence properties were quite comparable with long time thermochemical approach. The doping process was also investigated for different Mn/Zn concentrations in two approaches. The results demonstrated that the doping occurred more effectively in the microwave activated synthesis.     

硒化镉发光量子点的制备及其在有机发光器件中的应用

硒化镉量子点具有随粒径尺寸改变,而产生发光波长调变的特性,目前已被广泛研究。本研究是由化学溶胶法合成不同粒径尺寸的核壳型CdSe／ZnS硒化镉量子点,其表面包覆十六烷基胺,避免分子团聚现象。在由硒化镉成核温度的控制,成功地制备一系列具有各种尺寸粒径的核壳型硒化镉量子点(2—6nm)。本研究也合成了含有纳米金粒子于核壳型硒化镉量子点,实验结果发现：硒化镉发光效率明显的提高。在有机发光器件的应用方面,将发光波长为505nm核壳型CdSe／ZnS量子点掺入溶有发光波长为570nm铱化合物的氯仿溶液时,其溶液的光致发光光谱表明,原量子点的发光特性消失,只有铱化合物的发光依然存在,且其发光强度呈现明显增强趋势,我们推测此现象源自于量子点到铱化合物能量转移的机制。我们也以含有核壳型硒化镉量子点的铱化合物与PVK混合材料为发光层,成功的制作发光二极管器件,器件的发光效率因核壳型硒化镉的掺杂,明显提高2倍多。     

ZnS:Mn交流电致发光的效率与Mn浓度的关系和浓度猝灭

从实验上确定了交流电致发光薄膜Y2O3-ZnS:Mn-Y2O3的发光效率与Mn浓度的关系:在低浓度下(10-5～10-4g/g),发光效率随Mn浓度线性增加,在10-3g/g附近发光效率达到最大值,当Mn浓度继续增加时,发光效率开始下降.在ZnS:Mn薄膜中存在两种发光中心—单个Mn中心和Mn对,它们的衰减都是指数形式,它们激发态的寿命随Mn浓度增加而减.Mn对发光中心与单个Mn中心之比随Mn浓度增加而增加.从而减少了有效的发光中心数目,这是浓度猝灭的原因之一.发光效率在高Mn浓度时下降的另外原因是由于电隅极子之间共振能量传递引起浓度猝灭.     

Morphological characteristics of amorphous Ge2Sb2Te5 films after a single femtosecond laser pulse irradiation

The morphology of materials resulting from laser irradiation of the single-layer and the multilayer amorphous Ge₂Sb₂Te₅ films using 120 fs pulses at 800 nm was observed using scanning electron microscopy and atomic force microscopy. For the single-layer film, the center of the irradiated spot is depression and the border is protrusion, however, for the multilayer film, the center morphology changes from a depression to a protrusion as the increase of the energy. The crystallization threshold fluence of the single-layer and the multilayer film is 22 and 23 mJ/cm², respectively.     

Magnetic reversal mechanism in strong perpendicular magnetic anisotropic CoPt/AlN multilayer film

Magnetic reversal mechanism of the Sub/AlN5 nm/[CoPt2 nm/AlN5 nm]₅ nano multilayer film, which shows strong perpendicular magnetic anisotropy (K_u=6.7×10⁶ erg/cm³), has been studied. The angle-dependent magnetic hysteresis loops of this highly perpendicular anisotropic CoPt/AlN multilayer film were measured in the present work, applying a magnetic field along different angles φ with respect to the film normal. It demonstrates that the magnetic reversal of the CoPt ultrathin layers in the CoPt/AlN multilayer film is occurred by the reversible magnetization rotation and the irreversible displacement of domain walls. The φ-dependent part of coercive field is resulted from the internal stress according to the Kondorsky and Kersten model. The φ-independent part of coercive field implies some random and isotropy pinning centers (e.g., vacancies, dislocations, grain boundaries) in the ultrathin CoPt layers. Our work is useful for coercivity control of metal/ceramics layered structures, in particular the perpendicular magnetic tunneling junctions.     

SrS:Ce/ZnS:Mn-A di-band phosphor for near-UV and blue LED-converted white-light emitting diodes

The SrS:Ce/ZnS:Mn phosphor blends with various combination viz 75:25, 50:50 and 25:75 were assign to generate the white-light emission using near-UV and blue-light emitting diodes (LED) as an excitation source. The SrS:Ce exhibits strong absorption at 427 nm and the corresponding intense emission occurs at 480 and 540 nm due to electron transition from 5d(²D)−4f(²F_5/2, _7/2) of Ce³⁺ ion as a result of spin-orbit coupling. The ZnS:Mn excited under same wavelength shows broad emission band with λ_max=582 nm originates due to 3d (⁴G−⁶S) level of Mn²⁺. Photoluminescence studies of phosphor blend excited using near-UV to blue light confirms the emitted radiation varies from cool to warm white light in the range 430-600 nm, applicable to LED lightings. The CIE chromaticity coordinate values measured using SrS:Ce/ZnS:Mn phosphor blend-coated 430 nm LED pumped phosphors in the ratio 75:25, 50:50 and 25:75 are found to be (0.235, 0.125), (0.280, 0.190) and (0.285, 0.250), respectively.     

Photophysical and photoluminescence properties of co-activated ZnS:Cu,Mn phosphors

ZnS:Cu,Mn phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux at 900 °C. The samples were characterized by X-ray powder diffraction, UV-vis absorbance spectra and photoluminescence spectra. All samples possess cubic structure. Cu has a much stronger effect on the absorption property of ZnS than Mn. Incorporation of Mn into ZnS host only slightly enhances the light absorption, while addition of Cu remarkably increases the ability of absorption due to ground state Cu⁺ absorption. The emission spectra of the ZnS:Cu,Mn phosphors consist of three bands centered at about 452, 520 and 580 nm, respectively. Introduction of Mn significantly quenches the green luminescence of ZnS:Cu. The excitation energy absorbed by Cu is efficiently transferred to Mn activators non-radiatively and the Mn luminescence can be sensitized by Cu behaving as a sensitizer (energy donor).     

Photoluminescence characteristics of ZnS nanocrystallites co-doped with Cu and Cd

ZnS nanocrystallites co-doped with Cu²⁺ and Cd²⁺ have been prepared by precipitation from homogeneous solutions of transition metal (Zn²⁺, Cu²⁺ and Cd²⁺) salt compounds, with S²⁻ as precipitating anion formed by decomposition of thioacetamide (TAA). X-ray diffraction (XRD) patterns of the samples show that the average crystallite size of the doped and undoped ZnS nanocrystallites is Novel luminescence phenomena (green emission) have been observed from the co-doped ZnS nanocrystals. The photoluminescence (PL) property of the co-doped samples is significantly different from that of ZnS nanocrystallites doped with Cu²⁺ or Cd²⁺.