999 resultados para photoluminescent materials


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Two series of films has been prepared by using a new regime of plasma enhanced chemical vapor deposition (PECVD) in the region adjacent to the phase transition from amorphous to crystalline state. The photoelectronic properties of the films have been investigated as a function of crystalline fraction. In comparison with typical a-Si:H, these diphasic films with a crystalline fraction less than 0.3 show a similar optical absorption coefficient, higher mobility life-time product ( LT) and higher stability upon light soaking. By using the diphasic nc-Si/a-Si films as the intrinsic layer, a p-i-n junction solar cell has been prepared with an initial efficiency of 9. 10 % and a stabilized efficiency of 8.56 % (AM 1.5, 100 mW/cm(2)).

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Waveguides induced by one-dimensional spatial photovoltaic solitons are investigated in both self-defocusing-type and self-focusing-type photorefractive photovoltaic materials. The number of possible guided modes in a waveguide induced by a bright photovoltaic soliton is obtained using numerical techniques. This number of guided modes increases monotonically with increasing intensity ratio, which is the ratio between the peak intensity of the soliton and the sum of the background illumination and the dark irradiance. On the other hand, waveguides induced by dark photovoltaic solitons are always single mode for all intensity ratios, and the higher the intensity ratio, the more confined is the optical energy near the centre of the dark photovoltaic soliton. Relevant examples are provided where photorefractive photovoltaic materials are of self-defocusing and self-focusing types. The properties of soliton-induced waveguides in both self-defocusing-type and self-focusing-type materials are also discussed.

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采用水热法结合后续热处理制备了一系列纯的和稀土离子(Eu3+,Dy3+)掺杂的黔具有纳米/微米结构的无机氧化物材料,包括YB03、姚03、Ga203和硅基MCM一攀41介孔分子筛体系。研究了这些体系的水热产物的晶体形貌、结构以及它们的生乖~一_长机理,并通过进一步热处理得到了保持水热产物纳米/微米结构形貌的发光材料,报道了以上各个体系材料的光致发光性能。一把姚03和Eu203粉末直接加入H3Bo3水溶液中,调节pH一1一4,在180一270夸_少℃水热处理得到了具有vaterite结构的YBo3:Eu3+晶体。xRD和FEsEM结果证明一扭03:E矿"晶体是由厚度小于50nm的纳米晶片构成的花状和猴头菇状的微米级晶丫体。水热温度提高时纳米晶片的厚度没有增加,形貌也不变,但是结晶度和发光一强度有所提高。pH值对纳米晶片之间的距离、角度和晶片数量有影响。pH低时,纳米晶片更多且包裹得更紧,形成了猴头菇状;而pH高时,晶片分得更开一些呈花朵状。这与pH值低时结晶成核较快较多有关。YB03:E矿+水热和固相法样品在24Onm激发下的发光谱峰位相同。但水热样品比固相法样品具有较高的红橙比[Eu3+:I(,D。一7F2)/I(SD。一7FI)],增加了12一37%。在24oC下制备的花03:Eu3+水热样品具有最大的结晶度和发光强度。报道了三种晶形调节剂对水热晶体形貌的影响结果。硝酸钻水溶液用氨水调节至pH一8一n,200oC下水热处理24小时,产物经xRD确定是单斜晶系的碱式硝酸盐叽O(0H)9困03)。FEsEM观察发现产物是一种具有几_三叶形截面的棱柱。改变合成条件可以调节三叶形棱柱的尺寸。增加氨水量时,PH从8调到n后,棱柱直径可从微米级调节到亚微米级,即从3一5林m左右下降到200一300纳米,同时长径比也有所增加,从pH一8的5增加到pH=n的10。调节机制可解释为较高的pH条件下结晶成核作用进行较快,形成了更多的晶核。三叶形棱柱的生长机理是、O(OH)9困03)的晶核依靠内在的趋势长成棒状纳米粒子;并通过一种直接的聚集生长,这些起始的纳米棒沿着它们横截面的径向方向快速自堆积成一种Y型结构的棒束;然后沿着棱柱轴向和平行于棱柱叶片方向的晶面同时优先生长,而垂直于叶片方向上的晶面生长得相对缓慢,导致三叶形棱I、-纳米/微米结构氧化物材料的水热合成、形貌与发光性质研究柱的形成。、经过高温相转变得到了姚03三叶形棱柱。采用同样方法可以制得姚03:E矿+的三叶形棱柱发光粉,其光谱与固相法样品的一致。将Gacl3一HZO一NaOH体系在pH=6一8时于180℃下水热处理得到了正交晶系的Gao0H晶体,其形貌分别是宽度在200一30Onm之间长径比约1:7的四方棱柱(pH=6)和长径比约1:3纺锤状的纳米棒束(pH=8)。使用HZO/DEG混合溶剂可以增加棱柱的长径比,1:Ivol时增加到1:15;1:Zvol时获得的是长达几十微米的四方棱柱纳米线6Go0OH纳米棒是从最初的胶状沉淀中成核后沿着c轴优先生长而成的。pH值的高低可导致Ga0OH晶体从四方棱柱到纳米棒束的不同形貌。DEG的存在对晶体的生长可能有两点作用:一是抑制晶核形成;二是降低晶体沿着横截面晶面的生长速度。经过高温锻烧的产物是保持着前驱体形貌的p一GaZO3晶体。254nm激发下p一GaZO3纳米棒的发射谱是从300nm到600nln的宽峰,最大值在455nln。发光的平均寿命是64ns。其蓝光发射起源于氧空位给体提供的电子和来自受体嫁空位或者嫁氧空位对的空穴之间的复合。采用相似方法制备了p一GaZO3:Dy纳米棒束,并与固相法样品对比了光谱性质的异同。将三种5102基材料:MCM一41型分子筛(直接分子筛CMS和萃取分子筛EMS)、无规颗粒(ASP)和干凝胶(SG)进行从室温到1000℃的不同温度不同时间热处理。254nm激发下,MCM一41没有发光现象。而ASP和SG系列样品随着热处理温度不同而显示不同的PL。说明ASP和SG与MCM一41有着不同的发光机理。排除了ASP和SG样品的发光中心是来自5102网络本身的结构缺陷,认为是其中所含有机物在热处理中产生的碳杂质引起。结果也表明MCM41中模板剂在热处理的碳化产物并没有引起MCM一41的PL。在365nm激发下,MCM一41与ASP、SG的PL现象大致相同。表明所有系列的样品的发光机理相同。CMS和EMS两个系列在300℃以上处理的样品的PL相似,说明模板剂的存在及其碳化并没有影响MCM一41的PL。所有系列样品在365nm激发下的PL认为是起源于5102网络中与氧相关的结构缺陷三Si一0.,而不是碳掺杂作用引起的。

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Using the numerical unrestricted Hartree-Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a (0, π) mode spin-density wave and the superconductivity as the doping concentration changes. There might be a small region in the electron-doping side where the magnetism and superconductivity coexist. The superconducting pairing is found to be spin singlet,orbital even, and coexisting sxy + dx~2-y~2 wave (even parity).