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The efficiency droop behaviors of GaN-based green light-emitting diodes (LEDs) are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level (<1 A/cm2 ) with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs. 相似文献
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通过水热法合成并表征了3个基于V型配体构筑的新颖配位聚合物{[Cd(BIDPS)(PA)(H2O)]·CH3OH}n(1)、{[Zn(BIDPS)(p-bdc)]·H2O}n(2)和[Mn(BIDPT)(NBA)]n(3)(BIDPS=4,4''-二(1-咪唑基)苯砜,H2PA=帕莫酸,p-H2bdc=对苯二甲酸,BIDPT=4,4''-二(1-咪唑基)苯硫醚,H2NBA=4,4''-氮杂二基二苯甲酸)。单晶结构分析表明化合物1和2具有二维网络结构,化合物1进一步通过倾斜穿插形成三维结构,化合物2通过分子间氢键形成了三维网络结构。化合物3属于3-连接六边形的蜂窝状结构,通过C—H …π作用形成三维超分子结构。化合物1和2在水中具有很好的稳定性和荧光性质,可作为高灵敏度、高选择性荧光探针检测水溶液中的Fe3+和Cr2O72-,并能抵抗多种竞争离子的干扰。同时研究了其对Fe3和Cr2O72-的荧光猝灭机理。 相似文献
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设G是一个顶点集为V(G),边集为E(G))的简单图.S_k(G)表示图G的拉普拉斯特征值的前k项部分和.Brouwer et al.给出如下猜想:S_k(G)≤e(G)+((k+1)/2),1≤k≤n.证明了当k=3时,对边数不少于n~2/4-n/4的图及有完美匹配或有6-匹配的图,猜想是正确的. 相似文献
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