Binary Amine-Phosphine Passivation of Surface Traps on CdSe Nanocrystals
Binary Amine-Phosphine Passivation of Surface Traps on CdSe Nanocrystals
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DOI：
10.1021/jp911207v
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发表时间：
2010-01-28
影响因子：
3.7
通讯作者：
Shin, Seung Koo
中科院分区：
文献类型：
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作者：
Kim, Wonjung;Lim, Sung Jun;Shin, Seung Koo
表面陷阱，如电子和空穴陷阱，猝灭半导体纳米晶体的光致发光（PL）。我们发现了一个二元配体系统，可以有效地钝化裸CdSe纳米晶体上的表面陷阱，从而使纳米晶体高度发光。采用胶体合成法制备了锌-碲化镉纳米晶体，并在室温下通过改变氯仿中丙胺（PA）和三丁基膦（TBP）的量来监测其光学性质。初始的CdSe纳米晶体大多被脂肪酸羧酸覆盖，其量子效率很低，具有多指数PL衰减。过量PA的加入会引起吸收光谱和发射光谱的蓝移，量子效率和PL寿命略有增加，而TBP的加入会降低PL强度。令人惊讶的是，无论配体添加的顺序如何，PA和TBP的添加都使纳米晶体发光的量子效率接近50%，并且几乎是单指数的PL衰减。利用x射线光电子能谱（XPS）和电喷雾电离质谱（ESIMS）进一步表征了胺膦钝化后溶液中溶解的化学物质。XPS数据表明，脂肪酸羧酸酯覆盖在制备的纳米晶体表面，胺和磷化氢将羧酸酯从表面去除。ESI质谱鉴定了被配体溶解在溶剂中的化学物质。综上所述，我们的研究结果表明，伯胺和叔膦将表面附着原子溶解到溶液中，并协同钝化CdSe纳米晶体上的表面悬空键，从而可重复地产生明亮的CdSe纳米晶体。
Surface traps, such as electron and hole traps, quench the photoluminescence (PL) of semiconductor nanocrystals. We find a binary ligand system that effectively passivates those surface traps on bare CdSe nanocrystals, thereby making the nanocrystals highly luminescent. Zinc-blende CdSe nanocrystals are prepared by colloidal synthesis, and their optical properties are monitored by varying the amounts of propylamine (PA) and tributylphosphine (TBP) in chloroform at room temperature. The starting CdSe nanocrystals that are mostly covered with fatty acid carboxylates show very low quantum efficiency with a multiexponential PL decay. Addition of excess PA induces blueshifts in both absorption and emission spectra with a slight increase in quantum efficiency and PL lifetime, whereas that of TBP reduces the PL intensity. Surprisingly, addition of both PA and TBP makes nanocrystals emit light with an similar to 50% quantum efficiency and a nearly single-exponential PL decay, regardless of the sequence of ligand addition. We further characterize the chemical species dissolved into the Solution after amine-phosphine passivation by using X-ray photoelectron spectroscopy (XPS) and electrospray ionization mass spectrometry (ESIMS). The XPS data indicate that fatty acid carboxylates are covered on the surface of as-prepared nanocrystals and both amine and phosphine remove carboxylates from the surface. The ESI mass spectra identify the chemical species dissolved into the solvent by ligand. Taken all together, our results suggest that primary amine and tertiary phosphine dissolve surface adatoms into the solution and cooperatively passivate surface dangling bonds on CdSe nanocrystals, thereby reproducibly yielding bright CdSe nanocrystals.