Jin Min, Huang Yu-hua, Luo Ji-xiang
Guang Pu Xue Yu Guang Pu Fen Xi. 2015 Feb;35(2):420-3.
The authors measured the absorption and the fluorescence spectra of the quantum dots CdSe/ZnS with 4 nm in size at different concentration with the use of the UV-Vis absorption spectroscopy and fluorescence spectrometer. The effect of quantum dots CdSe/ZnS's concentration on its fluorescence was especially studied and its physical mechanism was analyzed. It was observed that the optimal concentration of the quantum dots CdSe/ZnS for fluorescence is 2 micromole x L(-1). When the quantum dot's concentration is over 2 micromol x L(-1), the fluorescence is decreased with the increase in the concentration. While the quantum dot's concentration is less than 2 micromol x L(-1), the fluorescence is decreased with the decrease in the concentration. There are two main reasons: (1) fluorescence quenching and 2) the competition between absorption and fluorescence. When the quantum dot's concentration is over 2 micromol x L(-1), the distance between quantum dots is so close that the fluorescence quenching is induced. The closer the distance between quantum dots is, the more serious the fluorescence quenching is induced. Also, in this case, the absorption is so large that some of the quantum dots can not be excited because the incident light can not pass through the whole sample. As a result, the fluorescence is decreased with the increase in the quantum dot's concentration. As the quantum dot's concentration is below 2 micromol x L(-1), the distance between quantum dots is far enough that no more fluorescence quenching is induced. In this case, the fluorescence is determined by the particle number per unit volume. More particle number per unit volume produces more fluorescence. Therefore, the fluorescence is decreased with the decrease in the quantum dot's concentration.
作者使用紫外可见吸收光谱仪和荧光光谱仪，测量了尺寸为4纳米的量子点CdSe/ZnS在不同浓度下的吸收光谱和荧光光谱。特别研究了量子点CdSe/ZnS的浓度对其荧光的影响，并分析了其物理机制。观察到量子点CdSe/ZnS产生荧光的最佳浓度为2微摩尔×L⁻¹。当量子点浓度超过2微摩尔×L⁻¹时，荧光随浓度增加而降低。而当量子点浓度小于2微摩尔×L⁻¹时，荧光随浓度降低而降低。主要有两个原因：（1）荧光猝灭和（2）吸收与荧光之间的竞争。当量子点浓度超过2微摩尔×L⁻¹时，量子点之间的距离非常近，从而引发荧光猝灭。量子点之间的距离越近，引发的荧光猝灭就越严重。此外，在这种情况下，吸收非常大，以至于一些量子点无法被激发，因为入射光无法穿透整个样品。结果，荧光随量子点浓度的增加而降低。当量子点浓度低于2微摩尔×L⁻¹时，量子点之间的距离足够远，不会再引发荧光猝灭。在这种情况下，荧光由单位体积内的粒子数决定。单位体积内的粒子数越多，产生的荧光就越多。因此，荧光随量子点浓度的降低而降低。
