Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ, UK.
Phys Chem Chem Phys. 2013 Jul 14;15(26):11119-27. doi: 10.1039/c3cp50800e. Epub 2013 May 31.
Excited state relaxation in zinc sulfide (ZnS) nanoparticles is studied as a model for the fate of the excited state in inorganic nanoparticles in general. A series of time-dependent density functional theory optimisations on the S1 and T1 excited states predict the existence of not merely isolated minima, as found before, but rather a connected cascade of excited state minima ending up in a conical intersection between the excited state energy surface and the ground state. The localisation of the excited state in the different minima increases down the cascade, while the barriers separating these minima, studied here for the first time for nanoparticles, are predicted to be in some cases electronic (strongly avoided crossing) in origin. The cartoon picture of excited state relaxation in inorganic nanoparticles that involves relaxation to the bottom of only one approximately harmonic well followed by photoluminescence appears for the ZnS nanoparticles studied here to be at best rather simplistic. The localisation cascade is finally found to strongly affect the excited state properties of nanoparticles and predicted to lead to the formation of defected nanoparticles after de-excitation in selected cases.
研究了硫化锌 (ZnS) 纳米粒子中的激发态弛豫，以此作为一般无机纳米粒子中激发态命运的模型。一系列关于 S1 和 T1 激发态的时变密度泛函优化预测，不仅存在孤立的极小值，如以前发现的那样，而是存在一连串的激发态极小值，最终在激发态能量面和基态之间形成一个锥形交叉。不同极小值中的激发态定位随着级联的下降而增加，而这里首次研究的这些极小值之间的势垒，在某些情况下，据预测是电子起源的（强烈避免交叉）。在涉及仅弛豫到一个近似简谐势阱的底部然后进行光致发光的无机纳米粒子中激发态弛豫的卡通图，对于这里研究的 ZnS 纳米粒子来说，最好是相当简单的。最终发现，局域化级联强烈影响纳米粒子的激发态性质，并预测在某些情况下会导致在去激发后形成有缺陷的纳米粒子。
