In a new study published in Nature Communications, Prof. WU Zhikun's research group from the Institute of Solid State Physics (ISSP) of the Hefei Institute of Physical Science (HFIPS), collaborating with other research groups, gave a unite explanation for multiple photoluminescence (PL) including crystallization-induced PL weakening (CIPW), aggregation-induced quenching (ACQ) and aggregation-induced emission (AIE) phenomena.
On the basis of theoretical calculations and PL lifetime measurements, WU and his collaborators proposed an excitation electron transfer model to interpret the CIPW phenomenon, that was, with the decrease of interparticle distance, the interparticle and intraparticle non-radiative transfers of excited electrons accelerated.
CIPW phenomenon was revealed in ultrasmall metal nanoparticles by the same team in a study conducted in 2017. However, the fundamentals for the phenomenon were not understood, which inspired their study enthusiasm. This novel model sheds light on CIPW and, at the same time, interprets the ACQ and AIE phenomena. While in the AIE case, the twisted structure (or steric hindrance) prevents the approach of luminophores, thus inhibiting the non-radiative excitation electron transfer between the neighboring luminophores.
In this research, by tuning the crystallographic structures, they obtained a pair of conformational isomer crystals of gold nanoclusters (Au60S8r and Au60S8n) with different interparticle distance. And the investigation on PL revealed that the emission intensity of Au60S8r with longer interparticle distance was more extensive than that of Au60S8n with shorter interparticle distance, which indicates the interparticle distance-dependent PL. To verify this, high pressure was introduced to tune the interparticle distance.
Upon the compression, the emissions of both Au60S8r and Au60S8n obviously decreased and the maximum PL intensities conformed to the negative exponential function of the pressure during the investigated pressure range. Moreover, the vanished emission could be somehow restored. These results confirmed the correlationship between emission intensity and interparticle distance.
These works were supported by the National Natural Science Foundation of China, the Natural Science Foundation of Anhui Province, the CAS/SAFEA International Partnership Program for Creative Research Teams and the CASHIPS Director's Fund.
(a, b) Crystallographic structures of Au60S8 nanoclusters (a) Au60S8r and (b) Au60S8n (The insets correspond to their optical images). (Image by GAN Zibao)
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