Ning Sui

Exciton Relaxation Dynamics in Photo-Excited CsPbI3 Perovskite Nanocrystals.

The exciton relaxation process of CsPbI3 perovskite nanocrystals (NCs) has been investigated by using transient absorption (TA) spectroscopy. The hot exciton relaxation process is confirmed to exist in the CsPbI3 NCs, through comparing the TA data of CsPbI3 NCs in low and high energy excitonic states. In addition, the Auger recombination and intrinsic decay paths also participate in the relaxation process of CsPbI3 NCs, even the number of exciton per NC is estimated to be less than 1. Excitation intensity-dependent TA data further confirms the existence of Auger recombination. Meanwhile, the spectral data also confirms that the weight of hot exciton also increase together with that of Auger recombination at high excitation intensity when CsPbI3 NCs in high energy excitonic states.

Manipulating fluorescence characteristics of conjugated fluorescent molecules incorporated into three-dimensional poly(methyl methacrylate) opal photonic crystals

We compare the fluorescence characteristics of conjugated molecules (coumarin 6, C-6) in solution, aggregation state, and poly(methyl methacrylate) PMMA opal photonic crystals (PCs), and investigate the manipulation mechanism of PCs on C-6. We find that the PCs effectively inhibit the aggregate-induced fluorescence quenching of C-6 by breaking the intermolecular interaction and manipulate the fluorescence characteristics of C-6 by changing the photonic stop band (PSB). The emission traces of C-6 have been analyzed using the continuous rate distribution model. The control of fluorescence characteristics of C-6 in PCs depends on the mesh microporous structure and the PSB of PCs.

Charge carrier dynamics investigation of CuInS2 quantum dots films using injected charge extraction by linearly increasing voltage (i-CELIV): the role of ZnS Shell

The role of ZnS shell on the photo-physical properties within CuInS2/ZnS quantum dots (QDs) is carefully studied in optoelectronic devices. Linearly increasing voltage technique has been employed to investigate the charge carrier dynamics of both CuInS2 and CuInS2/ZnS QDs films. This study shows that charge carriers follow a similar behavior of monomolecular recombination in this film, with their charge transfer rate correlates to the increase of applied voltage. It turns out that the ZnS shell could affect the carrier diffusion process through depressing the trapping states and would build up a potential barrier.

Temperature-dependent charge carrier dynamics investigation of heterostructured Cu2S-In2S3 nanocrystals films using injected charge extraction by linearly increasing voltage

The temperature-dependence of charge carrier dynamics in the films based on novel heterostructured Cu2S-In2S3 nanocrystals (NCs) is investigated using charge carrier extraction by a linearly increasing voltage technique; meanwhile, the CuInS2 nanorod (NR) film is used as a reference. The carriers in the Cu2S-In2S3 NC film follow the monomolecular recombination mechanism, which is similar to that in the CuInS2 NR film. The corresponding diffusion rate would accelerate with the applied voltage, indicating that the Cu2S-In2S3 NCs could potentially promote the movement of the carrier and simultaneously affect the monomolecular recombination in comparison with that in the CuInS2 NR film. This study would be beneficial in the development of nano-devices with NR films and high performance Cu2S-In2S3 NCs solar cells.

Emission and energy transfer characteristics of coumarin 6 molecules doped in opal polymer photonic crystal

The emission of coumarin 6(C-6) doped in opal polymethylmethacrylate(PMMA) photonic crystal(PC) was effectively manipulated. Meanwhile the energy transfer(ET) of C-6 in PCs, which are infiltrated with sulforhodamine B(S-B), was influenced by the concentration of energy acceptor in solution, the size of PMMA microsphere(SM) and the photonic stop band(PSB). The results should be beneficial to people to further understand the potential application of PCs in optoelectronic fields.

Studying the emission complexity of conjugated molecules by manipulating the molecular aggregate state

We prepared quantum dots (QDs) based on a conjugated molecule (coumarin 6, C-6), which is considered to be a mesoscopic aggregate, to build a bridge linking the monodisperse state (solution state) and macroscopic aggregates (powder state). Their spectral features, including steady spectral data, dynamic features and fluorescence quantum yields, have been compared in detail. All dynamic data were modelled using the continuous rate distribution function. The final results showed that the fluorescence quantum yield of organic quantum dots based on C-6 gradually decreases as the size of the QDs increases, which may be attributed to enhancement of the rate of non-radiative relaxation, which originates from the aggregation. This is beneficial for further understanding the optical characteristics of conjugated molecules.

Concentration dependent carriers dynamics in CsPbBr3 perovskite nanocrystals film with transient grating

The concentration dependence of the carrier dynamics is a key parameter to describe the photo-physical properties of semiconductor films. Here, we investigate the carrier dynamics in the CsPbBr3 perovskite nanocrystal film by employing the transient grating (TG) technique with continuous bias light. The concentration of initial carriers is determined by the average number of photons per nanocrystals induced by pump light (⟨N⟩). The multi-body interaction would appear and accelerate the TG dynamics with ⟨N⟩. When ⟨N⟩ is more than 3.0, the TG dynamics slightly changes, which implies that the Auger recombination would be the highest order multi-body interaction in carrier recombination dynamics. The concentration of non-equilibrium carriers in the film is controlled by the average number of photons per nanocrystals excited by continuous bias light (⟨nne⟩). Increasing  ⟨nne⟩ would improve the trapping-detrapping process by filling the trapping state, which would accelerate the carrier diffusion and add the co...

Studying of the photoluminescence of MEH-PPV-Au nanoparticles hybrid system

The photoluminescence (PL) characteristics of MEH-PPV hybrid films blended with Au nanoparticles are studied in detail. Due to the strong coupling effect between the surface plasmon of Au nanoparticles and the emission of MEH-PPV, the introduction of Au nanoparticles could enhance the PL intensity and modulate the shape of absorption and excitation spectra, according to our steady spectroscopy experiments. Besides, the relaxation dynamic experiments show that the non-radiative rate in the hybrid system decreases. The temperature and the excitation intensity (EI)-dependent PL spectral data indicate that hybrid MEH-PPV films have lower activation energy and higher thermal exchange rate. As a result, the thermal accumulation effect and the non-linearity of EI-induced PL enhancement are suppressed in hybrid films.

π-Conjugated Unit-Dependent Optical Properties of Linear Conjugated Oligomers

The optical properties of three linear conjugated oligomers (F-P, F-P-F, and P-F-P-F-P), where phenothiazine (P) and fluorene (F) groups arrange alternately, are investigated. With the enhancement of the π-conjugated system, their absorption and emission bands both gradually red shift, and their two-photon properties are also improved. Meanwhile, their fluorescence dynamic traces are analyzed with continuous rate distribution model, exhibiting that their decay rates gradually accelerate and the rate distribution width become narrower. The quantum chemical calculation offers their molecular structures and transition mechanism, showing that the enhancement of π-conjugated system should be responsible for the improvement of two-photon properties.

Theoretical and experimental studies on photophysical characteristics of low bandgap polymers

The basic photophysical characteristics of low bandgap polymer poly{2,7′-9,9-dioctylfluorene-alt-5-diethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione}(PDPP-F) have been systematically investigated by means of theoretical and experimental methods. The quantum chemical calculations clarify the molecular structure and electronic transition properties of PDPP-F. The transient absorption data were used to compare the relaxation dynamics of PDPP-F in chlorobenzene and solid film. It is observed that the dynamics process of simulated emission relaxes much faster in comparison with that of excited state absorption in both the solution and solid film. Moreover, the excitation intensity-dependent dynamics of PDPP-F confirms that the interaction among intrachain excitons may occur under photoexcitation in the solution and solid film.