Activity enhancement of a photo-generated carrier in CsPbBr3 nanocrystals improved by Cd element.

Doping Cd element into perovskite materials is an effective strategy to improve the photoelectric property. However, the further discussion for carrier dynamic behavior in perovskites affected by Cd element remains not sufficient. In this research letter, based on steady and transient spectroscopy, it is found that adding Cd element into CsPbBr3 nanocrystals can enhance the activity of photo-generated carriers and accompany with the optimization of crystal structure. The former improves the carrier heating effect, which makes carrier keep high temperature for a long time and accelerate the bimolecular and the Auger recombination simultaneously. The latter can restrict the monomolecular recombination through passivating the defect states. Finally, they together improve the photoluminescence characteristics of the Cd doped CsPbBr3 nanocrystals and make them exhibit a huge potential in the fields of optoelectronics or photo-catalysis.

Solvent-dependent ultrafast optical response of conjugated push-pull chromophores.

Two new difluoroboron ß-carbonyl cyclic ketonate complexes C2B and DC2B were investigated using several spectroscopic methods. Relative to the absorption spectra, the fluorescence spectra were more affected by the polarity of the solvent. Also, compound C2B showed a more pronounced Stokes' shift after solvent polarity increased. Transient absorption measurements then demonstrated the relaxation behaviour of the excited state compound molecule. The kinetic results showed that the excited state C2B in tetrahydrofuran (THF) can return from the intramolecular charge-transfer (ICT) state and the initial excited state to the ground state. The kinetic relaxation pathway after THF was replaced by dimethyl sulfoxide became single. When the carbazole unit was introduced, DC2B also exhibited an ICT state but there was no significant difference in the excited state relaxation path after solvent polarity was changed. The results indicated that C2B is more susceptible to solvent polarity regulation. The global fit results revealed that an increase in the solvent polarity prolonged the lifetime of the ICT state of compound C2B and had the opposite effect on compound DC2B. These results provide guidance for understanding the relationship between solvent polarity and the designing and synthesizing advanced compound materials.

Spontaneous emission of semiconductor quantum dots in inverse opal SiO2 photonic crystals at different temperatures.

The photoluminescence (PL) characteristics of CdSe quantum dots (QDs) infiltrated into inverse opal SiO2 photonic crystals (PCs) are systemically studied. The special porous structure of inverse opal PCs enhanced the thermal exchange rate between the CdSe QDs and their surrounding environment. Finally, inverse opal SiO2 PCs suppressed the nonlinear PL enhancement of CdSe QDs in PCs excited by a continuum laser and effectively modulated the PL characteristics of CdSe QDs in PCs at high temperatures in comparison with that of CdSe QDs out of PCs. The final results are of benefit in further understanding the role of inverse opal PCs on the PL characteristics of QDs.

[Low driving voltage in organic light-emitting diodes with NPB/MoO3/NPB as a hole transport layer].

Driving voltage of organic light-emitting diodes (OLEDs) was lowered by applying (NPB/MoO3)(x)/NPB as a hole transport layer (HTL). (NPB/MoO3)(x) was multi-layer periodic (MLP) structure with x changed from 0 to 3. Compared with the conventional device with 0-periodic structure, the driving voltage of the device with 1-periodic structure was the lowest. This was due to charge transfer (CT) complex formation between NPB and MoO3. The driving voltage of tris (8-hydroxyquinoline) aluminum (Alq3)-based organic light-emitting devices (OLEDs) could be lowered by 0. 8 V at 1 000 cd x m(-2) by using multiple structure of NPB/MoO3/NPB.

Investigation on "Excimer" Formation Mechanism of Linear Oligofluorenes-Functionalized Anthracenes by Using Transient Absorption Spectroscopy.

We study the photophysical characters of two oligofluorenes-functionalized anthracenes molecules with different fluorine-vinylene (FV) units, which exhibits that "excimer" state appears in the solution after photoexcitation. The dynamic data shows that two mechanisms are responsible for the generation of "excimer". The fast one is controlled by the arene-arene interaction between molecules and the slow one is influenced by the diffusion motion of molecules. Increasing the number of FV units may suppress the DM-dependent "excimer" and enhance the yield of intrinsic fluorescence, which finally improves the fluorescence property of molecules in solution.

Investigation on Photophysical Properties of D-π-A-π-D-Type Fluorenone-Based Linear Conjugated Oligomers by Using Femtosecond Transient Absorption Spectroscopy.

The effects of π-spacer and electron donor groups on the photophysical behaviors of fluorenone-based linear conjugated oligomers have been systemically investigated. Solvent-dependent steady-state measurements exhibit that the fluorene vinylene (FV) spacer and the electron-donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength.