Minzhao Xue

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres–nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor–acceptor (D–A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Forster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D–A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Nanocrystalline Films Formation of 4,7-Bis(4-triphenylamino)benzo-2,1,3-thiadiazole through Electrophoretic Deposition

The nanocrystalline films of an amorphous triphenylamine derivative have been firstly formed by a facile electrophoretic deposition (EPD) method from a solution of protonated 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole. The films are composed of nanoparticles which diameters are controllably varied from 20 to 200 nm. Compared with spin-coating films, EPD films possess lower band gap and higher energy level of the highest occupied molecular orbital (HOMO), which means superior intermolecular charge-transfer ability and more excellent hole-transporting property. The facile method for preparing nanocrystalline films could also spread to other amorphous triphenylamine derivatives.

Study on the PSL mechanism in BaFCl:Eu2+ phosphors

In this paper, the ESR and photoluminescence (PL) of BaFCl and BaFCl:Eu2+ radiated or un-radiated by X-ray were observed. The single electron in the color center could be produced in BaFCl without Eu2+. A series of traps of different energy level in BaFCl lattice were formed, and some shallow traps of them could be bleached by Vis-light, and the other deep traps could not. The bleaching effects on ESR and photostimulated luminescence (PSL) were investigated. An F-H-Eu2+ complex (F color center, H color center and Eu2+ complex) in the lattice of BaFCl:Eu2+ was suggested when the phosphor was X-ray irradiated. The Eu2+ located in the complex has only contribution to the ESR signal, but has no contribution to PL spectrum. The excitation of both F-center and located Eu2+ could decompose the complex to induce bleaching. The 440 nm light could excite the F-centers and the 220 nm and 270 nm could excite the located Eu2+, and the excitation disturbed the F-H-Eu2+ complex and caused a decrease of the PSL.