The structure-property characteristics of a series of newly synthesized intramolecular charge- transfer （ICT） compounds, single-branch monomer with triphenylmethane as electron donor and 2,1,3-benzothiadiazole as ac...The structure-property characteristics of a series of newly synthesized intramolecular charge- transfer （ICT） compounds, single-branch monomer with triphenylmethane as electron donor and 2,1,3-benzothiadiazole as acceptor, the corresponding two-branch dimer and three- branch trimer, have been investigated by means of steady-state and femtosecond time- resolved stimulated emission fluorescence depletion （FS TR-SEP FD） techniques in different polar solvents. The TD-DFT calculations are further performed to explain the observed ICT properties. The interpretation of the experimental results is based on the comparative studies of the series of compounds which have increased amount of identical branch moiety. The similarity of the absorption and fluorescence spectra as well as strong solvent-dependence of the spectral properties for the three compounds reveal that the excited state of the dimer and trimer are nearly the same with that of the monomer, which may localize on one branch. It is found that polar excited state emerged through multidimensional intramolecular charge transfer from the donating moiety to the acceptor upon excitation, and quickly relaxed to one branch before emission. Even so, the red-shift in the absorption and emission spectra and decreased fluorescence radiative lifetime with respect to their monomer counterpart still suggest some extent delocalization of excited state in the dimer and trimer upon excitation. The similar behavior of their excited ICT state is demonstrated by FS TR-SEP FD measurements, and shows that the trimer has the largest charge-separate extent in all studied three samples. Finally, steady-state excitation anisotropy measurements has further been carried out to estimate the nature of the optical excitation and the mechanism of energy redistribution among the branches, where no plateau through the ICT band suggests the intramolecular excitation transfer process between the branches in dimer and trimer.展开更多
Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absor...Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3+ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3+/Yb3+ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3+ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3+ singly doped crystal to 23.01 ms for Er3+/Yb3+ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3+/Yb3+ co-doped crystals are analyzed, and the possible energy transfer processes from Yb3+ to Er3+ are proposed.展开更多
ZnS:Mn2+ nanocrystals(NCs) with particle size from 1.9 nm to 3.2 nm are synthesized via chemical precipitation method with different [S2-]/[Zn2+] ratios.The size-dependent decay for Mn emission exhibits a double expon...ZnS:Mn2+ nanocrystals(NCs) with particle size from 1.9 nm to 3.2 nm are synthesized via chemical precipitation method with different [S2-]/[Zn2+] ratios.The size-dependent decay for Mn emission exhibits a double exponential behavior.And two lifetime values,in millisecond time domain,can both be shortened with size increasing,which is attributed to enhanced interaction between host and Mn2+ impurity.A molecular structure model is proposed to interpret the tendency of two lifetime components,which is correlated to the number of S vacancy(Vs) defects around Mn2+.展开更多
基金We sincerely thank Prof. Yong-fang Li for providing the samples. S. Vdovi5 thanks CAS for support through a CAS Research Fellowship for International Young Researchers. This work was supported by National Natural Science Foundation of China, the Chinese Academy of Sciences, and the State Key Project for Fundamental Research.
文摘The structure-property characteristics of a series of newly synthesized intramolecular charge- transfer （ICT） compounds, single-branch monomer with triphenylmethane as electron donor and 2,1,3-benzothiadiazole as acceptor, the corresponding two-branch dimer and three- branch trimer, have been investigated by means of steady-state and femtosecond time- resolved stimulated emission fluorescence depletion （FS TR-SEP FD） techniques in different polar solvents. The TD-DFT calculations are further performed to explain the observed ICT properties. The interpretation of the experimental results is based on the comparative studies of the series of compounds which have increased amount of identical branch moiety. The similarity of the absorption and fluorescence spectra as well as strong solvent-dependence of the spectral properties for the three compounds reveal that the excited state of the dimer and trimer are nearly the same with that of the monomer, which may localize on one branch. It is found that polar excited state emerged through multidimensional intramolecular charge transfer from the donating moiety to the acceptor upon excitation, and quickly relaxed to one branch before emission. Even so, the red-shift in the absorption and emission spectra and decreased fluorescence radiative lifetime with respect to their monomer counterpart still suggest some extent delocalization of excited state in the dimer and trimer upon excitation. The similar behavior of their excited ICT state is demonstrated by FS TR-SEP FD measurements, and shows that the trimer has the largest charge-separate extent in all studied three samples. Finally, steady-state excitation anisotropy measurements has further been carried out to estimate the nature of the optical excitation and the mechanism of energy redistribution among the branches, where no plateau through the ICT band suggests the intramolecular excitation transfer process between the branches in dimer and trimer.
基金the National Natural Science Foundation of China (Nos.51272109,50972061 and 61078061)the Natural Science Foundation of Zhejiang Province (No.R4100364)+1 种基金the Natural Science Foundation of Ningbo City (No.2012A610115)the K. C. Wong Magna Fund in Ningbo University
文摘Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3+ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3+/Yb3+ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3+ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3+ singly doped crystal to 23.01 ms for Er3+/Yb3+ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3+/Yb3+ co-doped crystals are analyzed, and the possible energy transfer processes from Yb3+ to Er3+ are proposed.
基金supported by the National Natural Science Foundation of China(Nos.60877029,10904109,60977035 and 60907021)the Natural Science Foundation of Tianjin(No.09JCYBJC01400)the Tianjin Key Subject for Materials Physics and Chemistry
文摘ZnS:Mn2+ nanocrystals(NCs) with particle size from 1.9 nm to 3.2 nm are synthesized via chemical precipitation method with different [S2-]/[Zn2+] ratios.The size-dependent decay for Mn emission exhibits a double exponential behavior.And two lifetime values,in millisecond time domain,can both be shortened with size increasing,which is attributed to enhanced interaction between host and Mn2+ impurity.A molecular structure model is proposed to interpret the tendency of two lifetime components,which is correlated to the number of S vacancy(Vs) defects around Mn2+.
