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Articles by Yufeng Li
Total Records ( 2 ) for Yufeng Li
  Fangfang Jian , Jian Zheng , Pusu Zhao and YuFeng Li
  The title complex, [Co(II)(C7H10N2)2Cl2], has been synthesized and characterized by elemental analysis, UV-vis spectra and X-ray single crystal diffraction. It crystallizes in the monoclinic system, space group P2/c, with lattice parameters a = 8.1370(16) Aring, b = 6.4990(13) Aring, c = 16.416(5) Aring, β = 98.99(3)° and Z = 2. The crystal structure of the title compound consists of monomeric molecules of [Co(II)(C7H10N2)2Cl2] with C2 symmetry and the two-fold axis through the Co(II) ion and the mid-point of two Cl- anions. TG/DTG data indicate that thermal decomposition of the compound takes place in two steps and the residue is Co. Density functional theory (DFT) calculations of the structure, electronic spectra, natural population analysis and the thermodynamic properties at different temperatures have been performed. The calculated results show that electronic transitions are mainly derived from the contribution of an intraligand (IL) π → π* transition, metal-to-ligand charge transfer (MLCT) and d-d transition. Bond strength of Co-Cl is stronger than that of Co-N, which agrees with the experimental data. The correlation equations of the thermodynamic properties of C0p,m and Sm0 with temperature are also obtained.
  C. Wetzel , Yufeng Li , J. Senawiratne , Mingwei Zhu , Yong Xia , S. Tomasulo , P.D. Persans , Lianghong Liu , D. Hanser and T. Detchprohm
 

An enhancement of radiative recombination in GaInN/GaN heterostructures is being pursued by a reduction of defects associated with threading dislocations and a structural control of piezoelectric polarization in the active light-emitting regions. First, in conventional heteroepitaxy on sapphire substrate along the polar c-axis of GaN, green and deep green emitting light-emitting diode (LED) wafers are being developed. By means of photoluminescence at variable low temperature and excitation density, internal quantum efficiencies of 0.18 for LEDs emitting at 530 nm and 0.08 for those emitting at 555 nm are determined. Those values hold for the high current density of 50 A/cm2 of high-power LED lamps. In bare epi dies, we obtain efficacies of 16 lm/W. At 780 A/cm2 we obtain 22 lm when measured through the substrate only. The 555 nm LED epi material under pulsed photoexcitation shows stimulated emission up to a wavelength of 485 nm. This strong blue shift of the emission wavelength can be avoided in homoepitaxial multiple quantum well (MQW) and LED structures grown along the non-polar a- and m-axes of low-dislocation-density bulk GaN. Here, wavelength-stable emission is obtained at 500 and 488 nm, respectively, independent on excitation power density opening perspectives for visible laser diodes.

 
 
 
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