Fluorinated nitroxides as ESR probes of solvation

Some newly synthesized fluorinated nitroxides, such as t-butyl perfluoroalkyl nitroxides Bu^tN(O) R_f (R_f=CF₃, 5; C₂F₅, 6; n-C₃F₇, 7) and s-butyl perfluoroacyl nitroxides Bu^sN(O) COR_f (R_f=CF₃, 9; n-C₃F₇, 10) have been employed as ESR probes of solvation in different common organic solvents. In aprotic solvents, the measured a_N values for each of the nitroxyl probes show a linear correlation with the cybotactic polar solvent parameters E_T (Dimroth) and Z (Kosowar), i.e. a_N=bE_T+c, and a_N=b′Z+c′. The physical significance for the slope (b or b′), the slope×E_T or slope×Z, the extrapolated intercept on a_N axis, c or c′, are linked, respectively, to the sensitivity of a specific nitroxide toward solvation, the magnitude of the overall solvation effect on the a_N value, and the intrinsic a_N value of each nitroxide in the ideal gaseous state. The intercept on the a_N axis may also serve as a new measure of electronegativity for perfluoroalkyl groups, CF₃, C₂F₅, n-C₃F₇, and perfluoroacyl groups, CF₃CO, n-C₃F₇CO. In protic solvents, i.e. alcohols and carboxylic acids, however, a_N values of all the probes, kept almost no change with the increase in E_T and Z. Furthermore, the plots of a_N versus non-cybotactic solvent constants, such as dipolar moment (μ) and dielectric constant (ε), all show random variations.     

Mechanism transition of self-pumped phase conjugation in KTa1 −xNbxO3:Fe crystals

Mechanism transitions of Self-Pumped Phase Conjugation (SPPC) with wavelength and doping concentration are observed in KTN:Fe (KTa_{1 –x} Nb _x O₃:Fe with _x = 0.48) crystals. The SPPC mechanism in KTN: Fe (0.4 wt. %) crystal transforms from Stimulated Photorefractive Backscattering and Four-Wave Mixing (SPB-FWM) to cat (or total internal reflection) as the wavelength increases from 514.5 nm to 620 nm. SPPC at 514.5 nm is formed with the cat mechanism in a 0.2 wt. % doped KTN:Fe crystal, while with the SPB-FWM mechanism in a 0.4 wt. % doped one. These mechanism transitions are discussed with respect to the dependence of the backscattering gain coefficient of the crystals on wavelength and doping concentration.     

稀土磷酸盐发光材料的微波合成

稀土磷酸盐发光材料的微波合成徐文国，田一光，刘淼，刘海堂，方光华，庞文琴（吉林大学化学系，环境科学系，长春，１３００２３）关键词微波合成，稀土磷酸盐，微晶玻璃，玻璃态，发光材料稀土磷酸盐发光材料的研究是当前材料科学的热门研究课题。它们一般通过高温固相...