求专业翻译

The optical transitions in Fe3+occurbetween energy levels with different spin multiplicities,therefore are forbidden and are always associated with weakbands in spectra. Moreover, transitions between energylevels with different electronic configurations originate broadbands. In this work we study the Fe3+ impurity ion in theLiGa5O8–LiGaSiO4–Li5GaSi2O8 system. The ionic radii ofFe3+ and Ga3+ are both 0.64 Å, while for Li+ and Si4+ are0.68 Å and 0.42 Å, respectively. The radii values and thesimilar valence indicate that substitution of Ga3+ ions ismore likely to be by Fe3+ ions. In spite of the proximity ofionic radii values, the probability of introduction of Fe3+ inLi+ sites is low, due to the great difference of charge andelectronic configuration between the two cations. On theother hand, lithium valence would cause a large change inatomic positions to compensate charges, and we believe thatin our sample (see below) Fe3+ ions enter uniquely in Ga3+sites. However, the entrance of Fe3+ ion in Li+ sites has beenobserved in LiNbO3 [26] and in LiAlO2 [21]. We haveobserved broad absorption and emission bands in the visibleand near-infrared spectral regions at room and low temperatures.The photoacoustic spectra in the visible region aresimilar to photoluminescence excitation spectra, showingthat all visible wavelengths can be used for luminescenceexcitation in spite of the intensity lost in non-radiativeprocesses. The luminescence spectra show broad bandsbetween 400 nm and 800 nm, which suggests that thissystem could be used as wide light tunable source, dependingon the excitation wavelength. The crystal field and interelectronicparameters values obtained from experimental data andTanabe–Sugano matrices [24, 25] show that the impurity isin tetrahedral sites and that the interaction between theimpurity and its neighborhood is strongly covalent.