Elektronenstrukturelle Deutung einfacher Kristallstrukturen

A survey is given on conclusions regarding the crystal structure which were possible in consequence of the recent progress in the theory of electronic structure of solids. The theory for the so-called simple metals has a well-developed quantitative form. The statements on the crystal structure represent only a part of the knowledge gained on a unified basis in electronic theory. For transition and noble metals and for covalently bound systems qualitative conclusion are possible at least.     

Luminescence of Fe3+ in AIPO4

Emission and excitation spectra for Fe³⁺ in AIPO₄ single crystals are reported and discussed. With excitation in the near UV emission bands originating from higher exicted states are observed in addition to weak bands between 13 300 and 14 800 cm^?1.     

A comparison of selected organic tracers for quantitative scalar imaging in the gas phase via laser-induced fluorescence

Single crystal of La₃Ga_5.5Ta_0.5O₁₄ (LGT) containing intentionally 0.5 % of Ho³⁺ and 1 % of Yb³⁺ was grown by the Czochralski method. Examination of chemical composition of the grown crystal revealed that luminescent holmium and ytterbium ions are preferably retained in the melt and their actual concentrations are 0.12 and 0.24 %, respectively. Spectroscopic investigation performed encompassed IR host absorption spectra and Raman spectra at room temperature, optical absorption and luminescence spectra of Ho³⁺ and Yb³⁺ at room temperature and at 5 K, and luminescence decay curves at room temperature. It was found that all spectral bands recorded show important inhomogeneous line broadening. This feature was attributed to structural disorder inherent to the crystal lattice in which pentavalent Ta⁵⁺ ions occupy octahedral Ga(1) sites together with trivalent Ga³⁺ ions. Despite small concentrations of luminescent ions, the occurrence of nonradiative interaction that feeds the ⁵I₆ and ⁵I₇ levels of Ho³⁺ ions by transfer of an excitation from the ²F_5/2 level of Yb³⁺ ions was evidenced. Based on examination of spectroscopic parameters evaluated, it was concluded that LGT:Ho, Yb may be considered as a potential intermediate-gain laser active material able to emit infrared radiation from the ⁵I₇ → ⁵I₈ transition of Ho³⁺ around 2 micrometres upon laser-diode pumping into Yb³⁺ absorption band.