Blue minerals and gems have always been subjects of fascination to man. In particular lapislazuli is and was highly esteemed and also used as a precious stone and as a pigment. The host compound is the zeolite-type sodalite and the colour centres are S 2 2 and S 3 2 , whose amount ratio determines the specific hue, varying from violet blue to blue to green. But Se 2 2 can also be substituted into the sodalite cages in high percentages, giving the pigment a brilliant red colour. It is even possible to incorporate the rather voluminous radical species Te 2 and Te 2 2 into the sodalite matrix. Because the otherwise unstable colour centres are completely screened from the atmosphere and isolated from each other in the cages, they can be fully characterised by various spectroscopic techniques.

Es wird über die Synthese eines brillant‐roten Selen‐Ultramarins mit Pigmenteigenschaften berichtet. Strukturelle und elektronenmikroskopische Untersuchungen ergaben, daß die Nosean‐Struktur mit unterbesetzter Na+‐Lage und einer ebenfalls defizitären anionischen Position, die die farbgebende Spezies enthält, vorliegt. Spektroskopische Messungen deuten darauf, daß die Farbe auf das radikalische Anion Se2− zurückgeht. Hydrothermal gezüchtete Einkristalle sind rosa und enthalten nur sehr geringe Mengen an Se2−, die spektroskopisch deutlich, doch strukturell nicht nachweisbar waren.

The granulometric characterization of synthetic amorphous silica (SAS) nanomaterials (NMs) still demands harmonized standard operation procedures. SAS is produced as either precipitated, fumed (pyrogenic), gel and colloidal SAS and these qualities differ, among others, with respect to their state of aggregation and aggregate strength. The reproducible production of suspensions from SAS, e.g., for biological testing purposes, demands a reasonable amount of dispersing energy. Using materials representative for each of the types of SAS, we employed ultrasonic dispersing (USD) at energy densities of 8–1440 J/mL and measured resulting particle sizes by dynamic light scattering and laser diffraction. In this energy range, USD had no significant impact on particle size distributions of colloidal and gel SAS, but clearly decreased the particle size of precipitated and fumed SAS. For high energy densities, we observed a considerable contamination of SAS suspensions with metal particles caused by abrasion of the sonotrode’s tip. To avoid this problem, the energy density was limited to 270 J/mL and remaining coarse particles were removed with size-selective filtration. The ultrasonic dispersion of SAS at medium levels of energy density is suggested as a reasonable compromise to produce SAS suspensions for toxicological in vitro testing.

Ab initio molecular-orbital methods using a newly constructed large, flexible basis set of the atomic-naturalorbital type and extensive treatments of electron correlation were used to accurately predict the ground-state potential-energy curves of Se 2 and Se 2 Ϫ. In addition, the potential curves of low-lying electronically excited states of the Se 2 Ϫ anion, which are coupled to the ground state through the electronic dipole operator, are determined. Calibration of the accuracy expected for the employed theoretical models is achieved by calculations on electronically excited states of neutral Se 2 , for which accurate experimental data are available. Besides reporting accurate predictions for spectroscopic constants, electron affinities, and transition matrix elements, particular emphasis is laid on the use of the computed dimer potential-energy curves for interpreting the recently investigated peculiar optical properties of diatomic selenium species embedded in solid host matrices. Further, the equilibrium geometries and relative stabilities of the C 2v and D 3h forms of the neutral Se 3 cluster, the electron affinity of Se 3 , and the low-lying electronic states of Se 3 Ϫ have been investigated theoretically. ͓S1050-2947͑96͒06509-2͔

The unique optical properties of Se2- radicals located in the cages of the sodalite structure are reported. By means of luminescence, photoluminescence excitation, and absorption spectroscopy, three different centers are identified. Two of them are Se2- anions in sites with presumably a tetrahedral Na4(4+) coordination and a Na3(3+) environment with cation deficiency, respectively, giving rise to a red luminescence band with two different progressions. The third center is the intermediate Se2 molecule, created photochemically by UV laser excitation. It induces an additional blue luminescence. The electronic properties of the Se2- centers, particularly in the excited states, are significantly influenced by steric constraints imposed by the limited space in the sodalite host polyhedra. Thus, the sodalite structure can be viewed as a model system for studying effects of this kind on chromophores imbedded in the cages of the zeolite-type lattice.