Aggregation induced emission (AIE) is an amazing property for light emitting materials and has attracted much attention. Here, we report a new kind of AIE materials: fluorenone derivates 2,7-dip-tolyl-fluorenone (DTFO) and 2,7-bis(4-(tert-butylthio)phenyl)-fluorenone (DSFO). Strong light emissions with a large Stokes shift and long lifetime in the solid state originate from the formation of excimers. The crystal structure of DSFO shows that every two molecules are bound together even in the ground state by intermolecular hydrogen bonds and form a particular dimer. When this dimer is excited, it turns into an excimer without arrangement adjustment and likewise without repulsive interactions when the excimer decays back to the dimer; so, the nonradiative decay pathways that exist in common excimers are greatly reduced and thus induce a strongly enhanced luminescence in the solid state. OLED devices employing DTFO as light emitting layers are fabricated and evaluated.

MgO nanocrystalline powders prepared by sol-gel method present room-temperature ferromagnetism, whereas MgO bulk exhibits diamagnetism. The vacuum annealing of MgO nanocrystalline powders reduces ferromagnetism. The observed room-temperature ferromagnetism in MgO nanocrystalline powders possibly originates from Mg vacancies at/near the surfaces of nanograins. Mg vacancies can induce local magnetic moments. Large concentrations of Mg vacancies at the surfaces of nanograins possibly establish magnetic percolation.

No abstract

Increasing the ethanol concentration in the tetraethoxysilane (TEOS)-hexadecyltrimethylammmonium bromide (C 16 TMABr)-ammonia-water system at room temperature permits one to obtain a succession of different mesophases in the order MCM-41 f MCM-48 f lamellar phase f radial hexagonally ordered phase. First, the original hexagonal (MCM-41) phase is replaced by a cubic phase (MCM-48) and later, upon ethanol addition, by a lamellar phase. Such phase succession is the result of the cosurfactant behavior of the ethanol. At lower alcohol concentration, scanning electron microscopy (SEM) shows only undefined or barely spherical structures, indicating that the ethanol has only a limited effect on the external morphology. When the alcohol concentration is further increased, it will mainly act as a cosolvent producing spherical particles. A TEM study reveals the radial arrangement of the pores within the spherical particles. A hexagonal closed pore packing can be considered on a local scale around the center of the spherical particle. This hexagonal pore arrangement is the result of a combination of a very slow equilibrium toward the hydrolysis of the TEOS, its good homogenization in the synthesis solution due to the solvating effect of the alcohol, and the interference of the alcohol on the cooperative process of the micelle formation. To complete the study, parallels have been drawn with other alcohols such as methanol and propanol.