[Study on the Preparation of Ba3Si6O9N4 : Eu(2+) Phosphor and the Characterization of Their Luminescence Properties].

Ba3Si6O9N4 : Eu(2+) phosphors were synthesized by two-step synthesis processes based on high temperature solid phase using BaSiO3 as a precursor. The influence mechanism of the Eu(2+) doping concentration to the luminescence properties of Ba3Si6O9N4 : Eu(2+) phosphors were mainly investigated. This paper made a comparison between the luminescence properties of Ba3Si6ON4 : Eu(2+) phosphors prepared by two-step processes and solid- state reaction method. The results showed that the Ba3Si6O9N4 : Eu(3+) phosphors synthesized by two-step processes had higher purity and higher crystallinity. There exists concentration quenching in Ba3Si6O9N4 : Eu(2+) phosphors for both two-step processes and solid-state reaction when the doping concentration x is more than 9%. Both the concentration quenching mechanism of Ba3 Si 09 N4 : EuI+ phosphor prepared by solid-state reaction and two-step processes is electric dipole-dipole interaction. The emission peak of Ba3Si6O9N4 : Eu(2+) phosphors (peak 489 nm) prepared by two-step processes had a blue shift compared to the emission peak of Ba3Si6O9N4 : Eu2+ phosphors (peak 512nm) prepared by solid-state reaction. The emission peak of Ba3Si6O9N4 : Eu2+ phosphors prepared by two-step processes relatively close to the theoretical value (480 nm). The spectrum analysis result showed that the element component of Ba3Si6O3N4 : Eu2+ phosphors prepared by two-step processes was closer to the theoretical value, it means that the two-step processes can effectively reduce the lattice defects. The Ba3Si6O9N4 : Eu(2+) phosphors synthesized by two-step processes had better thermal stability, which demonstrates to be a highly promising phosphor for white-LED applications.

Unusual cold crystallization behavior in physically aged poly(L-lactide).

A comparative study of cold crystallization behavior in poly(L-lactide) (PLLA) annealed below and just above the glass transition temperature (T(g)) has been conducted. Annealing benefits the generation of local order and the subsequent cold crystallization process, which becomes significant in PLLA annealed just above T(g). Surprisingly, morphological observation reveals high density nuclei in PLLA annealed below T(g), contrary to its relatively slow crystallization kinetics. This unusual crystallization behavior in physically aged PLLA arises from the retarded crystal growth rate because of incomplete recovery of reduced segmental mobility above T(g). In contrast, annealing just above T(g) has little influence on the crystal growth rate, and the increased nucleation density alone accounts for the accelerated crystallization rate.