Fluorescence properties have been studied for Mn:ZnS crystallites with average diameter of 4 nm prepared by an aqueous colloidal method under 266 nm light excitation. The intensity ratio of the blue band at ∼430 nm to the orange band at ∼590 nm has decreased after the preparation on a time scale of hours in aqueous solution. On the other hand, hyperfine structures of Mn 2+ in the electron paramagnetic resonance spectrum have increased markedly on the same time scale in solution samples. These phenomena are attributed to the redistribution of defect centers in nanocrystals. Such phenomena have not been observed in samples incorporated into poly(vinyl alcohol). The orange emission is mainly due to the 6 A 1 r 4 T 1 transition of Mn 2+ , while the blue emission is tentatively assigned to the donor-acceptor pair transition in which the acceptor is related to the Zn 2+ vacancy. Fluorescence decay times of the blue and orange bands have been found to be ∼10 ns and ∼1 ms, respectively, the latter being the same as in the bulk samples. A weak fluorescent component with fast kinetics observed in the orange region has been identified as a tail of the blue band. No lifetime shortening of the Mn 2+ emission due to quantum confinement has been observed, contrary to reports in the literature.

No abstract

No abstract

Pyrolysis of a silica gel hybrid with a starburst dendrimer gives porous silica, in which the pore-size is successfully controlled by the size of the organic component used.