Premium
Synthesis and Optical Properties of Europium‐Doped ZnS: Long‐Lasting Phosphorescence from Aligned Nanowires
Author(s) -
Cheng B. C.,
Wang Z. G.
Publication year - 2005
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200500092
Subject(s) - materials science , phosphorescence , dopant , nanowire , europium , wurtzite crystal structure , acceptor , photoluminescence , doping , ion , luminescence , optoelectronics , fluorescence , optics , condensed matter physics , chemistry , physics , organic chemistry , zinc , metallurgy
Quasi‐aligned Eu 2+ ‐doped wurtzite ZnS nanowires on Au‐coated Si wafers have been successfully synthesized by a vapor deposition method under a weakly reducing atmosphere. Compared with the undoped counterpart, incorporation of the dopant gives a modulated composition and crystal structure, which leads to a preferred growth of the nanowires along the [01 $\bar 1$ 0] direction and a high density of defects in the nanowire hosts. The ion doping causes intense fluorescence and persistent phosphorescence in ZnS nanowires. The dopant Eu 2+ ions form an isoelectronic acceptor level and yield a high density of bound excitons, which contribute to the appearance of the radiative recombination emission of the bound excitons and resonant Raman scattering at higher pumping intensity. Co‐dopant Cl – ions can serve not only as donors, producing a donor–acceptor pair transition with the Eu 2+ acceptor level, but can also form trap levels together with other defects, capture the photoionization electrons of Eu 2+ , and yield long‐lasting (about 4 min), green phosphorescence. With decreasing synthesis time, the existence of more surface states in the nanowires forms a higher density of trap centers and changes the crystal‐field strength around Eu 2+ . As a result, not only have an enhanced Eu 2+ 4f 6 5d 1 –4f 7 intra‐ion transition and a prolonged afterglow time been more effectively observed (by decreasing the nanowires' diameters), but also the Eu 2+ related emissions are shifted to shorter wavelengths.