As one of the most popular nanocrystals （NCs）, aqueous CdTe NCs have very weak green emission under con- ventional synthesis conditions. In this work, we report the first example of blue-emitting CdTe NCs directly s...As one of the most popular nanocrystals （NCs）, aqueous CdTe NCs have very weak green emission under con- ventional synthesis conditions. In this work, we report the first example of blue-emitting CdTe NCs directly synthe- sized in aqueous solution by slowing down the growth rate after nucleation. The key for the synthesis is the optimi- zation of NC growth conditions, namely pH range of 7.5 to 8.5, TGA/Cd ratio of 3.6, Cd/Te ratio of 10, and Te concentration of 2 × 10-5 mol/L, to get a slow growth rate after nucleation. The as-prepared blue-emitting CdTe NCs have small size （as small as 1.9 nm） and bright emission [with 4% photoluminescence quantum yield （PL QY） at 486 nm and 17% PLQY at 500 nm]. Transmission electron microscopy （TEM） images of the as-prepared CdTe show monodispersed NCs which exhibit cubic zinc blend structure. Moreover, time-resolved PL decay and X-ray photoelectron spectroscopy （XPS） results show the as-prepared NCs have better surface modification by ligand, which makes these luminescent small CdTe NCs have higher photoluminescence quantum yield, compared with NCs synthesized under conventional conditions.展开更多
Metal-enhanced fluorescence of semiconductor nanocrystals （NCs） is the current investigation focus. In this work, we directly observed metal-enhanced fluorescence of CdTe@PAA nanaospheres in aqueous solution. The en...Metal-enhanced fluorescence of semiconductor nanocrystals （NCs） is the current investigation focus. In this work, we directly observed metal-enhanced fluorescence of CdTe@PAA nanaospheres in aqueous solution. The enhanced magnitude of photoluminescence （PL） was closely related to solution pH values, and the maximal PL enhancement is about 9 times compared with the ones without Au NPs. Furthermore, based on the results of absorptions and fluorescence lifetimes of CdTe@PAA-Au mixed solution at different pH values, we studied the mechanisms and physics processes of pH-dependent enhanced PL induced by Au NPs. The pH-dependent PL of CdTe@PAA-Au mixed solutions are due to the constantly changing distances between Au NPs and CdTe@PAA nanaospheres with pH. In the CdTe@PAA-Au mixed solutions, CdTe@PAA nanospheres in close proximity to the Au NPs are exposed to the increased electric fields in between and around the NPs, effectively resulting in significant increases in their absorption cross section. This lends itself to a subsequent increase in the excitation and eventually in the fluorescence emission from the CdTe@PAA nanospheres.展开更多
文摘As one of the most popular nanocrystals （NCs）, aqueous CdTe NCs have very weak green emission under con- ventional synthesis conditions. In this work, we report the first example of blue-emitting CdTe NCs directly synthe- sized in aqueous solution by slowing down the growth rate after nucleation. The key for the synthesis is the optimi- zation of NC growth conditions, namely pH range of 7.5 to 8.5, TGA/Cd ratio of 3.6, Cd/Te ratio of 10, and Te concentration of 2 × 10-5 mol/L, to get a slow growth rate after nucleation. The as-prepared blue-emitting CdTe NCs have small size （as small as 1.9 nm） and bright emission [with 4% photoluminescence quantum yield （PL QY） at 486 nm and 17% PLQY at 500 nm]. Transmission electron microscopy （TEM） images of the as-prepared CdTe show monodispersed NCs which exhibit cubic zinc blend structure. Moreover, time-resolved PL decay and X-ray photoelectron spectroscopy （XPS） results show the as-prepared NCs have better surface modification by ligand, which makes these luminescent small CdTe NCs have higher photoluminescence quantum yield, compared with NCs synthesized under conventional conditions.
基金Supporting information for this article is available on the WWW under http：//dx.doi.org/10.1002/cjoc.201200078 or from the author.Acknowledgement This work is supported by the National Natural Science Foundation of China （Nos. 60877024, 61177033 and 21104009）, the Specialized Research Fund for the Doctoral Program of Higher Education （Nos. 20090092110015 and 20090092120022）, the China Postdoctoral Science Foundation （No. 20110490123）, the Jiangsu Planned Projects for Postdoctoral Research Funds （No. 1101074C）, the Foundation of the Anhui Province for Outstanding Young Talents in University （No. 2011SQRL137） and the Program of Huainan Normal University （No. 2010QNL06）.
文摘Metal-enhanced fluorescence of semiconductor nanocrystals （NCs） is the current investigation focus. In this work, we directly observed metal-enhanced fluorescence of CdTe@PAA nanaospheres in aqueous solution. The enhanced magnitude of photoluminescence （PL） was closely related to solution pH values, and the maximal PL enhancement is about 9 times compared with the ones without Au NPs. Furthermore, based on the results of absorptions and fluorescence lifetimes of CdTe@PAA-Au mixed solution at different pH values, we studied the mechanisms and physics processes of pH-dependent enhanced PL induced by Au NPs. The pH-dependent PL of CdTe@PAA-Au mixed solutions are due to the constantly changing distances between Au NPs and CdTe@PAA nanaospheres with pH. In the CdTe@PAA-Au mixed solutions, CdTe@PAA nanospheres in close proximity to the Au NPs are exposed to the increased electric fields in between and around the NPs, effectively resulting in significant increases in their absorption cross section. This lends itself to a subsequent increase in the excitation and eventually in the fluorescence emission from the CdTe@PAA nanospheres.
