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Mathew A.,DST Unit of Nanoscience DST UNS | Varghese E.,DST Unit of Nanoscience DST UNS | Choudhury S.,se National Center For Basic Science | Pal S.K.,se National Center For Basic Science | Pradeep T.,DST Unit of Nanoscience DST UNS
Nanoscale | Year: 2015

An efficient method to enhance visible luminescence in a visibly non-luminescent organic-soluble 4-(tert butyl)benzyl mercaptan (SBB)-stabilized Au25 cluster has been developed. This method relies mainly on enhancing the surface charge density on the cluster by creating an additional shell of thiolate on the cluster surface, which enhances visible luminescence. The viability of this method has been demonstrated by imparting red luminescence to various ligand-protected quantum clusters (QCs), observable to the naked eye. The bright red luminescent material derived from Au25SBB18 clusters was characterized using UV-vis and luminescence spectroscopy, TEM, SEM/EDS, XPS, TG, ESI and MALDI mass spectrometry, which collectively proposed an uncommon molecular formula of Au29SBB24S, suggested to be due to different stapler motifs protecting the Au25 core. The critical role of temperature on the emergence of luminescence in QCs has been studied. The restoration of the surface ligand shell on the Au25 cluster and subsequent physicochemical modification to the cluster were probed by various mass spectral and spectroscopic techniques. Our results provide fundamental insights into the ligand characteristics determining luminescence in QCs. This journal is © The Royal Society of Chemistry.

Udayabhaskararao T.,DST Unit of Nanoscience DST UNS | Pradeep T.,DST Unit of Nanoscience DST UNS
Journal of Physical Chemistry Letters | Year: 2013

Catching metals in the nonmetallic form in solution, as they grow to bulk, is one of the most exciting areas of contemporary materials research. A new kind of stabilization to catch the nonmetallic form of noble metals with small thiols has evolved as an exciting area of synthesis during the past decade. Gold clusters stay in the frontline of this research, yielding new molecules composed of a few to several hundreds of atoms. By taking guidelines from gold cluster research, various new protocols for silver nanoclusters were developed. In this Perspective, we highlight the recent advances on the synthesis of atomically precise silver, gold, and their alloy clusters with a special emphasis on silver. As a result of intense efforts of the recent past, clusters such as Ag7,8(SR)7,8, Ag7(-S-R-S-)4, Ag9(SR)7, Ag32(SR)19, Ag 44(SR)30, Ag140(SR)53, Ag 280(SR)140, and Ag152(SR)60 (SR and S-R-S refer to thiolate and dithiolate ligands, respectively) were added to the literature. Moreover, silver-covered and gold-covered alloy clusters have also been synthesized. Early reports of the crystallization of such clusters are available. Several of these clusters are shown to act as sensors, catalysts, and pesticide degradation agents, which suggests that these materials may find applications in daily life in the foreseeable future. © 2013 American Chemical Society.

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