Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 5, Issue 1, Pages 167-173Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jz402443y
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Funding
- IISER Pune
- Department of Science and Technology (DST)
- DAE-BRNS grant Govt. of India [2013/20/37C/1/BRNS/954]
- Nanoscience Unit Grant of DST, Govt. of India [SR/NM/NS-42/2009]
- CSIR, Govt. of India
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
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Donor-Acceptor transition was previously suggested as a mechanism for luminescence in (ZnS)(1-x)(AgInS2)(x) nanocrystals. Here we show the participation of delocalized valence/conduction band in the luminescence. Two emission pathways are observed: Path-1 involves transition between a delocalized state and a localized state exhibiting higher energy and shorter lifetime (similar to 25 ns) and Path-2 (donor-acceptor) involves two localized defect states exhibiting lower emission energy and longer lifetime (>185 ns). Surprisingly, Path-1 dominates (82% for x = 0.33) for nanocrystals with lower x, in sharp difference with prior assignment. Luminescence peak blue shifts systematically by 0.57 eV with decreasing x because of this large contribution from Path-1. X-ray absorption fine structure (XAFS) study of (ZnS)(1-x)(AgInS2)(x) nanocrystals shows larger AgS4 tetrahedra compared with InS4 tetrahedra with Ag-S and In-S bond lengths 2.52 and 2.45 angstrom respectively, whereas Zn-S bond length is 2.33 angstrom along with the absence of second nearest-neighbor Zn-S-metal correlation.
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