Time resolved spectroscopic studies on some nanophosphors |
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Authors: | Harish Chander Santa Chawla |
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Affiliation: | (1) Electronic Materials Division, National Physical Laboratory, Dr K S Krishnan Road, New Delhi, 110 012, India |
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Abstract: | Time resolved spectroscopy is an important tool for studying photophysical processes in phosphors. Present work investigates
the steady state and time resolved photoluminescence (PL) spectroscopic characteristics of ZnS, ZnO and (Zn, Mg)O nanophosphors
both in powder as well as thin film form. Photoluminescence (PL) of ZnS nanophosphors typically exhibit a purple/blue emission
peak termed as self activated (SA) luminescence and emission at different wavelengths arising due to dopant impurities e.g.
green emission for ZnS: Cu, orange emission for ZnS: Mn and red emission for ZnS: Eu. The lifetimes obtained from decay curves
range from ns to ms level and suggest the radiative recombination path involving donor-acceptor pair recombination or internal
electronic transitions of the impurity atom. A series of ZnMgO nanophosphor thin films with varied Zn: Mg ratios were prepared
by chemical bath deposition. Photoluminescence (PL) excitation and emission spectra exhibit variations with changing Mg ratio.
Luminescence lifetime as short as 10−10 s was observed for ZnO and ZnMgO (100: 10) nanophosphors. With increasing Mg ratio, PL decay shifts into microsecond range.
ZnO and ZnMgO alloys up to 50% Mg were prepared as powder by solid state mixing and sintering at high temperature in reducing
atmosphere. Time resolved decay of PL indicated lifetime in the microsecond time scale. The novelty of the work lies in clear
experimental evidence of dopants (Cu, Mn, Eu and Mg) in the decay process and luminescence life times in II–VI semiconductor
nanocrystals of ZnS and ZnO. For ZnS, blue self activated luminescence decays faster than Cu and Mn related emission. For
undoped ZnO nanocrystals, PL decay is in the nanosecond range whereas with Mg doping the decay becomes much slower in the
microsecond range. |
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Keywords: | Photoluminescence (PL) time resolved decay lifetime nanophosphor |
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