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submitted on 28.04.2020 and posted on 29.04.2020by Dongxu Zhu, Valerio Pinchetti, Rosaria Brescia, Fabrizio Moro, Marco Fanciulli, Aiwei Tang, Ivan Infante, Luca De Trizio, Sergio Brovelli, Liberato Manna
We report here the synthesis
of undoped and Cu-doped Cs2ZnCl4 nanocrystals (NCs), in
which we could tune the concentration of Cu from 0.7% to 7.5%. According to electron
paramagnetic resonance analysis, in 0.7% and 2.1% Cu-doped NCs the Cu ions were
present in the +1 oxidation state only, while in NCs at higher Cu
concentrations we could detect Cu(II) ions. The undoped Cs2ZnCl4
NCs were non emissive, while the Cu-doped samples had a bright intra-gap photoluminescence
(PL) at 2.6eV mediated by band-edge absorption. The PL quantum yield was maximum (~55%) for the samples with low Cu concentration (≤ 2.1%) and it systematically
decreased when further increasing the concentration of Cu, reaching 15%
for the NCs with the highest doping level (7.5%). Density functional theory calculations indicated that the
PL emission could be ascribed only to Cu(I) ions: these ions introduce intra-gap
states that promote the formation of
self-trapped excitons, through which an efficient emission takes place.