Bright Blue Emitting Cu-Doped Cs2ZnCl4 Colloidal Nanocrystals

Posted on 22.06.2020 - 16:05
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%. Cs2ZnCl4 has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl4 tetrahedra surrounded by Cs+ cations. According to our 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 (isovalently substituting the Zn­(II) ions). The undoped Cs2ZnCl4 NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at ∼2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (∼55%) for the samples with a low Cu concentration ([Cu] ≤ 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (∼2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu­(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped Cs2ZnCl4 NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.

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Zhu, Dongxu; Zaffalon, Matteo L.; Pinchetti, Valerio; Brescia, Rosaria; Moro, Fabrizio; Fasoli, Mauro; et al. (2020): Bright Blue Emitting Cu-Doped Cs2ZnCl4 Colloidal Nanocrystals. ACS Publications. Collection. https://doi.org/10.1021/acs.chemmater.0c02017
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