We report the composition-dependent optical properties of Bi-doped Cs 2 Ag 1−x Na x InCl 6 nanocrystals (NCs) having a double perovskite crystal structure. Their photoluminescence (PL) was characterized by a large Stokes shift, and the PL quantum yield increased with the amount of Na up to ∼22% for the Cs 2 Ag 0.4 Na 0.6 InCl 6 stoichiometry. The presence of Bi 3+ dopants was crucial to achieve high PL quantum yields (PLQYs) as nondoped NC systems were not emissive. Density functional theory calculations revealed that the substitution of Ag + with Na + leads to localization of AgCl 6 energy levels above the valence band maximum, whereas doping with Bi 3+ creates BiCl 6 states below the conduction band minimum. As such, the PL emission stems from trapped emission between states localized in the BiCl 6 and AgCl 6 octahedra, respectively. Our findings indicated that both the partial replacement of Ag + with Na + ions and doping with Bi 3+ cations are essential in order to optimize the PL emission of these systems.
The vast majority of lead halide perovskite (LHP) nanocrystals (NCs) are currently based on either a single halide composition (CsPbCl 3 , CsPbBr 3 , and CsPbI 3 ) or an alloyed mixture of bromide with either Cl – or I – [i.e., CsPb(Br:Cl) 3 or CsPb(Br:I) 3 ]. In this work, we present the synthesis as well as a detailed optical and structural study of two halide alloying cases that have not previously been reported for LHP NCs: Cs 2 PbI 2 Cl 2 NCs and triple halide CsPb(Cl:Br:I) 3 NCs. In the case of Cs 2 PbI 2 Cl 2 , we observe for the first time NCs with a fully inorganic Ruddlesden–Popper phase (RPP) crystal structure. Unlike the well-explored organic–inorganic RPP, here, the RPP formation is triggered by the size difference between the halide ions. These NCs exhibit a strong excitonic absorption, albeit with a weak photoluminescence quantum yield (PLQY). In the case of the triple halide CsPb(Cl:Br:I) 3 composition, the NCs comprise a CsPbBr 2 Cl perovskite crystal lattice with only a small amount of incorporated iodide, which segregates at RPP planes’ interfaces within the CsPb(Cl:Br:I) 3 NCs. Supported by density functional theory calculations and postsynthetic surface treatments to enhance the PLQY, we show that the combination of iodide segregation and defective RPP interfaces are most likely linked to the strong PL quenching observed in these nanostructures. In summary, this work demonstrates the limits of halide alloying in LHP NCs because a mixture that contains halide ions of very different sizes leads to the formation of defective RPP interfaces and a severe quenching of LHP NC’s optical properties.
Increasing water pollution and the lack of largescale purification processes pose a great environmental burden. In the present work, water-borne polyurethane composite membranes containing TiO 2 active particles are prepared via a single-step electrospinning procedure by using water as the unique solvent. The mats are then explored as photocatalytic platforms for wastewater treatment. Despite the fact that the amount of embedded TiO 2 is found to influence the nanofiber dimension (i.e., 540−840 nm), the fabricated mats are generally characterized by self-standing nature, high porosity, marked thermal stability, and excellent mechanical resistance. TiO 2 particles are proved to endow the composite membranes with photocatalytic features when irradiated with solar light, giving marked adsorption ability and abatement capacity. In addition, mat reusability is demonstrated over five cycles showing no activity loss. Due to their low cost, great efficiency, and high fabrication rate, the proposed composite mats represent a promising class of recyclable filtering materials.
Layered double perovskite are currently investigated as emerging halide-based materials for optoelectronic applications. Herein, we present the synthesis of Cs4MnxCd1-xSb2Cl12 (0 ≤ x ≤ 1) nanocrystals (NCs). X-ray powder diffraction...
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