ABSTRACT
Tin-based perovskites are becoming promising alternatives to lead-based perovskites with eco-friendly merit and tantalizing photophysical properties. Unfortunately, the lack of facile, low-cost synthesis approaches associated with extremely poor stability greatly restrict their practical applications. Herein, a facile room-temperature "coprecipitation" method utilizing ethanol (EtOH) solvent and salicylic acid (SA) additive is proposed for synthesizing highly stable cubic phase CsSnBr3 perovskite. Experimental results show that ethanol solvent and SA additive can not only effectively prevent the oxidation of Sn2+ during the synthesis processes but also stabilize the as-synthesized CsSnBr3 perovskite. These are mainly ascribed to the protection effect of ethanol and SA, which are attached on the surface of CsSnBr3 perovskite by coordinating with Br- and Sn2+ ions, respectively. As a result, CsSnBr3 perovskite can be obtained in open air and exhibits exceptional oxygen resistibility under moist air conditions (temperature: 24.2-25.8 °C; relative humidity: 63-78%). Absorption remains unchanged and photoluminescence (PL) intensity is vastly maintained (â¼69%) after storage for 10 days, better than bulk CsSnBr3 perovskite film synthesized by spin-coating method whose PL intensity is decreased to 43% after storage for 12 h. This work represents a step toward stable tin-based perovskite by a facile and low-cost strategy.
ABSTRACT
Engineering oxygen coordination environments of cations in oxides has received intense interest thanks to the opportunities for the discovery of novel oxides with unusual properties. Herein, the synthesis of stoichiometric layered BaBiO2.5 by a nontopotactic phase transformation of perovskite BaBiO3 is presented. By analyzing the synchrotron X-ray diffraction data by the maximum-entropy method/Rietveld technique, it was found that Bi is involved in an unusual chemical bonding situation with four oxygen atoms featuring one ionic bond and three covalent bonds, which results in an asymmetric coordination geometry. Photophysical characterization revealed that this peculiar structure shows near-infrared luminescence differing from that of conventional Bi-containing compounds. Experimental and theoretical results led to the proposal of an excitonic nature of the luminescence. This work highlights that synthesizing materials with uncommon Bi-O bonding and Bi coordination geometry provides a pathway to the discovery of systems with new functionalities. This could inspire interest in the exploration of a range of materials containing heavier p-block elements with prospects for finding systems with unusual properties.
ABSTRACT
Doping of semiconductors by introducing foreign atoms enables their widespread applications in microelectronics and optoelectronics. We show that this strategy can be applied to direct bandgap lead-halide perovskites, leading to the realization of ultrawide photoluminescence (PL) at new wavelengths enabled by doping bismuth (Bi) into lead-halide perovskites. Structural and photophysical characterization reveals that the PL stems from one class of Bi doping-induced optically active center, which is attributed to distorted [PbI6] units coupled with spatially localized bipolarons. Additionally, we find that compositional engineering of these semiconductors can be employed as an additional way to rationally tune the PL properties of doped perovskites. Finally, we accomplished the electroluminescence at cryogenic temperatures by using this system as an emissive layer, marking the first electrically driven devices using Bi-doped photonic materials. Our results suggest that low-cost, earth-abundant, solution-processable Bi-doped perovskite semiconductors could be promising candidate materials for developing optical sources operating at new wavelengths.
ABSTRACT
A low-temperature topochemical reduction strategy is used herein to prepare unconventional phosphors with luminescence covering the biological and/or telecommunications optical windows. This approach is demonstrated by using Bi(III)-doped Y2O3 (Y(2-x)Bi(x)O3) as a model system. Experimental results suggest that topochemical treatment of Y(2-x)Bi(x)O3 using CaH2 creates randomly distributed oxygen vacancies in the matrix, resulting in the change of the oxidation states of Bi to lower oxidation states. The change of the Bi coordination environments from the [BiO6] octahedra in Y(2-x)Bi(x)O3 to the oxygen-deficient [BiO(6-z)] polyhedra in reduced phases leads to a shift of the emission maximum from the visible to the near-infrared region. The generality of this approach was further demonstrated with other phosphors. Our findings suggest that this strategy can be used to explore Bi-doped or other classes of luminescent systems, thus opening up new avenues to develop novel optical materials.
