For example, the PbS NCs are used as light-absorbing materials in photodetectors and solar cells due to the strong optical absorption in nearinfrared regions. [7] The CdSe-based NCs have been heavily investigated in LEDs aiming to realize full-color display because of their narrow photoluminescence (PL) line widths and the wide tunable spectral range. [8] Due to the high surface-area-tovolume ratio, molecules or ions ligands that bind to the under-coordinated sites on NCs surface to keep the colloidal stability are imperative. [9] The ligands usually have two heads connected by alkyl chain. One of the heads is polar group (e.g., carboxy group, ammonium group) that coordinates with the NCs surface atoms. Another head is nonpolar group (e.g., alkyl group) that stretches into solution. The ligands not only offer colloidal stability but also play critical roles through all lifetimes of NCs. Before reaction, ligands coordinate with reagent to form soluble precursors in the solution. During reaction, the ligands can regulate crystallization kinetics through affecting supplying rate of the precursors and the formation of monomers thus affecting the size and shape of NCs. Beyond these, ligands can also terminate the growth of NCs and prevent undesired ripening. Even after synthesis, the surface defects of NCs can be eliminated through post-treatment by ligands.Ligands are indispensable for perovskite nanocrystals (NCs) throughout the whole lifetime, as they not only play key roles in the controllable synthesis of NCs with different sizes and shapes, but also act as capping shell that affects optical properties and electrical coupling of NCs. Establishing a systematic understanding of the relationship between ligands and perovskite NCs is significant to enable many potential applications of NCs. This review mainly focuses on the influence of ligands on perovskite NCs. First of all, the ligandsdominated size and shape control of NCs is discussed. Whereafter, the surface defects of NCs and the bonding between ligands and perovskite NCs are classified, and corresponding post-treatment of surface defects via ligands is also summarized. Furthermore, advances in engineering the ligands towards the high performance of optoelectronic devices based on perovskite NCs, including photodetector, solar cell, light emitting diode (LED), and laser, and finally to potential challenges are also discussed.
Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices due to their abnormal photovoltaic effect. However, the current reported efficiency is still low. Hence, it is urgent to develop narrow-band gap ferroelectric materials with strong ferroelectricity by low-temperature synthesis. In this paper, the perovskite bismuth ferrite BiFeO3 (BFO) thin films were fabricated on SnO2: F (FTO) substrates by the sol–gel method and they were rapidly annealed at 450, 500 and 550 °C, respectively. The microstructure and the chemical state’s evolution with annealing temperature were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), and the relationship between the microstructure and electric, optical and photovoltaic properties were studied. The XRD, SEM and Raman results show that a pure phase BFO film with good crystallinity is obtained at a low annealing temperature of 450 °C. As the annealing temperature increases, the film becomes more uniform and has an improved crystallinity. The XPS results show that the Fe3+/Fe2+ ratio increases and the ratio of oxygen vacancies/lattice oxygen decreases with increasing annealing temperature, which results in the leakage current gradually being reduced. The band gap is reduced from 2.68 to 2.51 eV due to better crystallinity. An enhanced photovoltaic effect is observed in a 550 °C annealed BFO film with a short circuit current of 4.58 mA/cm2 and an open circuit voltage of 0.15 V, respectively.
Fluorescent materials generally show diverse light-emitting, simple manufacturing processes, long service life, long-term reliability properties, gradually become a hotspot in the field of anti-counterfeiting. The phosphors with multi-function for the...
Cesium lead halide perovskite nanocrystals (NCs) have attracted enormous interest in light-emitting diode, photodetector and low-threshold lasing application in terms of their unique optical and electrical performance. However, little attention has been paid to other structures associated with CsPbBr3, such as CsPb2Br5. Herein, we realize a facile method to prepare dual-phase NCs with improved stability against polar solvents by replacing conventional oleylamine with cetyltrimethyl ammonium bromide (CTAB) in the reprecipitation process. The growth of NCs can be regulated with different ratios of toluene and ethanol depending on solvent polarity, which not only obtains NCs with different sizes and morphologies, but also controls phase transition between orthorhombic CsPbBr3 and tetragonal CsPb2Br5. The photoluminescence (PL) and defect density calculated exhibit considerable solvent polarity dependence, which is ascribed to solvent polarity affecting the ability of CTAB to passivate surface defects and improve stoichiometry in the system. This new synthetic method of perovskite material will be helpful for further studies in the field of lighting and detectors.
needed to excite the electrons from the ground state to the conduction band. However, this strict requirement for highenergy photonic sources which is easily to pose great threat to human body limits their popularity in civil scenes. By comparison, visible light (≈400-700 nm) is harmless to our skin or eyes. In addition, the blue chip based white light emitting diodes are common light sources in nowadays human life. [6] Thus, it is a trend to promote the development of persistent phosphors which can be excited by the visible light. It is worth noting that some persistent phosphors can absorb light with low photon energy such as deep-red or near-infrared (NIR) so that accelerate the release process of trapped electrons, which is the wellknown photostimulation process. [1d] But it is different from the energy storage process (that is photoexcitation), and the latter will be discussed carefully in this paper. To date, some phosphors have been reported to realize the visible light storage and achieved commercial success, such as SrAl 2 O 4 : Eu 2+ , Dy 3+ (green), [7] CaAl 2 O 4 : Eu 2+ , Nd 3+ (blue), [8] Sr 2 MgSi 2 O 7 : Eu 2+ , Dy 3+ (azure), [9] Y 2 O 2 S: Mg 2+ , Ti 4+ , Eu 3+ (red). [10] In addition, Pan et al. have designed Zn 3 Ga 2 Ge 2 O 10 : Cr 3+ in 2011, in which the NIR afterglow can be induced by almost all visible light wavelength. [11] Bessière et al. have proposed a deep-red emissive phosphor ZnGa 2 O 4 : Cr 3+ in 2014, [12] which further enrich the luminous band of afterglow materials.Persistent phosphor, as an eco-friendly energy storage material, usually needs high-energy photonic rays in the storage process, such as ultraviolet (UV) light, X-ray, or even γ-ray. This strict requirement for light source which is harmful to human health greatly limits the popularity of persistent phosphors in the daily life. Here, a novel broadband orange persistent emissive phosphor LiGaO 2 :1%Mn 2+ (LGOM) is reported which supports efficient wide band excitation from UV to green light. The afterglow excited by 470 nm light even reaches ≈80% as intensity as UV excitation. The afterglow of LGOM excited by common blue lamp (450-460 nm) can be pictured by the smart phones for more than 48 h. The mechanism of visible light storage is discussed through the thermal-luminescence measurements. In addition, interestingly, its persistent emissive color can shift from orange-yellow to orange-red after ceasing the excitation source. This unique broadband orange afterglow phosphor which supports efficient wide range visible-light excitation, afterglow color shift, and long-lasting luminescence is expected to have potential applications in the fields of emergency direction, anticounterfeiting, decoration design, etc.
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