Chemical vapor deposition growth of single-crystalline cesium lead halide microplatelets and heterostructures for optoelectronic applications

Orgaruc-inorganic hybrid halide perovskites,such as CH3NH3PbI3,have emerged as an exciting class of materials for solar photovoltaic applications;however,they are currently plagued by insufficient environmental stability.To solve this issue,all-inorganic halide perovskites have been developed and shown to exhibit significantly improved stability.Here,we report a single-step chemical vapor deposition growth of cesium lead halide (CsPbX3) microcrystals.Optical microscopy studies show that the resulting perovskite crystals predominantly adopt a square-platelet morphology.Powder X-ray diffraction (PXRD) studies of the resulting crystals demonstrate a highly crystalline nature,with CsPbC13,CsPbBr3,and CsPbI3 showing tetragonal,monoclinic,and orthorhombic phases,respectively.Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show that the resulting platelets exhibit well-faceted structures with lateral dimensions of the order of 10-50 μm,thickness around 1 μm,and ultra-smooth surface,suggesting the absence of obvious grain boundaries and the single-crystalline nature of the individual microplatelets.Photoluminescence (PL) images and spectroscopic studies show a uniform and intense emission consistent with the expected band edge transition.Additionally,PL images show brighter emission around the edge of the platelets,demonstrating a wave-guiding effect in high-quality crystals.With a well-defined geometry and ultra-smooth surface,the square platelet structure can function as a whispering gallery mode cavity with a quality factor up to 2,863 to support laser emission at room temperature.Finally,we demonstrate that such microplatelets can be readily grown on a variety of substrates,including silicon,graphene,and other two-dimensional materials such as molybdenum disulfide,which can readily allow the construction of heterostructure optoelectronic devices,including a graphene/perovskite/ graphene vertically-stacked photodetector with photoresponsivity ＞ 105 A/W.The extraordinary optical properties of CsPbX3 platelets,combined with their ability to be grown on diverse materials to form functional heterostructures,can lead to exciting opportunities for broad optoelectronic applications.     

Electrical and optical property of annealed Te-doped GaSb

GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system. In this work, Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550 ℃ for 100 h in ambient antimony. The annealed samples have been studied by Hall effect measurement, infrared (IR) optical transmission, Glow discharge mass spectroscopy (GDMS) and photoluminescence (PL) spectroscopy. After annealing, Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility, along with an improvement of below gap IR transmission. Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level. The mechanism of the variation of the defect and its influence on the material properties are discussed.     

Influence of MEOBiPA content on the properties of novel photoluminescent thermosensitive hydrogels

In order to establish a dual functional hydrogel, a special monomer, methacryloyloxy‐ethylene‐oxy‐carbonyl bis[4‐(phenyl‐isopropyl)phenyl]amine (MEOBiPA), was prepared from bis[4‐(phenyl‐isopropyl)phenyl]‐4‐cyanophenyl amine and 2‐hydroxyethyl methacrylate. Subsequently, a series of thermosensitive hydrogels was obtained through copolymerization of N‐isopropyl acrylamide (NIPAAm) with MEOBiPA by UV irradiation (named the NM series). The effect of MEOBiPA content on the swelling behavior, mechanical properties and drug release behavior of the hydrogels was further investigated. Results showed that the swelling ratios of the NM copolymeric hydrogels decreased from 4.73 to 1.74 g g^?1 when the MEOBiPA content in the hydrogel increased from 0.1 to 0.9 mol%. Both gel strength and crosslinking density of the NM hydrogels increased with increasing MEOBiPA. Conversely, the thermosensitive behavior of NM hydrogels significantly decreased upon increase of MEOBiPA content. Likewise, the caffeine release ratio also decreased from 70% to 25%. Notably, the intensity of photoluminescence increased with increasing MEOBiPA content in the hydrogels. Further, the corresponding copolymers of the hydrogels were prepared using free radical polymerization. The UV absorbance and photoluminescent behavior of the MEOBiPA, NIPAAm/MEOBiPA copolymeric hydrogels and their corresponding copolymers in different polar solvents were also investigated. © 2015 Society of Chemical Industry     

Highly Luminescent Covalently Linked Silicon Nanocrystal/Polystyrene Hybrid Functional Materials: Synthesis,Properties, and Processability

Silicon nanocrystals (SiNCs) have received much attention because of their exquisitely tunable photoluminescent response, biocompatibility, and the promise that they may supplant their CdSe quantum dot counterparts in many practical applications. One attractive strategy that promises to extend and even enhance the utility of SiNCs is their incorporation into NC/polymer hybrids. Unfortunately, methods employed to prepare hybrid materials of this type from traditional compound semiconductor (e.g., CdSe) quantum dots are not directly transferable to SiNCs because of stark differences in surface chemistry. Herein, the preparation of chemically resistant SiNC/polystyrene hybrids exhibiting exquisitely tunable photoluminescence is reported and material processability is demonstrated by preparing micro and nanoscale architectures.     

Absolute photoluminescence quantum yield of perylene dye ultra-thin films

Using integrating sphere method we have determined the absolute photoluminescence quantum yield (QY) of two perylene derivatives in ultra-thin films. Monomolecular and multilayer films were deposited onto quartz substrates by using Langmuir–Blodgett technique. The method adopted by us allows to evaluate QY with a high accuracy for samples having absorbance down to 0.01. The evaluated luminescence quantum yield of mono- and multilayers of two 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes was in the range of 7–12%.     

Preparation and characterization of alternating copolymers containing fluorene and hexyl‐ or perfluorohexyl‐substituted thiophene

Alternating copolymers containing fluorene and hexyl‐ or perfluorohexyl‐substituted thiophene were synthesized by a palladium‐catalyzed cross‐coupling reaction, and the structures of the polymers were confirmed using nuclear magnetic resonance spectroscopy. The absorption spectra of polymers containing perfluorohexyl substituents show shorter maximum wavelength due to the steric hindrance between fluorene and substituted thiophene units. In addition, the perfluorohexyl substituents can effectively interrupt the conjugation length of the polymers, which leads to an increase in the optical bandgap and decrease in the photoluminescence quantum yield. Solid‐state UV‐visible absorption and emission maxima of the polymers containing perfluorohexyl‐substituted thiophene units are blue‐shifted in comparison to those of polymers in solution due to the packing structure of perfluoroalkyl chains. © 2014 Society of Chemical Industry     

Uranium speciation and its site occupancy in alkaline‐earth borophosphates

Alkaline‐earth (calcium, strontium, and barium) borophosphates doped with uranium (U) are prepared through conventional solid‐state reaction route. The form of stabilized uranium in these solid matrices was characterized and investigated using X‐ray diffraction (XRD), photo luminescence (PL) and extended X‐ray absorption fine structure (EXAFS). XRD measurements confirmed the single phase formation of uranium‐doped alkaline‐earth borophosphate samples. The PL characteristics of uranium in calcium and barium borophosphate are studied for the first time. Photoluminescence studies indicated presence of uranium as Uranyl in SrBPO₅ and CaBPO₅ matrices whereas in case of BaBPO₅ the indication was for uranate species. The life time data corroborated the presence of a different uranium species in SrBPO₅, CaBPO₅, and BaBPO₅. The site occupancy of uranium was further probed using EXAFS which confirmed that in case of BaBPO₅, uranium enters the host as uranate whereas in case of SrBPO₅ and CaBPO₅, uranium enters as Uranyl.     

Precipitation and Optical Properties of CsPbBr3 Quantum Dots in Phosphate Glasses

CsPbBr₃ quantum dots were precipitated in phosphate glasses through heat treatment. Controlled formation of CsPbBr₃ quantum dots was realized by adjustment of heat‐treatment conditions. Absorption and photoluminescence spectra of CsPbBr₃ quantum dots were tuned from 432 to 521 nm. Upon ultraviolet or blue light excitation, efficient photoluminescence from these CsPbBr₃ quantum dots doped phosphate glasses was observed.