Search results for "Halide"
showing 10 items of 324 documents
Polymorphism and the glasslike state of cyanide mixed crystals: A mesoscopic problem.
1990
The martensitic aspect of the structural phase transitions of the alkali cyanides and their solid solutions with the alkali halides is discussed. It is suggested that the polymorphism is intimately connected with the problem of mesoscopic transformation strains. At intermediate CN concentrations a competition between glasslike inhomogeneous strains, modulated strains, and ferroelastic strains is observed.
Short-lived luminescence of mixed silver halides
1993
Abstract Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr1−xClx, (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag0i and Ag2+V-c. It is shown that the effective activation energy of Ag0i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its a…
Low-dimensional non-toxic A 3 Bi 2 X 9 compounds synthesized by a dry mechanochemical route with tunable visible photoluminescence at room temperature
2019
We have synthesized fifteen inorganic and hybrid organic-inorganic non-toxic A3Bi2X9 compounds (A = K+, Rb+, Cs+, CH3NH3+ and HC(NH2)2+; X = I−, Br−, Cl−) through dry mechanochemistry. We demonstrate that this synthetic method is very well suited to prepare compounds from poorly soluble precursors, allowing thus the preparation of so far unreported compounds. X-ray diffraction analysis demonstrates the high crystallinity of the so-formed ternary bismuth halides. Furthermore, we show that, through substitution of the A-cation and X-anion, the bandgap of these compounds can be tuned to absorb throughout the whole visible spectrum. As-prepared powders of Cs3Bi2Br9 and Cs3Bi2I9 without any pass…
Tunable luminescent lead bromide complexes
2020
Lead halides are used extensively to prepare perovskite-based devices but it is less known that lead halides can also form luminescent complexes in solvents. Using polyethylene glycol as a solvent, a lead bromide complex with a photoluminescence quantum yield over 20% is obtained and the photoluminescence peak can be shifted around 50 nm with different alkylammonium bromides.
Controlling the Phase Segregation in Mixed Halide Perovskites through Nanocrystal Size
2019
Mixed halide perovskites are one of the promising candidates in developing solar cells and light-emitting diodes (LEDs), among other applications, because of their tunable optical properties. Nonetheless, photoinduced phase segregation, by formation of segregated Br-rich and I-rich domains, limits the overall applicability. We tracked the phase segregation with increasing crystalline size of CsPbBr3–xIx and their photoluminescence under continuous-wave laser irradiation (405 nm, 10 mW cm–2) and observed the occurrence of the phase segregation from the threshold size of 46 ± 7 nm. These results have an outstanding agreement with the diffusion length (45.8 nm) calculated also experimentally f…
Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)2PbI4 Perovskite Thin Films: Implications fo…
2021
An outstanding potentiality of layered two-dimensional (2D) organic–inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundament…
Photostimulable energy transfer in doped nanostructures of alkali halides
1998
Abstract In nanostructures of doped alkali halides, unrelaxed H-centres produced in the exciton decay are able to escape from the surface thus producing in the grains of polycrystalline film an excess concentration of F-centres, which has a great tendency to form an interacting F-centre chain or a canal. Role of this F-centre chain in photostimulable energy transfer is analysed. It is concluded that specific interaction of unrelaxed H-centres and electrons with the F-centre chain (or the canal) leads to the temperature-independent exciton or electron transport at any distance. Hence, the temperatureindependent photostimulated luminescence (PSL) response production and retrieval are experime…
Continuous-Flow Synthesis of Orange Emitting Sn(II)-Doped CsBr Materials
2021
An ongoing demand toward lead-free all-inorganic cesium metal halide perovskites has presented Sn(II) as an ideal substitute of Pb(II) for applications in optoelectronic devices. The major concern regarding Sn(II) is the instability due to the ambient oxidation to Sn(IV). To expand the scope of traditional perovskite and analogues, herein the synthesis and optical performance of Sn(II)-doped CsBr, a new material formed by interstitial doping of Sn(II) into the CsBr matrix, are reported for the first time. This material is prepared following an antisolvent mediated recrystallization method using a continuous flow reactor, which is beneficial for scaling up the production compared to traditio…
Luminescence of biexcitons in silver halide crystals
1998
Abstract As it is known from Urbach rule, free excitons defining the fundamental absorption edge in AgBr 1 − x Cl x (0 ⩽ x ⩽ 1). The process of primary Frenkel defect creation which involves free exciton states even in AgCl and biexciton creation in AgCl are discussed. The fast luminescence band at ≈3.0 eV observed in AgCl under high-density pulsed electron beam and laser excitation has been studied. It is shown that its intensity is a non-linear function of the excitation density. We suggest that the fast luminescence comes from biexcitons; binding energies of such biexcitons in AgBr 1 − x Cl x (0 ⩽ x ⩽ 1) are estimated.
Perovskite CH3NH3PbI3–XClx Solar Cells and their Degradation (Part 1: A Short Review)
2021
Development of hybrid organic-inorganic perovskite solar cells (PSC) has been one of the hottest research topics since 2013. Within brief literature review, we would like to achieve two objectives. Firstly, we would like to indicate that a whole set of physical properties, such as high change carrier mobility, very low recombination rates, large carrier life time and diffu-sion length, large absorption coefficients and very weak exciton binding energies, are defining high power conversion efficiency (PCE) of methyl ammonium lead trihalide SC. The second objective is to draw attention to some, in our opinion, important aspects that previously have not been satisfactory addressed in literatur…