The luminescent properties of metal halides are determined by the inorganic framework and solvent molecules.

The luminescent properties of metal halides are usually considered to be determined by the inorganic framework. In this work, we propose that the luminescent properties of metal halides are determined by both the inorganic framework and the solvent [Denoted as (inorganic framework + n·solvent molecules), n = 0, 1, 2…] through the abundant solvatochromic or thermochromic effect of tetrabutylammonium lead bromides [TPB, T = TBA (tetrabutylammonium), P = Pb (lead), B = Br (bromide)] containing water (H2O) and ethanol (EtOH). One-dimensional (1D) TPB can form ligands of [[Pb5Br18]8- + 2H2O(H)], [[Pb5Br18]8- + 2H2O(H) + 2H2O] and [[Pb5Br18]8- + 2EtOH] by solvent or heat treatment has completely different luminescent properties resulting from different solvents. They exhibit broad spectral emission due to strong electron-phonon coupling, as do other 1D metal halides. However, the 1D TPB containing only [[Pb5Br18]8- achieves extremely rare narrow-band green emission, with full width at half maximum (FWHM) of 21 nm at room temperature and 8 nm at low temperature, color gamut covers 95 % of the International Telecommunication Union recommendation 2020 standard. This work provides new guidance for the modulation of photophysical properties of metal halides, as well as new materials for the display and smart materials fields.

Structural Transformation and Photoluminescent Property of Manganese-Doped Bismuth-Based Perovskites.

Here, we synthesized pure Cs3Bi2Cl9 (CBC) and manganese (Mn)-doped crystals with different feeding ratios, leading to changes in structure and luminescence. The crystals Cs3Bi2Cl9-Mn (CBCM) formed by doping a minor amount of Mn2+ (Bi/Mn = 8:1) maintain the orthorhombic phase structure of the host, but when Bi/Mn = 2:1, the crystal structure is more inclined to form Cs4MnBi2Cl12 (CMBC) of a trigonal phase. Combined with density functional theory (DFT) calculation, the results demonstrate that a moderate amount of Mn2+ doping can create impurity energy levels in the forbidden band. However, as the structure transitions, the type of energy band structure changes from indirect to direct, with completely different electronic orbital features. Temperature-dependent time-resolved and steady-state photoluminescence spectroscopies are used to explore the structure-related thermal properties and transitional process. Differences energy transfer routes are revealed, with CBCM relying on intersystem energy transfer and CMBC mainly depending on direct excitation of Mn2+ to produce d-d transitions. Furthermore, since CMBC is temperature-sensitive, we perform the first photoluminescent (PL) lifetime temperature measurement using CBMC and obtain a maximum relative sensitivity of 1.7 %K-1 and an absolute sensitivity of 0.0099 K-1. Our work provides insight into the mechanism of Mn2+ doping-induced luminescence and offers a potentially effective doping strategy for improving the PL properties of lead-free metal halide perovskites.

Photophysical properties of tetrabutylammonium metal chlorides with different inorganic frameworks.

The luminescence of single crystals of (TBA)PbCl3, (TBA)2Sb2Cl8, (TBA)3Bi2Cl9 and (TBA)SnCl5·2EtOH (TBA = tetrabutylammonium, EtOH = Ethanol) synthsized were assigned distinctively to the centres of self-trapped excitons (STEs), TBA+, TBA+ and co-emission of STEs and TBA+. This work demonstrates that organic cations without benzene or aromatic rings can also be used as the sole luminescence centres for metal halides.

Highly Sensitive Dual-Mode Optical Thermometry of Er3+/Yb3+ Codoped Lead-Free Double Perovskite Microcrystal.

In this Letter, erbium (Er3+) and ytterbium (Yb3+) codoped perovskite Cs2Ag0.6Na0.4In0.9Bi0.1Cl6 microcrystal (MC) is synthesized and demonstrated systematically to the most prospective optical temperature sensing materials. A dual-mode thermometry based on fluorescence intensity ratio and fluorescence lifetime provides a self-reference and highly sensitive temperature measurement under dual wavelength excitation at a temperature from 300 to 470 K. Combined with the white-light emission derived from self-trapped excitons (STEs), the characteristic emission peak of Er3+ ions can be observed under 405 nm laser excitation. The fluorescence intensity ratio (FIR) between perovskite and Er3+ is used as temperature-dependent probe signal, of which maximum value for relative and absolute sensitivities reaches to 1.40% K-1 and 8.20 × 10-2 K-1. Moreover, Er3+ luminescence becomes stronger with the feeding Yb3+ increasing under 980 nm laser excitation. The energy transfer of Er3+ and Yb3+ is revealed by power-dependent photoluminescence (PL) spectroscopy, and the involved upconversion mechanism pertains to the two-photon excitation process. The results reveal that the Er3+/Yb3+ codoped lead-free double perovskite MC is a good candidate for a thermometric material for the novel dual-mode design.

The surfactant effect on electrorheological performance and colloidal stability.

The impact of two nonionic surfactants, namely Span 20 and Span 85, on the electrorheological response and colloidal stability of urea-coated barium titanyl oxalate (BTRU)/silicone oil suspensions is investigated. We quantitatively analyze the surfactant effect on modified ER performance through the measurements of yield stress and current density, as well as the tuned suspension stability through calculation of the Turbiscan stability index (TSI) and naked-eye observations of sedimentation phenomena. The surfactant effect on particle-oil interactions and agglomeration effects is examined by measuring the permeability of silicone oil when mixed with the Span surfactant and the cluster size of particles in dispersing medium, respectively. Our results indicate that with the presence of a Span surfactant, the yield stress of the suspension exhibits a local maximum at certain Span concentrations. We hypothesize that below the optimal Span concentration, the ER properties are enhanced by the increase of the electrostatic interaction between particles. Above the limiting concentration, the ER activity is weakened by the formation of a double-layer surfactant structure that generates a steric hindrance effect. We discover that the addition of the Span surfactant favors the improvement of the particle agglomeration phenomenon, thereby promoting colloidal stability of the suspension. Consequently, in the consideration of both ER properties and suspension stability, an optimal ER fluid with the addition of 0.4 wt% Span 85 is acquired with remarkable integrated ER properties.

Microwave-assisted ultrafast synthesis of silver nanoparticles for detection of Hg²âº.

Silver nanoparticles (AgNPs) were successfully prepared in aqueous solution by a one-pot procedure based on a rapid microwave-assisted green approach. L-Cysteine acted as a capping agent in the process of AgNP formation. The structural and morphological characteristics of the L-cysteine-capped AgNPs were investigated by the UV-vis, CD, FL, FTIR, XRD, TEM and EDX analysis. It was found that the well-dispersed crystalline AgNPs were formed after irradiation for 90 s and had sphere-like morphology. Such strategy may facilitate new ways to the synthesis of other metal nanoparticles, such as Au, Pt and Pd. In addition, the synthesized AgNPs were developed as a platform for the detection of Hg(2+) and showed a high sensitivity on the order of 1×10(-8) M. This sensing system could discriminate Hg(2+) from a wide range of cations (Ca(2+), Ba(2+), Mn(2+), etc.). The selectivity and sensitivity of AgNPs indicated its potential use as a sensor for Hg(2+) detection in the ecosystems.