High thermal stability of all‐inorganic perovskite nanocrystals (NCs) offers their potential application in various fields such as solar cells and light‐emitting diodes. However, the cubic cesium lead iodide (α‐CsPbI3) with the most appropriate bandgap for light harvesting is thermodynamically unstable at room temperature and spontaneously transforms into the undesired orthorhombic δ‐CsPbI3. Here, a simple method is demonstrated to synthesize orthorhombic γ‐CsPbI3 NCs using 3‐aminopropyl triethoxysilane molecules as capping ligands. The crystalline structure and morphology of these γ‐CsPbI3 NCs hardly change after exposure to ethanol even though they are capped with fewer ligands. Their high stability is also demonstrated by retaining their photoluminescence (PL) intensity after heating/cooling cycles in the range of 295–375 K, in contrast to a quick destruction of α‐CsPbI3 NCs under the same condition. More importantly, temperature‐dependent PL spectra reveal that the exciton/electron–phonon coupling and exciton recombination process of these γ‐CsPbI3 NCs strongly depend on their particle sizes. This finding may enable versatile design of stable γ‐CsPbI3 NCs with different sizes meeting diverse demands for various applications.

This study presents a method for detecting contamination events of sources of drinking water based on the Dempster-Shafer (D-S) evidence theory. The detection method has the purpose of protecting water supply systems against accidental and intentional contamination events. This purpose is achieved by first predicting future water-quality parameters using an autoregressive (AR) model. The AR model predicts future water-quality parameters using recent measurements of these parameters made with automated (on-line) water-quality sensors. Next, a probabilistic method assigns probabilities to the time series of residuals formed by comparing predicted water-quality parameters with threshold values. Finally, the D-S fusion method searches for anomalous probabilities of the residuals and uses the result of that search to determine whether the current water quality is normal (that is, free of pollution) or contaminated. The D-S fusion method is extended and improved in this paper by weighted averaging of water-contamination evidence and by the analysis of the persistence of anomalous probabilities of water-quality parameters. The extended D-S fusion method makes determinations that have a high probability of being correct concerning whether or not a source of drinking water has been contaminated. This paper's method for detecting water-contamination events was tested with water-quality time series from automated (on-line) water quality sensors. In addition, a small-scale, experimental, water-pipe network was tested to detect water-contamination events. The two tests demonstrated that the extended D-S fusion method achieves a low false alarm rate and high probabilities of detecting water contamination events.

We report the enhancement of green upconversion luminescence in tetrahedral LiYF:Yb/Er nanoparticles by Mn ion doping, which is different from the enhanced single-band red emission dominated by Mn ions in cubic NaLnF:Yb/Er (Ln = Y, Gd, Lu) nanoparticles. The energy levels of the first excited state T of Mn in tetrahedral LiYF:Gd and cubic NaGd(Y)F are compared by detection of emissions from Mnvia the energy transition from Gd to Mn with excitation at 275 nm. The coordination environments of Mn in these two host lattices have been investigated by X-ray absorption fine structure measurements. The results demonstrate that the formation of tetrahedral MnF in tetragonal LiYF arising from the replacement of Ln ions with Mn ions leads to a higher energy level of the MnT state than that in octahedral MnF in cubic NaYF. The high-lying excited state of tetrahedral MnF is close to the green emitting S state of Er and thus enhances green upconversion emission in tetragonal LiYF:Yb/Er, while the low-lying excited state of octahedral MnF dominates red emission in cubic NaYF:Yb/Er. These findings provide direct evidence for the key roles of the host lattices and more possibilities in modulating the upconversion behaviour of lanthanide-based nanoparticles by transition-metal ion doping to achieve the desired goals of specific applications.

Room temperature recrystallization is a simple and convenient method for synthesis of all-inorganic perovskite nanomaterials with excellent luminescent properties. However, the fast crystallization usually brings the colloidal stability and uncontrollable synthesis issues in the formation of all-inorganic perovskite. In the present study, we present a new strategy to prepare the quantum confined CsPbBr3 nanocrystals with controlled morphology under ambient condition. With the assist of fatty acid-capped precursor, the crystallization and the following growth rate can be retarded. Thanks to the retarded reaction, the morphology can be varied from nanowires to nanoplates and the thickness can be controlled from 5 to 7 monolayers by simply adjusting the amount of octylammonium cations and oleic acid. The nanoplates exhibit a higher photoluminescence quantum yield than the nanowires possibly due to fewer defects in the nanoplates.

Noninvasive light focusing and imaging through a scattering medium can be achieved by wavefront shaping using the photoacoustic signal as feedback. Unfortunately, the signal to noise ratio (SNR) of the traditional photoacoustic method is very low, which limits the wavefront shaping focusing speed and intensity. In this paper, we propose a completely new photoacoustic-signal-extraction method which combines wavelet denoising and correlation detection. With this method, the SNR of the photoacoustic signal reaches 25.2, 6.5 times higher than that of the unprocessed photoacoustic signal. Moreover, we achieve the simultaneous multipoint focusing, which is crucial for improving the speed of scanning imaging. The superior performance of the proposed method was experimentally demonstrated in extracting and denoising the photoacoustic signals deeply buried in noise, one critical step in in vivo photoacoustic imaging.