Intense Hydrochromic Photon Upconversion from Lead-Free 0D Metal Halides For Water Detection and Information Encryption.

Hydrochromic materials that change their luminescence color upon exposure to moisture have attracted considerable attention owing to their applications in sensing and information encryption. However, the existing materials lack high hydrochromic response and color tunability. This study reports the development of a new and bright 0D Cs3 GdCl6 metal halide as the host for hydrochromic photon upconversion in the form of polycrystals (PCs) and nanocrystals. Lanthanides co-doped cesium gadolinium chloride metal halides exhibit upconversion luminescence (UCL) in the visible-infrared region upon 980 nm laser excitation. In particular, PCs co-doped with Yb3+ and Er3+ exhibit hydrochromic UCL color change from green to red. These hydrochromic properties are quantitatively confirmed through the sensitive detection of water in tetrahydrofuran solvent via UCL color changes. This water-sensing probe exhibits excellent repeatability and is particularly suitable for real-time and long-term water monitoring. Furthermore, the hydrochromic UCL property is exploited for stimuli-responsive information encryption via cyphertexts. These findings will pave the way for the development of new hydrochromic upconverting materials for emerging applications, such as noncontact sensors, anti-counterfeiting, and information encryption.

Octahedral distortion driven by CsPbI3 nanocrystal reaction temperature - the effects on phase stability and beyond.

Cesium lead iodide (CsPbI3) perovskite nanocrystals (NCs) suffer from a known transformation at room temperature from their red-emitting (black) to non-emitting (yellow) phase, induced by the tilting of PbI6 octahedra. While the reported attempts to stabilize CsPbI3 NCs mainly involve Pb2+-site doping as well as compositional and/or NC surface engineering, the black phase stability in relation only to the variation of the reaction temperature of CsPbI3 NCs is surprisingly overlooked. We report a holistic study of the phase stability of CsPbI3 NCs, encompassing dispersions, films, and even devices by tuning the hot-injection temperature between 120-170 °C. Our findings suggest that the transition from the black to the yellow phase occurs after over a month for NCs synthesized at 150 °C (150@NCs). Structural refinement studies attribute the enhanced stability of 150@NCs to their observed lowest octahedral distortion. The 150@NCs also lead to stable unencapsulated solar cells with unchanged performance upon 26 days of shelf storage in dry air. Our study underlines the importance of scrutinizing synthesis parameters for designing stable perovskite NCs towards long-lasting optoelectronic devices.

Mechanochemistry as a Green Route: Synthesis, Thermal Stability, and Postsynthetic Reversible Phase Transformation of Highly-Luminescent Cesium Copper Halides.

Cesium copper halides (CCHs) show promise for optoelectronic applications, and their syntheses usually involve high-temperatures and hazard solvents. Herein, the synthesis of highly luminescent and phase-pure Cs3Cu2X5 (X = Cl, Br, and I) and CsCu2I3 via a solvent-free mechanochemical approach through manual grinding is demonstrated. This cost-effective approach can produce CCHs on a scale of tens to hundreds of grams. Rietveld refinement analysis of the X-ray diffraction patterns of the as-synthesized CCHs reveals their structural details. Notably, the emission characteristics of green-emitting, chloride-based CCHs remain stable even at elevated temperatures-maintaining 80% of initial PL efficiency at 150 °C. Lastly, a postsynthetic reversible transformation between zero- and one-dimensional CCH materials is demonstrated, indicating the labile nature of their crystal structure. The proposed study suggests that mechanochemistry can be an alternative and promising synthetic tool for fabricating high-quality lead-free metal halides.

Robust, Brighter Red Emission from CsPbI3 Perovskite Nanocrystals via Endotaxial Protection.

Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI3-Cs4PbI6 hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI3 NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI3 NCs in Cs4PbI6 matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI3 NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stability-maintaining 65% of their original PL efficiency at 150 °C-and improved aqueous stability.

Correction: Highly stable hetero-structured green-emitting cesium lead bromide nanocrystals via ligand-mediated phase control.

Correction for 'Highly stable hetero-structured green-emitting cesium lead bromide nanocrystals via ligand-mediated phase control' by G. Krishnamurthy Grandhi et al., Nanoscale, 2019, 11, 21137-21146.

Highly stable hetero-structured green-emitting cesium lead bromide nanocrystals via ligand-mediated phase control.

Green-emissive Cs4PbBr6 shows promise for light-emitting diode devices superior to that of CsPbBr3 NCs owing to their stability and high photoluminescence efficiency. Nevertheless, there is still no consensus regarding the basis of their green emission, which decelerates their advance in light-emitting applications. Herein, a systematic investigation on the concentration of capping ligands (oleylamine and oleic acid), which determines the predominant phase between CsPbBr3 and Cs4PbBr6 for a given Cs to Pb feed ratio, is conducted. This study deduces that oleylamine to oleic acid ratio plays a crucial role in obtaining either green-emissive or non-emissive Cs4PbBr6 NCs. Scrutiny of Cs4PbBr6 microscopic and optical data in addition to their emission quenching study with a hole-withdrawing molecule reveals that the green emission originates from the CsPbBr3 impurity phase. Furthermore, stable green emission is observed for CsPbBr3/Cs4PbBr6 nanocrystals when CsPbBr3 particles are well protected by the Cs4PbBr6 matrix. These CsPbBr3/Cs4PbBr6 films remained highly luminescent even after UV exposure for hours or annealing at ∼150 °C for days in addition to their long-term stability under an ambient atmosphere, which are the desirable properties for various practical applications.

Transient speech compromise following sublabial transsphenoidal surgery: a case report and findings of a small preliminary study.

Sublabial transsphenoidal surgical removal of pituitary tumors is a common procedure with minimal complications. Although many investigators have reported oral sensory compromises following surgery, none has reported any postoperative compromise in speaking ability. In this article, we describe the case of a 33-year-old woman who developed transient but severe speech symptoms after she underwent sublabial transsphenoidal surgery. This case prompted us to undertake a brief retrospective analysis of our experience with this procedure in other patients, which revealed that speech compromise is far more common than heretofore realized.

Part-word repetitions by persons who stutter: fragment types and their articulatory processes.

One of the core features of developmental stuttering is part-word repetition followed by fluent production (resolution) of the target word. The purpose of the study is to compare the spectro-temporal dimensions of fragments with the spectro-temporal dimensions of the resolution to define fragment types and develop articulatory interpretation of termination-restart cycles. From the acoustic recordings of six adult males who stutter, 142 stuttering events on words beginning with stops were isolated, excerpted, and digitized. The stuttering events occurred during either spontaneous speech or reading. The consecutive articulatory phases of fragments were classified and compared with the corresponding phases in resolutions. We found that (a) there are two basic types of fragments--those with vowels and those without, (b) the type of fragment produced is strongly influenced by the voicing status of the stop, (c) the fragments without vowels tend to have longer stop closure duration than the stops in the resolutions, (d) there are two subtypes in fragments with vowels--those with vowels shorter than and those with vowels longer than the vowels in the resolutions, (e) the shorter vowels differ spectro-temporally from the vowels in resolutions, and (f) the longer vowels differ temporally from the vowels in the resolutions. We discuss the articulatory implications of the acoustic data for each fragment type in the context of speech as an act designed to achieve contextually conditioned acoustic goals.

Stuttering induced by theophylline.

We retrospectively evaluated three fluent asthmatic children who developed speech dysfluency following administration of theophylline. The dysfluency ceased in all three, following discontinuation of the medication. The medication was re-instituted in two patients, prompting return of dysfluency. It is unknown whether the patients had characteristics of "acquired stuttering" or "developmental stuttering." We urge appropriate testing should this complication again occur. This might then provide pharmacologic information regarding stuttering.

Neurologic aspects of spasmodic dysphonia.

We discuss the etiology of 100 spasmodic dysphonia patients. Seventy-one patients had underlying essential tremor, 25 had Meige's syndrome, 12 were hypothyroid, and 27 had either a functional disturbance or focal dystonia. Six patients had intermittent breathy dysphonia. A large corpus of spasmodic dysphonia patients have organic neurolaryngeal disease.