Raman piezospectroscopic evaluation of intergrowth ferroelectric polycrystalline ceramic in biaxial bending configuration

The piezospectroscopic (PS) effect was studied in an intergrowth bismuth layer-structure ferroelectricceramicBi₅TiNbWO₁₅ according to a micro-Raman spectroscopic evaluation. By using a ball-on-ring flexure configuration, a biaxial stress was generated in a Bi₅TiNbWO₁₅ plate-like specimen and in situ collected Raman spectra were acquired and analyzed under several loading conditions. As the observed spectral line contained signals arising from the whole illuminated in-depth region, the laser probe information was deconvoluted (by means of an in-depth probe response function obtained according to the defocusing method) in order to deduce biaxial PS coefficients for the three Raman bands of Bi₅TiNbWO₁₅ located at 763, 857, and 886 cm−1, respectively. The biaxial PS coefficients of these bands were derived to be −1.74±0.16, −2.51±0.16, and −2.64±0.31 cm⁻¹/GPa, respectively, and should be referred to the c axis of the Bi5TiNbWO15 crystal

Spectrally resolved microprobe cathodoluminescence of intergrowth Bi₅ˍₓLaₓTiNbWO₁₅ ferroelectrics

Spectrally resolved cathodoluminescence measurements of Bi₅ˍₓLaₓTiNbWO₁₅(x=0–1.50) ceramics at room temperature showed three distinct luminescence bands located at about 380, 502, and 660nm, respectively, which were tentatively assigned to F+ center, oxygen vacancy-related defect and octahedron structure-related luminescence center, respectively. These assignments could be made in light of electron irradiation experiments with different exposure times. Bands related to oxygen vacancies were clearly enhanced by lanthanum doping, indicating that charge compensation occurred by the substitution of Bi for La3+ in perovskitelike structured intergrowth ferroelectrics. We observed that, for contents of La³⁺ x>0.75, La³⁺ ions entered the [Bi₂O₂]²⁺ layer according to a doping mechanism which is briefly discussed in this letter.This work was supported by the Ministry of Sciences and Technology of China through 973-project 2002CB613307 and National Natural Science Foundation of China NSFC No. 50572113

Physisorption-based charge transfer in two-dimensional SnS2 for selective and reversible NO2 gas sensing

Nitrogen dioxide (NO2) is a gas species that plays an important role in certain industrial, farming, and healthcare sectors. However, there are still significant challenges for NO2 sensing at low detection limits, especially in the presence of other interfering gases. The NO2 selectivity of current gas-sensing technologies is significantly traded-off with their sensitivity and reversibility as well as fabrication and operating costs. In this work, we present an important progress for selective and reversible NO2 sensing by demonstrating an economical sensing platform based on the charge transfer between physisorbed NO2 gas molecules and two-dimensional (2D) tin disulfide (SnS2) flakes at low operating temperatures. The device shows high sensitivity and superior selectivity to NO2 at operating temperatures of less than 160 °C, which are well below those of chemisorptive and ion conductive NO2 sensors with much poorer selectivity. At the same time, excellent reversibility of the sensor is demonstrated, which has rarely been observed in other 2D material counterparts. Such impressive features originate from the planar morphology of 2D SnS2 as well as unique physical affinity and favorable electronic band positions of this material that facilitate the NO2 physisorption and charge transfer at parts per billion levels. The 2D SnS2-based sensor provides a real solution for low-cost and selective NO2 gas sensing

Poly(vinyl alcohol)-Modified Colloidal Silicon Nanoparticles for Flexible Screen Printing Inks and Anticounterfeiting Applications

Homogeneous colloidal silicon nanoparticles (Si NPs) were synthesized at ambient temperatures. With the incorporation of poly(vinyl alcohol) (PVA), the absolute photoluminescence quantum yield (APLQY) and photochromic stability of the fluorescent colloid (p-Si NPs) were significantly enhanced compared to Si NPs. In the absence of additional high-temperature treatments or doped fluorophores, colloid p-Si NPs exhibit blue-green luminescence under ultraviolet excitation. Subsequently, the highly dispersed p-Si NPs solution underwent heat treatment, resulting in a suitable viscosity for direct screen printing. The printed pattern appears transparent under natural light and blue-green under ultraviolet light, showing good invisibility. These patterns possess notable characteristics, including high adhesion, uniformity, stain resistance, and excellent stability. Consequently, they can be efficiently developed for anticounterfeiting labels and printing inks. Notably, the ink also has the characteristics of low toxicity and substantial biocompatibility, offering promising avenues for the synthesis and application of environmentally friendly benign nano anticounterfeiting ink