Decoding Upconversion-Emitting Phase in Complex Composites Through Single-Particle-Level Upconversion Imaging and Density Functional Theory Calculations.

The crystal structure and phase stability of a host lattice plays an important role in efficient upconversion phenomena. In stable hosts, lanthanides doping should not generally change the crystal structure of the host itself. But when phase of a system drastically changes after lanthanide doping resulting in multiple phases, accurate identification of upconverting phase remains a challenge. Herein, an attempt to synthesize lanthanide-doped NiMoO4 by microwave hydrothermal method produced MoO3/Yb2Mo4O15/NiMoO4 micro-nano composite upconversion phosphor. A combined approach of density functional theory (DFT) calculations and single-particle-level upconversion imaging has been employed to elucidate the phase stability of different phases and upconversion properties within the composite. Through single-particle-level imaging under 980 nm excitation, an unprecedented resolution in visualizing individual emitting and non-emitting regions within the composite has been achieved, thereby allowing to accurately assign the Yb2Mo4O15 as a sole upconversion emitting phase in the composite. Result of the DFT calculation further shows that the Yb2Mo4O15 phase is the most thermodynamically preferred over other lanthanide-doped phases in the composite. This comprehensive understanding not only advances the knowledge of upconversion emission from composite materials but also holds promise for tailoring optical properties of materials for various applications, including bioimaging, sensing, and photonics, where controlled light emission is crucial.

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations.

In most inorganic phosphors, increasing the concentration of activators inevitably causes the concentration quenching effect, resulting in reduced emission intensity at a high level of activator doping and the conventional practice is to limit the activator concentration to avoid the quenching. In contrast, SiAlON ceramics preserve their chemical composition over a very wide range of doping of activator ions, which favors the adjustment and optimization of the luminescence properties avoiding concentration quenching. Here, we investigate the photoluminescence properties of Ho-doped SiAlON (Ho-SiAlON) ceramics phosphors prepared by the hot-press method. Ho-SiAlON ceramics show strong green visible (554 nm) as well as infrared (2046 nm) broadband downshifting emissions under 348 nm excitation. It is shown that there is no concentration quenching, even at a very high level of Ho doping. The emission intensity of the 554 nm band increased two-fold when the Ho concentration is doubled. The results show that the Ho-SiAlON ceramics can be useful for efficient green phosphors.

Enhancement of Efficiency of a TiO2-BiFeO3 Dye-Synthesized Solar Cell through Magnetization.

Enhancement in the efficiency of a TiO2 dye-sensitized solar cell (DSSC) has been demonstrated by introducing ferromagnetic perovskite BiFeO3 and controlling the magnetic field, which induces two-dimensional material-like properties in the bulk of the TiO2-BiFeO3 DSSC (a 3-dimensional material). The effect of the concentration of BiFeO3 as well as the magnetization direction on the performance of the TiO2-BiFeO3 DSSC has been investigated. After magnetization, it was confirmed that the current density, efficiency, and open circuit voltage of the TiO2-BiFeO3 DSSC were increased. The observed phenomena have been explained in terms of the Hall effect which is responsible for the reduction of the degree of freedom of the electron movement resulting in the two-dimensional material-like properties in the bulk of the TiO2-BiFeO3 DSSC.

A sustainable composite of rice-paper/BaMoO4 nanoparticles for the photocatalytic elimination of the recalcitrant 2,6-dichlorobenzamide (BAM) pesticide in drinking water and its mechanisms of degradation.

This research reports the use of biodegradable and flexible composites for the removal of the 2,6-dichlorobenzamide (BAM) pesticide from drinking water. Rice paper (a biodegradable substrate) and Ag/BaMoO4 (MOBA) nanoparticles were employed to fabricate these composites. The SEM images showed that the MOBA nanoparticles with sizes of 300-800 nm decorated the surface of the biodegradable substrate and formed porous agglomerates, which have sizes of 1-3 µm. The MOBA powders were dispersed in drinking water polluted with BAM and were exposed to 4 h of UV-VIS irradiation, producing a maximum degradation of 82% for the BAM. Moreover, the flexible and biodegradable rice/MOBA composite produced a maximum removal percentage of 95% for the BAM. Also, we studied the effect of pH of the initial solution utilizing both powders and composites. From here, we found that a pH of 10 leads to a complete degradation of BAM after 4h, while a pH of 3 degraded only 37-47% of BAM for the same reaction time. According to the scavenger experiments, the •OH radical and the h+ were the main oxidizing agents for the BAM. Overall, the biodegradable photocatalytic composites are a reliable and a low-cost alternative to eliminate pesticides from the drinking water and can find application in water purification processes.

Current status on synthesis, properties and applications of CsPbX3(X = Cl, Br, I) perovskite quantum dots/nanocrystals.

The quantum confinement effect and interesting optical properties of cesium lead halide (CsPbX3; X = Cl, Br, I) perovskite quantum dots (QDs) and nanocrystals (NCs) have given a new horizon to lighting and photonic applications. Given the exponential rate at which scientific results on CsPbX3NCs are published in the last few years, it can be expected that the research in CsPbX3NCs will further receive increasing scientific interests in the near future and possibly lead to great commercial opportunities to realize these materials based practical applications. With the rapid progress in the single-photon emitting CsPbX3QDs and NCs, practical applications of the quantum technologies such as single-photon emitting light-emitting diode, quantum lasers, quantum computing might soon be possible. But to reach at cutting edge of stable perovskite QDs/NCs, the study of fundamental insight and theoretical aspects of crystal design is yet insufficient. Even more, it has aroused many unanswered questions related to the stability, optical and electronic properties of the CsPbX3QDs. Aim of the present review is to illustrate didactically a precise study of recent progress in the synthesis, properties and applications of CsPbX3QDs and NCs. Critical issues that currently restrict the applicability of these QDs will be identified and advanced methodologies currently in the developing queue, to overcome the roadblock, will be presented. And finally, the prospects for future directions will be provided.

Electronic structure, thermodynamic stability and high-temperature sensing properties of Er-α-SiAlON ceramics.

α-SiAlON ceramics have been in use as engineering ceramics in the most arduous industrial environments such as molten metal handling, cutting tools, gas turbine engines, extrusion molds, thermocouple sheaths, protective cover for high-temperature sensors, etc., owing to their outstanding mechanical, thermal and chemical stability. Taking advantage of the intrinsic properties of α-SiAlONs, we investigate, in this paper, the possibility of using the Er-doped α-SiAlON (Er-α-SiAlON) ceramic as a high-temperature sensing material via its unique near-infrared to visible upconversion property. We first use neutron diffraction and density functional theory calculations to study the electronic structure and thermodynamic stability of Er-α-SiAlON. It is found that the interstitial doping of Er stabilizes the α-SiAlON structure via chemical bonds with O-atoms with N:O ratio of 5:2 in the seven-fold coordination sites of the Er3+ ion. Temperature-dependent upconversion emissions are then studied under 980 and 793 nm excitations over a temperature range of 298-1373 K and the fluorescence intensity ratio (FIR) technique has been employed to investigate the temperature sensing behavior. Temperature-dependent Raman behavior is also investigated. We demonstrate that using Er-α-SiAlON as a sensing material, the limit of temperature measurement via the FIR technique can be pushed well beyond 1200 K.

Microwave hydrothermal synthesis and upconversion properties of BiVO4 nanoparticles.

Nanomaterials are the subject of extensive investigations due to their applications in medicine, multimodal imaging, volumetric displays, and photonics. Here, lanthanide-doped bismuth vanadate (BiVO4) upconverting nanoparticles (UCNPs) have been reported. The nanoparticles have been synthesized by a microwave hydrothermal method. As-synthesized nanoparticles are highly crystalline in the tetragonal zircon phase with particles about 200 nm in size. Under 980 nm excitation, intense multicolor visible and near-infrared upconversion emissions are observed. Moreover, broadband infrared downshifting emissions are also observed. Time-resolved emission measurements have been carried out to investigate the involved upconversion and energy transfer mechanism. The BiVO4-based UCNPs may provide a new class of nanomaterials for multifunctional applications.

Influence of SiC and TiC nanoparticles reinforcement on the microstructure, tribological, and scratch resistance behavior of electroless Ni-P coatings.

Two different ceramic carbide nanoparticles (SiC, and TiC) were separately incorporated into the Ni-P matrix via the electroless deposition method. As prepared Ni-P, Ni-P-SiC, and Ni-P-TiC coatings were subjected to heat treatment at 400 °C for 1 h. The surface morphology, microstructural transformation, Vicker's microhardness, tribological and scratch resistance properties were studied with reference to the different carbide reinforcements as well as heat treatment. Inter-nodular space, craters and kinks are created due to the branching effect of nodules in the surface of the Ni-P-SiC (TiC) composite coatings. After the heat treatment, the matrix phase transformation was not altered due to the incorporation of SiC or TiC into the Ni-P coating; however, a slight increase in residual stress was identified from the XRD analysis. In addition, the content of carbon deposition was found to be higher in the matrix of Ni-P-SiC composite coating than that in the Ni-P-TiC coating. The agglomeration of SiC particles was higher than TiC particles in the coating matrix, which was also supported by the result of Zeta potential measurement. Heat treatment improved wear and coefficient of friction in the Ni-P-SiC and Ni-P-TiC composite coatings. Compared to Ni-P-SiC coating, Ni-P-TiC coating revealed the enhanced tribological and scratch resistance performance after the heat treatment.

Upconversion luminescence properties of BaMoO4: Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) micro-octahedrons.

Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) doped BaMoO4 micro-octahedrons were synthesized by a hydrothermal process. The as-prepared phosphors were characterized by x-ray powder diffraction, field emission scanning electron microscopy, elemental mapping, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The upconversion luminescence properties of the samples were investigated under 980 nm near infrared excitation. The different concentrations of Er3+, Tm3+, and Ho3+ were used for tuning the multicolor (blue, green, and red) emissions. The multicolor emissions were investigated by Commission Internationale de l'Elcairage chromaticity and decay lifetime. The photon process as well as the energy transfer mechanism between the Yb3+ to Er3+, Tm3+, and Ho3+ were described.

Understanding the multifunctionality in Cu-doped BiVO4 semiconductor photocatalyst.

A visible light-induced, Cu-doped BiVO4 photocatalyst was synthesized by a microwave hydrothermal method. The photocatalytic efficiency was investigated in the degradation of model water pollutants like Methylene Blue (dye) and ibuprofen (pharmaceuticals), as well as the inactivation of Escherichia coli (bacteria). The Cu-doped BiVO4 samples showed better efficiency than undoped BiVO4, and the 1wt.% Cu-doped BiVO4 sample showed the best efficiency. The degradation of Methylene Blue reached 95%, while the degradation of ibuprofen reached 75%, and the inactivation of E. coli reached 85% in irradiation with visible light. The appearance of additional absorption band shoulders and widening of the optical absorption in the visible range makes the prepared powder an efficient visible light-driven photocatalyst. Moreover, the formation of an in-gap energy state just above the valance band as determined by density functional theory (DFT) first principle calculation, facilitates the wider optical absorption range of the doped system. Similarly, this in-gap energy state also acts as an electron trap, which is favorable for the efficient separation and photoexcited charge carriers' transfer process. The formation of oxygen vacancies due to doping also improved the separation of the charge carrier, which promoted the trapping of electrons and inhibited electron hole recombination, thus increasing the photocatalytic activity. No decrease in the efficiency of the 1wt.% Cu-doped BiVO4 photocatalyst in the degradation of ibuprofen over three consecutive cycles revealed the stability of the photocatalyst towards photocorrosion. These findings highlight the multifunctional applications of Cu-doped BiVO4 in wastewater containing multiple pollutants.

Microwave hydrothermal synthesis and upconversion properties of Yb3+/Er3+ doped YVO4 nanoparticles.

Yb3+ and Er3+ doped YVO4 (Yb3+/Er3+:YVO4) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb3+/Er3+:YVO4 nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to 2H11/2, 4S3/2 to 4I15/2 and 4F9/2 to 4I15/2 transitions of Er3+ respectively. The emission intensity is found to depend strongly on the concentration of Yb3+. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.