Biocompatible, Europium-Doped Fluorapatite Nanoparticles as a Wide-Range pH Sensor

The development of a simple, biocompatible, pH sensor with a wide range of detection, using a single fluorescent probe is highly important in the medical field for the early detection of diseases related to the pH change of tissues and body fluids. For this purpose, europium-doped fluorapatite (FAP: Eu) nanoparticles were synthesized using the coprecipitation method. Doping with the rare earth element europium (Eu) makes the non-luminescent phosphate mineral fluorapatite, luminescent. The luminous response of the sample upon dissolution in hydrochloric acid (HCl), in highly acidic to weakly basic media, makes it a potential pH sensor. A linear variation was observed with an increase in pH, in both the total intensity of emission and the R-value or the asymmetry ratio. The ratiometric pH sensing enabled by the variation in R-value makes the sensor independent of external factors. The structural, optical, and photoluminescent (PL) lifetime analysis suggests a particle size-dependent pH sensing mechanism with the changes in the coordinated water molecules around the Eu3+ ion in the nanoparticle. Given its exceptional biocompatibility and pH-dependent fluorescence intensity for a wide range of pH from 0.83 to 8.97, the probe can be used as a potential candidate for pH sensing of biological fluid.

Enhanced room temperature gas sensing properties of low temperature solution processed ZnO/CuO heterojunction

The development of room temperature gas sensors having response towards a specific gas is attracting researchers nowadays in the field. In the present work, room temperature (29 °C) ethanol sensor based on vertically aligned ZnO nanorods decorated with CuO nanoparticles was successfully fabricated by simple cost effective solution processing. The heterojunction sensor exhibits better sensor parameters compared to pristine ZnO. The response of the heterojunction sensor to 50 ppm ethanol is, at least, 2-fold higher than the response of the ZnO bare sensor. Also the response and recovery time of ZnO/CuO sensor to 50 ppm ethanol are of 9 and 420 s whereas the values are 16 and 510 s respectively for ZnO sensor. The vertical alignment of ZnO nanorods as well as its surface modification by CuO nanoparticles increased the effective surface area of the device and the formation of p-CuO/n-ZnO junction at the interface are the reasons for the improved performance at room temperature. In addition to ethanol, the fabricated device has the capability to detect the presence of reducing gases like hydrogen sulfide and ammonia at room temperature.

Rolling and unrolling of graphene sheets via in situ generation of superparamagnetic iron oxide nanoparticles

This manuscript reports a novel method for the automatic rolling and unrolling of reduced graphene oxide sheets using in situ generated superparamagnetic iron oxide nanoparticles. The graphene oxide synthesized through a low temperature modified hydrothermal method is subjected to hydrothermal reduction to obtain reduced graphene oxide (rGO). The as-prepared rGO was subjected to a second level of hydrothermal reduction in the presence of in situ generated superparamagnetic iron oxide nanoparticles, which led to the formation of graphene nanoscrolls decorated with superparamagnetic iron oxide nanoparticles. The nanoscrolls are unrolled to produce rGO sheets when the iron oxide nanoparticles are washed with hydrochloric acid. The repeatability of nanoscroll formation was examined by repeating the hydrothermal reaction for the in situ generation of superparamagnetic iron oxide nanoparticles in the presence of opened up rGO sheets. This reaction again made the rGO sheets scrolled. A blank reaction was also carried out without iron oxide particles to confirm the necessity of Fe3O4 in nanoscroll formation.

Enhanced optical, magnetic and hydrogen evolution reaction properties of Mo1−xNixS2 nanoflakes

Due to exceptional electronic, optoelectronic and catalytic properties, MoS₂ has attracted extensive research interest in various applications. In the present scenario, the exploitation of noble-metal-free catalysts for hydrogen evolution is of great interest. Herein, we report the structural, optical, magnetic and electrocatalytic properties of pure and nickel-substituted MoS₂ nanostructures synthesized by the hydrothermal method. X-ray diffraction (XRD) analysis reveals that all samples exhibit the hexagonal structure of MoS₂ and the formation of NiS₂ at higher concentrations of nickel. Vibrating sample magnetometer (VSM) measurements of the Mo_1−xNi_xS₂ nanostructures show a hysteresis loop at room temperature with a higher saturation magnetization for 1% Ni-substituted MoS₂ nanostructures, confirming the ferromagnetic behaviour of the sample. The indirect-to-direct band gap transition of few-layered nanostructures was confirmed by the optical absorption spectrum showing bands in the 600–700 nm and 350–450 nm regions. This study also highlights the excitation wavelength-dependent down- and up-conversion photoluminescence of the as-synthesized samples, providing new horizons for the design of MoS₂-based optical and spintronic devices. The electrocatalytic effect of 3% Ni-substituted MoS₂ nanostructures has been found to be higher than that of other deposit concentrations as it corresponds to the efficient hydrogen evolution reaction (HER).

Hydrothermal synthesis of Mo_1–xNi_xS₂ nanostructures as efficient catalyst for hydrogen evolution reaction.

Observation of Room Temperature Photoluminescence from Asymmetric CuGaO2/ZnO/ZnMgO Multiple Quantum Well Structures

Asymmetric (CuGaO2/ZnO/ZnMgO) and symmetric (ZnMgO/ZnO/ZnMgO) multiple quantum well (MQW) structures were successfully fabricated using pulsed laser deposition (PLD) and their comparison were made. Efficient room temperature photoluminescent (PL) emission was observed from these MQWs and temperature dependent luminescence of asymmetric and symmetric MQWs can be explained using the existing theories. A systematic blue shift was observed in both MQWs with decrease in the confinement layer thickness which could be attributed to the quantum confinement effects. The PL emission from asymmetric and symmetric MQW structures were blue shifted compared to 150 nm thick ZnO thin film grown by PLD due to quantum confinement effects.

Transparent p-n Heterojunction Thin Film Diodes

Transparent p-n heterojunction diodes are fabricated using p-type CuYO2:Ca and n-type ZnO:Al thin films on a glass substrate coated with indium-tin oxide (ITO). The contact between the n-ZnO:Al / p-CuYO2:Ca heterojunction is found to be rectifying, while the ITO / ZnO:Al contact is ohmic. The typical ratio of forward to reverse current is 15 in the range -3 to 3V. The diode current-voltage characteristics are dominated by the flow of space charge limited current, which is ascribed to the existence of an insulating ZnO interfacial layer. The diode structure has a total thickness of 0.85 μm and an optical transmission of 40%-50% in the visible region.

Polycrystalline coating of hydroxyapatite on TiAl6V4 implant material grown at lower substrate temperatures by hydrothermal annealing after pulsed laser deposition

Hydroxyapatite (HA) is a bioactive ceramic material that mimics the mineral composition of natural bone. This material does not possess acceptable mechanical properties for use as a bulk biomaterial; however, it does demonstrate significant potential for use as a coating on metallic orthopaedic and dental prostheses. Pulsed laser deposition (PLD) of thin films of HA on TiAl6V4 have shown crystalline coatings to be obtained at temperatures of the order of 350-500 degrees C. This condition of high substrate temperature promoted the oxidation of the substrate surface prior to the growth of the HA layer and the oxidation layer degraded the adhesion of the coating to the substrate. In this study, thin films of HA were deposited on TiAl6V4 alloy at a lower temperature of 200 degrees C by PLD and crystallized by a hydrothermal treatment at 100 degrees C. The film was subjected to mechanical as well as cell viability tests in vitro. The thickness, roughness, crystallanity, composition ratio, adhesive strength, and cell adhesion of the film suggest the application of this technique for producing bioactive implants.

The photoluminescence of SrS:Cu nanophosphor

Strontium sulfide doped with copper has been regarded as one of the most promising inorganic materials for the blue-green color phosphor. A wet chemical precipitation method with post-annealing is presented for the synthesis of copper-doped SrS nanoparticles. XRD studies revealed the phase purity of SrS particles with rocksalt structure. TEM images showed the formation of nanoparticles with an average size of 7 nm. Green photoluminescence emission (PL) at 535 nm was observed for an excitation wavelength of 356 nm, the intensity of which was greater than that of coarser phosphor particles synthesized by solid state reaction. Low temperature PL showed a redshift with decreasing temperature which is due to aggregated copper centers. Luminescent decay at room temperature was found to be faster than the reported values of the corresponding transition in thin film samples. A blueshift in the absorption edge was observed for the nanophosphor with respect to the bulk due to reduction in particle size.

Nuclear quadrupole resonance studies of transparent conducting oxides

We report (63,65)Cu spin-lattice relaxation rates measured by nuclear quadrupole resonance (NQR) in the delafossite compound CuYO(2) and CuYO(2):Ca over a temperature range from 200 to 450K. CuYO(2):Ca is a prototype transparent oxide exhibiting p-type electrical conductivity. Relaxation rates in CuYO(2):Ca are enhanced by one to two orders of magnitude relative to undoped material, exhibit much stronger temperature dependence, and contain contributions from magnetic and quadrupolar relaxation mechanisms with roughly equal strengths. Relaxation in undoped CuYO(2) is of purely quadrupolar origin and is attributed to interactions with lattice phonons. The main focus of this paper is the magnetic contribution to the relaxation rate in CuYO(2):Ca which is attributed to the hyperfine fields of carriers. It is argued that the dynamics of the hyperfine field are dominated by the hopping rate for carrier transfers between neighboring atoms in the copper planes of the delafossite structure. Comparison of the magnetic relaxation rates with the DC conductivity permits an estimate of the carrier concentration and mobility.