NIR-to-NIR and NIR-to-Vis up-conversion of SrF2:Ho3+ nanoparticles under 1156 nm excitation

Recently, the up-converting (UC) materials, containing lanthanide (Ln3+) ions have attracted considerable attention because of the multitude of their potential applications. The most frequently investigated are UC systems based on the absorption of near-infrared (NIR) radiation by Yb3+ ions at around 975-980 nm and emission of co-dopants, usually Ho3+, Er3+ or Tm3+ ions. UC can be observed also upon excitation with irradiation with a wavelength different than 975-980 nm. The most often studied systems capable of UC without the use of Yb3+ ion are those based on the properties of Er3+ ions, which show luminescence resulting from the excitation at 808 or 1532 nm. However, also other Ln3+ ions are worth attention. Herein, we focus on the investigation of the UC phenomenon in the materials doped with Ho3+ ions, which reveal unique optical properties upon the NIR irradiation. The SrF2 NPs doped with Ho3+ ions in concentrations from 4.9% to 22.5%, were synthesized by using the hydrothermal method. The structural and optical characteristics of the obtained SrF2:Ho3+ NPs are presented. The prepared samples had crystalline structure, were built of NPs of round shapes and their sizes ranged from 16.4 to 82.3 nm. The NPs formed stable colloids in water. Under 1156 nm excitation, SrF2:Ho3+ NPs showed intense UC emission, wherein the brightest luminescence was recorded for the SrF2:10.0%Ho3+ compound. The analysis of the measured lifetime profiles and dependencies of the integral luminescence intensities on the laser energy allowed proposing the mechanism, responsible for the observed UC emission. It is worth mentioning that the described SrF2:Ho3+ samples are one of the first materials for which the UC luminescence induced by 1156 nm excitation was obtained.

One-pot synthesis of rGO functionalized TEA / NiSe embedded nanocomposites for supercapacitor application

NiSe and NG-NiSe as electrode materials for supercapacitor application were prepared by hydrothermal technique. The XRD confirms the product formation by showing a hexagonal crystalline structure for pure NiSe and...

Morphology of metallic foams synthetized by plasma electrolysis deposition

The aim of our work is to understand the mechanism governing the growth of metallic foams synthetized by plasma electrolysis deposition. This paper reports the influence of the applied voltage on the morphology and microstructure of copper and gold foams. The evolution of strands morphology and size is investigated by field emission scanning electronic microscopy (FE-SEM). The role of the voltage in the growth of metallic foams is then discussed. Finally, the crystalline structure of the strands is determined by transmission electronic microscopy (TEM) and selected area electron diffraction.

Nanomaterial gas sensors for biosensing applications: A Review

Background: Nanomaterial is one of the most used materials for various gas sensing application to detect toxic gases, human breath, and other specific gas sensing. One of the most important applications of nanomaterial based gas sensors is as biosensing applications. In this review article, the gas sensors for biosensing are discussed by classifying gas sensors on the basis of crystalline structure and different categories of nanomaterial. Methods: In this paper, firstly rigorous efforts has been made to find out research questions by going through structured and systematic survey of available peer reviewed high quality articles in this field. The papers related to nanomaterial based biosensors are then reviewed qualitatively to provide substantive findings from the recent developments in this field. Results: In this review article, firstly classifications of nanomaterial gas sensors have been presented on the basis of crystalline structure of nanomaterial and different types of nanomaterial available for biosensing applications. Further, the gas sensors based on nanomaterial for biosensing applications are collected and reviewed in terms of their performance parameters such as sensing material used, target gas component, detection ranges (ppm-ppb), response time, operating temperature and method of detection etc. The different nanomaterials possess slightly different sensing and morphological properties due to their structure, therefore, it can be said that a nanomaterial must be selected carefully for particular application. The 1D nanomaterials show best selectivity and sensitivity for gases available in low concentration ranges due to their miniaturised structure as compared to 2D and 3D nanomaterials. However, these 2D and 3D nanomaterials also so good sensing properties compared to bulk semiconductor materials. The polymer and nanocomposites have opened door for future research and have great potential for new generation gas sensor for detecting biomolecules. Conclusion: These nanomaterials extend great properties towards sensing application of different gases for lower concentration of particular gas particles. Nano polymer and nano composites have great potential to be used gas sensor for detection of biomolecules.

A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode

A p-type Cu3Ta7O19 semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu3Ta7O19 + x/2 O2 → Cu(3−x)Ta7O19 + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm−2 up to >0.5 mA cm−2, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm−2) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.