The Dynamics of Luminescence

Domestic light providing devices have always been an important component of life and continue to provide us light beyond sunset. These devices continue to be improved frequently to allow ease of use and to enhance their efficiency. The tungsten electric light bulbs are widely used, which are based on incandescence of a continuously heated tungsten element. However, their use will soon be short lived because of the increased usage of fluorescent tubes and light-emitting diode (LED) devices, which are based on luminescence emission. These emission materials that display luminescence are called phosphors, and their emission is based on electron transitions. In the following chapter, we shall look into photoluminescence from both intrinsic and extrinsic defects, covering both down- and upconversion (UP). We will look into the concept of energy transfer and persistent luminescence and lastly provide related applications of luminescence in the modern days

Unveiling Semiconductor Nanostructured Based Holmium-Doped ZnO: Structural, Luminescent and Room Temperature Ferromagnetic Properties

This research work describes the synthesis of ZnO nanostructures doped with Ho3+ ions using a conventional sol–gel synthesis method. The nanostructured produced exhibited a wurtzite hexagonal structure in both ZnO and ZnO:Ho3+ (0.25, 0.5, 0.75 mol%) samples. The change in morphology with addition of Ho3+ dopants was observed, which was assigned to Ostwald ripening effect occurring during the nanoparticles’ growth. The photoluminescence emission properties of the doped samples revealed that Ho3+ was emitting through its electronic transitions. Moreover, reduced surface defects were observed in the Holmium doped samples whose analysis was undertaken using an X-ray Photoelectron Spectroscopy (XPS) technique. Finally, enhanced room temperature ferromagnetism (RT-FM) for Ho3+-doped ZnO (0.5 mol%) samples with a peak-to-peak line width of 452 G was detected and found to be highly correlated to the UV–VIS transmittance results

Modulating Charge Mobility in Microwave Synthesized Ti-doped ZnS Nanoparticles for Potential Photoanode Applications

Doping ZnS nanoparticles with different metal and/or non-metal ions is one of the ways to improve their properties. That is because dopants introduce strain into the lattice of the ZnS nanoparticles. The influence of Ti on the ZnS nanoparticles was investigated on the structural properties, optical properties, and also electrical impedance spectroscopy (EIS). The presence of Ti in the crystal lattice of the ZnS introduced strain into the crystal structure, hence causing a lattice expansion and reducing the crystallite sizes of the ZnS nanoparticles. Ti doping was observed to increase the energy band gap of ZnS nanoparticles and also reduce the charge carrier recombination. Doping Ti into ZnS was observed to decrease the charge transfer resistance of ZnS nanoparticles with an increase in dopant concentration indicating an improved charge transfer mobility owing to the presence of strain in the crystal lattice

Advantage of Dimethyl Sulfoxide in the Fabrication of Binder-Free Layered Double Hydroxides Electrodes: Impacts of Physical Parameters on the Crystalline Domain and Electrochemical Performance

The electrode fabrication stage is a crucial step in the design of supercapacitors. The latter involves the binder generally for adhesive purposes. The binder is electrochemically dormant and has weak interactions, leading to isolating the active material and conductive additive and then compromising the electrochemical performance. Designing binder-free electrodes is a practical way to improve the electrochemical performance of supercapacitors. However, most of the methods developed for the fabrication of binder-free LDH electrodes do not accommodate LDH materials prepared via the co-precipitation or ions exchange routes. Herein, we developed a novel method to fabricate binder-free LDH electrodes which accommodates LDH materials from other synthesis routes. The induced impacts of various physical parameters such as the temperature and time applied during the fabrication process on the crystalline domain and electrochemical performances of all the binder-free LDH electrodes were studied. The electrochemical analysis showed that the electrode prepared at 200 °C-1 h exhibited the best electrochemical performance compared to its counterparts. A specific capacitance of 3050.95 Fg−1 at 10 mVs−1 was achieved by it, while its Rct value was 0.68 Ω. Moreover, it retained 97% of capacitance after 5000 cycles at 120 mVs−1. The XRD and FTIR studies demonstrated that its excellent electrochemical performance was due to its crystalline domain which had held an important amount of water than other electrodes. The as-developed method proved to be reliable and advantageous due to its simplicity and cost-effectiveness

Investigating the Impact of the Washing Steps of Layered Double Hydroxides (LDH) on the Electrochemical Performance

The washing of layered double hydroxides (LDH) material is mostly purposed to discard the unreacted products after the reaction has been completed. However, this study demonstrated that the washing stage can also be targeted to optimise the electrochemical performance of LDH by using an appropriate solvent. Solvents, namely, ethanol, acetone, and an ethanol–acetone solution (2:1) were used for the washing of LDH and the impacts thereof on the structural, physical, chemical, morphological, and electrochemical properties were investigated. Using Williamson–Hall analysis, we observed modifications on the crystalline domain. The specific surface area and pore parameters for all the samples were also differently affected. The Fourier transform infrared (FTIR) measurements displayed evident changes in the basic sites. The electrochemical performances of samples were analysed. The sample washed with the ethanol–acetone solution exhibited a specific capacitance of 1807.26 Fg−1 at 10 mVs−1, which is higher than that of other samples as well as low internal resistance compared to its counterpart. This demonstrates that the use of an appropriate solvent during the washing stage of LDH affects the electrochemical properties

Synthesis, Characterization, and Supercapacitor Performance of a Mixed-Phase Mn-Doped MoS₂ Nanoflower

The fascinating features of 2D nanomaterials for various applications have prompted increasing research into single and few-layer metal dichalcogenides nanosheets using improved nanofabrication and characterization techniques. MoS2 has recently been intensively examined among layered metal dichalcogenides and other diverse transition metal-based materials, that have previously been studied in various applications. In this research, we report mixed-phase Mn-doped MoS2 nanoflowers for supercapacitor performance studies. The confirmation of the successfully prepared Mn-doped MoS2 nanoflowers was characterized by XRD, SEM-EDS, RAMAN, and BET research techniques. The mixed-phase of the as-synthesized electrode material was confirmed by the structural changes observed in the XRD and RAMAN studies. The surface area from the BET measurement was calculated to be 46.0628 m2/g, and the adsorption average pore size of the electrode material was 11.26607 nm. The electrochemical performance of the Mn-doped MoS2 electrode material showed a pseudo-capacitive behavior, with a specific capacitance of 70.37 Fg−1, and with a corresponding energy density of 3.14 Whkg−1 and a power density of 4346.35 Wkg−1. The performance of this metal-doped MoS2-based supercapacitor device can be attributed to its mixed phase, which requires further optimization in future works

Eco-friendly synthesized few layered graphene: main physico-chemical nanocharacterizations for optical quenching applications

The importance of green process in the synthesis of nanomaterials becomes universally known. In this study, we report on the efficiency of Aspalathus linearis's plant extract known as Rooibos tea on the synthesis of graphene via a bio-active process. Using several nanocharcterization techniques, our investigations on the main physico-chemical properties confirmed the ability of this plant extract as a reducing and capping agent on performing an effective reducing process leading to a wide and flat FLrGO sheets without folds along their length and of a mean size of 265 nm. Furthermore, this eco-friendly cost-effective process allows the control and modulation of the optical and the electrical properties of the prepared graphene. Moreover, this material was positively tested as silver NPs fluorescence quencher. Hence, Rooibos shows its ability as an effective chelating agent in the production of graphene sheets which serves electronic and optoelectronic related quenching applications