Variation Of Luminescence Properties Research Articles

Phase engineering of seamless heterophase homojunctions with co-existing 3R and 2H phases in WS2 monolayers.

Self-organized semiconductor-semiconductor heterostructures (3R-2H) that coexist in atomically thin 2D monolayers forming homojunctions are of great importance for next-generation nanoelectronics and optoelectronics applications. Herein, we investigated the defect controlled growth of heterogeneous electronic structure within a single domain of monolayer WS2 to enable in-plane homojunctions consisting of alternate 2H semiconducting and 3R semiconducting phases of WS2. X-ray photoelectron, Raman, and photoluminescence spectroscopy along with fluorescence and Kelvin probe force microscopy imaging confirm the formation of homojunctions, enabling a direct correlation between chemical heterogeneity and electronic heterostructure in the atomically thin WS2 monolayer. Quantitative analysis of phase fractions shows 59% stable 2H phase and 41% metastable 3R phase estimated over WS2 flakes of different sizes. Time-resolved fluorescence lifetime imaging confirms distinct contrast between 2H and 3R phases with two distinct lifetimes of 3.2 ns and 1.1 ns, respectively. Kelvin probe force microscopy imaging revealed an abrupt change in the contact potential difference with a depletion width of ∼2.5 μm, capturing a difference in work function of ∼40 meV across the homojunction. Further, the thermal stability of coexisting phases and their temperature dependent optical behavior show a distinct difference among 2H and 3R phases. The investigated aspects of the controlled in plane growth of coexisting phases with seamless homojunctions, their properties, and their thermal stability will enable the development of nanoscale devices that are free from issues of lattice mismatch and grain boundaries.

Variations in luminescence properties of quartz and feldspar from modern fluvial sediments in three rivers

Abstract Studies of modern sediments, their sedimentology and depositional processes are important for understanding the behaviour of the luminescence characteristics of quartz and feldspar in fluvial settings. Previous studies have shown large variations in OSL characteristics of quartz from different fluvial systems, while the IRSL and pIRIR signals from K-feldspar have been understudied. We test the effects of fluvial setting on luminescence characteristics by collecting modern (

Influence of Anion/Cation Substitution (Sr2+ → Ba2+, Al3+ → Si4+, N3– → O2–) on Phase Transformation and Luminescence Properties of Ba3Si6O15:Eu2+ Phosphors

A series of promising cyan, green, and yellow emission (Ba, Sr)3(Si, Al)6(O, N)15:Eu2+ phosphors were synthesized by a Pechini-type sol–gel ammonolysis method. Variations in luminescence properties and crystal structure caused by the modification of phosphor composition were studied in detail. The prefired temperatures of the precursors play a key role in the process of forming the final products. Under UV light excitation, the as-prepared Ba3Si6O15:Eu2+ phosphor presents a strong cyan emission located at 498 nm. Moreover, the as-prepared oxynitride phosphors, Eu2+-activated (Ba1–ySry)3Si6–xAlxO15−μNδ (x = 0–1.2, y = 0–0.6), display a broader excitation band covering the entire visible region. Under blue light excitation, Ba3Si6–xAlxO15−μNδ:Eu2+ phosphors show a intense and narrow green emission at 520 nm, and the luminescent intensity can be enhanced by increasing Al content within a certain range. However, (Ba1–ySry)3Si6O15−μNδ:Eu2+phosphors exhibit green (520 nm) to yellow (554 nm) emission with increa...

Luminescence Quantum Efficiency of Nanocrystalline ZnS:Mn2+. 1. Surface Passivation and Mn2+ Concentration

The luminescence quantum efficiency of nanocrystalline ZnS:Mn2+ is studied to provide a better understanding on how the quantum efficiency is influenced by the Mn2+ concentration, the nature of the passivating polymer, and the synthesis conditions. The results show an increase of the luminescence quantum efficiency with the Mn2+ concentration in the nanocrystals for very low Mn2+ concentrations. Between 0.3 and 1.5 at. % Mn2+ the increase in quantum efficiency levels off, to reach an almost constant level between 1.5 and 5.6 at. % Mn2+. Up to a concentration of 5.6 at. %, no concentration quenching is observed. The influence of the nature of the passivating polymer is investigated by comparing the luminescence quantum efficiencies for nanoparticles coated with poly(vinylbutyral) (PVB), poly(vinyl alcohol) (PVA), methacrylic acid (MA), or sodium polyphosphate (PP) or without a passivating polymer. For the presently used synthesis method (in water), the highest quantum efficiencies (around 4%) are obtained for nanocrystalline ZnS:Mn2+ capped with PP. Nanoparticles synthesized in a nitrogen atmosphere have higher quantum yields than nanoparticles made in ambient air. In general, large variations in luminescence properties are observed due to unintentional variations in the synthesis conditions. For research on the luminescence properties and quantum efficiencies of nanocrystalline ZnS:Mn2+, it is very important to check the reproducibility of results, to standardize synthesis conditions, and to measure absolute quantum efficiencies rather than relative changes in luminescence intensity.

Variations in luminescence properties of single quartz grains and their consequences for equivalent dose estimation

In this paper examples of variability of luminescence properties between single grains of quartz extracted from natural samples or from crushed single crystals are shown. It is demonstrated how measurements of glow curves, PSL (photon stimulated luminescence) decay curves, thermal activation characteristics using multi-grain aliquots can lead to a misinterpretation of the obtained data. The possible consequences for different D E estimation techniques applied to multi-grain aliquots or to single grains and normalisation techniques applied to multi-grain aliquots are discussed. In particular pre-dose, multi-aliquot additive, and single grain PSL SAR D E estimation methods are considered.

Variation of luminescence properties of the reaction solution during preparation of a component of Ziegler-Natta catalyst by the reaction of Tb with Ph3CCl

Photoluminescence is used to test lanthanide-C bonds and to identify unstable intermediates in the synthesis of Ph3CTbCl2, a component of Ziegler-Natta catalyst.