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In this work we compare luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with 10 and 30 QWs. The aim is to increase the intensity of faster blue QW emission and decrease the luminescence of the QW defect band, showing a slower luminescence decay time, which is undesired for fast scintillator applications. We demonstrate that increasing the number of InGaN QWs is an efficient method to reach this goal. The luminescence improvement of the sample with higher number of QWs is explained by the influence of the increased size of V‐pits with increased QW number. Thinner QWs on the side wall of V‐pits serve as barriers which separate carriers from dislocations penetrating through the V‐pit centre, supressing thus the non‐radiative and radiative recombination on defects. Based on cathodoluminescence (CL) results, the scintillator structure design is discussed. Scintillator structures with higher number of QWs can take advantage of both, improved luminescence efficiency and thicker active region. [ABSTRACT FROM AUTHOR]

Abstract: Single- and double-layer InAs/GaAs quantum dot structures with strain-reducing layers (SRLs) were prepared by metalorganic vapor-phase epitaxy using the Stranski–Krastanow growth mode. Structures were studied in-situ by reflectance anisotropy spectroscopy (RAS), and ex-situ by photoluminescence (PL). These structures, with very intense room temperature PL at wavelengths from 1.25 to 1.55μm according to growth and structure parameters, were grown along while monitored with RAS. Strong correlation between RAS signal and PL intensity was found. Dependence of PL emission maximum position on SRL composition and capping layer thickness is shown. [Copyright &y& Elsevier]

Fast emitting polymeric scintillators are requested in advanced applications where high speed detectors with a large signal-to-noise ratio are needed. However, their low density implies a weak stopping power of high energy radiation and thus a limited light output and sensitivity. To enhance their performance, polymeric scintillators can be loaded with dense nanoparticles (NPs). We investigate the properties of a series of polymeric scintillators by means of photoluminescence and scintillation spectroscopy, comparing standard scintillators with a composite system loaded with dense hafnium dioxide (HfO 2 ) NPs. The nanocomposite shows a scintillation yield enhancement of +100% with an unchanged time response. We provide for the first time an interpretation of this effect, pointing out the local effect of NPs in the generation of emissive states upon interaction with ionizing radiation. The obtained results indicate that coupling fast conjugated emitters with optically inert dense NPs could lead to surpassing the actual limits of pure polymeric scintillators.

The surface properties of biomolecular gradients are widely known to be important for controlling cell dynamics, but there is a lack of platforms for studying them in vitro using inorganic materials. The changes in various surface properties of an Al x Ga 1- x N film (0.173 ≤ x ≤ 0.220) with gradient aluminum content were quantified to demonstrate the ability to modify interfacial characteristics. Four wet chemical treatments were used to modify the surface of the film: (i) oxide passivation by hydrogen peroxide, (ii) two-step functionalization with a carboxylic acid following hydrogen peroxide pretreatment, (iii) phosphoric acid etch, and (iv) in situ functionalization with a phosphonic acid in phosphoric acid. The characterization confirmed changes in the topography, nanostructures, and hydrophobicity after chemical treatment. Additionally, X-ray photoelectron spectroscopy was used to confirm that the chemical composition of the surfaces, in particular, Ga 2 O 3 and Al 2 O 3 content, was dependent on both the chemical treatment and the Al content of the gradient. Spectroscopic evaluation showed red shifts in strain-sensitive Raman peaks as the Al content gradually increased, but the same peaks blue-shifted after chemical treatment. Kelvin probe force microscopy measurements demonstrated that one can modify the surface charge using the chemical treatments. There were no predictable or controllable surface charge trends because of the spontaneous oxide-based nanostructured formations of the bulk material that varied based on treatment and were defect-dependent. The reported methodology and characterization can be utilized in future interfacial studies that rely on water-based wet chemical functionalization of inorganic materials., Competing Interests: The authors declare no competing financial interest.