High-efficient up-conversion of photoluminescence in CdSe quantum dots grown in ZnSe matrix

The intensive up-conversion photoluminescence at low temperatures in CdSe/ZnSe structures with single CdSe inserts of the nominal thickness 1.5 monolayer was observed. Excitation power dependensies show a nearly quadratic character up-converted photoluminescence signal from CdSe quantum dots. Up-conversion photoluminescence mechanism was interpreted on the basis of a non-linear process of two-step two-photon absorption through deep defect states including cation vacancies localized at the interface of quantum dots. This observation of photoluminescence up-conversion demonstrates the influence of quantum dot environment on its properties

Transient photoluminescence of shallow donor bound excitons in GaN

We present a detailed study of photoluminescence transients for neutral donor bound excitons (DBEs) in GaN, notably the ON donor DBE at 3.4714 eV and the SiGa DBE at 3.4723 eV. The studied samples are thick strain free nominally undoped bulk GaN samples, with a spectroscopic linewidth <0.5 meV at 2 K. The photoluminescence (PL) decay curves for these no-phonon (NP) lines are strongly nonexponential, and do not allow a proper assessment of the characteristic BE decay time. The decay of the LO-phonon replicas as well as the so-called two-electron transitions (TETs) at lower energies show a nicely exponential behavior, and allow extraction of DBE decay times of about 1.1 ns for the Si DBE and 1.8 ns for the O DBE, respectively. The initial nonexponential decay behavior of the NP lines has been studied in both the common front surface excitation-detection mode and with detection in transmission through the sample. This initial decay is explained as related to scattering processes in the near surface region, involving the DBEs and free excitons (FEs). Light scattering processes may also contribute to this complex decay shape. The DBE-LO-phonon decay does not discriminate between the O and Si DBEs because of spectral overlap involving different LO modes. The TET decays at 2 K are very different for transitions related to the DBE ground state and DBE excited states (going to p-like donor final states), for T>10 K thermalization between the DBE ground state and DBE excited states produces a common decay time. Thermalization between free and bound excitons appears to occur above about 20 K, when the DBE decay follows the FE decay. A simple two-level modeling of exciton capture and recombination for the PL decay curves of the FE and the DBEs, as commonly used in the literature, is shown to be generally inadequate. A broad PL background in the TET spectral region is suggested to be related to a radiative Auger process, where the DBEs recombine while leaving the donors ionized.Original Publication: Bo Monemar, Plamen Paskov, Peder Bergman, Galia Pozina, A.A. Toropov, T.V. Shubina, T. Malinauskas and A. Usui, Transient photoluminescence of shallow donor bound excitons in GaN, 2010, Physical Review B Condensed Matter, (82), , 235202. http://dx.doi.org/10.1103/PhysRevB.82.235202 Copyright: American Physical Society http://www.aps.org

Polarized micro-photoluminescence spectroscopy of GaN nanocolumns

International audienceWe propose inversion domains (IDs) to be the origin of the 3.42 eV photoluminescence (PL) band in GaN epilayers and nanocolumns. A shift of the band relatively to the near‐edge PL band is induced presumably by different strain in the IDs. Micro‐PL studies of nanocolumns enriched by IDs reveal anti‐correlated intensity variation as well as a similarity between temperature and power dependences of both bands. A change of dominant polarization takes place across the spectra, being likely related to variation of exciton level ordering at tensile strain. Discrete narrow lines observed in the spectra are considered as manifestation of strain‐induced one‐dimensional carrier confinement in the ID

Anti-biofilm and wound-healing activity of chitosan-immobilized Ficin

© 2020 Biofouling is among the key factors slowing down healing of acute and chronic wounds. Here we report both anti-biofilm and wound-healing properties of the chitosan-immobilized Ficin. The proposed chitosan-adsorption approach allowed preserving ~90% of the initial total activity of the enzyme (when using azocasein as a substrate) with stabilization factor of 4.9, and ~70% of its specific enzymatic activity. In vitro, the chitosan-immobilized Ficin degraded staphylococcal biofilms, this way increasing the efficacy of antimicrobials against biofilm-embedded bacteria. In vivo, in the presence of Ficin (either soluble or immobilized), the S.aureus-infected skin wound areas in rats reduced twofold after 4 instead of 6 days treatment. Moreover, topical application of the immobilized enzyme resulted in a 3-log reduction of S. aureus cell count on the wound surfaces in 6 days, compared to more than 10 days required to achieve the same effect in control. Additional advantages include smoother reepithelisation, and new tissue formation exhibiting collagen structure characteristics closely reminiscent of those observed in the native tissue. Taken together, our data suggest that both soluble and immobilized Ficin appear beneficial for the treatment of biofilm-associated infections, as well as speeding up wound healing and microbial decontamination