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We report on the nature of charge-neutral exciton emission decay, exciton-trion conversion as well as their phonon coupling in exfoliated WSe2 nanosheets subjected to ~ 1.3 MeV energetic γ-photons. Steady-state photoluminescence (PL) spectra, upon deconvolution, showed prominent emission peaks at ~ 680 nm, ~ 712 nm, and ~ 730 nm and ascribed to 2s, and 1s excitons and trions respectively, while the chalcogen vacancy (VSe) mediated defect emission peak found at ~ 790 nm. From the X-ray photoelectron spectroscopy (XPS) analysis, we noticed a clear shifting of the fundamental peaks due to W and Se toward higher binding energy values and were attributed to the radiation-induced alteration in the oxidation states locally, taking advantage of the manifestation of point defects/vacancies. Moreover, the time-resolved PL spectra signify an anomalous variation in the fast parameter (0.4–0.86 ns), and with slow parameter (2.46–3.82 ns) getting slower with increasing γ-dose. A slight variation in the exciton-phonon coupling factor is noted with Se-ph < 1 indicating a weaker interaction and featuring maximal envelope over all the phonon replica near the zero-phonon line. In contrast, trion-phonon coupling factor, St-ph > 1, or < 1 depending on its spin degeneracy (ζ = 2 s + 1; with 2, for s = 1/2 and 4 for s = 3/2). The highest St-ph value determined was ~ 1.82 ± 0.2 which declines monotonically with increasing dose but remained greater than unity up to a γ-dose as high as 96 kGy. The implication of trion-phonon coupling has immense scope in nano-photovoltaics, and nano-electronics as well as heat sinks in nanogenerators. [ABSTRACT FROM AUTHOR]

The optimum Mn-incorporation and interrelated luminescence characteristics of solid-state derived, PbO-free, nanoscale PbTiO3 systems are reported. X-ray diffraction analysis of the nanosystems predicts a maximum value of tetragonality (∼1.06), for a given stoichiometry, namely Mn:Ti = 0.11. Photoluminescence (PL) studies reveal an intense emission peak (λem ∼ 604 nm), which is ascribed to the disordered inorganic phase of lead titanate containing non-bridging oxygen defects. The incorporation of Mn into the lead titanate system has resulted in a more symmetric PL peak owing to its association with Mn2+-related orange emission. Excessive Mn-doping was found to hinder the radiative process significantly owing to the presence of untreated MnO2 phase or the development of a thin MnO2 overlayer on the nanostructure surface. [ABSTRACT FROM AUTHOR]

In this work, we discuss Raman active vibrational and photoluminescence (PL) features of hydrothermally derived cubic phase, manganese selenide (MnSe) quantum dots (QDs) coated with markedly different coating agents, such as, cetyl trimethyl ammonium bromide (CTAB), thioglycolic acid (TGA) and dextran molecules. The homogeneously grown QDs, upon adequate coating, offered a size variation between 5 and 11 nm as evident from imaging through transmission electron microscopy (TEM). The Raman spectra of the QDs have revealed the most prominent peak positioned at ∼680 nm and is ascribed to the third overtone of the longitudinal optical (LO(Γ)) mode. Moreover, the numerous, mixed modes which existed for the uncoated QDs, were found to be suppressed after adequate surface passivation due to surfactant coating. The prominent blue-violet emission response of the MnSe QDs, was seen to be highly symmetric and positioned at ∼428 nm. Furthermore, time resolved PL studies have predicted bi-exponential decay characteristics with a fast component (τ 1 ∼ 0.10 ns) that remains nearly unaffected, but the slow component (τ 2) has varied with the nature of coating agent. In particular, the dextran coated MnSe QDs exhibited a maximal τ 2 value (∼5.5 ns) due to complete surface passivation of the QDs. The influence of surfactants on the vibrational and PL emission parameters of a magneto-fluorescent candidate, like MnSe, would bring new insights for their relevance in nano-photonics and nano-biotechnology to act as active probes for imaging, sensing and targeted therapeutics. • Surface anchored MnSe quantum dots (QDs) have been derived through a rapid hydrothermal route. • Raman active, mixed vibrational modes are found to be suppressed after coating with surfactants. • Highly symmetric, blue-violet emission and positioned at ∼428–430 nm, has been witnessed for all the QD-types. • While fast decay parameter is approximately 0.10 ns, the slow decay component is altered with the nature of coating agent. [ABSTRACT FROM AUTHOR]

Abstract: Bare and silica coated CdS quantum dots are prepared following chemical route. Swift heavy ion (SHI) irradiation of the samples was carried out with 160MeV Ni12+ ion beam with fluences 1012–1013 ions/cm2. Photoluminescence (PL) studies of all the samples were carried out with excitation wavelength 325nm. The surface state emission is dominant in case of bare samples while e–h recombination is observed in case of coated samples. Red shift in the absorption response in the optical absorption spectra of bare samples reveal size enhancement of the quantum dots after irradiation. No such shift is observed for coated samples. The coated samples also exhibit enhanced photo stability. [Copyright &y& Elsevier]