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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]

We report on the effect of 80 keV Ar+ ion irradiation on the luminescence response of zinc oxide (ZnO) nanosticks synthesized using a simple microemulsion route. The formation of nanoscale rods was confirmed from the transmission electron microscopy, whereas the hexagonal wurtzite phase of the nanorods was detected in an X-ray diffraction pattern. The photoluminescence pattern of the nanorods was dominated by various native defect states of ZnO, which are responsible for the quenching of the typical band edge emission of ZnO. Under Ar+ ion irradiation at a fluence of 1×1013 ions/cm2, the band edge emission was recovered owing to the suppression of oxygen vacancy defects. In addition, the formation of new zinc vacancy and ionized zinc interstitial defects were also evident. Conversely, the band edge emission was found to be quenched as a result of the creation of more oxygen vacancy (VO) defects due to ion irradiation (fluence: 1×1015 ions/cm2). The nuclear energy loss of the Ar+ ions in ZnO is responsible for the formation of point (vacancy-related) defects, while relatively small amount of electronic energy loss of the Ar+ ion results in the ionization of the neutral zinc interstitial (Zni) defects. The energy deposition scheme of the energetic ions has been elaborated with the help of theoretical modeling that explains the observed features quite satisfactorily. [ABSTRACT FROM AUTHOR]

Abstract: We report on the 80-MeV nitrogen ion irradiation on spherical ZnO nanoparticles fabricated by way of solid state mixing. The structural and compositional analyses of the as-synthesized ZnO nanoparticles were done by X-ray diffraction, electron microscopy and energy dispersive spectroscopy studies. As evident from the optical absorption spectra, the energetic ion irradiation, on the nanoparticle system, is governed by evolution of new characteristic absorption features owing to modification in the electronic states. Again, in the luminescence spectra, though the near band-edge emission was not observable for pristine ZnO, it was recovered (at ∼385nm) upon irradiation. As far as the defect related emission is concerned, a competition between the formation and annihilation of different defects (especially, zinc vacancies and interstitials) at different ion fluences was realized. Correlating the luminescence spectra and the theoretical investigation, it can be understood that during irradiation the formation of zinc related defects are energetically favorable than the oxygen related counterparts. Exploration of defect related radiative features corresponding to definite structural organization/modification would help in making next generation light emitting and display devices, where a select emission response is desired. [Copyright &y& Elsevier]

Abstract: PbS quantum dots of average size 10nm are encapsulated in a matrix (polyvinyl alcohol (PVA)) following chemical route. They are irradiated with 160MeV Ni12+ ion beam with fluences 1012–1013 ions/cm2. Red shift in the absorption response in the optical absorption spectra reveal size enhancement of the quantum dots after irradiation and was confirmed by transmission electron microscopy (TEM). Photoluminescence (PL) study was carried out with excitation wavelength 325nm on both unirradiated and irradiated samples at different fluences and fluence-dependent surface states and excitonic emission is observed in the PL study. The Huang–Rhys coupling constant decreases significantly after swift heavy ion (SHI) irradiation and shows a decreasing trend with increase in ion fluence. [Copyright &y& Elsevier]

This study explores the impact of 60 MeV N5+ ion irradiation on few layer WSe 2 systems. The structural analysis exhibit an anomalous variation in crystallite size with increasing grain growth after irradiation. Raman spectroscopy study reveals increased disorder, enhanced intensities of prominent modes, and an eight-fold rise in AFM-measured roughness from 27.2 nm to 212.6 nm. HR-TEM shows voids in nanosheets post-irradiation. In addition, DFT calculations on monolayer with vacancy clusters shows modification of WSe 2 bandgap from 1.48 eV to 0.37 eV. Interrelated structural, morphological and electronic structure calculations would provide useful insights upon controlled radiation exposure. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report on the surfactant assisted synthesis of gadolinium oxide (Gd2O3) nanoparticles and their characterization through various microscopic and spectroscopic tools. Exhibiting a monoclinic phase, the nanoscale Gd2O3 particles are believed to be comprising of crystallites with an average size of ∼3.2nm, as revealed from the X-ray diffraction analysis. The transmission electron microscopy has predicted a particle size of ∼9nm and an interplanar spacing of ∼0.28nm. Fourier transform infrared spectroscopy studies show that Gd–O inplane vibrations at 536.8 and 413.3cm−1 were more prominent for 80-keV Ar-ion irradiated Gd2O3 nanosystem than unirradiated system. The photoluminescence (PL) spectra of irradiated specimen have revealed an improvement in the symmetry factor owing to significant enhancement of surface-trap emission, compared to the band-edge counterpart. Irradiation induced creation of point defects (oxygen vacancies) were predicted both from PL and electron paramagnetic resonance (EPR) studies. Further, the Raman spectra of the irradiated sample have exhibited notable vibrational features along with the evolution of a new peak at ∼202cm−1. This can be ascribed to an additional Raman active vibrational response owing to considerable modification of the nanostructure surface as a result of ion bombardment. Probing nanoscale defects through prime spectroscopy tools would find a new avenue for precise tuning of physical properties with generation and annihilation of defects. [Copyright &y& Elsevier]

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]