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We report on the substantial persistent photoconductivity (PPC) response exhibited by the zinc oxide (ZnO) nanorod-based ultraviolet (UV) photodetection system. An increase in photocurrent and, hence, rise in PPC was observed for larger UV exposure times at regular intervals. Triggered by quantum efficiency, the increment in sustained conduction band electrons is proposed as the main reason behind the increased photocurrent response. In contrast, the trap centers located below the conduction band are expected to slow down the recombination rate, which accounts for the rise in PPC. The lowering of PPC upon annealing suggests the surface dependent nature of the PPC. The growth and decay mechanism of PPC has a direct relevance while assessing figure of merit of prototype nanostructure-based optical sensor and UV photodetectors. [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]

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]

We report processing and luminescence decay characteristics of Cd1-xZnxS composite nanocrystals (NCs) conjugated with bovine serum albumin (BSA) proteins. Time-resolved study on unconjugate NCs (with dimensions less than the bulk exciton Bohr radius) suggests that in the radiative emission, the fast (τ1) and the slow (τ2) carrier components are equally competitive for a given stoichiometry. Conversely, bioconjugate NCs advocate that the decay component due to the free exciton recombination is ∼9 times faster than the component due to the surface recombination emission. The observation of two distinct decay parameters is due to the fact that the NCs have experienced photostability by way of binding and protecting NC surface with biomolecules (BSA) as binding agents. The occurrence of two decay constants would help in extracting information with regard to the nature of surface recombination, free-exciton relaxation along with the strength of emission. Furthermore, with the increase in % Zn, slow carrier component gets slower owing to the incorporation of extra surface traps due to Zn/Cd incompatibility while making perfect lattice sites in the NCs. As a result, surface emission intensity gets improved compared to the radiative intensity due to core-state direct transitions. Understanding photoluminescence decay of bioconjugated NCs, on a comparative basis, would find scope for biomolecular labelling, sensing and electrophysiology applications. [ABSTRACT FROM AUTHOR]

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]

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]