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Low-energy (50keV) hydrogen implantation at a dose of 5×1012 ions/cm2 was performed on pulsed laser-deposited ZnO thin films. The films were subsequently rapid thermal annealed at 750°, 800, 850° and 900°C in ambient oxygen to remove any implantation-related defects. X-ray diffraction study confirmed deposition of highly c-axis-oriented 〈002〉 ZnO films in all of the samples. Hydrogen implantation did not have any effect on the carrier concentrations or Hall mobility of the samples. A low temperature photoluminescence study showed dominant donor-bound exciton peaks around 3.36eV along with a shoulder at 3.37eV corresponding to the free exciton peak for all of the samples. However, the integrated photoluminescence peak intensity revealed an enhanced intensity of the implanted sample (×4 times) and annealed samples (up to 100×) compared to the as-deposited sample. This enhanced luminescence from the hydrogen-implanted samples may be useful in fabricating highly efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Lithium ions were implanted at low energies (40 and 50keV) and at a dosage of 5×1013 ions/cm2 over 〈002〉 ZnO thin films that had been deposited by pulsed laser deposition. The implanted samples were subsequently treated by rapid thermal annealing at 750°C. Scanning electron microscopy images revealed improved grain formation for the implanted samples. However, a presence of microvoids was also observed in these samples; the amount of microvoids tended to increase on high-temperature annealing. Dominant donor-bound-exciton peaks is observed in all the samples along with some defect related to the exciton bound peaks although with a lesser intensity compared to as-deposited sample. [Copyright &y& Elsevier]

Abstract: Strontium silicate (Sr2SiO4) samples doped with varying Eu3+content were prepared via sol–gel route and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS) and photoluminescence (PL) techniques. The synthesis temperature could be brought down to 600°C for formation of a singe phase sample. The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Eu3+ ions was evaluated based on which the quenching mechanism was verified to be a multipole–multipole interaction. Based on the time-resolved emission data (TRES), it was inferred that, two different types of Eu3+ ions were present in the matrix. The first type was a long lived species (τ=4.7ms) present at 10-coordinated ‘Sr’sites and the other was a short lived species (τ=1.2ms) present at the 9-coordinated ‘Sr’sites which gets selectively excited at 296nm. Judd–Ofelt (J–O) intensity parameters for both the species were evaluated. The trend observed for the two species in the J–O parameters, Ω 2 and Ω 4 were different confirming their existence in two different environments. The color coordinates of the system were evaluated and plotted on a CIE index diagram. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. [Copyright &y& Elsevier]

Abstract: Phosphorus irradiation at a low energy (50keV) and at a dosage of 8×1014 ions/cm2 was carried out on 〈002〉 ZnO films grown by using a pulsed laser deposition technique (Sample A). Subsequent rapid thermal annealing at 650°C and 750°C was performed to remove defects resulting from the irradiation (samples B and C, respectively). Atomic force microscopy was used to determine the root mean square roughness, which was 10.07, 8.66, and 9.31nm for samples A, B, and C, respectively. Low-temperature photoluminescence measurements revealed increased deep-level defect peaks following irradiation; however, the subsequent annealing minimized the defects. Although the dominant donor-bound exciton peak verifies the n-type conductivity of the films, the free–electron–to–acceptor and donor-to-acceptor pair peaks in the irradiated samples confirm an increase in acceptor concentration. [Copyright &y& Elsevier]

We report the dispersion of Cd 1− x Zn x S/ZnS core/shell nanocrystals (NCs) in ferroelectric liquid crystal (FLC) into different concentrations. Absorbance of white light, photoluminescence (PL), contrast, polarizing optical microscopy and Fourier transformed infrared spectroscopy (FTIR) have been performed to disclose the nature of FLC/NCs composite. The presence of NCs, in different concentration, quenches the PL of FLC material. The mechanism of quenching is explained by the modified Stern–Volmer quenching equation. The maximum contrast for FLC/NCs was found at 0.25 wt% of dopant concentration which is the optimized concentration of NCs in FLC from application point of view. Contrast was further supported by polarizing optical micrographs (POMs). The change in POM also indicates the change in molecular alignment of FLC owing to concentration of NCs which also affect the optical properties of composites. FTIR spectra reveal that the NCs strongly interact with FLC molecules and changes their molecular dynamics associated with the central core and aliphatic chain. The present FLC/NCs composite has potential application in ultraviolet to visible light conversion, ultraviolet light storage applications and high contrast PL displays. [ABSTRACT FROM AUTHOR]

Abstract: Photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) of rare-earths (RE) doped BaSO4 and MgSO4 phosphors were studied. Undoped and doped phosphors containing different concentrations of dopant were synthesized by solid-state reaction method. X-ray diffraction (XRD) pattern of the samples matched well with their standard data of Joint Committee on Powder Diffraction’s (JCPD) file. In the PL spectrum of Dy doped samples, peaks around 470 and 580 nm were observed due to transition of Dy3+ ion. Eu doped BaSO4 showed PL peak at 380 nm due to transition of Eu2+ ion, however, in the PL spectrum of MgSO4:Eu phosphors, transition of Eu3+ was also observed along with transition of Eu2+ ion. Dy doped γ-ray-irradiated BaSO4 and MgSO4 phosphors showed at least two distinct peaks in their TL glow curves. The first peak occurred in range 120–150 °C and the second peak was observed in the range 220–230 °C. The TL glow curve of γ-ray-irradiated BaSO4:Eu contained a distinct peak at 170 °C. Two distinct peaks, one at 110 °C and another at 220 °C were observed in the TL glow curve of γ-ray-irradiated MgSO4:Eu phosphors. TL spectra showed that RE ions act as luminescence centre in BaSO4 and MgSO4 system. When the ML was excited impulsively by dropping a load on to the γ-ray-irradiated samples, only one sharp peak was observed in the ML intensity versus time curve of Dy doped samples, however, two peaks were observed in the ML intensity versus time curve of Eu doped BaSO4 and MgSO4 phosphors. The ML spectra of samples showed the characteristic emission of rare-earth impurities. Experimental results suggest that although almost similar states are responsible for PL, TL and ML, the luminescence efficiency of the phosphors depends on the mode of excitation. [Copyright &y& Elsevier]

Abstract: We demonstrate 7-fold increase of photoluminescence efficiency in GaAs/(InAs/GaAs) quantum dot hetero-structure, employing high energy proton irradiation, without any post-annealing treatment. Protons of energy 3–5MeV with fluence in the range (1.2–7.04)×1012 ions/cm2 were used for irradiation. X-ray diffraction analysis revealed crystalline quality of the GaAs cap layer improves on proton irradiation. Photoluminescence study conducted at low temperature and low laser excitation density proved the presence of non-radiative recombination centers in the system which gets eliminated on proton irradiation. Shift in photoluminescence emission towards higher wavelength upon irradiation substantiated the reduction in strain field existed between GaAs cap layer and InAs/GaAs quantum dots. The enhancement in PL efficiency is thus attributed to the annihilation of defects/non-radiative recombination centers present in GaAs cap layer as well as in InAs/GaAs quantum dots induced by proton irradiation. [Copyright &y& Elsevier]

We demonstrate a ten-fold increase in photoluminescence (PL) efficiency from 50keV H− ion-implanted InAs/GaAs quantum dots (QDs) at a temperature of 8K and/or 145K. Enhancement occurred without post-annealing treatment. PL efficiency increased with increasing implantation fluence from 6×1012 ions/cm2 up to an optimum value of 2.4×1013 ions/cm2, beyond which PL efficiency decreased drastically (up to a fluence of 2.4×1015 ions/cm2). Passivation of non-radiative recombination centres (due to direct interaction of H− ions with lattice defects) and de-excitation of photo-generated carriers to QDs through quantum mechanical tunnelling via H− ion-induced defects (e-traps) that are created near the QD–cap layer interface, resulted in PL efficiency enhancement. Shallow e-traps with activation energy ~90meV and 30meV created near the conduction band of GaAs cap layer for the samples implanted with H− of fluence 6×1012 and 2.4×1013 ions/cm2 respectively are identified using low temperature PL study. Contribution of de-trapped electrons from the e-traps to the QDs enhanced the PL efficiency at 145K. Cross-section transmission electron microscopy and X-ray diffraction study revealed that the structural damage created by H− ions at the high fluence level of 2.4×1015 ions/cm2, caused the degradation in PL efficiency. [ABSTRACT FROM AUTHOR]

BaSO4:Eu2+ phosphor has been investigated for its photoluminescence (PL), thermoluminescence (TL), TL kinetics, optically stimulated luminescence (OSL) and thermally assisted OSL (TA-OSL) response. PL spectra showed the characteristic emission of Eu2+ ion at 375 nm when excited by 320 nm. The luminescence lifetime has been measured as 40 and 628 μs of fast and slow components respectively. The TL parameters such as trap depth (E), frequency factor (s) and the order of kinetics (b) are determined. The phosphor is found to be 6 and 4 times more sensitive than CaSO4:Dy and α-Al2O3:C, respectively, in TL mode. However, its OSL sensitivity is 75% of α-Al2O3:C. It is found to possess three OSL components having photoionization cross-sections of 1.4 × 10−17, 1.2 × 10−18 and 5.2 × 10−19 cm2 respectively. The temperature dependence of OSL studies showed that integrated TA-OSL signal increases with stimulation temperature between 50 and 250 °C, while between 260 and 450 °C the signal intensity decreases. This behavior is interpreted to arise from competing effects of thermal assistance (activation energy E A = 0.063 ± 0.0012 eV) and depletion of trapped charges. This increase of OSL at elevated temperature can be employed for enhancing the sensitivity of phosphor for radiation dosimetry. [ABSTRACT FROM AUTHOR]

Abstract: Random networks of ZnO nanowires (ZnO-NWs) have been fabricated on the Si/SiO2 substrates by hydrothermal process using ZnO-nanoparticles as seed. The ZnO-NWs networks have been modified by depositing ultrathin CuO layers (nominal thickness: 10nm) using thermal evaporation of Cu followed by oxygen annealing at 600°C. The results of photoluminescence measurements on ZnO-NWs and CuO:ZnO-NWs networks suggest formation of a p–n junction between p-CuO and n-type ZnO. The gas sensing characteristics of both ZnO-NWs and CuO:ZnO-NWs networks have been investigated. It has been demonstrated that CuO:ZnO-NWs network has selective response toward H2S with a sensitivity of ∼40 (for 10ppm) at an operating temperature of 200°C. A sensing mechanism based on the destruction of p–n junctions due to the formation of metallic CuS (product of chemical reaction between CuO and H2S) has been proposed. [Copyright &y& Elsevier]

Abstract: α-Al2O3 single crystals were irradiated to various thermal neutron fluences in the range of 1014 to 1018 n/cm2 with associated fast neutron fluence and gamma rays in the CIRUS reactor. The neutron irradiation of α-Al2O3 crystals in the reactor introduces considerable oxygen vacancies in the crystals, which is confirmed by the presence of F (203 nm) and F+ (225 and 255 nm) bands in their optical absorption (OA) spectra. The concentration of the F and F+ centers increases with the increase in neutron fluence and are responsible for the observed TL and OSL in the α-Al2O3 single crystals. The F/F+ concentration ratio of α-Al2O3 samples irradiated to thermal neutron fluence of 1018 n/cm2 (with an associated fast neutron fluence of 7 × 1015 n/cm2) is 0.68. The photoluminescence and OA studies indicate formation of excess F+ center in the neutron irradiated Al2O3 single crystals. The TL glow curve of the reactor neutron irradiated Al2O3 is different from the TL glow curve structure of the TLD-500 single crystal. [Copyright &y& Elsevier]

Abstract: Zinc acetate derived precursor used in the present sol–gel synthesis of zinc oxide nanoparticles is described. The reaction product obtained before and after reflux of propanolic zinc acetate solution have been studied by UV–vis, photoluminescence and FT-IR studies which confirm the formation of oligomeric precursor Zn4O(Ac)6 (Ac=CH3COO). The formation of ∼7nm zinc oxide nanoparticles were confirmed by X-ray diffraction (XRD) and Transmission electron microscopic studies (TEM). The gaseous ammonia gas sensing characteristics of the nano-zinc oxide sensor showed high sensitivity compared to sensor fabricated with commercial zinc oxide powder. [Copyright &y& Elsevier]

The radiation treatment of polymeric materials at higher doses followed by analyses of their structural, optical and surface properties probes/scrutinizes their reliability for applications at various platforms. Kapton H is one of the imperative and indispensable polymers used for thermal shielding because of its features of large flammability and high temperature radiation resistance. Furthermore, the insulation of cables, lower de- gassing and nuclear power plant- electrical instruments are a few other applications of this crucial material. The irradiation of this polymer to exalted gamma dose increases its aptness in copious fields by remodelling (shaping) certain attributes. The present study includes the exposure of 30 μm thick samples of Kapton H at different doses of gamma radiation exposure ranging from 100 kGy to 1200 kGy. The free volume was observed to be modified in positron annihilation lifetime spectroscopy experiments. The X- ray diffraction (XRD) studies revealed increased amorphization and hence modified particle size. The UV- visible (UV-vis) spectroscopy showed displacement in the absorption peak in the direction of longer wavelength regime thereby decreasing the band gap energy as per Tauc's relation calculations. In addition to these results, Fourier transform infrared (FTIR) spectroscopy and photoluminescence studies were also carried out. [ABSTRACT FROM AUTHOR]