Deoxyglucose-conjugated persistent luminescent nanoparticles for theragnostic application in fibrosarcoma tumor model

Deoxyglucose conjugated nanoparticles with persistent luminescence have shown theragnostic potential. In this study, deoxyglucose-conjugated nano-particles with persistent luminescence properties were synthesized, and their theragnostic potential was evaluated in fibrosarcoma cancer cells and a tumor model. The uptake of nano-formulation was found to be higher in mouse fibrosarcoma (WEHI-164) cells cultured in a medium without glucose. Nanoparticles showed a higher killing ability for cancer cells compared to normal cells. A significant accumulation of nanoparticles to the tumor site in mice was evident by the increased tumor/normal leg ratio, resulting in a significant decrease in tumor volume and weight. Histopathological studies showed a significant decrease in the number of dividing mitotic cells but a greater number of apoptotic/necrotic cells in nanoparticle-treated tumor tissues, which was correlated with a lower magnitude of Ki-67 expression (a proliferation marker). Consequently, our results showed the potential of our nano-formulation for cancer theragnosis.

Mesoporous Silica-Coated Upconversion Nanoparticles Assisted Photodynamic Therapy Using 5-Aminolevulinic Acid: Mechanistic and In Vivo Studies

Exclusively red-emitting upconversion nanoparticles (UCNPs) with the composition NaErF₄:0.5%Tm as a core and NaYF₄ as a shell were synthesized for performing photodynamic therapy (PDT). A possible mechanism was proposed for core-shell UCNPs formation. For loading a maximum amount of 5-aminolevulinic acid (5-ALA), mesoporous silica coating was performed on UCNPs. Studies under dark conditions confirmed the biocompatibility of 5-ALA-loaded UCNPs formulation (UCNPs-5-ALA) with MCF-7 cells. Meanwhile, studies under light-exposed conditions exhibited effective cytotoxicity against MCF-7 cells. Studies employing D₂O-based cell cultured media and addition of DABCO in cell culture established that the cell death was due to oxidation of cellular components by reactive oxygen species (ROS) triggering the apoptosis. The formation of ROS was confirmed by DCF(H)DA-based ROS analysis via fluorescence microscopy to demonstrate the ROS production, which mediates the programmed cell death. Additionally, we have validated the apoptosis in MCF-7 cells with flow cytometry analyses. This was further confirmed by an electrophoretic mobility shift assay on nuclear extract and measurement of mitochondrial membrane potential. In the case of animal model studies, the formulation UCNPs-5-ALA without irradiation (980 nm) did not possess any in vivo cytotoxicity on tumor-induced SCID mice and there was a minimum migration of UCNPs-5-ALA to the vital organs but maximum retention at the tumor site only. Meanwhile, only the mice treated with UCNPs-5-ALA and irradiated on the tumor region with 980 nm laser (500 mW) for 20 min possessed a tumor with a size reduced to about 75% as compared with the corresponding control groups. To the best of our knowledge, this type of study was conducted for the first time employing exclusively red-emitting phosphors for effective PDT.

Facile Synthesis of a Pt(IV) Prodrug of Cisplatin and Its Intrinsically 195mPt Labeled Analog: A Step Closer to Cancer Theranostic

Background, Aims and Objectives:

Cisplatin is extensively used in chemotherapy for treatment of a broad range of cancers. But its undesired side reactions with biomolecules that lead to severe side effects especially on kidney and nervous system, are limiting its clinical utility. To reduce its side effects, the kinetically inert Pt(IV) prodrug was recognized as an alternative approach from satisfactory results of preliminary experiments. But, its approval as anticancer drug for clinical use requires detailed investigations of its anticancer action and pharmacological pathways by employing its analogue which can be traced by a suitable technique. As a step closer towards translation of Pt(IV)-based prodrug from research to clinical level, a protocol for efficient synthesis of ^195mPt-radiolabeled Pt(IV) prodrug was devised.

Materials and Methods:

In order to achieve the aim, we started synthesis from elemental platinum avoiding lengthy steps. The synthesis protocol was standardized on its cold analogue, as [PtCl₂(NH₃)₂(OCOCH₂CH₂COOH)₂] which has been characterized with nuclear magnetic resonance (¹H, ¹³C{1H} and ¹⁹⁵Pt{1H}) spectroscopy, microanalyses and cyclic voltammetry. Also, cytotoxicity of [PtCl₂(OCOCH₂CH₂COOH)₂(NH₃)₂] was evaluated against MCF-7 human breast cancer cell lines using cisplatin as test control.

Results:

Intrinsically, ^195mPt-labeled analogue of prodrug was obtained with high radionuclidic and radiochemical purity. It was confirmed by chromatography and γ-ray spectrometry.

Conclusion:

The ^195mPt-radiolabeled prodrug was synthesized in a facile manner. It can be utilized in evaluating the mechanism of anticancer action and pharmacokinetics by enabling synergistic use of molecular imaging and targeted drug delivery.

Generation of Multiply Charged Argon Ions in Nanosecond Laser Field Ionization of Argon Clusters

Zhang and co-workers ( J. Phys. Chem. Lett. 2020, 11, 1100-1105) have recently reported results of experiments involving irradiation of argon clusters doped with bromofluorene chromophores by nanosecond-long pulses of 532 nm laser light. Multiply charged ions of atomic argon (Arⁿ⁺, 1 ≤ n ≤ 7) and carbon (Cⁿ⁺, 1 ≤ n ≤ 4) are observed, which are sought to be rationalized using an evaporation model. The distinguishing facet of exploding clusters being progenitors of energetic ions and electrons constitutes the key driver for contemporary research in laser-cluster interactions; it is, therefore, important to point out inconsistencies that are intrinsic to the model of Zhang and co-workers. In light of similar reports already in the literature, we show that their model is of limited utility in describing the dynamics that govern how fast, multiply charged atomic ions result from laser irradiation of gas-phase clusters. We posit that it is plasma behavior that underpins cluster heating and cluster explosion dynamics.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y₂GeO₅ and Y₂Ge₂O₇ having dopant Eu³⁺ in their respective YO₇ polyhedra. Whereas for Y₂GeO₅:Eu³⁺, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y₂Ge₂O₇:Eu³⁺, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu³⁺ present in YO₇ of Y₂GeO₅ has a greater number of tetra-coordinated oxygen (O_tetra) and yttrium atom as first and second neighbors, respectively (Eu³⁺-O_tetra-Y³⁺ linkages). Conversely, in Y₂Ge₂O₇ host, the Eu³⁺ ion mostly has tricoordinated oxygen (O_tri) as its nearest neighbor and germanium ions next to O_tri (Eu³⁺-O_tri-Ge⁴⁺ linkage). Theoretical calculations reveal that while Y₂GeO₅:Eu has O_tetra(4Y) dominating at the Fermi level and the 4f state of Eu³⁺ remains inert toward mixing, in Y₂Ge₂O₇:Eu, the Fermi level has major contribution from O_tri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu³⁺-O_tri-Ge⁴⁺ linkages in geometrical and electronic structure of Y₂Ge₂O₇:Eu owing to the GeO₄ surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu³⁺ by GeO₄ and subsequent occurrence of Eu³⁺-O_tri-Ge⁴⁺ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (O_tri) oxygen by highly charged small Ge⁴⁺ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and O_tri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuO_x polyhedra surrounded by covalent units like PO₄, SiO₄, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Synthesis of 2-deoxy-d-glucose coated Fe3O4 nanoparticles for application in targeted delivery of the Pt(iv) prodrug of cisplatin – a novel approach in chemotherapy

Pt(IV) prodrug of cisplatin was loaded on 2DG functionalized silica coated Fe₃O₄ nanoparticles. The formulation alone exhibited biocompatibility whereas Pt(IV) loaded formulation exhibited cytotoxicity comparable with cisplatin.

The synthesis of rare earth metal-doped upconversion nanoparticles coated with d-glucose or 2-deoxy-d-glucose and their evaluation for diagnosis and therapy in cancer

Silica coated NaY_0.8Yb_0.16Tm_0.04F₄ NPs functionalized with d-glucose or 2-deoxy-d-glucose were prepared. Cytotoxicity and uptake studies on MCF-7 cells revealed the potential of formulation in bioimaging, therapy.

Synthesis and characterization of monodispersed water dispersible Fe3O4 nanoparticles and in vitro studies on human breast carcinoma cell line under hyperthermia condition

Monodispersed Fe₃O₄ magnetic nanoparticles (MNPs) having size of 7 nm have been prepared from iron oleate and made water dispersible by functionalization for biomedical applications. Three different reactions employing thioglycolic acid, aspartic acid and aminophosphonate were performed on oleic acid coated Fe₃O₄. In order to achieve a control on particle size, the pristine nanoparticles were heated in presence of ferric oleate which led to increase in size from 7 to 11 nm. Reaction parameters such as rate of heating, reaction temperature and duration of heating have been studied. Shape of particles was found to change from spherical to cuboid. The cuboid shape in turn enhances magneto-crystalline anisotropy (K_u). Heating efficacy of these nanoparticles for hyperthermia was also evaluated for different shapes and sizes. We demonstrate heat generation from these MNPs for hyperthermia application under alternating current (AC) magnetic field and optimized heating efficiency by controlling morphology of particles. We have also studied intra-cellular uptake and localization of nanoparticles and cytotoxicity under AC magnetic field in human breast carcinoma cell line.

(TMT)n clusters as dilute debris-free tin source for generation of multiply charged tin ions-of relevance in extreme ultraviolet (EUV) lithography, under intense laser irradiation

RATIONALE

Multiply charged tin ions ([Sn]8+ to [Sn]13+ ) are considered as ideal-emitters at extreme ultraviolet (EUV) wavelength ~ 13.5 nm, pertinent to advanced micro-electronic device fabrication. Solid tin targets have been widely explored for the generation of these ions, but debris generation has restricted their utilization. Tin-containing molecular clusters have, however, the potential to act as dilute and debris-free sources for the generation of tin ions, as investigated in the present study.

METHODS

Efficient coupling of laser energy with clusters has been utilized for the generation of multiply charged tin ions. The ions generated have been characterized using time-of-flight mass spectrometry. By varying experimental parameters, the yield of multiply charged tin ions has been manipulated, for tetramethyltin (TMT) clusters. In addition, the energetic electrons and photons liberated upon laser-cluster interaction have been probed utilizing an in-house developed retarding field analyser.

RESULTS

Interaction of tetramethyltin clusters with 1064 nm picosecond laser pulses of intensity ~ 1013 W/cm2 leads to the generation of multiply charged tin ions (up to [Sn]14+ ) and carbon ions (up to [C]4+ ). Efficient laser-cluster interaction is evident from the generation of multiply charged tin ions with ionization energy ~ 282 eV ([Sn]14+ ). By varying the experimental conditions, the distribution of multiply charged tin ions can be influenced to obtain significant relative ion yield of multiply charged tin ions from [Sn]8+ to [Sn]13+ .

CONCLUSIONS

Tetramethyltin clusters have the potential to act as dilute and debris-free source for EUV lithographic applications, in contrast to bulk tin targets. The inherent properties of clusters, such as higher local density and the pulsed nature of the cluster source, are appropriate for EUV lithographic applications.

Tailoring Ion Charge State Distribution in Tetramethyltin Clusters under Influence of Moderate Intensity Picosecond Laser Pulse: Role of Laser Wavelength and Rate of Energy Deposition

Systematic manipulation of ionic-outcome in laser-cluster interaction process has been realized for studies carried out on tetramethyltin (TMT) clusters under picosecond laser conditions, determined by choice of laser wavelength and intensity. As a function of laser intensity, TMT clusters exhibit gradual enhancement in overall ionization of its cluster constituents, up to a saturation level of ionization, which was distinct for different wavelengths (266, 355, and 532 nm). Simultaneously, systematic appearance of higher multiply charged atomic ions and shift in relative abundance of multiply charged atomic ions towards higher charge state was observed, using time-of-flight mass spectrometer. At saturation level, multiply charged atomic ions up to (C²⁺, Sn²⁺) at 266 nm, (C⁴⁺, Sn⁴⁺) at 355 nm, and (C⁴⁺, Sn⁶⁺) at 532 nm were detected. In addition, at 355 nm intra-cluster ion chemistry within the ionized cluster leads to generation of molecular hydrogen ion (H₂⁺) and triatomic molecular hydrogen ion (H₃⁺). Generation of multiply charged atomic ions is ascribed to efficient coupling of laser pulse with the cluster media, facilitated by inner-ionized electrons produced within the cluster, at the leading edge of laser pulse. Role of inner-ionized electrons is authenticated by measuring kinetic energy distribution of electrons liberated upon disintegration of excessively ionized cluster, under the influence of picosecond laser pulse. Graphical Abstract ᅟ.

Covalent bridging of surface functionalized Fe3O4 and YPO4:Eu nanostructures for simultaneous imaging and therapy

Magnetic luminescent hybrid nanostructures (MLHN) have received a great deal of attention due to their potential biomedical applications such as thermal therapy, magnetic resonance imaging, drug delivery and intracellular imaging. We report the development of bifunctional Fe3O4 decorated YPO4:Eu hybrid nanostructures by covalent bridging of carboxyl PEGylated Fe3O4 and amine functionalized YPO4:Eu particles. The surface functionalization of individual nanoparticulates as well as their successful conjugation was evident from Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), zeta-potential and transmission electron microscopy (TEM) studies. X-ray diffraction (XRD) analysis reveals the formation of highly crystalline hybrid nanostructures. TEM micrographs clearly show the binding/anchoring of 10 nm Fe3O4 nanoparticles onto the surface of 100-150 nm rice grain shaped YPO4:Eu nanostructures. These MLHN show good colloidal stability, magnetic field responsivity and self-heating capacity under an external AC magnetic field. The induction heating studies confirmed localized heating of MLHN under an AC magnetic field with a high specific absorption rate. Photoluminescence spectroscopy and fluorescence microscopy results show optical imaging capability of MLHN. Furthermore, successful internalization of these MLHN in the cells and their cellular imaging ability are confirmed from confocal microscopy imaging. Specifically, the hybrid nanostructure provides an excellent platform to integrate luminescent and magnetic materials into one single entity that can be used as a potential tool for hyperthermia treatment of cancer and cellular imaging.

Role of electron heating in efficient interaction of a nanosecond laser with the cluster media: a case study on tetrahydrofuran cluster system

Interaction of tetrahydrofuran clusters with nanosecond laser pulses has been investigated at 532 and 1064 nm, using a time-of-flight mass spectrometer and home-built electron analyzer setup.

Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation

Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO.

Efficient coupling of nanosecond laser pulses with the cluster medium: Generation of hydrogen-like [C](5+) atomic ions

RATIONALE

Clusters exhibit diverse photochemical behavior as a function of laser parameters, i.e. wavelength, pulse duration and intensity. One such aspect of cluster photochemistry is the generation of energetic multiply charged atomic ions, upon efficient interaction of clusters with intense laser pulses. In the present work, mass spectrometric investigations have been carried out on clusters of tetrahydrofuran (THF, C4 H8 O) - a saturated cyclic ether - subjected to nanosecond laser pulse (spanning from UV to IR wavelength range) with the aim of shedding light on the complex mechanism of laser-cluster interactions, which is still ambiguous.

METHODS

THF clusters, generated via supersonic expansion of room-temperature THF vapours seeded in argon, were subjected to gigawatt intensity laser pulses (355, 532 and 1064 nm) obtained from a nanosecond Nd:YAG laser. The ions generated upon laser-cluster interaction were characterized using a time-of-flight mass spectrometer.

RESULTS

At 355 nm, THF clusters exhibit the usual multiphoton dissociation/ionization behavior while, at 532 nm, observation of multiply charged atomic ions of carbon (up to [C](4+) ) and oxygen (up to [O](3+) ) was ascribed to Coulomb explosion of THF clusters. For studies carried out at 1064 nm, multiply charged atomic ions of carbon up to [C](5+) having an ionization energy of ~392 eV were observed, at a laser intensity of 10(10) W/cm(2) .

CONCLUSIONS

The observation of [C](5+) atomic ions signifies efficient coupling of the laser energy with the cluster medium, using a nanosecond laser pulse. The results have been rationalized on the basis of a three-stage cluster ionization mechanism, suggesting the crucial role of the threshold laser intensity for initiating ionization within the cluster and generation of optimum charge centers for efficient extraction of energy from the laser pulse.

Ionisation of methyl iodide clusters using nanosecond laser pulses: detection of multiply charged positive ions, negative ions and energetic electrons

Methyl iodide clusters have been ionised using laser pulses of intensity ∼10⁹ W cm⁻² at 266, 355, 532 and 1064 nm and the ions produced in the laser–cluster interaction were analysed with a time-of-flight mass spectrometer.

Synthesis of oleic acid functionalized Fe3O4 magnetic nanoparticles and studying their interaction with tumor cells for potential hyperthermia applications

In the present study, oleic acid (OA) functionalized Fe3O4 magnetic nanoparticles (MN) were synthesized following modified wet method of MN synthesis. The optimum amount of OA required for capping of MN and the amount of bound and unbound/free OA was determined by thermogravimetric analysis (TGA). Further, we have studied the effect of water molecules, associated with MN, on the variation in their induction heating ability under alternating current (AC) magnetic field conditions. We have employed a new approach to achieve dispersion of OA functionalized MN (MN-OA) in aqueous medium using sodium carbonate, which improves their biological applicability. Interactions amongst MN, OA and sodium carbonate were studied by Fourier transform infrared spectroscopy (FT-IR). Intracellular localization of MN-OA was studied in mouse fibrosarcoma cells (WEHI-164) by prussian blue staining and confocal laser scanning microscopy (CLSM) using nile blue A as a fluorescent probe. Results showed MN-OA to be interacting mainly with the cell membrane. Their hyperthermic killing ability was evaluated in WEHI-164 cells by trypan blue method. Cells treated with MN-OA in combination with induction heating showed decreased viability as compared to respective induction heating controls. These results were supported by altered cellular morphology after treatment of MN-OA in combination with induction heating. Further, the magnitude of apoptosis was found to be ~5 folds higher in cells treated with MN-OA in combination with induction heating as compared to untreated control. These results suggest the efficacy of MN-OA in killing of tumor cells by cellular hyperthermia.

Effect of cluster expansion on photoionization of iron pentacarbonyl doped inert gas clusters under gigawatt intensity laser irradiation

RATIONALE

The aim of the investigation was to understand the variation in ionization dynamics of inert gas clusters upon doping with species with lower ionization energy than the inert gas constituent. It was postulated that the use of dopant species having lower ionization energy would lead to facile ionization of doped inert gas clusters, resulting in enhancement of the charge state of atomic ions compared with those obtained for pure inert gas clusters.

METHODS

Inert gas clusters (Ar(n), Kr(n) or Xe(n)) doped with iron pentacarbonyl were generated by supersonic expansion and subjected to gigawatt intensity laser pulses (266, 355, 532 and 1064 nm wavelengths) obtained from a nanosecond Nd:YAG laser. The ions generated upon laser-cluster interaction were characterized using a time-of-flight mass spectrometer.

RESULTS

Upon interaction of the laser with the doped inert gas clusters, the charge states of the atomic ions were found to increase with the laser wavelength. However, the highest observed charge states were found to be lower for doped inert gas clusters than for pure inert gas clusters, at all laser wavelengths.

CONCLUSIONS

Wavelength-dependent generation of multiply charged atomic ions has been explained based on the three stage model, i.e. multiphoton ionization ignited-inverse bremsstrahlung heating, and electron ionization. This model explains enhancement in the charge state of atomic ions with increasing wavelength based on inverse bremsstrahlung heating of the inner ionized electron, which is a more efficient process at longer wavelengths. Inefficient coupling of laser energy in the case of doped inert gas clusters compared with pure inert gas clusters has been rationalized on the basis of accelerated disintegration of the cluster due to facile initial ionization of dopant molecules having low ionization energy. The results suggest that a longer laser wavelength and a slower rate of cluster expansion facilitate the efficient transfer of optical energy into cluster systems.

Re-dispersion and film formation of GdVO4 : Ln3+ (Ln3+ = Dy3+, Eu3+, Sm3+, Tm3+) nanoparticles: particle size and luminescence studies

GdVO(4) : Ln(3+) (Ln(3+) = Dy(3+), Eu(3+), Sm(3+), Tm(3+)) nanoparticles are prepared by a simple chemical route at 140 °C. The crystallite size can be tuned by varying the pH of the reaction medium. Interestingly, the crystallite size is found to increase significantly when pH increases from 6 to 12. This is related to slower nucleation of the GdVO(4) formation with increase of VO(4)(3-) present in solution. The luminescence study shows an efficient energy transfer from vanadate absorption of GdVO(4) to Ln(3+) and thereby enhanced emissions are obtained. A possible reaction mechanism at different pH values is suggested in this study. As-prepared samples are well dispersed in ethanol, methanol and water, and can be incorporated into polymer films. Luminescence and its decay lifetime studies confirm the decrease in non-radiative transition probability with the increase of heat treatment temperature. Re-dispersed particles will be useful in potential applications of life science and the film will be useful in display devices.

Multiphoton ionization and Coulomb explosion of C2H5Br clusters: a mass spectrometric and charge density study

Using time-of-flight mass spectrometry (TOFMS), laser-induced photochemistry of ethyl bromide clusters has been investigated at three different wavelengths (viz. 266, 355 and 532  nm) utilizing nanosecond laser pulses of ~5 × 10(9)  W/cm(2). An interesting finding of the present work is the observation of multiply charged atomic ions of carbon and bromine at 355 and 532  nm, arising from the Coulomb explosion of (C(2)H(5)Br)(n) clusters. At 266  nm, however, the (C(2)H(5)Br)(n) clusters were found to exhibit the usual multiphoton dissociation/ionization behaviour. The TOFMS studies are complemented by measuring the total charge density of the ionized volume at 266, 355 and 532  nm, using the parallel plate method, and the charge densities were found to be ~2 × 10(9), 6 × 10(9) and 2 × 10(11)  charges/cm(3), respectively. The significantly higher charge density and the presence of energetic, multiply charged atomic ions at 532  nm are explained by the higher ponderomotive energy of the 532  nm photon, coupled with the Coulomb stability of the residual multiply charged ethyl bromide clusters generated upon laser irradiation, due to their larger effective cluster size at 532  nm than at 355 and 266  nm.

Defect stabilization in ZnO nanorods by Mg2+ doping

Luminescent ZnO and Zn0.95Mg0.05O nanorods with length around 0.5 to 3 microm and diameter 100-150 nm were prepared by a facile solvothermal method. On hydriding at room temperature, a change of morphology from nanorods with aspect ratio 5-10 to particles of sizes 100 nm has been observed in both ZnO and Zn0.95Mg0.05O. While hydrided Zn0.95Mg0.05O showed an enhanced defect related green emission, the same got suppressed in hydrided ZnO. Even though it is observed that zinc vacancies are present in both as prepared ZnO and Zn0.95Mg0.05O, luminescence studies indicate that zinc vacancies get stabilized in Zn0.95Mg0.05O on hydrogenation.

Luminescence studies on low temperature synthesized ZnGa2O4:Ln3+ (Ln = Tb and Eu) nanoparticles

ZnGa2O4 nanoparticles doped with lanthanide ions (Tb3+ and Eu3+) were prepared at a low temperature of 120 degrees C based on urea hydrolysis in ethylene glycol medium. X-ray diffraction studies have confirmed that strain associated with nanoparticles changes as Tb3+ gets incorporated in the ZnGa2O4 lattice. Based on steady state emission and excitation studies of ZnGa2O4:Tb nanoparticles, it has been inferred that ZnGa2O4 host is characterized by a broad emission around 427 nm and there exists energy transfer between the host and Tb3+ ions. Unlike this, for ZnGa2O4:Eu nanoparticles, very poor energy transfer between the host and Eu3+ ions is observed. These nanoparticles when coated with ligands like oleic acid results in their improved dispersion in organic solvents like chloroform and dichloromethane.

Effect of structure, particle size and relative concentration of Eu(3+) and Tb(3+) ions on the luminescence properties of Eu(3+) co-doped Y(2)O(3):Tb nanoparticles

Eu(3+) co-doped Y(2)O(3):Tb nanoparticles were prepared by the combustion method and characterized for their structural and luminescence properties as a function of annealing temperatures and relative concentration of Eu(3+) and Tb(3+) ions. For Y(2)O(3):Eu,Tb nanoparticles annealed at 600 and 1200 °C, variation in the relative intensity of excitation transitions between the (7)F(6) ground state and low spin and high spin 4f(7)5d(1) excited states of Tb(3+) is explained due to the combined effect of distortion around Y(3+)/Tb(3+) in YO(6)/TbO(6) polyhedra and the size of the nanoparticles. Increase in relative intensity of the 285 nm peak (spin-allowed transition denoted as peak B) with respect to the 310 nm peak (spin-forbidden transition denoted as peak A) with decrease of Tb(3+) concentration in the Y(2)O(3):Eu,Tb nanoparticles heated at 1200 °C is explained based on two competing effects, namely energy transfer from Tb(3+) to Eu(3+) ions and quenching among the Tb(3+) ions. Back energy transfer from Tb(3+) to Eu(3+) in these nanoparticles is found to be very poor.

Wavelength-dependent Coulomb explosion in carbon disulphide (CS2) clusters: generation of energetic multiply charged carbon and sulphur ions

A gigawatt laser-induced Coulomb explosion has been observed in carbon disulphide (CS(2)) clusters generating energetic, multiply charged [C](m+) (m = 1-4) and [S](n+) (n = 1-6) atomic ions of carbon and sulphur. The Coulomb explosion shows wavelength dependence. Comparison of these results with our earlier work shows that the polarizability and dipole moment might help in energy absorption from the laser field but they are not mandatory conditions for this low-intensity Coulomb explosion. The results show that in a field of 10(9) W/cm(2), absorption of 266 and 355 nm laser radiation by CS(2) clusters leads to multiphoton dissociation/ionization whereas at 532 nm the whole cluster explodes generating multiply charged atomic ions.

Energy pooling in multiple ionization and Coulomb explosion of clusters by nanosecond-long, megawatt laser pulses

We report the results of experiments that establish the possibility of bringing about multiple ionization and Coulomb explosion of molecular clusters with nanosecond laser pulses at intensities as small as 10(9) W cm(-2). We demonstrate several new facets of the laser-cluster interaction in the low-intensity, long-pulse domain: (i) The choice of laser wavelength for a given cluster species is very crucial. (ii) Excited electronic states play a very important role in the ionization dynamics. (iii) When field ionization is insignificant and ponderomotive energies are very small, it is energy pooling rather than inverse bremsstrahlung that determines how clusters absorb energy from the optical field.

Laser Spectroscopic Excitation Function and Reaction Threshold Studies of the H + DCl → HCl + D Gas-Phase Isotope Exchange Reaction

The dynamics of the gas-phase hydrogen atom exchange reaction H + DCl --> HCl + D were studied using the pulsed laser photolysis/laser induced fluorescence "pump-and-probe" method. Laser photolysis of H2S at 222 nm was used to generate nonequilibrium distributions of translationally excited hydrogen atoms at high dilution in a flowing moderator gas (Ar)/reagent (DCl) mixture. H and D atoms were detected with sub-Doppler resolution via Lyman-alpha laser induced fluorescence spectroscopy, which allowed the measurement of the line shapes of the moderated H atom Doppler profiles as well as the concentration of the D atoms produced in the H + DCl --> HCl + D reaction. From the measured H atom Doppler profiles, the time evolution of the initially generated nascent nonequilibrium H atom speed distribution toward its room-temperature thermal equilibrium form was determined. In this way, the excitation function and the reaction threshold (E0 = 0.65 +/- 0.13 eV) for the H + DCl --> HCl + D reaction could be determined from the measured nonequilibrium D atom formation rates and single collision absolute reaction cross-section values of 0.12 +/- 0.04 A2 and 0.45 +/- 0.11 A2 measured at reagent collision energies of 1.0 and 1.4 eV, respectively.

Photoionization of CH(3)I mediated by the C state in the visible and ultraviolet regions

Three/two-photon resonant multiphoton ionization (MPI) of the CH3I monomer has been studied in the gas phase at 532 and 355 nm using time-of-flight mass spectrometry. Under low laser intensity (approximately 10(9) W/cm2) the mass spectra showed peaks at m/z 15, 127 and 142, corresponding to [CH3]+, [I]+ and [CH3I]+ species, at both these wavelengths. The laser power dependence for [CH3I]+, [I]+ and [CH3]+ ions showed a three-photon dependence at 532 nm. For the same three ions, photoionization studies at 355 nm gave a power dependence of 2. Both these results suggest that a vibronic energy level at approximately 7 eV, lying in the Rydberg C state, acts as a resonant intermediate level in ionization of CH3I. In the case of 355 nm, with increasing intensity additional peaks at m/z 139 and 141 were observed which could be assigned to [CI]+ and [CH2I]+ fragments. In contrast, for high intensity radiation at 532 nm ( approximately 2 x 10(10) W/cm2), only the [CI]+ fragment was observed. At these wavelengths, fragment ions observed in mass spectra mainly arise from photodissociation of the parent ion. Experiments at another wavelength in the visible region (564.2 nm) confirmed the results obtained at 532 nm. In order to assess the role of the A state in these MPI experiments, additional experiments were performed at 266 and 282.1 nm, which access the A state directly via a one-photon transition, and showed absence of a surviving precursor ion. Reaction energies for various possible dissociation channels of CH3I/[CH3I]+/[CH2I]+ were calculated theoretically at the MP2 level using the GAMESS electronic structure program.

Multiphoton dissociation/ionization of CHCl3 and CFCl3 at 355 nm: an experimental and theoretical study

Nonresonant laser-induced multiphoton dissociation/ionization studies have been conducted for trichloromethane (CHCl3) and trichlorofluoromethane (CFCl3) at 355 nm, using time-of-flight mass spectrometry (TOFMS). The molecular ion signal was found to be missing for both these compounds, and very similar fragmentation patterns were observed. Ab initio molecular electronic structure calculations were performed to help understand the fragmentation pattern of these molecules in the laser field. The energetics of different dissociation channels in the ground states of [CHCl3]+*, [CHCl2]+, [CFCl3]+* and [CFCl2]+, as well as neutral CHCl3, CHCl2*, CFCl3 and CFCl2* systems, were calculated. On comparing theoretical results with experimentally observed ion signals and their relative abundances in TOFMS, it is inferred that these molecules undergo sequential Cl atom elimination followed by photoionization of the fragments. The absence of [CFCl]+ has been interpreted on the basis of resonant A state-mediated two-photon absorption by CFCl, and the subsequent prompt photodissociation processes occurring for this state.