Experimental investigation of the structural features of polycarbonate (PC) filled with bismuth nitrate pentahydrate (BNP) composite films in terms of free volume defects probed by positron annihilation lifetime spectroscopy.

The effect of bismuth nitrate pentahydrate (BNP) on the properties and microstructural features of polycarbonate (PC) has been investigated using PALT, XRD, SEM, EDX, TG, ATR-FTIR and tensile mechanical measurements. Positron Annihilation Lifetime Spectroscopy reveals that the ortho-positronium lifetime and its corresponding intensity significantly decrease as the filler level of BNP in PC (in the composite) increases from 0.3 wt% up to 5.

High cubicity of DO ice inside spherical nanopores of MIL-101(Cr) framework: a neutron diffraction study.

Although cubic ice (ice I) is considered to be an important phase of water that impacts ice cloud formation in the Earth's upper atmosphere, its properties have not been studied to the same extent as those of hexagonal ice (ice I). This is because pristine ice I is not formed in simple laboratory conditions. Ice I formed in ambient conditions has a stacking disordered array of both hexagonal and cubic-structured hydrogen-bonded water molecules.

Tailoring defect structure and dopant composition and the generation of various color characteristics in Eu and Tb doped MgF phosphors.

A novel approach to generate a wide range of color characteristics such as near white, yellow, orange and red in MgF, by proper tailoring of the defect structure and varying the composition of Eu and Tb dopant ions have been presented here. It has been observed from positron annihilation lifetime spectroscopy (PALS) study that various defect centers such as mono vacancies and their cluster forms exist in the system, whose amount varies upon varying the dopant ion's composition. The experimentally observed positron lifetime values of the defect centers also matched well with the theoretically calculated lifetime values using the MIKA-DOPPLER package.

Engineering defect clusters in distorted NaMgF perovskite and their important roles in tuning the emission characteristics of Eu dopant ion.

An attempt has been made to explore various new defect clusters in distorted NaMgF perovskite and their important role in tuning optical properties. We have tried to tailor the defect clusters and to understand the impact on the luminescence of the lanthanide, for example the Eu ion. Defect engineering has been carried out by doping aliovalent dopant ions to create a charge imbalance in the matrix, which in turn led to the creation of various mono-, di- and new cluster vacancies.

Evolution of confined ice nano structures at different levels of pore filling: a synchrotron based X-ray diffraction study.

We have thoroughly investigated the crystal structure of ice evolved from super cooled water confined in MCM-41 cylindrical nano pores through a synchrotron-based X-ray diffraction (XRD) technique for two different levels of pore filling. A rigorous analysis of XRD data shows that the nucleation dynamics and the structure of nucleated ice highly depend on the level of pore filling. In the nearly fully hydrated pores, ice crystallites start nucleating inside the pores below 240 K and creep out of the pores to form bulk crystals having crystalline structure of a mixed phase of hexagonal and cubic forms.

Nanodiamonds as a state-of-the-art material for enhancing the gamma radiation resistance properties of polymeric membranes.

We report, for the first time, the development of gamma radiation resistant polysulfone (Psf)-nanodiamond (ND) composite membranes with varying concentrations of NDs, ranging up to 2 wt% of Psf. Radiation stability of the synthesized membranes was tested up to a dose of 1000 kGy. To understand the structure-property correlationship of these membranes, multiple characterization techniques were used, including field-emission scanning electron microscopy, atomic force microscopy, drop shape analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, gel permeation chromatography, positron annihilation spectroscopy, and small angle X-ray scattering.

EPR Evidence of Liquid Water in Ice: An Intrinsic Property of Water or a Self-Confinement Effect?

Liquid water (LW) existence in pure ice below 273 K has been a controversial aspect primarily because of the lack of experimental evidence. Recently, electron paramagnetic resonance (EPR) has been used to study deeply supercooled water in a rapidly frozen polycrystalline ice. The same technique can also be used to probe the presence of LW in polycrystalline ice that has formed through a more conventional, slow cooling one.

Exploring Defect-Induced Emission in ZnAlO: An Exceptional Color-Tunable Phosphor Material with Diverse Lifetimes.

Activator-free zinc aluminate (ZA) nanophosphor was synthesized through a sol-gel combustion route, which can be used both as a blue-emitting phosphor material and a white-emitting phosphor material, depending on the annealing temperature during synthesis. The material also has the potential to be used in optical thermometry. These fascinating color-tunable emission characteristics can be linked with the various defect centers present inside the matrix and their changes upon thermal annealing.

Positron annihilation and nuclear magnetic resonance study of the phase behavior of water confined in mesopores at different levels of hydration.

We investigated the molecular origin of the phase behavior of water confined in MCM 41 mesopores at different levels of hydration using positron annihilation spectroscopic and nuclear magnetic resonance techniques. The level of hydration influenced the phase behavior of the nanoconfined water. Two transitions above and below the bulk freezing temperature were observed depending on the level of hydration.

Water sensitivity in Zn4O-based MOFs is structure and history dependent.

Moisture can cause irreversible structural collapse in metal-organic frameworks (MOFs) resulting in decreased internal surface areas and pore volumes. The details of such structural collapse with regard to pore size evolution during degradation are currently unknown due to a lack of suitable in situ probes of porosity. Here we acquire MOF porosity data under dynamic conditions by incorporating a flow-through system in tandem with positronium annihilation lifetime spectroscopy (PALS).

Interpenetration, porosity, and high-pressure gas adsorption in Zn4O(2,6-naphthalene dicarboxylate)3.

Microporous coordination polymers (MCPs) have emerged as strong contenders for adsorption-based fuel storage and delivery in large part because of their high specific surface areas. The strategy of increasing surface area by increasing organic linker length has shown only sporadic success; as demonstrated by many members of the iconic Zn4O-based IRMOF series, for example, accessible porosity is often limited by interpenetration or pore collapse upon guest removal. In this work, we focus on Zn4O(ndc)3 (IRMOF-8, ndc = 2,6-naphthalene dicarboxylate), which exhibits typical surface areas of only 1000-2000 m(2)/g even though a surface area of more than 4000 m(2)/g is expected from geometric analysis of the originally reported crystal structure.

Evidence of Positronium Bloch states in porous crystals of Zn4O-coordination polymers.

Positronium (Ps) is shown to exist in a delocalized state in self-assembled metalorganic crystals that have large 1.3-1.5 nm cell sizes.

Effect of temperature on positronium annihilation in silica gel.

A systematic temperature-dependent study of positronium annihilation rate within the void spaces (micro- and mesopores) of silica gel material has been performed through positronium annihilation spectroscopy. The results find their plausible interpretation through a novel theoretical explanation based on vibrational interaction of thermally energized atoms on the surface layer of the pores with positronium, which in fact justifies the observed increase in the annihilation rate of the latter, with the increase in temperature.