Mn²⁺-induced substitutional structural changes in ZnS nanoparticles as observed from positron annihilation studies

Abstract

Zinc sulfide nanoparticles doped with different concentrations of manganese ions (Mn(2+)) were synthesized at various temperatures to investigate the effects of substitution and the associated defect evolution. Positron lifetime and Doppler broadening measurements were used as probes. The initial stage of defect recovery was dominated by the occupation of Zn(2+) vacancies by Mn(2+) ions, bringing in characteristic changes in the positron lifetimes, intensities and Doppler broadened lineshape parameters. Detailed analyses considering the presence of one and two types of defects were carried out to identify the type of defects which trap positrons at the different dopant concentrations. Electron paramagnetic resonance studies indicated increased Mn-Mn interaction and the formation of Mn clusters with further doping. The results are in striking contrast to those for nanorods, where vacancy recombination transformed their interior into regions free of defects.

Positron annihilation studies of NiO nanoparticles prepared through two different chemical routes

“…To assess its suitability for device fabrication and technological use, detailed knowledge of the size, morphology, atomic distribution and defects within and at the surfaces of nanocrystallites is important. Positron annihilation spectroscopy can be used for the detection and characterization of defects like vacancies and interfaces in nanomaterials [2]. In this work, positron lifetime and Doppler broadening measure-ments were carried out on two sets of NiO samples of different mean grain sizes and prepared through two different methods -solvothermal and sol-gel -and the results are reported.…”

Quantum Dot-Based OFF/ON Probe for Detection of Glutathione

“…Figure b shows the PL spectrum of the Qdots exhibiting bright yellow-orange emission at ∼592 nm. This emission was attributed to the 4 T 1 → 6 A 1 transition of Mn 2+ ions in the Qdot core. − …”

“…They also reported that the fluorescence quenching (electron transfer) of these Qdots depended on their sizes. In contrast, our study is focused on sensitive detection of GSH using Mn dopant-based Qdots (where the 4 T 1 => 6 A 1 Mn 2+ ion transition is independent of Qdot size − ). Moreover, direct attachment of dopamine to Qdots could possibly have enhanced the efficiency of the electron transfer process because of “zero-length” coupling.…”

Crystal Defects and Cation Redistribution Study on Nanocrystalline Cobalt-Ferri-Chromites by Positron Annihilation Spectroscopy

“…Further, the sample with the source embedded in it was maintained under dry vacuum conditions during the experiments. This is done to eliminate the possibility of the trapping of positrons and quenching of positronium (the metastable bound state of the positron and an electron) by the air and gases otherwise getting trapped within the powdered sample [13]. The positron lifetime measurements were carried out using a slow-fast coincidence spectrometer, having a time resolution (FWHM) of 200 ps for the gamma rays from 60 Co source under experimental conditions.…”