Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac<1018 cm-3. The obtained experience has been used to investigate THM-grown single crystals. The measured longitudinal and radial dependence of the vacancy concentration can be explained by the temperature profile in the grown (Hg,Cd)Te ingots

Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac<1018 cm-3. The obtained experience has been used to investigate THM-grown single crystals. The measured longitudinal and radial dependence of the vacancy concentration can be explained by the temperature profile in the grown (Hg,Cd)Te ingots

Understanding the electromagnetic interaction of metal organic framework reactants in aqueous solution at microwave frequencies

Preparation of metal organic frameworks (MOFs) via microwave heating is becoming increasingly popular due to reduced reaction times and enhanced control of MOF particle size. However, there is little understanding about the detailed interaction of the electric field portion of the wave with reactants during the synthesis of MOFs. In order to overcome this lack of fundamental understanding, information about the dielectric properties of the reactants is required. In this work the dielectric constants (ε′) and loss factors (ε′′) of benzene-1,4-dicarboxylic acid (H2BDC; also known as terephthalic acid) and a number of M(III) (M = metal) salts dissolved in deionized water were measured as a function of frequency, temperature and concentration and with varying anions and cations. Dielectric data confirm the aqueous M(III) salts to be strong microwave absorbers, particularly at 915 MHz. M(III) salts with mono-anionic ligands (for example chlorides and nitrates) exhibit higher losses than di-anionic salts (sulfates) demonstrating that the former are heated more effectively in an applied microwave field. Of the M(III) salts containing either singly- or doubly-charged anions, those containing Fe(III) have the highest loss indicating that they will heat more efficiently than other M(III) salts such as Cr(III) and Al(III). Interestingly, H2BDC exhibits little interaction with the electric field at microwave frequencies

Non-contact universal sample presentation for room temperature macromolecular crystallography using acoustic levitation

Macromolecular Crystallography is a powerful and valuable technique to assess protein structures. Samples are commonly cryogenically cooled to minimise radiation damage effects from the X-ray beam, but low temperatures hinder normal protein functions and this procedure can introduce structural artefacts. Previous experiments utilising acoustic levitation for beamline science have focused on Langevin horns which deliver significant power to the confined droplet and are complex to set up accurately. In this work, the low power, portable TinyLev acoustic levitation system is used in combination with an approach to dispense and contain droplets, free of physical sample support to aid protein crystallography experiments. This method facilitates efficient X-ray data acquisition in ambient conditions compatible with dynamic studies. Levitated samples remain free of interference from fixed sample mounts, receive negligible heating, do not suffer significant evaporation and since the system occupies a small volume, can be readily installed at other light sources

Current trend in synthesis, Post-Synthetic modifications and biological applications of Nanometal-Organic frameworks (NMOFs)

Since the early reports of MOFs and their interesting properties, research involving these materials has grown wide in scope and applications. Various synthetic approaches have ensued in view of obtaining materials with optimised properties, the extensive scope of application spanning from energy, gas sorption, catalysis biological applications has meant exponentially evolved over the years. The far‐reaching synthetic and PSM approaches and porosity control possibilities have continued to serve as a motivation for research on these materials. With respect to the biological applications, MOFs have shown promise as good candidates in applications involving drug delivery, BioMOFs, sensing, imaging amongst others. Despite being a while away from successful entry into the market, observed results in sensing, drug delivery, and imaging put these materials on the spot light as candidates poised to usher in a revolution in biology. In this regard, this review article focuses current approaches in synthesis, post functionalization and biological applications of these materials with particular attention on drug delivery, imaging, sensing and BioMOFs

Electron paramagnetic resonance related to optical charge-transfer processes in ZnSe:Ti

In ZnSe crystals grown by different techniques, titanium ions are incorporated as Ti2+(d2) and Ti3+(d1) centers on Zn sites. A strong Jahn-Teller (JT) effect acts on the doubly degenerate 2E ground state of Ti3+. The electron paramagnetic resonance (EPR) at T=3 K indicates a quasistatic JT effect of the ground state and a quasidynamic one of the first excited state for the strain-split vibronic 2E−2A2 manifold. These effects are distinguished by their angular variations and the g values. Ti2+ causes an isotropic EPR signal. Excitation and sensitization spectra of Ti2+ and Ti3+ luminescence transitions are explained within a one-electron model connecting internal (d-d) with charge-transfer transitions involving the valence and conduction bands. Both charge states are sensitive to illumination with near-infrared light. The ions can be mutually converted, as shown by photo-EPR and sensitization experiments. The Ti2+/Ti3+ donor level is situated approximately 8500 cm−1 below the edge of the conduction band

Luminescence of tungsten impurities in ZnSe

Abstract. A new near-infrared luminescence band due to internal transitions of tungsten in ZnSe crystals is described. It is characterized by a weak zero-phonon line (ZPL) at v = D 10 700 cm−1 (λ = 934:6 nm) and 40 partially strong phonon satellites which reveal the presence of quasilocalized modes with energies of 33, 77, and 100 cm−1. A magnetic field does not split the ground state, indicating that this is a 1A1 state of a low-spin configuration of W2C .5d4/. The lifetime of the excited state is .47 ± 2/ µs. Intense absorption bands around 12 000 and 13 000 cm−1 dominating the PLE spectrum are assigned to internal W transitions. Under excitation with 9400 cm−1 (1.064 µm) a further emission appears starting at 6655 cm−1 with a weak ZPL followed by several stronger phonon lines. The distances between these peaks coincide in some cases with the quasilocalized modes of the former emission. Therefore, this luminescence is probably also related to tungsten centres

Vapour growth, EPR and optical study of Znse:Ti single crystals

Znse:Ti crystals were grown by seeded chemical vapour transport (SCVT) in a hydrogen atmosphere. In situ doping with titanium was carried out from an additional TiSe source in the quartz ampoule at 1460 K. The Good homogeneity of the Ti distribution and the presence of only a few defects have been demonstrated by etch pit and X-ray topography studies. For the frist time, Ti3+ (3d1) centres in a II–VI semiconductor compund are detected. The concentration of localized centres of Ti2+ and Ti3+ in high-resistivity material determined by EPR is about 5 × 1016 cm−3. Fe3+, Ni2+ and traces of Mn2+ are additionally observed. Below 77K an anisotropic EPR spectrum of Ti3+ (d1) is recorded, indicating both a dynamic and a static Jahn–Teller effect of the 2E(D) ground state. At lower temperatures clear evidence of the static Jahn–Teller effect is observed. The frist emission and excitation spectra of Ti impurities in II–VI compounds are presented. An emission near 3400 cm−1 is assigned to the 3T2(F) → 3A2(F) transition of Ti2+ (d2). Its excitation structures coincide with the known absorption bands to 3T1(P) and 3T1(F). A further structured luminescence band at 4700 cm−1 is related to 2T2 → 2E(D) transition of Ti3+ (d1). Ti ions form a deep donor level Ti2+/Ti3+ situated approximately 14,100 cm−1 above the valence band. This photo-ionization threshold is derived from the excitation measurements in accordance with previous photoconductivity experiments

Optical and paramagnetic properties of titanium centres in ZnS

ZnS:Ti crystals grown by different methods are investigated at low temperatures (2 K $\leq T \leq 80$ K) by electron paramagnetic resonance (EPR) and optical spectroscopies, mainly with regard to their photoluminescence properties, including excitation and sensitisation spectra. The more familiar lattice-neutral Ti$^{2+}(d^2)$ ion on a cubic site (AN) presents an isotropic EPR signal with g=1.928 observable up to 80 K. Signals of axial PN and AS sites are detected in the same temperature range. This Ti2+ ion exhibits the $^3T_2(F) \rightarrow{}^3A_2(F)$ transition in emission, structured by no-phonon lines (NPL) of centres in various environments, with the AN site represented at 3613 cm-1, and the $^3T_1(F)$ and $^3T_1(P)$ bands in excitation spectra. Substitutional Ti$^{3+}(d^1)$ is identified by an anisotropic EPR spectrum at T = 3.5 K, indicating a quasistatic Jahn-Teller effect at the doubly degenerate $^2E(D)$ ground state, while in the first excited vibronic state a quasidynamic JT effect in the strain-split vibronic $^2E/^2A_2$ manifold is found. A new luminescence band centred at 4500 cm-1 with NPL structures near 5000 cm-1 represents AN, PN and AS sites in the $^2T_2(D) \rightarrow{}^2E(D)$ transition. Charge-transfer processes are described in a one-particle model, depicting the Ti3+/Ti2+ donor level at 12 900 cm-1 below the conduction-band edge