Compositional and spectrochemical analyses of Cr-spinels in the Sittampundi Anorthosite Complex, Southern India: Implications for remote observation of spinels on the Moon

The spectroscopic techniques such as Laser Raman, Fourier Transform Infrared (FTIR), and hyperspectral have been used widely to understand the mineral chemistry and crystal structure and identify the functional phases and organic molecules in geological materials on Earth and other planetary bodies. The present study used these spectroscopic techniques combined with X-ray Diffraction (XRD) and Electron Probe Micro Analysis (EPMA) to understand the spectral-compositional relationships of the Cr-spinel (Chromian spinel) present in chromitite bodies associated with Sittampundi Anorthosite Complex (SAC), southern India. The bands/lenses of Cr-spinel are found as layers (few centimeters to 6 m thick) intercalated with anorthosites and clinopyroxenites of the SAC. The cumulate Cr-spinels of the study area exhibit compositions ranging between Al-chromite and Cr-spinel. Fe-, Al-rich Cr-spinel is a characteristic of the SAC with Cr₂O₃ content ranging from ~32-37 wt% and Cr# (Cr/[Cr + Al]) in the 0.44 to 0.53 range. The XRD spectra of these Cr-spinels have shown characteristic peaks corresponding to its constituent phases, with the highest peak at 36.11°. The observed longward shift in the Raman A_1g peak (~705-714 cm^-1) is likely to be caused by the substitution of Al³⁺ in the spinel structure. The Raman A_1g peak position near 705 cm^-1 in the spectra is attributed to the coexistence of (Mg, Fe) in the tetrahedral site and (Al, Cr) in the octahedral site. The broader and stronger 2 µm band position in the hyperspectral data is at relatively shorter wavelengths than typical Cr-spinels due to enhanced Al content (Al₂O₃ ~ 25 wt%) in the SAC samples. The 2 µm band position is observed to have a longward shift with increasing Cr₂O₃ and Cr# abundances and a corresponding shortward shift with enhanced Al₂O₃ content in Cr-spinels. The linear relationship between the 2 µm band position and Cr/Al abundances indicates that this absorption band is significant in distinguishing Cr-spinels from Al-spinels. Based on spectral and compositional resemblance, Fe- and Al-rich Cr-spinels in SAC are considered as probable terrestrial (functional) analogues for similar lunar spinel compositions given that evidence-based correlation of intricate processes involved in their formation under the lunar and terrestrial conditions. The present study demonstrates the approach of applying spectrochemical characteristics of terrestrial analogue spinels for remote identification of lunar spinels and retrieving their compositional ranges from the spectral reflectance parameters.

Dilute magnetic ions mediated magneto-dielectric, optical and ferroelectric response of MgAl2O4spinels

Magnesium aluminate (MgAl2O4) commonly termed as spinel has been a subject of intense research due to its excellent thermal, optical and dielectric characteristics. These properties in such compounds can efficiently be tuned by introducing small contents of different transition metals. In this work, dilute contents of transition metals (Mn, Fe, Co, and Ni) are incorporated in MgAl2O4to produce the dilute magnetic compositions of these aluminates. Crystallographic information reveals the formation of spinel cubic crystal structure with Fd-3m space group. Magnetic measurements demonstrate a clear magnetization response to an external magnetic field establishing dilute magnetic behavior of these spinels. The increase in ferroelectric characteristics with the incorporation of transition elements suggests that these materials are quite suitable for energy storage devices. A sharp variation in dielectric constant and magneto-dielectric coupling with the response to the external magnetic field, further exposes them as an excellent candidate for magneto-dielectric applications.

Influence of the pumping wavelength on laser properties of Fe2+ ions in ZnSe crystal

ZnSe:Fe²⁺ active laser crystal properties at different excitation wavelengths (2.94 and 4.1 μm) were investigated, and noticeable variations of the fluorescence spectra shape and their maxima positions, as well as changes in decay times, were observed. A stepwise shift of the laser oscillation wavelength from 4.7 μm at 2.94 μm pumping to 4.95 μm at 4.1 μm pumping was achieved at room temperature.

Spectroscopic and laser properties of bulk iron doped zinc magnesium selenide Fe:ZnMgSe generating at 4.5 - 5.1 µm

The Fe:Zn(1-x)Mg(x)Se (x = 0.19, 0.27, and 0.38) solid solutions spectroscopic properties were investigated and laser oscillations were achieved for the first time. The increase of the magnesium concentration in the Fe:ZnMgSe crystal was shown to result in an almost similar long wavelength shift of both absorption and fluorescence spectra of about 60 nm per each 10% of magnesium. With the Fe:ZnMgSe crystal temperature decrease, the fluorescence spectrum maximum shifts towards shorter wavelength resulting mainly from strong narrowing of the longest wavelength fluorescence line. Laser radiation wavelength dependence on the magnesium concentration as well as on temperature was observed. The Fe:ZnMgSe x = 0.38 laser oscillation wavelength increased from 4780 nm at 80 K to 4920 nm at 240 K using the optical resonator without any intracavity spectrally-selective element. In comparison with the Fe:ZnSe laser operating in similar conditions, these wavelengths at both temperatures were shifted by about 500 nm towards mid-IR region.

Power scaling of ultrafast laser inscribed waveguide lasers in chromium and iron doped zinc selenide

We report demonstration of Watt level waveguide lasers fabricated using Ultrafast Laser Inscription (ULI). The waveguides were fabricated in bulk chromium and iron doped zinc selenide crystals with a chirped pulse Yb fiber laser. The depressed cladding structure in Fe:ZnSe produced output powers of 1 W with a threshold of 50 mW and a slope efficiency of 58%, while a similar structure produced 5.1 W of output in Cr:ZnSe with a laser threshold of 350 mW and a slope efficiency of 41%. These results represent the current state-of-the-art for ULI waveguides in zinc based chalcogenides.

Magnetic ground state of an individual Fe(2+) ion in strained semiconductor nanostructure

Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe(2+) dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe(2+) spin configuration can be modified by subjecting the Fe(2+) ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz= ± 2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe(2+) ion. Magnetic character of the Fe(2+) ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe(2+) spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations.

Singlet-Triplet Excitations and Long-Range Entanglement in the Spin-Orbital Liquid Candidate FeSc2S4

Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate the characteristic length of the singlet correlations to be ξ/(a/2)≈8.2 (where a/2 is the nearest neighbor lattice constant), which establishes FeSc2S4 as a SOL with long-range entanglement.

EPR and optical absorption spectral studies on sphalerite mineral

The mineral sphalerite (Zn,Fe)S has been characterized by a combination of X-ray diffraction, EPR and NIR spectroscopy. The optical absorption spectrum of mineral sphalerite is due to an iron impurity only, which is in a distorted octahedral environment. The g=2.2 is attributed to iron and g and A value observed in the spectrum 1.999 and 6.0 mT are assigned to Mn(II) impurity in the mineral. These results indicate that iron and Mn(II) impurity have entered the lattice by substitution. The EPR results confirm the presence of manganese in a distorted octahedral environment. It is evident from the chemical analysis that iron is present in higher concentrations. NIR results are due to the presence of water and sulphide fundamentals which also support the formula of the mineral. No sulphate in the sphalerite mineral was observed.

Synthesis and characterizations of ultra-small ZnS and Zn(1-x)Fe(x)S quantum dots in aqueous media and spectroscopic study of their interactions with bovine serum albumin

This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe(3+) ion concentration as dopant on the optical properties of ZnS was studied. The size of quantum dots was determined to be about 1nm, using scanning tunneling microscopy. The synthesized nanoparticles were characterized by X-ray diffraction, UV-Vis absorption and photoluminescence emission spectroscopies. The presence and amount of iron impurity in the structure of Zn((1-x))Fe(x)S nanocrystals were confirmed by atomic absorption spectrometry. A blue shift in band-gap of ZnS was observed upon increasing incorporation of Fe(3+) ion in the iron doped zinc sulfide quantum dots. The photoluminescence investigations showed that, in the case of iron doped ZnS nanoparticles, the emission band of pure ZnS nanoparticles at 427nm shifts to 442nm with appearance of a new sharp emission band around 532nm. The X-ray diffraction analysis indicated that the iron doped nanoparticles are crystalline, with cubic zinc blend structure, having particle diameters of 1.7±022nm. Finally, the interaction of the synthesized nanoparticles with bovine serum albumin was investigated at pH 7.2. The UV-Vis absorption and fluorescence spectroscopic methods were applied to compare the optical properties of pure and iron doped ZnS quantum dots upon interaction with BSA. It was proved that, in both cases, the fluorescence quenching of BSA by the quantum dots is mainly a result of the formation of QDs-BSA complex in solution. In the steady-state fluorescence studies, the interaction parameters including binding constants (K(a)), number of binding sites (n), quenching constants ( [Formula: see text] ), and bimolecular quenching rate constants (k(q)) were determined at three different temperatures and the results were then used to evaluate the corresponding thermodynamic parameters ΔH, ΔS and ΔG.