Paramagnetic Resonance Spectra Of Mn2 Research Articles

Mn-Doped cesium lead halide perovskite nanocrystals with dual-color emission for WLED

CsPbX3 perovskite nanocrystals (NCs) are promising materials for light-emitting optoelectronics, which possess optically tunable bandgap, bright photoluminescence (PL), and excellent photoluminescence quantum yield. However, doping this new class of promising NCs with optically active or magnetic transition metal ions are still limited. Based on the status quo, we synthesized Mn-doped CsPbCl3 and CsPb(Cl/Br)3 NCs by one-pot synthesis method using MnCl2·(H2O)4 as the precursor. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as reaction temperature and the Pb-to-Mn feed ratio. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 NCs, and well-defined electron paramagnetic resonance spectra of Mn2+ in host CsPbX3 NCs lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb2+. In spite of the excellent luminescent properties of Mn-doped CsPbX3 NCs, their instability is still an important issue that obstruct their practical applications. In this paper, we reported a screen printing technology to prepare Mn-doped CsPbCl3 epoxy resin (ER) orange film for enhancing the stability of Mn-doped CsPbCl3 NCs. More importantly is that we fabricated NCs-ER with Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor-in-glass (PiG) realized the chromaticity tuning for YAG:Ce3+ phosphor with white light-emitting-diodes (WLED). In short, warm WLED were constructed by blending the Ce-PiG and orange Mn-doped CsPbCl3-ER materials with the InGaN blue chips.

Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX3) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl3 and CsPb(Cl/Br)3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation. The strong sensitized luminescence from d-d transition of Mn2+ ions upon band-edge excitation of the CsPbX3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn2+ in host CsPbX3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb2+. These observations indicate that CsPbX3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.

Zero-field signal in the electron paramagnetic resonance spectrum of Mn+2 in silicate glasses

A 9.4–9.8 GHz electron paramagnetic resonance (EPR) study of Mn+2-doped Na2O–CaO–MgO–SiO2 glasses has revealed a nonresonant microwave magneto-absorption near zero magnetic field in addition to normal paramagnetic absorption due to Mn+2 ions, electron spin S=5/2. The low-field response has an opposite phase relative to paramagnetic signal and is independent of the mutual orientation of the magnetic field of the microwave H1 and static magnetic field H. In contrast, the paramagnetic signal is different for perpendicular H1⊥H and parallel H1∥H polarization of the microwave field, which is attributed to enhancement of forbidden magnetic dipolar transitions and suppression of the allowed transitions for parallel polarization. The low-field response is described in terms of microwave dielectric losses that derive from the magneto-induced charge migration in the first coordination sphere of Mn+2. As opposed to the spin-polarized tunneling that was described in ferromagnets between different valence forms of Mn, the observed effect is due to spin-dependent tunneling that occurs in the vicinity of Mn+2 in a diluted paramagnetic system.

Characterization of the Crystal Quality of Calcites by Electron Paramagnetic Resonance

AbstractThe linewidths Bpp and anisotropies in the electron paramagnetic resonance spectra of Mn2+ impurities are measured in calcite single crystals and used for the determination of the origin of line broadening. Two different mechanisms of broadening, structural and chemical, are distinguished. From the differing angular dependences of the observed linewidths, large differences in the crystal quality are inferred. The differences in quality are also apparent in the EPR spectra of powder calcites, but no information about the mechanisms can be obtained.

Host spin-lattice relaxation narrowing and the electron paramagnetic resonance of Mn(II) in single crystals of hexakis(pyridineN-oxide)cobalt(II) complexes

The electron paramagnetic resonance spectra of Mn(C5H5NO)6. X2 (X ≡ ClO- 4, BF- 4 and NO- 3) doped in single crystals of isomorphous paramagnetic Co(C5H5NO)6. X2 are studied at various temperatures. Zero-field splitting in all three crystals is axially symmetric and the magnitude of D is unusually large for an octahedral coordination polyhedron with all ligands identical. The sharp resonance of Mn(II) in the paramagnetic host observed at high temperatures is interpreted in terms of random modulation of the dipolar interaction between the guest Mn(II) and host Co(II) ions by the rapid spin-lattice relaxation of Co(II). The spin-lattice relaxation times of Co(II) ions at 300 K, estimated from the temperature dependent linewidth of the Mn(II) resonance, are 24 × 10-12, 28 × 10-12 and 23 × 10-12 s in perchlorate, fluoborate and nitrate crystals respectively. The temperature dependence of the relaxation is of the form 1/(at + bt 5) and below 270 K the direct process dominates.

EPR of Mn2+ in Strontium Tartrate Trihydrate Single Crystals

AbstractElectron paramagnetic resonance spectra of Mn2+ doped in single crystals of strontium tartrate trihydrate grown by a diffusion technique are investigated at room temperature. Mn2+ enters the lattice substitutionally and is trapped at two magnetically equivalent but crystallographically inequivalent sites. The EPR measurements give the following values for the spin‐Hamiltonian parameters: gx(= gy) = 1.9781, gz = 2.0012, Ax(= Ay) = −94.9 × 10−4 T, Az = −96.2 × × 10−4 T, BB(= D/3) = +160.9 × 10−4 T, B(= E) = +101.2 × 10−4 T, B = +0.013 × 10−4 T, and B = +0.088 × 10−4 T.

Electron paramagnetic resonance of Mn2+, VO2+, Cu2+, and x-ray induced centers in Rb2C2O4 ⋅ H2O single crystals

The electron paramagnetic resonance spectra of Mn2+, VO2+, Cu2+, and x-ray induced centers in Rb2C2O4 ⋅ H2O single crystals are studied at 9.45 GHz and 290 K. The spectra at 77 K show no appreciable change. The ions appear to enter the lattice at interstitial sites. The doublet separations of forbidden hyperfine transitions (Δm=±1) are studied in Mn2+ doped crystals. The x-ray irradiated single crystals exhibit singlet spectrum and show saturation effect. The spin-Hamiltonian parameters are evaluated at 290 K.

EPR of Mn 2+ in Cd(COO) 2· 3H 2O single crystals

The electron paramagnetic resonance spectrum of Mn 2+ has been investigated in cadmium oxalate trihydrate single crystals at room temperature. The spectrum, recorded in the X-band, consists of a set of lines all of which correspond to a single type of environment. None of the principal axes coincides with any crystallographic axis. The spectrum is satisfactorily described by a spin Hamiltonian with a rhombic crystalline electric field. The separations of the forbidden doublets (Δ m = ± 1) in different electronic transitions have been calculated and compared with the observed doublet separations.

Spatial proximity of two divalent metal ions at the active site of S-adenosylmethionine synthetase.

S-Adenosylmethionine synthetase from Escherichia coli is shown to require 2 divalent metal ions/enzyme subunit for maximal enzymatic activity. In the absence of substrate, the tetrameric enzyme binds 1 Mn(II) ion/subunit, whereas in the presence of a nucleotide substrate, adenylylimidodiphosphate, or the product pyrophosphate, there are two Mn(II)-binding sites/subunit. Electron paramagnetic resonance spectra of Mn(II) bound to the enzyme reveal a spin exchange interaction between 2 Mn(II) ions in complexes of enzyme and Mn(II) which also contain adenosylmethionine, K+, and either pyrophosphate or imidotriphosphate. Since a spin exchange interaction requires orbital overlap between the 2 ions, the metal ions must be bound close to one another, and they may share a common ligand.

Electron spin resonance studies of iron-group impurities in beryllium fluoride glasses

Electron spin resonance investigations have been carried out on unirradiated BeF 2 glasses. Two relatively intense resonances were observed in a water-free distilled glass known to contain 49 ppm Ni, 13 ppm Mn, and <20 ppm Fe. One of these was the paramagnetic resonance spectrum of Mn 2+. Analysis of the observed 19F superhyperfine structure demonstrated this manganese to occupy distorted octahedral sites in the glass network. The second resonance was shown by temperature and frequency dependence studies, coupled with computer line shape analysis, to be a ferromagnetic resonance signal due to precipitated ferrite phases. The data suggest that these ferrites are somewhat heterogeneous and most likely comprize magnetite-like phases similar to NiFe 2O 4. An optical extinction curve rising into the ultraviolet with an approximate λ −4 dependence is tentatively ascribed to light scattering by ferrite particles ∼1000 Å in diameter.

EPR of Mn2+ and VO2+ in K2C2O4 · H2O Single Crystals

AbstractThe electron paramagnetic resonance spectra of Mn2+ and VO2+ impurities in K2C2O4 · H2O are analysed in X‐band at 298 K. The ions do not appear to enter the lattice as substitutional impurites. The double separation of forbidden hyperfine transitions (Δm = ± 1) are studied in Mn2+ doped crystals. It is found that the different parts of the single crystals are characterized by different intensity ratios of two magnetically inequivalent complexes. This behaviour is prominent in VO2+ doped crystals.

Characterization of homologous divalent metal ion binding sites of vertebrate and molluscan myosins using electron paramagnetic resonance spectroscopy

The binding of Ca 2+, Mg 2+ and Mn 2+ to myosins from rabbit skeletal muscle, scallop striated adductor muscle and clam adductor muscle has been investigated. All three myosins bind two moles of divalent metal ion non-specifically and with high affinity (Mn 2+ > Ca 2+ > Mg 2+). In addition, the molluscan myosins bind about a further two moles of Ca 2+ specifically. Although rabbit myosin binds some Ca 2+ in the presence of an excess of free Mg 2+, this binding occurs at the nonspecific sites and should not be taken as evidence for a myosin-linked regulatory system of the type found in molluscan muscles. If such a system exists in vertebrate skeletal muscle, the homologous Ca 2+-specific sites must be lost during the early stages of the myosin preparation. The characteristic electron paramagnetic resonance spectrum of the bound Mn 2+ was utilized to confirm the homology of the non-specific sites in vertebrate and molluscan myosins. The sites are located on the “regulatory” class of light chain. Mn 2+ bound to scallop myosin has a broad electron paramagnetic resonance spectrum, in contrast to the well-resolved spectra that it gives when bound to many other myosin species. This situation was exploited to identify homologous nonspecific, divalent metal-ion sites on the regulatory light chains from a variety of muscle types, including frog skeletal, rabbit cardiac, chicken gizzard and molluscan adductor muscles. When these light chains are combined with desensitized scallop myofibrils the electron paramagnetic resonance spectra of Mn 2+ bound to the resultant hybrids are dominated by the signal from the non-specific site of the foreign regulatory light chain.

Electron paramagnetic resonance of Mn2+ doped in alkali trihydrogen selenite single crystals

The electron paramagnetic resonance spectra of Mn2+doped in MeH3(SeO3)2(Me = Li, Na, K, and Rb) single crystals have been studied at 298 K. In LiH3(SeO3)2, an axis of non-coincidence effect has been observed and Mn2+ spectra show line broadening of outer transitions. In NaH3(SeO3)2, Mn2+ substitutes for Na+ ions and is associated with second nearest neighbour Na+ ion vacancies. Below the ferroelectric phase transition temperature of this crystal every line of the spectrum appears to split into two. The spectra of Mn2+ doped LiH3(SeO3)2 and NaH3(SeO3)2 (in paraelectric phase) have been analysed using the spin-Hamiltonian for rhombic symmetry. However, in KH3(SeO3)2 and RbH3(SeO3)2 the Mn2+ ions give only one line. The linewidths and g values of the lines for KH3(SeO3)2 and RbH3(SeO3)2 are ΔHpp = 154 ± 15 G, g = 1.988 ± 0.008, and ΔHpp = 102 ± 10 G, g = 1.998 ± 0.006, respectively.

Electron Paramagnetic Relaxation and EPR‐Line Shapes of Manganese Ions in a Sulfonated Polystyrene Ion‐Exchange Resin at Various Degrees of Hydration

AbstractLine shapes of electron paramagnetic resonance spectra of Mn2+‐ions in a sulfonated polystyrene ion‐exchange resin at varying degrees of hydration and temperatures have been examined at two microwave frequencies, 9 and 35 GHz. From a comparison between measured and simulated EPR‐spectra, the correlation times for the process modulating the zerofield splitting (zfs) interaction and the magnitude of the zfs‐parameters have been determined. For all samples with a water concentration higher than three molecules per sulfonate group, the correlation times were in the range of 10–40 ps, indicating a relatively high mobility of the hydrated cations in the polymer matrix. At lower water concentrations, forbidden transitions (Δm = ±1) have been observed. Their intensities increase with falling water concentrations and temperatures. Their temperature dependence was used to determine the fraction of metal ions associated at low water concentrations with the anchored sulfonate groups for a mean life‐time, τass≥10ns.

Electron Paramagnetic Resonance Studies of Manganese(II)-Pyruvate Kinase-Substrate Complexes

Abstract Electron paramagnetic resonance spectra of Mn(II) bound to pyruvate kinase and its substrate and inhibitor complexes are examined in solution. The binary complex of Mn(II) with the enzyme gives a spectrum which indicates that the electronic symmetry of the bound cation is only moderately distorted upon liganding to the protein. The spectrum of the binary enzyme-Mn(II) complex is unaltered upon formation of ternary complexes with either ADP or ATP. However, when ternary complexes are formed with either pyruvate or P-enolpyruvate, there are gross changes in the position and shape of the spectral lines which correlate with changes in the electronic symmetry of the bound Mn(II) and the electron spin relaxation time, respectively. The former changes are indicative of changes in the ligands of the bound metal ion and the latter of the accessibility of the binding site to the bulk solvent. Minor changes are observed in the spectrum of the pyruvate complex upon addition of ATP or enzymatic enolization cofactors such as arsenate or inorganic phosphate. Preliminary studies of Mn(II) complexes with chelating agents have revealed a striking similarity in spectra for the 2:1 complex of iminodiacetic acid and Mn(II) and the ternary complex of manganese-pyruvate kinase and pyruvate. Neither the spectrum of the binary complex nor that of the ternary complex with pyruvate is influenced by the presence or absence of activating monovalent cations such as K+. In contrast, spectra for the ternary complex of P-enolpyruvate are influenced by the species of monovalent cation in solution. In the presence of the nonactivating tetramethylammonium cation, the spectrum for the P-enolpyruvate ternary complex is a superposition of spectra for two distinct species. One species gives a very anisotropic spectrum which resembles that obtained in the presence of K+, whereas the other species gives a much more isotropic spectrum which matches the spectrum for the ternary complex of the inhibitor, α-(dihydroxyphosphinylmethyl) acrylic acid. Higher temperatures favor the species with the anisotropic spectrum. Ternary complexes with the inhibitor, P-glycolate, and the pseudosubstrate, Z-P-enol-3-fluoropyruvate, give spectra which show the presence of two separate species in the presence of tetramethylammonium cations in analogy to the substrate P-enolpyruvate. Another pseudosubstrate, Z-P-enol-α-ketobutyrate, gives only the anisotropic spectrum in the presence of either tetramethylammonium or K+ cations. The presence of only one form of the ternary complex in the presence of tetramethylammonium ion with this weak substrate is attributed to steric restrictions imposed by the methyl group. With the normal substrate, P-enolpyruvate, the fraction of the ternary complex which exists in the anisotropic form for a given monovalent ion appears to be correlated with the activating effect that ion, being greatest for K+ and Rb+, intermediate for Na+ and Li+, and least for tetramethylammonium ion.

Pyrazoles and imidazoles as ligands. X. electron paramagnetic resonance spectra of Mn II in a tetragonal environment of four pyrazoles and two anions

Electron Paramagnetic Resonance Spectra have been recorded for some compounds of the type Mn(ligand) 4- (anion) 2, with pyrazole and 3(5)-methyl pyrazole as the ligands, and Cl −, Br −, I −, and NO 3 −, as the anions. The spectra show absorptions far from g eff=2 for all compounds at both X- and Q-band frequencies. these spectra can be interpreted on the basis of a slightly distorted D 4h symmetry for S=5/2, with D= 0.05–1.5 cm −1 and λ (being equal to E/D)=0.01–0.1 The different values of the parameters for the several compounds can be explained by differences in the axial ligand-field strengths.

Temperature Dependence of Fine Structure of Mn2+ Ions in Alkali Chlorides

The paramagnetic resonance spectra of Mn 2+ in three alkali chlorides, i.e. , LiCl, NaCl and KCl were measured over the temperature range from room to liquid nitrogen temperature. The fine structure constants D and E of a Mn 2+ -vacancy center varied linearly with temperature. In LiCl, these constants were almost insensitive to temperature. In NaCl and KCl, the constants were appreciably dependent on temperature, and the fractional changes of those were larger in KCl than in NaCl by a factor of about three. The behaviours under temperature were qualitatively interpreted from the view point of the ionic arrangements around Mn 2+ .

E P R of Mn 2+: N a F

The electron paramagnetic resonance spectrum of Mn 2− is studied at 4.2°K. The absolute signs of the spin-hamiltonian parameters a, D and A are determined. The relaxation times are examined using the power saturation method. It is found that the spin-lattice relaxation time T 1 is of the order of 10 −4 sec.

Paramagnetic Resonance of Mn2+ in Glasses and Compounds of the Lithium Borate System

The paramagnetic resonance spectra of Mn2+ ions in glasses and compounds of the lithium borate system have been investigated at 9.1 and 35 GHz. The spectrum for the Li2O·4B2O3 compound is found to exhibit six very sharp hyperfine lines centered on g=3.3 when observation is made at X band, while at 35 GHz the center of the principal hyperfine sextet is seen to have shifted to g=2.0. This spectrum is interpreted by assuming a spin Hamiltonian containing crystal-field terms comparable to the Zeeman energy at X band. By means of a computed diagram it is determined that | D | /h=3.7 GHz and | E/D | =0.333. The same diagram is found useful in interpreting the ESR spectra of Mn2+ in lithium borate glasses. It is shown that in the glasses the manganese ions experience wide spreads of crystal fields, giving rise to fine-structure parameters ranging from near zero to 4 GHz or greater, with an apparent constraint favoring | E/D | ratios of approximately ⅓. It is concluded that many of the Mn2+ sites in the glasses are probably distorted versions of the site occupied in the Li2O·4B2O3 compound.

Paramagnetic Resonance of Mn2+ in CsBr

The paramagnetic resonance spectra of Mn 2+ ions in single crystals of CsBr were studied at 9 and 35 GHz. Two different kinds of spectra were observed, which arise from Mn 2+ ions in two different environments; one is a Mn 2+ ion in an aggregated state, and another is a Mn 2+ , which substituted Cs + and is accompanied with a positive ion vacancy in a nearest neighbor cation site. The spin Hamiltonian constants of the spectrum corresponding to the latter were found as g // =1.95±0.02, g ⊥ =2.00±0.02, D =0.390±0.02 cm -1 , A =(90+2)×10 -4 cm -1 .