Spectra Of Cr3 Research Articles

EPR detection of Cr4+ centers in yttrium orthosilicate Y2SiO5

The EPR spectra of Czochralski grown Y2SiO5:Cr and Y2SiO5:53Cr crystals have been studied. In addition to the previously known spectra of Cr3+, the spectrum of the Cr4+ ion was detected and studied for the first time. The fine structure parameters of tetravalent chromium in Y2SiO5 host were obtained based on the analysis of the angular and frequency-field dependences of the EPR spectra. The conclusion about tetrahedral coordination of Cr4+ ion in this host was made. The concentrations ratio of c(Cr3+)/c(Cr4+) ions in the crystal has been evaluated.

Photoluminescence spectroscopy of Cr3+ in β-Ga2O3 and (Al0.1Ga0.9)2O3

Alloying β-Ga2O3 with Al2O3 to create (AlxGa1−x)2O3 enables ultra-wide bandgap materials suitable for applications deep into ultraviolet. In this work, photoluminescence (PL) spectra of Cr3+ were investigated in monoclinic single crystal β-Ga2O3, and 10 mol. % Al2O3 alloyed with β-Ga2O3, denoted β-(Al0.1Ga0.9)2O3 or AGO. Temperature-dependent PL properties were studied for Cr3+ in AGO and β-Ga2O3 from 295 to 16 K. For both materials at room temperature, the red-line emission doublet R1 and R2 occurs at 696 nm (1.78 eV) and 690 nm (1.80 eV), respectively, along with a broad emission band at 709 nm (1.75 eV). The linewidths for AGO are larger for all temperatures due to alloy broadening. For both materials, the R-lines blue-shift with decreasing temperature. The (lowest energy) R1 line is dominant at low temperatures due to the thermal population of the levels. For temperatures above ∼50 K, however, the ratio of R2 to R1 peak areas is dominated by nonradiative combination.

Determination of the Crystallization Temperature of Mullite by Luminescence Spectra of Europium and Chromium Ions

The luminescence spectra of Cr3+ and Eu3+ ions embedded in mullite ceramic samples are studied. The samples were annealed at temperatures from 600 to 1200°C. From the temperature of 800°C, the spectra demonstrated the presence of a newly-formed crystal phase. The appearing of the crystalline phase is revealed by significant changes in some parameters of the luminescence spectrum. At temperatures from 920 to 1200°C, the crystalline form manifested itself as a stable mullite phase.

Ruby Emission in the Range 400–800 nm with Excitation by Continuous-Wave CO2 Laser Pulses

Thermal emission spectra of ruby single crystals in the range 400–800 nm were studied experimentally as functions of the intensity at 10.6 μm of exciting pulses (~0.5 s) from a continuous-wave electrical-discharge CO2 laser. Spectra at excitation intensity 1–20 kW/cm2 were superpositions of the thermal emission continuum of the sapphire crystal lattice in the range 600–800 nm and selective emission spectra of Cr3+ that were observed for the first time for ruby and consisted of R-lines at 695 nm; N-lines at 715 nm; 2 T 1, 4 T 2 → 4 A 2 transition bands at ~672 and 643 nm; and 4 T 1, 2 T 2 → 4 A 2 transition bands at ~530 and 490 nm that were not observed in the luminescence spectrum. Time dependences of the shapes of selective emission spectra, quenching and shifts of the R 1 line, and the temperature dependence of ruby luminescence spectra were investigated.

Zero field splitting parameters of Cr3+ doped potassium sodium dl-tartrate tetrahydrate

The zero field splitting parameters (ZFSPs) D and E of Cr3+ ion doped potassium sodium dl-tartrate tetrahydrate (PSTT), KNaC4H4O6·4H2O are calculated using the superposition model. The theoretically calculated ZFSPs for Cr3+ in PSTT crystal are compared with the experimental values obtained by electron paramagnetic resonance. Theoretical ZFSPs are in good agreement with the experimental values. The energy band positions of optical absorption spectra of Cr3+ in PSTT single crystal calculated with the CFA package agree well with experimental values.

Combustion Synthesized Cr3+-doped–BaMgAl10O17 Phosphor: An Electron Paramagnetic Resonance and Optical Study

BaMgAl10O17 phosphors doped with Cr3+ ions were prepared by a combustion route at a furnace temperature of 773 K. The X-ray diffraction pattern revealed that the BaMgAl10O17 phosphor was in a hexagonal phase. Energy-dispersive X-ray mapping images demonstrated the presence of the dopant ion in the BaMgAl10O17 matrix. The bands observed in the optical absorption spectrum were characteristic of Cr3+ ions in octahedral geometry. Upon 555-nm excitation, an intense narrow red emission line centred at 690 nm due to the 2Eg → 4A2g transition of Cr3+ ions was observed. The electron paramagnetic resonance (EPR) spectrum of Cr3+ ions in BaMgAl10O17 phosphor showed multiple absorption bands having at least 6 g values. Based on the EPR data, various parameters such as the absolute number of spins, Gibbs potential, magnetic susceptibility and magnetic moments, Curie constant, etc., for the system were evaluated.

Local structure distortion models for Cr3+ centers in Tl2MgF4 and Tl2ZnF4 fluorine compounds

Theoretical analysis of the EPR spectra of Cr3+ centers in Tl2MgF4 (Tl2MgF4 and Tl2ZnF4) fluorine compounds have been carried out for the first time. The correlation between the experimental data and theoretical values regarding zero-field splitting (ZFS) provides suitable structural models to understand the local structure around the Cr3+ centers in Tl2MgF4 and Tl2ZnF4. A clear compression of the MF6 octahedron around tetragonal (TE) Cr3+ center has been shown in both crystals. The calculations for the monoclinic (MO) Cr3+ center reveal that the length of the four equatorial F-ligands (R2) is about 1.5% longer than that of the octahedral ZnF6 in undoped Tl2ZnF4 and the length of the axial F-ligands (R1) is quite shorter (∼9.5%) than R2. Also, it yields a quite large b2−1 and declined angle (27.46°, ∼30%) for z-axis. Our results indicate that the presence of the different structural formations may be considered around the orthorhombic (OR) Cr3+ center III and IV. It was suggested that the latter one can be attributed to an angular distortion relevant to the equatorial F-ligands along z∥[110]-axis.

Luminescence of 60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium

60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr3+ in octahedral coordination and Cr4+ in tetrahedral coordination. Energy transfer from Bi3+ to Nd3+ and Cr3+ has been demonstrated.

Influence of chromium concentration on the electron magnetic resonance linewidth of Cr3+ in SrTiO3

Electron magnetic resonance (EMR) spectra of Cr3+ ions in samples of chromium-doped strontium titanate (SrTiO3) have been studied at room temperature for chromium concentrations between 0.20 and 1.00 mol%. According to previous studies, chromium substitutes Ti4+ sites in the lattice and its preferred valence state is Cr4+, which is EMR silent in the X-band, but the trivalent state can be produced by illumination or codoping with Nb. In the present work, the codoping method was used; the results show the electron magnetic resonance linewidth of the Cr3+ spectrum increases with increasing chromium concentration and that the range of the exchange interaction between Cr3+ ions is about 0.96 nm.

Effect of ferroelastic domain pattern changes on the EPR spectra in TDM

This article presents polarized light microscopy studies of the ferroelastic domain structure and the analysis of electron paramagnetic resonance spectra of Cr3+ admixture ions in trigonal double molybdates. The correlation has been found between abnormal EPR lineshape and domain structure in ferroelastic phases of these crystals.

Phase transitions in K1− x Rb x Sc(MoO4)2 solid solutions

K1− x Rb x Sc(MoO4)2 single crystals doped with Cr3+ were studied by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy and optical microscopy. It has been found that the EPR spectra in solid solutions for x ≤ 0.2 are inhomogeneously broadened due to the random occupation of the next nearest-neighbour cation sites K+ and Rb+. The spin-Hamiltonian parameters describing the room-temperature EPR spectra of Cr3+ in K1− x Rb x Sc(MoO4)2 are calculated. The behaviour of the EPR spectra versus temperature reveals the existence of structural phase transitions in these crystals. The results show that a substitution of K+ by Rb+ suppresses the transition temperatures. The optical investigations carried out under the polarizing microscope have shown a ferroelastic nature of these transformations.

Cr 3 + electron paramagnetic resonance study of Sn1−xCrxO2 (0.00≤x≤0.10)

This paper reports on the liquid-helium-temperature (5 K) electron paramagnetic resonance (EPR) spectra of Cr3+ ions in the nanoparticles of SnO2 synthesized at 600 °C with concentrations of 0%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 5.0%, and 10%. Each spectrum may be simulated as overlap of spectra due to four magnetically inequivalent Cr3+ centers characterized by different values of the spin-Hamiltonian parameters. Three of these centers belong to Cr3+ ions in orthorhombic sites, situated near oxygen vacancies, characterized by very large zero-field splitting parameters D and E, presumably due to the presence of nanoparticles in the samples. The fourth EPR spectrum belongs to the Cr3+ ions situated at sites with tetragonal symmetry, substituting for the Sn4+ ion, characterized by a very small value of D. In addition, there appears a ferromagnetic resonance line due to oxygen defects for samples with Cr3+ concentrations of ≤2.5%. Further, in samples with Cr3+ concentrations of ≥2.5%, there appears an intense and wide EPR line due to the interactions among the Cr3+ ions in the clusters formed due to rather excessive doping; the intensity and width of this line increase with increasing concentration. The Cr3+ EPR spectra observed in these nanopowders are very different from those in bulk SnO2 crystals.

CsLiSO4/NH4LiSO4 system investigated by EPR

The single crystals of CsLiSO4 and the solid solutions Cs x (NH4)(1− x )LiSO4 have been investigated using the EPR technique. Two kinds of vanadyl doped samples were considered – as-grown from the aqueous solutions of appropriate compounds and after a thermal treatment. It has been established that in as-grown crystals the EPR spectra of vanadyl ions were very complex due to the presence of more than one paramagnetic site in the lattice. At least two such sites were identified and spin Hamiltonian parameters were calculated for all the sites. After annealing the crystals at about 400 K, a significant decrease in the intensities of the EPR lines of VO2+ complexes was observed. In well-annealed samples the complexity of the EPR spectra has been found to disappear. Additionally, the third kind of vanadyl complexes were created during this treatment. It has also been shown that the EPR spectra of Cr3+ ions in CsLiSO4 could be observed without any additional sample treatment reported in literature like an irradiation or thermal decomposition. It was established that the VO2+ and Cr3+, being sensitive to structural phase transition in the CsLiSO4, can be used as a probe for the structural changes in the CsLiSO4/NH4LiSO4 system.

EPR spectra of Cr3+-doped LuNbO4 crystals

Ferroelastic LuNbO4 single crystals containing 0.3 at. % Cr3+ ions have been grown by the floating zone technique, and their EPR spectra have been studied at a frequency of 9.8 GHz at room temperature. The lines on the spectra are due to the transitions caused by three paramagnetic centers formed as a result of the replacement of one isovalent position of a Lu3+ ion and two nonisovalent positions of Nb5+ions by Cr3+-ions. As a result of twinning, the line number is doubled and four principal directions arise along which the same spectra are obtained. The spectra of these centers were described by a spin Hamiltonian with S = 3/2, the D and E parameters ranging from 0.024 to 0.17 cm−1, and the g-factors g ∥ = 1.75–2.20 and g ⊥ = 1.90–2.13.

Two-photon excitation spectra of Cr3+:K2NaScF6

Two-photon excitation (TPE) spectra of Cr3+:K2NaScF6 exhibit unexpected features including a forbidden transition, extended progressions, a split zero-phonon line and anomalous polarization anisotropy. These features are explained by departures from standard approximations.

Electron-lattice coupling incongruent Co-doped LiNbO3:Cr3+:ZnO crystal

The importance of the role of the ion-lattice coupling indetermining the energy levels of Cr3+ ions in congruentLiNbO3 crystals doped with 2.9% of ZnO is demonstrated in thispaper. The Racah parameters: B = 533 cm-1, C = 3244 cm-1 and the crystal-field intensity Dq = 1527 cm-1 were determined and the Tanabe-Sugano diagram was constructed.The characteristics of the absorption and the emission spectra ofCr3+ ions in these crystals can be explained in terms of theconfigurational-coordinate diagram in the harmonic approximation,with good agreement obtained. The Huang-Rhys parameter S = 6.86 andthe lattice phonon energy ℏω = 343 cm-1 are alsoreported in this work.

Two-photon excitation spectroscopy of Cr3+:K2NaScF6elpasolite: II. Theoretical models

Two-photon excitation (TPE) spectra of Cr3+:K2NaScF6, excited bya Raman-shifted, Nd:YAG-pumped tunable dye laser, exhibit severalunexpected features. A weak TPE spectrum of the symmetry-forbidden 4A2g→ 4T2g transition is observed without a zero-phononline. The symmetry-allowed TPE spectrum of the 4A2g→ 4T1ag transition has a multi-phonon side band with anomalously extendedvibrational progressions, and an anomalously weak, split zero-phonon linewith anomalous polarization anisotropy. These observations are explained,respectively, in terms of theoretical models involving phonon assistance,departures from the closure approximation that permitelectron-latticecoupling in intermediate states and a low-temperature phase transitioninvolving librational instability. Hypothetical line-shape simulations arecompared with observed TPE spectra.

EPR Spectra of Cr3+ Ions in Sr3Ga2Ge4O14:Cr Single Crystals

The results of investigations of chromium‐doped Sr3Ga2Ge4O14 single crystals by the EPR‐spectroscopy method are presented. It is shown that activating chromium ions form Cr3+ → Ga3+ (Ge4+) substitution centers in the 1a‐octahedral positions of the lattice of Sr3Ga2Ge4O14. Depending on the combination of occupation of the 3f‐tetrahedral positions of the first cationic coordination sphere by Ga3+ and Ge4+ ions, Cr3+ centers of two types are formed. Their individual magnetic spectra are characterized by axial and rhombic symmetry. The magnetic multiplicity of the axial‐symmetry spectrum is equal to unity. There exist rhombic‐symmetry centers of two types differing in the orientation of the principal magnetic axes and the value of the spin‐Hamiltonian parameter E. The magnetic multiplicity of the individual magnetic spectra of rhombic centers of each type is equal to three. The detected EPR spectra of Cr3+ ions have been described by the spin Hamiltonian of rhombic symmetry. Its parameters and their spread have been determined.

Comparative studies of luminescence in congruent and stoichiometric VTE-treated linbo3:Cr

The luminescence spectra of Cr3+ impurity have been studied in the wide spectral (11500 to 13900 cm−1) and temperature (5 to 300K) ranges for initially congruent grown LiNbO3:Cr3+ (0·1% mol.) specimens. The samples were further stoichiometrised using the Vapour Transport Equilibrium (VTE) procedure. In contrast to the congruent samples, for which in the region of supposed 2E-4A2 transitions in Cr3+ ions 7 emission lines were detected, 12 emission lines were observed in stoichiometric VTE specimens. Moreover, in VTE crystals, we observed 5 so far unknown polarized lines centered at 12801, 12530, 12215, 11980 and 11720 cm−1 (T=80K) on the short-wavelength side of 4T2- 4A2 emission band. These new lines can be tentatively attributed to transitions in exchange-coupled pairs of Cr3+ ions.

An electron spin-resonance study of Cr3+ in LiSrxCa1-xAlF6 with x = 0, 0.5, 0.8, and 1

Electron spin-resonance (ESR) spectra of Cr3+ ions in LiSrxCa1-xAlF6 crystals with x = 0, 0.5, 0.8, and 1 have been measured at X-band microwave frequencies in the temperature range 1.3-300 K. The intense ESR lines from Cr3+ ions in these crystals have been fitted to a trigonal spin Hamiltonian to determine values of the g-tensor (g,g) and zero-field splitting, 2D. The principal g-values (g g1.974) are almost the same in all cases whereas 2D increases sequentially for x = 0, 0.5, 0.8, and 1. The value of |2D| for Cr3+:LiCaAlF6 decreases gradually as the temperature is increased from 1.3 K to 300 K. Over this same temperature range the value of |2D| for Cr3+:LiSrAlF6 increases. The ESR spectra for Cr3+ in LiSr0.5Ca0.5AlF6 and LiSr0.8Ca0.2AlF6 are inhomogeneously broadened by discrete centres with pseudo-trigonal symmetry, different configurations of which correspond to the random occupation of the second-nearest-neighbour cation sites by Ca2+ and Sr2+ ions.