Transition Mn Research Articles

Pressure Tuning Spectroscopy of Mn2+ in Bulk and Nanocrystalline Sulfide Semiconductors

ABSTRACTWe report the results of high pressure luminescence studies of the emission of Mn2+ in bulk Zn0.55Ga0.30S up to ∼214 kbar, bulk ZnS up to ∼184 kbar, and nanocrystalline ZnS (∼8 nm particle sizes) up to ∼300 kbar. We observed a strong redshift with pressure (-30(3) cm−1/kbar) for the 4T1→6A1 emission transition of Mn2+ in all three systems. We also observed emission quenching at high pressure in all three systems and attribute the quenching to a pressure induced phase change of the ZnS host lattice to a rocksalt (NaCl) phase.

Modeling of transitions in Mn2+ doped ZnS nanocrystals and predicting reduced lasing threshold current density and enhanced electro-optic effects in ZnCdSe–ZnMgSSe and InGaN–AlGaN pseudomorphic quantum dots

A three-dimensional coupled-well excitonic model is presented to explain the observed shift in the photoluminescence excitation spectrum, emission peak from Mn2+ ions, and five-to-six orders reduction of radiative lifetime in ZnS:Mn2+(35 Å) doped nanocrystals. For pseudomorphic cladded nanocrystals such as ZnCdSe–ZnMgSSe, a modified excitonic model predicts enhancements in the absorption coefficient (α∼160 000 cm−1) and electric field-dependent index of refraction change (Δn/n∼0.1–0.2), and a significant reduction of radiative lifetime τr∼14.5 fs. Optical gain and threshold current density (Jth) are computed for ZnCdSe–ZnMgSSe and InGaN–AlGaN quantum dot lasers. In the case of InGaN–AlGaN quantum dot lasers, the effect of dislocation-induced traps, enhancement of optical gain due to excitonic transitions, and dot size are considered in the computation of Jth. It is shown that InGaN dots with larger cross sections (∼200×250 Å, such as self-organized dots) and consisting of a trap density of 2.9×1017 cm−3 yield Jth of 4500 A/cm2 in comparison to 136 A/cm2 for dots of size 35×35×35 Å. This explains the observation of higher current density in InGaN quantum well lasers having self-organized dots.

Decay Process of Photoluminescence in CdMnTe

Photoluminescence (PL) spectra, time profiles of PL intensity and PL excitation spectra (PLE) for inter 3d multiplets (3d-MS) transition of Mn2‡ are observed in the semimagnetic semiconductor CdMnTe under high pressures. Those of inter 3d-MS and inter quantum levels (QL) transitions are also observed in quantum wells (CdTe/Cd0.4Mn0.6Te). The decay processes in these excited states are discussed. The decay process to the excited states of infrared photoluminescence is also discussed for various concentrations. In these excited states it is considered that large lattice relaxation is essential.

Manganese valency and the colour of the Mn2AsO4(OH) polymorphs eveite and sarkinite

AbstractPolarized optical absorption spectra of single crystals of the two dimorphic Mn2AsO4(OH)-minerals eveite and sarkinite show that minor concentrations of Mn3+ at the octahedral site determine the colour and cause the distinct pleochroism in green and yellow of eveite. In the sarkinite spectra only absorption bands due to spin-forbidden d-d transitions in Mn2+ at six- and five-coordinated sites are observed, which produce a weak flesh-red mineral colour and a very faint pleochroism.

Enhanced Photoluminescence for ZnS Nanocrystals Doped with Mn2+ Close to Carboxyl Groups and/or S2− Vacancies

AbstractZnS nanocrystals doped with Mn2+ ions are prepared by a solution process and subsequent UV irradiation to produce the samples with different S/(Zn+Mn) ratios and/or surface modification by acrylic acids. Coordination states around Mn2+, ions were examined at 9 and 35 GHz by electron paramagnetic resonance spectroscopy. The Mn2+ sites in the vicinity of 2- vacancies or carboxyl groups are observed at the frequencies more than 9 or 35 GHz, respectively, for nanocrystals, but are not for the bulk sample of 250 nm diameter. Such Mn2+ sites enhance the photoluminescence due to d-d transition of Mn2+ ions through energy transfer from S2- vacancies or carboxyl groups, excited simultaneously by a light of 350 nm for exciting ZnS.

Photoluminescence of ZnSe/ZnMnSe superlattices under hydrostatic pressure

Photoluminescence near 4450 Å (violet) and 5900 Å (yellow) from ZnSe/Zn1−xMnxSe strained-layer superlattices (SLS) is studied as a function of applied hydrostatic pressure up to ∼90 kbar for x=0.23, 0.33, and 0.51 at 9 K. For each of the three SLSs, the peak energy of the near-band-gap violet photoluminescence (PL) from exciton recombination increases sublinearly with pressure, and closely follows that of ZnSe. The observed dependence is consistent with type-I band alignment, at least at pressures where the violet PL intensity remains strong. For the x=0.23 SLS, the energy of the biexciton PL increases faster than that of the exciton, which suggests decreased confinement. The yellow PL is due to the 4T1 →6A1 intraionic transition in Mn2+ and the nearly linear decrease of the peak energy of this signal with pressure is explained by crystal-field theory. In most cases examined, the intensities of the violet and/or yellow PL decrease abruptly above a certain pressure that increases with x from ∼65 to ∼90 kbar. For the different cases, this suggests either the occurrence of a phase transition in the ZnxMn1−xSe layers or a band crossing.

Intraionic transition in Mn2+ in zinc-blende semiconductors

This paper gives a discussion of a proposed mechanism for the conversion of an ionic transition, forbidden in free Mn2+, to allowed in a zinc-blende crystal by virtue of a modulation of the crystal potential by dynamic polarization of the anions of the crystal. We prove that this proposed mechanism is not effective in this context.

Temperature Dependence of Inhomogeneous Broadening and Mn2+ Photoluminescence Energy Shift in CdMnTe

Energy shift in Mn2+ photoluminescence relating with an excitation energy was observed in CdMnTe at low temperature. The shift is considered as the selective excitation of inhomogeneously broadened states. Using this shift we estimated the inhomogeneous broadening of the d-d transition in Mn2+ ions. The temperature dependence of the inhomogeneous broadening is discussed.

Magnetic Ordering of Mn Overlayers on Fe (100)

ABSTRACTSpin polarized electron energy loss spectroscopy (SPEELS) was used to probe the magnetic state of mn over layers on Fe (100). Nonzero exchange asymmetries are measured and found to oscillate with a two monolayer period as the mn overlayer thickness is varied, proving that the surface layer of the mn overlayers has a net magnetic moment and that these (100) Magnetic layers are aligned antiferromagnetically. The average exchange splitting of the mn surface layer is found to be 2.9 eV, indicating that the mn surface has a magnetic moment of the order 3 μg. In addition, oxidized mn overlayer surfaces have been studied, and the spectral features in the range 0 to 6 eV energy loss can be assigned to 3d-3d transitions of Mn2+. No indication of magnetic ordering of the MnO overlayer has been oserved.

EPR study of the phase transition in Mn2+-doped ammonium hydrogen oxalate hemihydrate single crystals.

The EPR spectra of ${\mathrm{Mn}}^{2+}$-doped ${\mathrm{NH}}_{4}$${\mathrm{HC}}_{2}$${\mathrm{O}}_{4}$\ensuremath{\cdot}1/${2\mathrm{H}}_{2}$O single crystals have been studied at the X band between 123 and 290 K. ${\mathrm{Mn}}^{2+}$ ions substitute for ${\mathrm{NH}}_{4}^{+}$ ions. Below the phase-transition temperature ${\mathit{T}}_{\mathit{c}}$ of the crystal, each hyperfine line of the spectrum is split into two components. The critical exponent \ensuremath{\beta} has been determined to be 0.41(3) from the line splitting below ${\mathit{T}}_{\mathit{c}}$.

Optical generation of nonzero-wave-vector magnons in antiferromagnetic MnF2

Abstract New methods for the generation and detection of nonzero-wave-vector magnons are applied to a study of the dynamics of magnons in antiferromagnetic MnF2. The magnons are generated by pulsed optical excitation either of Er3+ centers into the upper level of the lowest 4F 9 2 (1) doublet followed by direct decay, or, at wave vectors close to the zone boundary, of a sideband of the 6A1g-4T1g transition of Mn2+ followed by breakup of exciton-magnon pairs. In the latter case, gradual lifting of degeneracy of the magnon branches permits both the intersublattice and intrasublattice rates to be measured. Detection is accomplished via the luminescence of the Er3+ center, or, at larger wave vectors, via the voltage induced in a pickup coil by the transient magnetization. Various decay processes are discussed in comparison with theoretical estimates.

Luminescence of Mn-doped Bi4Ge3O12

Excitation and emission spectra of Mn-doped Bi4Ge3O12 have been studied within the range 200 to 650 nm. Aside from the 490 mn intrinsic emission band, also present in pure crystals, a band with a peak at 580 nm is observed. This emission is attributed to the 4T1(4G)-6A1(6S) transition of Mn2+ in a cubic crystal field. The excitation spectra exhibit three different regions: (i) below 280 nm, the intrinsic band observed in pure crystals is also found; (ii) at about 290 nm, a band is observed to excite the Mn2+ emission (at 580 nm), and is attributed to an energy transfer from a Bi3+ ion, which is perturbed by the emitting Mn2+ ion; (iii) above 310 nm, small excitation bands of cubic Mn2+ are observed. An estimate of the Mn2+ crystal-field parameters gave the following values: B=720 cm-1, C=3270 cm-1 and Dq=665 cm-1.

Absorption spectra of Mn2+ in manganoan clinozoisite

EPR and optical absorption studies are reported on manganoan clinozoisite for the first time. The ESR spectrum shows a six-line transition due to Mn2+ ion and givesg ≈ 2.00 andA ≈ 84 × 10−4 cm−1. An intense resonance line atg=4.7 is identified as due to Fe3+. The optical absorption spectrum of clinozoisite mainly consists of six bands, located at 15380, 18510, 20400, 23520, 25180 and 34470 cm−1. The bands at 20400 and 25180 cm−1 are assigned to4 A 1,4 E(G) and4 E(D) states, respectively, since they are sharp and do not show any shifts on cooling to 80 K. The other bands at 15380, 18510, 23520 and 34470 cm−1 are assigned to4 T 1(G),4 T 2(G),4 T 2(D) and4 A 2(F) states, respectively, due to spin-forbidden transitions of Mn2+ sited in a distorted octahedron of oxygen atoms. The crystal field parameters which gave a good fit to the observed band positions areB=683 cm−1,C=2714 cm−1 andDq=683 cm−1.

Spectroscopic study of X-irradiated SrF2:Mn

The absorption spectrum of 70K X-irradiated SrF2:Mn is measured. It shows two main bands at 325 and 425 nm. From several option bleaching and thermal annealing experiments it is found that the 325 nm band is due to Vk-centres and the 425 nm band to Mn+ ions in a Sr2+ substitutional position. The X-ray excited emission and the TL of 70K X-irradiated samples are also measured. An emission band found at 500 nm is associated with the 4T1g(4G) to 6A1g(6S) transition of Mn2+ ions. The decay of the 500 nm emission under X-ray excitation is studied as a function of temperature. The lifetime of the 4T1g(6G) level is obtained as well as the different contributions to the decay probability. The results are in agreement with those of Mn in CaF2 and CdF2.

Electron paramagentic resonance and phase transitions in Mn2+ doped Cd(ClO4)2⋅6H2O

An electron paramagnetic resonance study of Mn2+ doped in Cd(ClO4)2⋅6H2O has been made from 328 K to liquid nitrogen temperature. The site symmetry of Cd2+ is trigonal with a water octahedron distorted parallel to the crystallographic c axis. Mn2+ substitutes for Cd2+ and exhibits a characteristic 30-line hyperfine spectrum at room temperature (298 K) for the magnetic field H along the c axis. The D parameter is small and therefore there is considerable overlapping of lines in the spectrum. The spectrum is axially symmetric. On lowering the temperature, phase transitions are found to occur at 272±1 and 115.5±1 K.

Estimation of critical exponents for the ferroelectric transition in Mn2+-doped tris-sarcosine calcium chloride (TSCC) by means of EPR

Abstract The static rotation angle of the EPR fine-structure tensor of Mn 2+ centers of ferroelectric TSCC correlates with the order parameter. Its temperature dependence shows two distinct regions. In the vicinity of the phase transition temperature the critical exponent is β = 0.322 ± 0.012, below this critical region its temperature dependence points at a phase transition of weak first order.

EPR investigations of the ferroelectric phase transition in Mn2+-doped tris-sarcosine calcium chloride (TSCC) single crystals

physica status solidi (a)Volume 16, Issue 2 p. K121-K123 Short Note EPR investigations of the ferroelectric phase transition in Mn2+-doped tris-sarcosine calcium chloride (TSCC) single crystals W. Windsch, W. Windsch Sektion Physik der Karl-Marx-Universität LeipzigSearch for more papers by this authorH. Bartuch, H. Bartuch Sektion Physik der Karl-Marx-Universität LeipzigSearch for more papers by this author W. Windsch, W. Windsch Sektion Physik der Karl-Marx-Universität LeipzigSearch for more papers by this authorH. Bartuch, H. Bartuch Sektion Physik der Karl-Marx-Universität LeipzigSearch for more papers by this author First published: 16 April 1973 https://doi.org/10.1002/pssa.2210160247Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume16, Issue216 April 1973Pages K121-K123 RelatedInformation

Angular Variation of Intensities of Forbidden Lines in CaCO3:Mn2+ in Parallel and Perpendicular Configurations

The angular variation of intensities of electronic forbidden (Δ M=2, Δ m=0) and nuclear forbidden (Δ M=1, Δ m=−1) transitions in Mn2+:CaCo3 in parallel and perpendicular configurations was investigated. The intensity expressions for these transitions, assuming that the direction of the rf magnetic field makes an arbitrary angle with the direction of the static magnetic field, were derived. It is found that there is a good agreement between the theoretical and experimental results. From the comparison of the spectra in the parallel and perpendicular configurations for θ=0 and 12 π, it is concluded that D, A, and B have the same sign.