Temperature dependence of the luminescence of nanocrystalline CdS/Mn

The temperature dependence of the luminescence properties of nanocrystalline CdS/Mn²⁺ particles is investigated. In addition to an orange Mn²⁺ emission around 585 nm a red defect related emission around 700 nm is observed. The temperature quenching of both emissions is similar (T_q≈100 K). For the defect emission the reduction in the lifetime follows the temperature dependence of the intensity. For the Mn²⁺ emission however, the intensity decreases more rapidly than the lifetime with increasing temperature. To explain these observations a model is proposed in which the Mn²⁺ ions are excited via an intermediate state involving shallowly trapped (≈40 meV) charge carriers.     

Electrical properties of copper-manganese spinel solutions and their cation valence and cation distribution

The cation valence and distribution in copper manganese spinels containing 1.0-1.6 mol copper per formula unit (Cu_xMn_3−xO₄) was resolved from their electrical conductivity and thermoelectric properties. The limit of thermal stability of the cubic spinel phase was also determined for each stoichiometry. A corrected phase diagram for the Cu-Mn-O system in air is proposed accordingly. The electronic defect structure could be described through a chemical approach, involving the competition between the redox of Cu⁺ and Mn⁴⁺ to Cu²⁺ and Mn³⁺ and the disproportionation of the Jahn-Teller ion Mn³⁺ into Mn²⁺ and Mn⁴⁺. Thermodynamic parameters for the redox reaction were determined from experimental data as well as calculated, confirming the validity of the modeled defect equilibria.     

Linear scaling of hyperfine- and superhyperfine interactions

The transfer of an electron from the occupied 2s(F^?) to the empty 4s (Mn²⁺-F^? by lattice-vibrational modulation of attractive nuclear potential is discovered to give rise to the correct reduction of the magnitude of hyperfine interaction of Mn²⁺ ion accompanied by a reduction of superhyperfine coupling of ¹⁹F. This predicted effect is in accord with the experiments in LiF:Mn²⁺ and KMgF₃:Mn²⁺.     

Red long-lasting luminescence in clinoenstatite

A long-lasting phosphor Ca_0.2Zn_0.9Mg_0.9Si₂O₆:Eu²⁺, Dy³⁺, Mn²⁺ was prepared by a sol-gel method. Nanoparticles crystallizing in a clinoenstatite structure were obtained. Long persistent phosphorescence in the red has been observed with persistence time over one hour at 680 nm and was attributed to Mn²⁺ emission. The persistent luminescence is suggested to involve Eu²⁺ as a sensitizer, Dy³⁺ or Dy³⁺-related defect as a trap center and Mn²⁺ as the luminescent center. However, the details of the mechanism are still under further investigation.     

Inverse bottleneck in Eu-Mn energy transfer

The energy transfer (ET) between Eu²⁺ and Mn²⁺ in Ca₅(PO₄)₃Cl has been investigated. At low intensities under 405 nm excitation, time-resolved experiments provide microscopic parameters for the energy transfer between adjacent Eu²⁺ and Mn²⁺ ions. At high intensities, we observe a non-linear component in the energy transfer process due to ground state depletion of the Mn²⁺ ions, leading not to a reduction, but to an increase in the energy transfer rate between Eu²⁺ and Mn²⁺ ions and also energy transfer between excited Mn²⁺ ions. This results in a sub-linear response of both Eu²⁺ and Mn²⁺ luminescence as a function of intensity. Our observations are quantitatively described by a model using energy transfer to Mn²⁺ ions in both the ground and the excited state.     

Localized magnon gap modes in the 2-d Ising antiferromagnets K2CoF4 and Rb2CoF4

The defect (Mn²⁺,Ni²⁺,Fe²⁺) induced magnon gap modes in the layered antiferromagnets K₂CoF₄ and Rb₂CoF₄ were investigated with the methods of FIR absorption-and IR emission spectroscopy. The anisotropic exchange-parameters describing the strongly localized Mn²⁺ spin excitations far below the host lattice magnon band and the Ni²⁺ excitations in the vacinity of this band are presented. In the diluted system K₂Co_1-cMn_cF₄ localized Mn²⁺ cluster modes up to about C≈0.1 were observed. The excitation energy of these modes can only be explained by assuming an anisotropic Mn²⁺-Mn²⁺ exchange which is in contrast to the pure isomorphous system K₂MnF₄. In the spin mismatch system K₂CoF₄: Fe the magnetic moments of the isolated Fe²⁺ impurities are pulled from the plane perpendicular to the c-axis and aligned parallel to the easy axis of the magnetic crystal.     

Interaction of dopant cations with 4:1 defect clusters in non-stoichiometric 3d transition metal monoxides: A theoretical study

The ASED-MO theory and a normalized ion energy model have been used to study the energetics of substitutional dopants in Mn, Fe, Co, and Ni non-stoichiometric monoxides; we find that certain dopants stabilize 4:1 defect clusters (4 octahedral M²⁺ vacancies surrounding an M³⁺ tetrahedral interstitial). For example, Fe³⁺-based 4:1 clusters in Mn_1−xO and Mn³⁺-based 4:1 clusters in Fe_1−xO have comparable stabilities to those in the undoped material, while Mn³⁺- and Fe³⁺-based 4:1 clusters in Co_1−xO and Ni_1−xO are significantly more stable than those in the undoped oxides. Cr³⁺ has a strong octahedral site preference energy in all cases, which prevents formation of doped 4:1 defect clusters. Despite a strong tetrahedral site preference energy, Zn²⁺ does not cause formation of 4:1 clusters because they would destabilize oxygen 2p orbitals.     

Multiphonon radiationless phenomena in Mn2+-Doped Ca1-x Sr x F2 and BaF2 Fluorites

This work investigates the surprising disappearance of the Mn²⁺ photoluminescence on passing from CaF₂:Mn²⁺ to SrF₂:Mn²⁺ or BaF₂:Mn²⁺ using pressure spectroscopy. We show that the loss of luminescence in these systems is associated with non-radiative thermally activated processes whose activation energy and pre-exponential rates strongly depend on the crystal volume irrespective of the chemical composition. A salient feature is the PL enhancement observed in the cotunnite high-pressure phase along the series. This enhancement is explained in terms of the large volume reduction at the phase transition, as well as by the presence of low-symmetry crystal fields attained at the cation sites leading to an increase of the radiative transition rate by the electric-dipole mechanism.     

Low-temperature flux growth of sulfates,molybdates, and tungstates of Ca,Sr, and Ba and investigation of doping with Mn<Superscript><Emphasis Type="Bold">6</Emphasis>+</Superscript>

The growth of undoped and Mn⁶⁺-doped molybdates and tungstates of alkali-earth metals and BaSO₄ has been investigated. Single crystals were grown by the flux method within the temperature range of 600–475 °C, using the ternary NaCl–KCl–CsCl solvent. Sizes of undoped crystals increase within the series tungstates<molybdates<sulfate and, depending on the cation, within the series Ca²⁺Sr²⁺<Ba²⁺. The Mn⁶⁺ ion tends to be reduced to Mn⁵⁺/Mn⁴⁺ with time in the chloride solution, but can be partly stabilized by the addition of alkali-metal carbonates or hydroxides. The incorporation of Mn⁶⁺ is governed by the coordination of the MnO₄^2- tetrahedron in the crystal. No significant doping was found for Ca and Sr compounds and only small amounts of Mn⁶⁺ were incorporated into BaMoO₄ and BaWO₄. Crystals with orthorhombic space group Pnma such as BaSO₄ exhibit significantly higher doping levels. The Mn⁶⁺ distribution in each crystal varies due to manganese reduction with growth time. Temperature-, time-, and concentration-dependent spectroscopy of BaSO₄:Mn⁶⁺ was performed. PACS 61.72.Ww; 81.05.Je; 81.10.Dn     

Materials for spintronic: Room temperature ferromagnetism in Zn–Mn–O interfaces

In this paper we study the room temperature ferromagnetism reported on Mn-doped ZnO and ascribed to spin polarization of conduction electrons. We experimentally show that the ferromagnetic behaviour is associated to the coexistence of Mn³⁺ and Mn⁺⁴ in MnO₂ grains where diffusion of Zn promotes the Mn⁴⁺→Mn³⁺ reduction. Potential uses of this material in spintronic devices are analysed.     

Eu2+,Mn2+在BaZnP2O7中的发光及Eu2+→Mn2+能量传递

采用高温固相法合成了BaZnP₂O₇:Eu²⁺,Mn²⁺荧光粉,并对其发光性质及Eu²⁺对Mn²⁺的能量传递机理进行了研究.Eu²⁺和Mn²⁺在380 nm和670nm的发射峰分别由Eu²⁺的5d—4f跃迁和Mn²⁺的⁴T₁(^{4关键词： 磷酸盐 2+}')" href="#">Eu²⁺ 2+')" href="#">Mn²⁺ 能量传递     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

Na2SrMg(PO4)2: Ce3+, Mn2+荧光粉的发光性质及其能量传递机理

采用高温固相法制备了Na₂SrMg(PO₄)₂: Ce³⁺, Mn²⁺ (NSMP: Ce³⁺, Mn²⁺) 荧光粉, 并对其发光性质及Ce³⁺ 对Mn²⁺ 的能量传递机理进行了研究. Ce³⁺ 和Mn²⁺ 在334 nm 和617 nm 的发射峰分别为Ce³⁺ 的5d→4f 跃迁和Mn²⁺ 的⁴T₁(⁴G)→⁶A₁(⁶S) 跃迁产生. Ce³⁺ 对Mn²⁺ 的发光有较强的敏化作用, 根据Dexter能量传递效率公式判断Na₂SrMg(PO₄)₂ 中Ce³⁺ 对Mn²⁺ 的能量传递属于电偶极-电四极相互作用引起的共振能量传递.     

Luminescence and energy transfer in Eu2+,Mn2+ codoped Na2BaMgP2O8 phosphor

Eu²⁺ single-doped and Eu²⁺/Mn²⁺-codoped Na₂BaMgP₂O₈ phosphors were prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Na₂BaMgP₂O₈:Eu²⁺,Mn²⁺ shows a broad blue emission band and a red emission band, which originate from Eu²⁺ occupying the Ba²⁺ sites and Mn²⁺ occupying the Mg²⁺ sites, respectively. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. Based on the principle of energy transfer, the relative intensities of blue and red emissions could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

Synthesis and color-tunable luminescence properties of novel calcium aluminate silicate chloride phosphors

Eu²⁺ and Mn²⁺ co-doped calcium aluminate silicate chloride phosphors with the chemical composition of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ have been prepared by a solid-state method, and their luminescence properties have been investigated by tuning the En²⁺/Mn²⁺ ions concentration. The phase formation and microstructure of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ phosphors have been illuminated by XRD and SEM analysis. Photoluminescence (PL) spectrum reveals that Ca₃Al₂Si₂O₈Cl₄:Eu²⁺ exhibits a strong blue emission band centered at 431 nm, while Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ can emit bluish-white light by adjusting the Mn²⁺ content appropriately. The energy transfer mechanism involving Eu²⁺–Mn²⁺ have also been investigated.     

Luminescence enhancement of ZnGa2O4:Mn by Ge and Li doping

Structural and optical properties of ZnGa₂O₄:Ge⁴⁺ and ZnGa₂O₄:Ge⁴⁺, Li⁺, Mn²⁺ phosphors were investigated by using X-ray diffraction (XRD), photoluminescence (PL) and cathodoluminescence (CL) measurements. The XRD patterns show that Ge-doped ZnGa₂O₄ has a spinel phase and its lattice constant increases with respect to ZnGa₂O₄. Emission wavelength shifts from 400 to 360 nm in comparison with ZnGa₂O₄ when Ge is doped in ZnGa₂O₄ and a peak related with oxygen defect was observed in Ge-doped ZnGa₂O₄. The CL luminance of ZnGa₂O₄:Ge⁴⁺, Li⁺, Mn²⁺ phosphors is seven times brighter than that of ZnGa₂O₄:Mn²⁺. This drastic luminance improvement can be attributed to Ge doping in ZnGa₂O₄ acting as donor ion and Li doping resulting in increasing conductivity of ZnGa₂O₄. These results indicate that ZnGa₂O₄:Ge⁴⁺, Li⁺, Mn²⁺ phosphors hold promise for potential applications in field-emission display devices with high brightness operating in green spectral regions.     

Luminescent properties of SrMg<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript> as a potential phosphor for ultraviolet light-emitting diodes

Eu²⁺ and Mn²⁺ co-doped SrMg₂(PO₄)₂ phosphors with blue and red two emission bands were prepared by the high temperature solid state method and their luminescent properties have been investigated as a function of activator and co-activator concentrations. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the Eu²⁺ emission spectrum and the excitation spectrum of Mn²⁺. Efficiencies of energy transfer were also calculated according to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission. According to the principle of energy transfer, we demonstrated that the phosphor SrMg₂(PO₄)₂:Eu²⁺,Mn²⁺ with double emission bands exhibited a great potential as a phosphor for ultraviolet light-emitting diodes and the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺. PACS 78.55.-m     

Photoluminescence and efficient energy transfer from Ce3+ to Tb3+ or Mn2+ in Ca9ZnLi(PO4)7 host

Structural and spectroscopic characterizations of the Ce³⁺/Tb³⁺(Mn²⁺) solely and Ce³⁺–Tb³⁺(Mn²⁺) doubly doped phosphate compound Ca₉ZnLi(PO₄)₇ with β-Ca₃(PO₄)₂ structure have been performed by powder X-ray diffraction and photoluminescence spectra measurements. The weak green emission from Tb³⁺ and red emission from Mn²⁺ are significantly enhanced by introduction of sensitizer Ce³⁺ ions due to an efficient resonant-type energy transfer from Ce³⁺ to activators Tb³⁺ or Mn²⁺. The energy transfer efficiency and the mechanism have been estimated based on spectroscopic data. Meanwhile, the critical distances for energy transfer between the Ce³⁺ and Tb³⁺ or Mn²⁺ ions are also calculated by the method of spectral overlapping.     

Anomalous magnetotransport in LaMn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>

The LaMn_1−x Te _x O_3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te⁴⁺, and Mn³⁺ ions are partly converted into Mn²⁺ and Mn⁴⁺ due to the excess oxygen and Te doping. The magnetotransport associated with Mn²⁺, Mn³⁺ and Mn⁴⁺ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn³⁺ is much larger or less than the sum of Mn²⁺ and Mn⁴⁺; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn³⁺ is close to the sum of Mn²⁺ and Mn⁴⁺. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism. Supported by the National Major Fundamental Research Program of China (Grant No. G1998061412) and the Foundation for Fostering Elitists of Beijing, China (Grant No. 20071D1100500379)     

Red emission from Mn on a tetrahedral site in MgSiN2

Solubility and photoluminescence properties of Mn²⁺ in MgSiN₂ host lattice are reported in this paper. X-ray diffraction (XRD) analysis shows that Mn²⁺ ions can be totally incorporated into MgSiN₂ host lattice, forming a complete solid solution with MnSiN₂. Mn²⁺ on a tetrahedral site exhibits a red emission band in the wavelength range of 550-750 nm in MgSiN₂. The long-wavelength emission of Mn²⁺ despite tetrahedral coordination in MgSiN₂ is attributed to the effect of strong crystal field experienced by Mn²⁺ in a nitrogen coordination environment. Also there exists energy transfer between MgSiN₂ host lattice and Mn²⁺ activator. The potential applications of this phosphor have been pointed out.