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.     

Characterization of the 2D antiferromagnets Rb2MnCl4 and Rb3Mn2Cl7 : Optical,Raman and magnetic circular dichroism studies

Below T_N, the site symmetry at the Mn²⁺ ion is centrosymmetric (Rb₂MnCl₄) and non-centrosymmetric (Rb₃Mn₂Cl₇) respectively. As a result, one expects the appearance of magnetic dipole or electric dipole exciton origins in the optical spectra. These were clearly seen via polarized absorption and magnetic circular dichroism measurements through the 4T₂(D) band. The zone edge magnon frequencies are found to be 80 cm^?1 (Rb₂MnCl₄) and 90 cm^?1 (Rb₃MnCl₂in7). The two compounds are also easily distinguished through their room temperature axial absorption (⁴T₂ (G) band) and Raman spectra. Low temperature data indicate that the tetragonal field plays an important role.     

Intense green/yellow emission in Ca8Zn(SiO4)4Cl2:Eu, Mn through energy transfer for blue-LED lighting

Eu²⁺ and Mn²⁺ co-doped Ca₈Zn(SiO₄)₄Cl₂ phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu²⁺ to Mn²⁺ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu²⁺ and a yellow band at 550 nm of Mn²⁺. The excitation spectra corresponding to 4f⁷-4f⁶5d transition of Eu²⁺ cover the spectral range of 370-470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu²⁺ followed by simultaneous increase of fluorescent intensity of Mn²⁺ with increasing Mn²⁺ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu²⁺ and Mn²⁺ co-doped Ca₈Mg(SiO₄)₄Cl₂ and Ca₃SiO₄Cl₂, demonstrating a potential application in phosphor converted white LEDs.     

Bicarbonate Coordinates to Mn3+ during Photo-Assembly of the Catalytic Mn4Ca Core of Photosynthetic Water Oxidation: EPR Characterization

Assembly of the catalytic cluster, Mn₄CaO _x Cl _y , comprising the water-oxidizing complex (WOC) of photosystem II (PSII), occurs during biogenesis in the presence of the apo-WOC-PSII complex, Mn²⁺, Ca²⁺ and Cl^? cofactors under weak illumination. The in vitro assembly process known as photo-activation involves several intermediates that have been resolved in previous kinetic studies. (Bi)carbonate has been shown to stimulate the rate of formation and yield of the first stable light-induced Mn³⁺ assembly intermediate (IM₁) from Mn²⁺ bound to the high-affinity assembly site in apo-WOC-PSII. ¹³C electron spin echo envelope modulation has previously revealed that (bi)carbonate is a ligand to this Mn²⁺. Herein, we use parallel-mode electron paramagnetic resonance (EPR) spectroscopy to characterize the Mn³⁺ photoproduct, which exists as a ternary complex with carbonate at the high-affinity assembly site (in the absence of Ca²⁺) formulated as [CO₃-Mn³⁺-apo-WOC-PSII]. The EPR-derived spectral parameters of IM₁ (the g value, ⁵⁵Mn hyperfine coupling constant (A _Z) and the ligand-field splitting parameters D/E) are independent of solution pH, in marked contrast to their strong pH dependence in the absence of bicarbonate. (Bi)carbonate coordination “chemically isolates” the IM₁ from external pH changes, much like that caused by Ca²⁺ coordination, revealing similar roles in photo-assembly. The cumulative results reveal that (bi)carbonate and Ca²⁺ coordination control the ligand field strength and symmetry around the initial high-affinity Mn³⁺, consistent with the possible formation of a μ₂-oxide bridge in IM₁, [Mn³⁺(O^2?)Ca²⁺]. These events greatly improve the quantum yield of subsequent steps in photo-assembly.     

EPR spectra of Mn2+ ions in precipitated divalent impurity phases in monocrystalline NaCl

The EPR spectra of Mn²⁺ ions embedded into precipitated phases of Mg²⁺, Cd²⁺, Fe²⁺ and Ca²⁺ in NaCl single crystals have been investigated. The spectrum from samples whose major impurity is Mg, Cd or Fe corresponds to Mn²⁺ substituting some divalent cation inside the Suzuki phase (6NaCl.MCl₂). The existence of such a phase has been ascertained by means of Raman spectroscopy. On the other hand, the EPR spectrum of Ca²⁺ doped samples has been attributed to Mn²⁺ inside various CaCl₂ precipitates.     

Far U.V. absorption spectra of manganese halides between 20 and 67 eV.

The absorption spectra of evaporated thin films of MnF₂, MnCl₂, MnBr₂ have been measured in the energy range 20–67 eV. The onset of the absorption of 3p Mn²⁺ is about 50 eV. At lower energies, the structures may be attributed to transitions from 2s F^-, 4s Br^- and 3d Mn²⁺ levels.     

White light emitting from single phased K2Ca1−x−yP2O7: xEu, yMn phosphors under UV excitation

A single phased white light emitting phosphors K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ were synthesized by solid state reaction method. The Effective energy transfer occurs in this phosphor due to the large spectral overlap between the emission of Eu²⁺ and the excitation of Mn²⁺. The emission hue of K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ from blue to white light can be obtained by tuning the Eu²⁺/Mn²⁺ content ratio. The energy transfer mechanism from Eu²⁺ to Mn²⁺ in this phosphor was carefully investigated and demonstrated to be via the dipole–quadrupole interaction.     

Emission-tunable phosphors Ca9MgM′ (PO4)7: Eu2+,Mn2+ (M′=Li,Na, K) for white light-emitting diodes

A series of single-composition phosphors Ca₉MgM′(PO₄)₇:xEu²⁺, yMn²⁺ (CMM′ P:Eu²⁺, Mn²⁺; M′=Li, Na, K; 0.003≤x≤0.03; 0 ≤y≤0.1) were synthesized by solid state reactions. Upon excitation at 337 nm, phosphors Ca₉MgM′ (PO₄)₇: Eu²⁺ exhibit strong blue emissions centered at 417 (Ca₉MgLi(PO₄)₇:Eu²⁺), 457 (Ca₉MgNa(PO₄)₇:Eu²⁺), and 453 (Ca₉MgK(PO₄)₇:Eu²⁺) nm respectively, which correspond to the 4f⁶5d¹→4f⁷ transitions of Eu²⁺ ions, Through an effective resonance-type energy transfer, CMM′P:Eu²⁺,Mn²⁺ phosphors exhibit a series of colors by adjusting the concentration of Mn²⁺. The result indicates that CMM′P:Eu²⁺,Mn²⁺ can be potentially used as a UV excited phosphor for white light-emitting diodes (LEDs).     

Photoluminescence of double-color-emitting phosphor Ca5(PO4)3Cl:Eu, Mn for near-UV LED

Eu²⁺ activated Ca₅(PO₄)₃Cl blue-emitting phosphors were prepared by the conventional solid state method using CaCl₂ as the chlorine source and H₃BO₃ as flux. The structure and luminescent properties of phosphors depend on the concentrations of Eu²⁺, the amount of CaCl₂ and the usage of the H₃BO₃ flux were investigated systematically. Eu²⁺ and Mn²⁺ Co-doped Ca₅(PO₄)₃Cl with blue and orange double-band emissions were also researched based on the optimal composition and synthesis conditions. The energy transfer between Eu²⁺ and Mn²⁺ was found in the phosphor Ca₅(PO₄)₃Cl:Eu²⁺, Mn²⁺, and the Co-doped phosphor can be efficiently excited by near-UV light, indicating that the phoshor is a potentional candidate for n-UV LED used phosphor.     

Luminescence and energy transfer in Eu, Mn co-doped Li4SrCa(SiO4)2 for white light-emitting-diodes

Li₄(Sr_0.96Eu_0.04)(Ca_1 − xMn_x)(SiO₄)₂ phosphors were synthesized by solid-state reactions and photoluminescence (PL) properties were investigated. These phosphors have intense absorption in n-UV region, which is suitable for excitation of UV LEDs. The orange-reddish emission of Mn²⁺ can be adjusted by changing the Mn²⁺/Eu²⁺ ratio. Energy transfer from Eu²⁺ to Mn²⁺ is observed. Li₄(Sr_0.96Eu_0.04)(Ca_1 − xMn_x)(SiO₄)₂ phosphors could be used in white LEDs.     

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.     

Diluted ferromagnetic semiconductor (LaCa)(ZnMn)SbO isostructural to “1111” type iron pnictide superconductors

We report discovery of ferromagnetism in(LaCa)(ZnMn)SbO isostructural to the well-studied iron-based superconductor LaFeAs(O1 xFx).Spin is induced by partial substitution of Mn2+for Zn2+,while charge is induced by substitution of Ca2+for La3+within the parent compound LaZnSbO.Ferromagnetism with Curie temperature(TC)is observed up to 40 K at the spin doping 0.15 by introducing Mn2+into the Zn2+sites for(La0.95Ca0.05)(Zn1 xMnx)SbO.The Hall coefficient measurement indicates p-type carrier for(La0.95Ca0.05)(Zn0.9Mn0.1)SbO with concentration of n~1020cm 3showing anomalous Hall effect below TC.     

用于白光LED的单一基质白光荧光粉Ca2SiO3Cl2:Eu2+，Mn2+的发光性质

用高温固相法合成了Eu²⁺，Mn²⁺共激活的Ca₂SiO₃Cl₂高亮度白色发光材料，并对其发光性质进行了研究. 该荧光粉在近紫外光激发下发出强的白色荧光，Eu^{2+中心形成峰值为419 nm和498 nm的特征宽带，通过Eu2+中心向Mn2+中心的能量传递导致了峰值为578 nm的发射，三个谱带叠加从而在单一基质中得到了白光. 激发光谱均分布在250—415 nm的波长范围，红绿蓝三个发射带的激发谱峰值分别位于385 nm，412 nm，370 nm和396 nm处，可以被InGaN管芯产生的紫外辐射有效激发. Ca₂SiO₃Cl₂:Eu2+，Mn2+是一种很有前途的单一基质白光LED荧光粉.}     

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.     

Temperature dependence of phase separation and magnetic anisotropy by electron spin resonance in Pr<Subscript>0.6</Subscript> Ca<Subscript>0.4</Subscript> Mn<Subscript>0.9</Subscript> Ru<Subscript>0.1</Subscript>O<Subscript>3</Subscript>

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr_0.6Ca_0.4Mn_1-xRu_xO₃ (x = 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic interactions due to the double exchange between the Mn³⁺ and Mn⁴⁺ species and super-exchange between the Ru⁵⁺ and Mn³⁺ species. The temperature dependence of the ESR spectra indicates development of magnetic phase separation in Pr_0.6Ca_0.4Mn_0.9Ru_0.1O₃ in contrast with the un-doped sample.     

THE STRUCTURE AND MAGNETIC PROPERTIES OF La2-2xSr1Ca2xMn2O7 (x=0.25－1.00)

In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La_2-2xSr₁Ca_2xMn₂O₇ have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn³⁺/Mn⁴⁺ ratio and Jahn-Teller-type lattice distortion of MnO₆ octahedra due to the introduction of Ca²⁺ ions.     

Nonradiative energy transfer from Mn2+ to Eu3+ in K2CaP2O7:Mn2+,Eu3+ phosphor

A series of color tunable phosphors K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ are synthesized by solid state reaction method. The energy transfer phenomenon from Mn²⁺ to Eu³⁺ has been observed in the Mn²⁺/Eu³⁺ codoped non-magnetic K₂CaP₂O₇ host, which was confirmed by PL spectra and decay curves. The Mn²⁺→Eu³⁺ energy transfer is controlled by quadrupole–quadrupole interaction between sensitizer and activator. The maximum efficiency of energy transfer is estimated to be 33% with x=0.125 and y=0.03 in K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ phosphor. The phosphors can emit light from green to yellow and eventually to orange under 400 nm excitation by changing the Mn²⁺/Eu³⁺ content ratio, indicating that K₂CaP₂O₇: Mn²⁺, Eu³⁺ would be potential candidates for use in lighting and displays applications.     

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.     

Substantial Ca doping site effect on structure of La0.5Ca0.5MnO3 at low temperature

Six possible structures of La_0.5Ca_0.5MnO₃ corresponding to different Ca doping sites are studied at low temperature using atomistic simulation techniques. It is found that Ca doping site has substantial effect on structure of La_0.5Ca_0.5MnO₃ and this effect may explain the existence of four similar phases with slightly different lattice parameters in La_0.5Ca_0.5MnO₃ at low temperature. Structures I and II are found to be favorable La_0.5Ca_0.5MnO₃ structures. They have an ordering arrangement of La³⁺ and Ca²⁺ ions and different arrangements of Mn³⁺ and Mn⁴⁺ ions, which may affect the charge, orbital and magnetic ordering in La_0.5Ca_0.5MnO₃ at low temperature.     

Synthesis and electrochemical characterization of M2Mn3O8 (M = Ca,Cu) compounds and derivatives

M₂Mn₃O₈ (M = Ca²⁺, Cu²⁺) compounds were synthesized and characterized in lithium cells. The M²⁺ cations, which reside in the van der Waals gaps between adjacent sheets of Mn₃O₈⁴⁻, may be replaced chemically (by ion-exchange) or electrochemically with Li. More than 7 Li⁺/Cu₂Mn₃O₈ may be inserted electrochemically, with concomitant reduction of Cu²⁺ to Cu metal, but less Li can be inserted into Ca₂Mn₃O₈. In the case of Cu²⁺, this process is partially reversible when the cell is charged above 3.5 V vs. Li, but intercalation of Cu⁺ rather than Cu²⁺ and Li⁺/Cu⁺ exchange occurs during the subsequent discharge. If the cell potential is kept below 3.4 V, the Li in excess of 4 Li⁺/Cu₂Mn₃O₈ can be cycled reversibly. The unusual mobility of + 2 cations in a layered structure has important implications both for the design of cathodes for Li batteries and for new systems that could be based on M²⁺ intercalation compounds.