Preparation, crystal structure, and photoluminescence of Ca2SnO4:Eu, Y

Eu³⁺-doped Ca₂SnO₄ (solid solutions of Ca_2−xEu_2xSn_1−xO₄, 0?x?0.3) and Eu³⁺ and Y³⁺-codoped Ca₂SnO₄ (Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄) were prepared by solid-state reaction at 1400 °C in air. Rietveld analysis of the X-ray powder diffraction patterns revealed that Eu³⁺ replaced Ca²⁺ and Sn⁴⁺ in Eu³⁺-doped Ca₂SnO₄, and that Eu³⁺ replaced Ca²⁺ and Y³⁺ replaced Sn⁴⁺ in Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄. Red luminescence at 616 nm due to the electric dipole transition ⁵D_o→⁷F₂ was observed in the photoluminescence (PL) spectra of Ca_2−xEu_2xSn_1−xO₄ and Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ at room temperature. The maximum PL intensity in the solid solutions of Ca_2−xEu_2xSn_1−xO₄ was obtained for x=0.1. The PL intensity of Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ was 1.26 times greater than that of Ca_2−xEu_2xSn_1−xO₄ with x=0.1.     

A novel red emitting phosphor Ca2SnO4: Eu

A novel red emitting phosphor, Eu³⁺-doped Ca₂SnO₄, was prepared by the solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Ca₂SnO₄: Eu³⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated a narrow size-distribution of about 500 nm for the particles with spherical shape. Photoluminescence measurements indicated that the phosphor exhibits bright red emission at about 615 nm under UV excitation. The excellent luminescence properties make it possible as a good candidate for plasma display panels (PDP) application. Splitting of the ⁵D₀-⁷F_J transitions of Ca₂SnO₄: Eu³⁺ suggests that the Eu³⁺ ions occupied two nonequivalent sites in the crystallite. The luminescence lifetime measurement showed a bi-exponential decay, providing other evidence for the existence of two different environments for Eu³⁺ ions.     

Role of crystallite size on the photoluminescence properties of SrIn2O4:Eu phosphor synthesized by different methods

Photoluminescence (PL) of Eu³⁺ was studied in SrIn₂O₄ host lattice. A complete solid solubility of Eu³⁺ has been found in the series SrIn_2−xEu_xO₄ [x=0-2.0]. The phase formation at a relatively low temperature and in a very short duration was achieved by combustion synthesis (CS). Concentration quenching of luminescence has been observed in SrIn_2−xEu_xO₄ [x=0.1-2.0] and the critical concentration for maximum emission was found to be with x=0.3. In order to find the role of crystallite size on the PL properties of SrIn₂O₄:Eu³⁺, the results obtained with phosphors synthesized by solid state reaction (SSR) and CS methods were compared.     

CaSb2O6:Bi3+,Eu3+荧光粉的制备和发光性质

采用共沉淀法及1 200 ℃后续煅烧4 h,成功制备了CaSb₂O₆:Bi³⁺,Eu³⁺荧光粉,并对其结构及发光性能进行了研究。所制备荧光粉颗粒为六边形类圆饼状,平均尺寸在100~600 nm之间。对CaSb₂O₆:Bi³⁺,Eu³⁺发光的机理分析表明,Bi³⁺对Eu³⁺的发光存在高效的敏化与能量传递。当Bi³⁺和Eu³⁺的掺杂浓度分别为0.5%和8%,Eu³⁺位于580 nm(⁵D₀→⁷F₀ )处的荧光发射显著增强,Bi³⁺,Eu³⁺共掺样品的荧光强度是CaSb₂O₆:Eu³⁺的10倍左右。调节Bi³⁺/Eu³⁺离子掺杂比,色坐标呈现了从蓝、白光到红光的变化,表明该荧光粉可分别作为蓝或红色荧光粉使用,甚至可实现从蓝、白光到红光的自由调控,这为白光LED荧光粉的发展提供了参考。     

Preparation and optical properties of SrF2:Eu nanospheres

SrF₂:Eu³⁺ nanospheres with homogeneous diameter have been synthesized by a microemulsion-mediated hydrothermal method for the first time, in which quaternary microemulsion of CTAB/water/cyclohexane/n-pentanol was used. The possible reaction mechanism and the luminescent properties of SrF₂:Eu³⁺ nanospheres were also investigated in this paper. The morphology and grain sizes of final products were characterized by field emission scanning electron microscopy and transmission electron microscopy, indicating that most of the products were nanospheres with an average diameter of ∼50 nm. Room-temperature emission spectra, recorded under 394-nm excitation, showed that the transition of ⁵D₀ → ⁷F₁ emission be dominating in SrF₂:Eu³⁺ nanospheres. From the dependence of the luminescence intensity on the concentration of Eu³⁺ ions, the optimal dopant concentration is 2 mol%.     

Controlled synthesis and luminescent properties of Eu(Eu), Dy-doped Sr3Al2O6 phosphors by hydrothermal treatment and postannealing approach

In this work, Sr₃Al₂O₆: Eu²⁺ (Eu³⁺), Dy³⁺ phosphors have been prepared by hydrothermal treatment and subsequently postannealing approach, using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, and CO(NH₂)₂ as starting materials. The as-obtained phosphors were characterized by means of XRPD, FESEM, and PL techniques. In addition, many reaction parameters were studied in detail, including the initial mole ratios, hydrothermal reaction temperature, calcination temperature and calcination atmosphere. Remarkably, two scientific merits exist herein: Sr₃Al₂O₆: Eu²⁺ (Eu³⁺), Dy³⁺ phosphors can be selectively obtained in a reducing atmosphere (H₂/Ar, 20%+80%) and in air, respectively; adding certain amount of sodium citrate can alter the shape and size of Sr₃Al₂O₆: Eu²⁺ (Eu³⁺), Dy³⁺ phosphors in essence. Besides, the luminescent properties of Sr₃Al₂O₆: Eu²⁺ (Eu³⁺), Dy³⁺ phosphors were studied by excitation spectra, emission spectra and decay curves.     

The synthesis mechanism of Ca3Al2O6 from soft mechanochemically activated precursors studied by time-resolved neutron diffraction up to 1000°C

The reaction pathway for the Ca₃Al₂O₆ formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO₃, was studied in situ by differential thermal analysis, constant heating rate dilatometry and time-resolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca₃Al₂O₆ stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al₂O₃, crystalline CaO, CaAl₂O₄ and Ca₁₂Al₁₄O₃₃ as transitory phases. Finally the nucleation and growth of the single phase Ca₃Al₂O₆ took place at 1300°C and exhibited porous structure due to CO₂ and H₂O release.     

Crystal growth, structural characterization and magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6

Single crystals of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ were synthesized by high temperature flux growth in molten K₂CO₃ and structurally characterized by single crystal X-ray diffraction. While Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca₃Co_1.34Rh_0.66O₆a=9.161(1) Å, c=10.601(2) Å; Ca₃FeRhO₆a=9.1884(3) Å, c=10.7750(4) Å; Ca₃CuRhO₆ adopts a monoclinic distortion of the K₄CdCl₆ structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca₃CuRhO₆ examined were twinned by pseudo-merohedry. Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO₆ octahedra and MO₆ trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are discussed.     

多级结构Mg3B2O6:Eu3+花状微球的制备、表征及其发光性能

以硝酸镁(Mg(NO₃)₂·6H₂O)和硼砂(Na₂B₄O₇·10H₂O)为原料,稀土元素Eu³⁺为激活剂,采用聚乙烯吡咯烷酮(PVP)辅助共沉淀法得到前驱体,并通过焙烧制备了多级结构Mg₃B₂O₆:Eu³⁺花状微球。通过XRD、SEM、TEM以及荧光光谱等手段分别对前驱体煅烧产物的结构、形貌、组成和荧光特性进行了表征。实验表明,在波长为393 nm激发光的激发下,所得到的产品在612 nm处有明显的特征发射峰,对应于Eu³⁺的(⁵D₀→⁷F₂)特征跃迁发射。这一荧光性质使得该材料在荧光灯、显示系统和光电设备应用中具有广阔的前景。同时我们还探讨了微球的形态、Eu³⁺的掺杂量及焙烧温度对花状微球荧光性能的影响。     

多级结构Mg3B2O6: Eu3+花状微球的制备、表征及其发光性能

以硝酸镁(Mg(NO₃)₂·6H₂O)和硼砂(Na₂B₄O₇·10H₂O)为原料, 稀土元素Eu³⁺为激活剂, 采用聚乙烯吡咯烷酮(PVP)辅助共沉淀法得到前驱体, 并通过焙烧制备了多级结构Mg₃B₂O₆: Eu³⁺花状微球。通过XRD、SEM、TEM以及荧光光谱等手段分别对前驱体煅烧产物的结构、形貌、组成和荧光特性进行了表征。实验表明, 在波长为393 nm激发光的激发下, 所得到的产品在612 nm处有明显的特征发射峰, 对应于Eu³⁺的(⁵D₀→⁷F₂)特征跃迁发射。这一荧光性质使得该材料在荧光灯、显示系统和光电设备应用中具有广阔的前景。同时我们还探讨了微球的形态、Eu³⁺的掺杂量及焙烧温度对花状微球荧光性能的影响。     

La7O6(BO3)(PO4)2:Eu3+/Tb3+荧光材料的制备及其光致发光性能

采用优化的高温固相方法制备了稀土离子Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La₇O₆（BO₃）（PO₄）₂：Eu³⁺材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为⁵D₀→⁷F₂特征能级跃迁,Eu³⁺的最优掺杂浓度为0.08,对应的CIE坐标为（0.610 2,0.382 3）;La₇O₆（BO₃）（PO₄）₂：Tb³⁺材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb³⁺的⁵D₄→⁷F₅能级跃迁,Tb³⁺离子的最优掺杂浓度为0.15,对应的CIE坐标为（0.317 7,0.535 2）。此外,对2种材料的变温光谱分析发现Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂荧光材料均具有良好的热稳定性。     

Vacuum Ultraviolet Excited Photoluminescence Properties of Y2O2S：Eu^3＋,Bi^3＋ Phosphor

As an Hg-free lamp using phosphor, the Bi^3＋ and EH^3＋ co-doped Y2O2S phosphors were prepared and their luminescence properties under vacuum ultraviolet（VUV） excitation were investigated. The VUV photoluminescent intensity of Y2O2S：Eu^3＋ was weak, however, considerably stronger red emission at 626 nm with good color purity was observed in Y2O2S：Eu^3＋,Bi^3＋ systems. Investigation on the photoluminescence reveals that the strong VUV luminescence of Y2O2S：Eu^3＋,Bi^3＋ at 147 nm is mainly because the Bi^3＋ acts as a medium and effectively performs the energy transfer process： Y^3＋-O^2-→Bi^3＋→Eu^3＋, while the intense emission band at 172 nm is attributed to the absorption of the characteristic ^1So-^1P1 transition of Bi^3＋ and the direct energy transfer from Bi^3＋ to Eu^3＋. The Y2O2S：Eu^3＋,Bi^3＋ shows excellent VUV optical properties compared with the commercial （Y,Gd）BO3：Eu^3＋. Thus, the Y2O2S：Eu^3＋,Bi^3＋ can be a potential red VUV-excited candidate applied in Hg-free lamps for backlight of liquid crystal display.     

稀土掺杂Lu3Al5O12荧光粉的发光特性及能量传递

采用高温固相法制备了Ce、Sm共掺Lu₃Al₅O₁₂荧光粉。通过X射线衍射分析、荧光光谱分析研究了样品的结构、发光特性,并通过理论计算研究了能量传递效率、能量传递的临界距离以及能量传递方式。X射线衍射分析表明所制备的荧光粉具有单一的石榴石结构;荧光光谱分析表明,在464 nm蓝光激发下,Sm³⁺的引入可增加Lu₃Al₅O₁₂：Ce,Sm发射光谱中红光成分,并且随着Sm³⁺浓度的增加,Ce³⁺发光强度逐渐减弱。计算出Ce³⁺、Sm³⁺之间的能量传递效率高达77.42%,确定了Ce³⁺、Sm³⁺之间的能量传递机制为偶极-偶极相互作用。     

Synthesis and spectral characteristics of Sr2Y8(SiO4)6O2: Eu polycrystals

Spectral-luminescent characteristics of Sr₂Y₈(SiO₄)₆O₂: Eu powder crystal phosphor with the apatite structure and high-intensity luminescence of Eu³⁺ ions have been studied. The charge state of europium in the samples has been characterized by means of X-ray L₃-adsorption spectroscopy. It was established that Eu³⁺ forms two types of optical centers. Besides, luminescence of Eu²⁺ions was found. Reduction Eu³⁺→Eu²⁺ was considered, which may be due to vacancy formation in the 4f crystal lattice position and to negative charge transfer by this vacancy to two ions. Thus, in the silicate lattice there exist inhomogeneously distributed oxygen-deficient centers, which are responsible for nonradiative transfer of excitation energy to Eu³⁺ and Eu²⁺ ions. To study electron-vibrational interactions in the crystal phosphor samples, their IR and Raman spectra were examined. In the luminescence spectrum of Eu²⁺, a series of low-intensity bands caused by interaction of the 4f⁶5d state of Eu²⁺ with silicate lattice vibrations was observed.     

Structure and magnetism of rare-earth-substituted Ca3Co2O6

Yttrium- and rare-earth-substituted derivatives of Ca_3−vR_vCo₂O₆ (RY, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) have been synthesized and structurally characterized by powder X-ray and neutron diffraction. All phases adopt the K₄CdCl₆-type structure with space group R3¯c), in which the trivalent R³⁺ substituents randomly occupy the Ca²⁺ site. The homogeneity range of Ca_3−vR_vCo₂O₆ extends to v≈0.90 for the substituents concerned. A significant increase in the Co2-O distances within the trigonal-prismatic Co2O₆ co-ordination polyhedra upon introduction of R³⁺ confirms that extra electrons from the R³⁺-for-Ca²⁺ substitution exclusively enter the Co2 site of the quasi-one-dimensional Ca_3−vR_vCo₂O₆ structure, thereby formally reducing its oxidation state. This is furthermore supported by magnetic susceptibility and low-temperature neutron diffraction measurements. The long-range ferrimagnetic ordering temperature is reduced upon R substitution and appears to vanish for v>∼0.30.     

Photoluminescence of new red phosphor SrZnO2:Eu

SrZnO₂:Eu³⁺ has been synthesized by solid-state reaction and its photoluminescence in ultraviolet (UV)-vacuum ultraviolet (VUV) range was investigated. The broad bands around 254 nm are assigned to CT band of Eu³⁺-O²⁻. With the increasing of Eu³⁺ concentration, Eu³⁺ could occupy different sites, which leads to the broadening of CT band. A sharp band is observed in the region of 110-130 nm, which is related to the host absorption. The phosphors emit red luminescence centered at about 616 nm due to Eu³⁺⁵D₀→⁷F₂ both under 254 and 147 nm, but none of Eu²⁺ blue emission can be observed.     

Preparation and characterization of optical spectroscopy of Lu2O3:Eu nanocrystals

Nanoscale Lu₂O₃:Eu powders were prepared by solution combustion synthesis. X-ray diffraction (XRD), high-resolution electronic microscope (HREM), Fourier transform infrared spectroscopy (FT-IR), excitation and emission spectra, as well as fluorescent decay curves were measured to characterize the structure and luminescent properties of the samples. The results show that the compound of composition Lu₂O₃ crystallizes in pure cubic structure. By changing the ratio of glycine to nitrate in the combustion process, the particle size varies from 40 nm to less than 5 nm. The emission and excitation spectra strongly depend on the particle size of the samples. Novel emission band, red-shift of charge transfer band (CTB) and shortening of lifetime were observed in nanoscale samples.     

Rietveld refinement and photoluminescent properties of a new blue-emitting material: Eu activated SrZnP2O7

A new efficient blue phosphor, Eu²⁺ activated SrZnP₂O₇, has been synthesized at 1000 °C under reduced atmosphere and the crystal structure and photoluminescence properties have been investigated. The crystal structure of SrZnP₂O₇ was obtained via Rietveld refinement of powder X-ray diffraction (XRD) pattern. It was found that SrZnP₂O₇ crystallizes in space group of P2₁/n (no. 14), Z=4, and the unit cell dimensions are: a=5.30906(2) Å, b=8.21392(3) Å, c=12.73595(5) Å, β=90.1573(3)°, and V=555.390(3) Å³. Under ultraviolet excitation (200-400 nm), efficient Eu²⁺ emission peaked at 420 nm was observed, of which the luminescent efficiency at the optimal concentration of Eu²⁺ (4 mol%) was estimated to be 96% as that of BaMgAl₁₀O₁₇:Eu²⁺. Hence, the SrZnP₂O₇:Eu²⁺ exhibit great potential as a phosphor in different applications, such as ultraviolet light emitting diode and photo-therapy lamps.     

新型红色荧光粉Sr3Al2O6的合成和发光性能研究

稀土金属离子激活的多铝酸盐发光材料，在可见光区具有较高的量子效率犤１～４犦，充分显示出这类荧光发光材料，在高效节能、环保、电光源与新一代可见光显示器领域的应用前景犤４～９犦。特别是SrAl２O４∶Eu２＋的持续发光现象的发现犤２，３犦，激起了对以稀土金属离子为激活剂，碱土铝酸盐为基质的长余辉无机发光材料体系的兴趣。研究表明其发光强度和余辉时间是传统硫化物发光材料的十倍以上，利用其长余辉储光－发光特性，有望开发新型发光油漆、涂料、发光陶瓷、发光塑料、薄膜、发光纸、发光纤维犤４犦。早在七十年代，荷兰菲利…     

Crystal structure of BaMg2Si2O7 and Eu luminescence

Crystal structure of BaMg₂Si₂O₇ was determined and refined by a combined powder X-ray and neutron Rietveld method (monoclinic, C2/c, no. 15, Z=8, a=7.24553(8) Å, b=12.71376(14) Å, c=13.74813(15) Å, β=90.2107(8)°, V=1266.44(2) Å³; R_p/R_wp=3.38%/4.77%). The structure contains a single crystallographic type of Ba atom coordinated to eight O atoms with C₁ (1) site symmetry. Under 325-nm excitation Ba_0.98Eu_0.02Mg₂Si₂O₇ exhibits an asymmetric emission band around 402 nm. The asymmetric shape of the emission band is likely associated with a small electron-phonon coupling in BaMg₂Si₂O₇. The integrated intensity of the emission band was observed to remain constant over the temperature range 4.2-300 K.