碳热还原法合成LaSi_3N_5∶Ce~(3+)蓝色荧光粉及其发光性能研究

利用碳热还原法制备了LaSi_3N_5∶Ce~(3+)蓝色荧光粉,重点研究了原料中掺C量和退火对样品纯度及发光性能的影响。通过X射线衍射仪和荧光光谱仪分别表征样品的晶体结构和发光性能。研究结果表明:1 600℃时能够合成主相为LaSi_3N_5∶Ce~(3+)的荧光粉。在360nm紫外光激发下样品可获得波段范围在380~600nm的单峰宽带发射谱,归结于Ce~(3+)的5d-4f的能级跃迁。当n_C/n_(La)=4/1时样品发光强度达到最大,并且光谱出现先红移后蓝移的现象。经过退火的样品的发光强度与退火前相比提高了60%~345%。将热处理后的n_C/n_(La)=4/1的样品与商用YAG混合涂覆在UV芯片上(λ_(em)=365nm)封装成WLED,证实了LaSi_3N_5∶Ce~(3+)在白光LED领域潜在的应用价值。     

Preparation and luminescent properties of phosphor MGd2(MoO4)4: Eu (M=Ca, Sr and Ba)

Intense red emitting phosphors MGd₂(MoO₄)₄: Eu³⁺ (M=Ca, Sr and Ba) have been synthesized by the simple sol-gel technique. The formation processes and the phase impurity of phosphors are characterized by thermogravimetry-differential thermal analysis (TG-DTA) and power X-ray diffraction (XRD). The narrower size distribution and the regular shape of the phosphor particles are also measured by Field emission scanning electronic microscopy (FE-SEM). Photo-luminescent properties of the phosphors are performed at room temperature. Their excitation spectra present strong absorption at 395 nm near-UV light and 465 nm blue light, which match well with commercial LED chips. The phosphors exhibit satisfactory and excellent red light dominated by 616 nm and their photoluminescence intensity is about 3-4 times stronger than that of phosphor YAG under the 465 nm excitation. In addition, the optimal concentrations of Eu³⁺ for phosphors MGd₂(MoO₄)₄ (M=Ca, Sr and Ba) have also been determined.     

Schif f碱配合物荧光粉的合成及光谱性能研究

有机电致发光材料具有主动发光、视角广、对比度高等显著特点。稀土有机配合物电致发光材料目前备受广大研究者的关注。以水杨醛和苯甲酸衍生物为原料,经酯化、肼化及希夫碱缩合合成了水杨醛对甲氧基苯甲酰腙(1-H₂L)、水杨醛对甲基苯甲酰腙(2-H₂L)、水杨醛对溴基苯甲酰腙(3-H₂L) 3种配体,以Pr(NO₃)₃为原料,合成了水杨醛酰腙系列镨稀土配合物,经红外光谱、紫外光谱等分析手段对该类配合物的结构进行表征,配体在3 136～3 141 cm-1出现羟基ν(OH)伸缩振动峰,在配合物的红外光谱中消失,配合物在3 330～3 368 cm-1之间的吸收峰归属为结晶的H₂O的ν(O-H)羟基弯曲振动吸收峰,配合物在与配体对应的3 140 cm-1均不出现羟基吸收峰,三种配体及配合物的吸收波形相似,反映出配体及配合物的结构基本一致,但配体与配合物的吸收波峰相差较大,据此可推测配体已经配位。采用荧光分光光度计测定了该类配合物的荧光光谱,并讨论了配体取代基的变化对荧光强度的影响。配体分别在352,369,365和417 nm波长监测下,于517 nm处出现发射峰。其中3-H₂L的荧光强度最高。配合物均在470 nm的蓝光激发下,分别于608和617 nm出现镨的电偶极跃迁特征发射峰,归属于3P₀→3F₂跃迁。配合物均可被470 nm蓝光激发,在608～617 nm处有较好的红光发射,该类荧光粉有望应用于OLED上进行应用。     

Facile synthesis and luminescence properties of octahedral YVO4:Eu microcrystals

Uniform octahedral YVO₄:Eu³⁺ microcrystals have been successfully prepared through a designed two-step hydrothermal conversion method. One-dimensional precursor Y₄O(OH)₉NO₃ was first prepared through a simple hydrothermal process without using any surfactant, catalyst or template. Subsequently, well-defined octahedral YVO₄ was synthesized at the expense of the precursor during a hydrothermal conversion process. XRD results demonstrate that the diffraction peaks of the final product can be well indexed to the pure tetragonal phase of YVO₄. The SEM and TEM images indicate that the as-prepared YVO₄ sample has regular octahedral shape with sharp corners and well-defined edges. The as-obtained YVO₄:Eu³⁺ phosphor shows strong red emission under ultraviolet excitation or low-voltage electron beam excitation. Furthermore, this facile and general conversion method may be of much significance in the synthesis of many other lanthanide compounds with uniform morphology.     

Donor doping process and white light generation in CaMoO4 powders with multivalence Pr codoping

Both trivalent praseodymium (Pr³⁺) and quadrivalent praseodymium (Pr⁴⁺) were doped in molybdate powders. Visible emission from matrix was enhanced by multivalent Pr codoping. It was proposed that Pr³⁺ ions was donor and supplied quasi-free electron when Pr³⁺ took place the Pr⁴⁺ sites. The result showed that multivalence codoping would be an effective way to enhance emission of CaMoO₄. White light can be generated from Ca_0.98Pr_0.02MoO₄ powder via combination of broadband emissions originated from CaMoO₄ matrix and radiative transition of Pr³⁺. It showed warm white light with T_c of 3450 K that implies promising application in white light emitting diodes (LEDs).     

Synthesis and characterization of Gd2O3:Eu phosphor nanoparticles by a sol-lyophilization technique

The characterization and luminescence properties of nanostructured Gd₂O₃:Eu³⁺ phosphors synthesized by a sol-lyophilization process are presented. After preparation of gadolinium-based sols from gadolinium nitrate and ammonium hydroxide, the so-prepared sols were freeze dried at −10°C and calcinated at different temperatures. For temperatures lower than 1300 K, highly crystalline samples with the cubic structure can be obtained without concomitant grain growth of the particles (<50 nm). The luminescence spectra contain all possible transitions of Eu³⁺ with C₂ symmetry and present two major features: an increase of the luminescence efficiencies of the phosphors in comparison with that obtained by solid-state reaction and the presence of an additional peak at about 609 nm at the vicinity of the ⁵D₀→⁷F_0…4 transition.     

Photoluminescent properties of white-light-emitting Li6Y(BO3)3:Dy3+ phosphor

In this study, lithium yttrium borate (LYBO) phosphor was doped with various concentrations of trivalent dysprosium ions. To produce these phosphors, the raw materials were sintered. The phase conformation, crystallinity, grain size, and overall morphology of the synthesized phosphors were studied with X-ray diffraction and scanning electron microscopy. The optimized LYBO phosphor, i.e., the LYBO phosphor that exhibited the highest X-ray- and ultraviolet (UV)-induced photoluminescent intensities, had a Dy³⁺ concentration of 4 mol%. Photoluminescence analysis showed that this phosphor could be easily excited with near-UV light (300–400 nm). The dominant photoluminescence bands were found in the blue (480 nm) and yellow (577 nm) regions of the visible spectrum. The light yield of the X-ray-induced luminescence of the optimized Li₆Y(BO₃)₃:Dy³⁺ was found to be 66% of that of the commercially available X-ray imaging material, Gd₂O₂S:Tb³⁺ (GOS). The chromaticity coordinates of the Li₆Y(BO₃)₃:Dy³⁺ phosphor were x = 0.34 and y = 0.32, which agree well with achromatic white (x = 0.33, y = 0.33). The results of this study show that the synthesized Li₆Y(BO₃)₃:Dy³⁺ phosphor could be used as X-ray imaging material.     

Synthesis of Y2O3:Eu phosphors by bicontinuous cubic phase process

A novel approach for preparation of red-emitting europium-doped yttrium oxide phosphor (Y₂O₃:Eu) by using the bicontinuous cubic phase (BCP) process was reported in this paper. The BCP system was composed of anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and aqueous yttrium nitrate/europium nitrate solution. Energy dispersive spectrometer analysis revealed the homogeneous precipitation occurred in the BCP structure. Thermogravimetric analysis measurements indicated the precursor powder was europium-doped yttrium hydroxide, Y_1−xEu_x(OH)₃. Scanning electron microscopy micrographs showed the precursor powder had a primary size about 30 nm and narrow size distribution. After heat treatment in furnace above 700 °C for 4 h, high crystallinity Y₂O₃:Eu phosphors was obtained. However, the primary size of particles grew to 50–200 nm and the dense agglomerates with a size below 1 μm were formed. X-ray diffraction patterns indicated the crystal structure of precursor powders and Y₂O₃:Eu phosphors were amorphous and body-centered cubic structure, respectively. The photoluminescence analysis showed that the obtained Y₂O₃:Eu phosphor had a strong red emitting at 612 nm and the quenching started at a Eu concentration of 10 mol%. This study indicated that the BCP process could be used to prepare the highly efficient oxide-based phosphors.     

Luminescence and EPR studies of Mn-activated SrAl12O19 phosphor prepared by facile combustion approach

Manganese-activated strontium hexa-aluminate (SrAl₁₂O₁₉) phosphor has been prepared at low temperature (500 °C) and in a very short time (<5 min) by urea combustion route. Powder X-ray diffraction pattern showed the presence of hexagonal SrAl₁₂O₁₉ phase. Scanning electron microscopy (SEM) indicated the presence of several particles with sizes of 200 nm. The luminescence of Mn²⁺ activated SrAl₁₂O₁₉ exhibits a strong green emission peak around 515 nm from the synthesized phosphor particles under excitation (451 nm). The luminescence is assigned to a transition from the upper ⁴T₁→⁶A₁ ground state of Mn²⁺ ions. EPR investigations also indicated the presence of Mn²⁺ ions in the prepared material. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between Mn²⁺ ions and the surrounding ligands. The variation of zero-field splitting parameter (D) with temperature is measured and discussed. The mechanism involved in the generation of a green emission has been explained in detail.     

Luminescence of Ce in hydrated rare earth bromides

Intense photoluminescence is reported for hydrated bromides of Gd, La and Y (LaBr₃·7H₂O, CeBr₃·7H₂O, YBr₃·8H₂O and GdBr₃·n H₂O) prepared by the wet chemical method and activated with Ce³⁺. Intensities are comparable to that for a commercial phosphor (SrB₄O₇:Eu²⁺—Sylvania 2052). Luminescence in hydrated salt is usually quenched. The observation of intense luminescence in hydrated bromides is remarkable.