Fabrication and characterizations of Cr3+-doped ZnGa2O4 transparent ceramics with persistent luminescence

0.5 at.% Cr:ZnGa₂O₄ precursor was synthesized by the co-precipitation method with nitrates as raw materials, using ammonium carbonate as the precipitant. Low-agglomerated Cr:ZnGa₂O₄ powders with an average particle size of 43 nm were obtained by calcining the precursor at 900℃ for 4 h. Using the powders as starting materials, 0.5 at.% Cr:ZnGa₂O₄ ceramics with an average grain size of about 515 nm were prepared by presintering at 1150℃ for 5 h in air and HIP post-treatment at 1100℃ for 3 h under 200 MPa Ar. The in-line transmittance of 0.5 at.% Cr:ZnGa₂O₄ ceramics with a thickness of 1.3 mm reaches 59.5% at the wavelength of 700 nm. The Cr:ZnGa₂O₄ ceramics can be effectively excited by visible light and produce persistent luminescence at 700 nm. For Cr:ZnGa₂O₄ transparent ceramics, the brightness of afterglow was larger than 0.32 mcd/m² after 30 min, which is far superior to that of Cr:ZnGa₂O₄ persistent luminescence powders.     

Fabrication,microstructure and optical characterizations of holmium oxide (Ho2O3) transparent ceramics

Ho₂O₃ transparent ceramics were fabricated by vacuum pre-sintering combined with hot isostatic pressing (HIP) post-treatment at relatively low temperature from high-purity Ho₂O₃ powder calcined at 1000 °C for 4 h. The optimal Ho₂O₃ ceramic sample prepared by vacuum pre-sintering at 1250 °C and HIP post-treating at 1450 °C has a dense microstructure with average grain size of 0.77 μm, and the in-line transmittances reach 80.7 % at 1550 nm and 76.7 % at 1064 nm. The effect of air annealing on the optical quality of Ho₂O₃ ceramics was studied, and the existence of compressed pores in the HIP-ed Ho₂O₃ ceramics was confirmed. The Verdet constants of Ho₂O₃ ceramics were measured to be -47.4 rad/(T m at 1064 nm and -15.4 rad/(T m at 1561 nm. High transmittance and large Verdet constant in the wavelength regions 1–1.07 μm, 1.3–1.5 μm make Ho₂O₃ transparent ceramics promising for magneto-optical devices for lasers based on Yb-, Nd-doped materials and telecom lasers.     

Translucent and persistent luminescent SrAl2O4:Eu2+Dy3+ ceramics

Ceramics that exhibit persistent luminescence are usually opaque, which limits their utility. In this work, a laser-sintering technique is employed to produce persistent luminescent SrAl₂O₄:Eu²⁺Dy³⁺ ceramics that has enhanced translucency in the visible spectral range. In this technique, a CO₂ laser was used as the main heating source for sintering with no atmosphere control employed. The ceramics sintered at a power density of 3.1 W/mm² yielded homogeneous grain size distributions and transmittance up to 40% in the range of 600–800 nm. Upon sintering in air, the ceramics exhibited the characteristic green emission from the Eu²⁺ ion, corresponding to the 5d→4f transition (514 nm) and a weak emission from the Eu³⁺ ion at 614 nm, corresponding to the ⁵D₀→⁷F₂ transition. The valence of europium ions was further studied by the X-ray absorption spectroscopy in the XANES region and those details are reported herein.     

燃烧法合成SrAl2O4:Eu2+,Dy3+发光材料及其性能研究

采用燃烧法在较低温度下快速合成了SrAlO:Eu2 ,Dy3 长余辉发光粉体,并利用XRD、荧光分光光度24计等测试手段,研究了合成粉体的物相结构以及工艺因素对材料发光性能的影响。结果表明,发光粉体的主晶相为SrAlO,属单斜晶系,晶胞参数为a=0.8442nm,b=0.8827nm,c=0.5162nm,β=97°;激发光谱主峰波长为24398nm、349nm、324nm,发射光谱主峰波长为516nm。     

Fabrication and characterizations of Ho3Sc2Al3O12 magneto-optical transparent ceramics

Currently, Faraday isolators and rotators for high-power lasers are popular research topics; therefore, finding magneto-optical materials with excellent Verdet constants and thermal properties is crucial. In this study, novel holmium scandium aluminum garnet (HoSAG) magneto-optical ceramics were fabricated using vacuum sintering. This study improved the traditional ball milling method and pre-synthesized powders with great sinterability after secondary ball milling and sieving. Different pre-synthesis temperatures were found to have significant effects on the particle size and micromorphology of the synthesized powders. HoSAG ceramics with 0.05 wt% MgO sintering aid and held at 1700°C for 30 h reached a transmittance of 76.7% at 1550 nm. Meanwhile, HoSAG transparent ceramics maintain higher transmittance in the infrared region (>1500 nm) than terbium gallium garnet (TGG) crystals, indicating better application prospects. The Verdet constants of HoSAG magneto-optical ceramics at 405, 532, 808, and 1064 nm were −421.5, −181.2, −65, and −32.3 rad T⁻¹ m⁻¹, respectively, which are slightly less than those of TGG magneto-optical ceramics. Moreover, the thermal conductivity of HoSAG ceramics at 300.00 K was 4.89 W m⁻¹ K⁻¹, which is comparable to that of the TGG ceramics.     

正交法优化纳米SrAl2O4:Eu2+,Dy3+制备工艺

采用溶胶-凝胶法合成了SrAl2O4:Eu2+,Dy3+纳米长余辉发光材料,利用正交设计法优化了制备工艺.在传统溶胶-凝胶法基础上,添加了硼酸,在950℃生成单一晶相,该法能使SrAl2O4生成温度降低150℃,生成的磷光体发光强度高、余辉时间长,平均晶粒尺寸为25～90nm.     

溶剂热法合成片状SrAl2O4:Eu2+,Dy3+长余辉荧光粉的研究

利用溶剂热法制备了由片组装的花状前驱体,1300℃烧结2h后获得了SrAl2O4:Eu2+,Dy3+片状荧光材料.利用XRD和SEM技术表征了在不同比例的乙醇和水的混合溶液中反应制得的荧光材料的物相组成和形貌,用荧光分光光度计测定了荧光材料的发光性质.结果发现,当乙醇和水的比例为3∶1时,所制备的荧光材料具有较高的结晶性,较好的形貌和较强的发光强度.     

掺铽的铝酸锶铕镝磷光体的发光特性及晶相分析

采用高温固相法在弱还原气氛下制备了掺入Tb3 的SrAl2O4:Eu2 ,Dy3 磷光体.研究了Tb3 对SrAl2O4:Eu2 ,Dy3 磷光体的发光性能的影响.结果发现,引入Tb3 以后,对基质SrAl2O4的晶体结构基本上没有影响,也未改变磷光体的发光光谱,却使磷光体的初始亮度显著提高,并使余辉时间延长.其余辉强度随时间的变化由最初的快衰减过程和随后的慢衰减过程组成,符合t-1.1的双曲线规律.并初步探讨了Tb3 的作用机制.     

Fabrication of transparent MgAl2O4 ceramics by gelcasting and cold isostatic pressing

Highly transparent MgAl₂O₄ ceramics have been fabricated by aqueous gelcasting combined with cold isostatic pressing (CIP), pressureless sintering and hot isostatic pressing (HIP) from high purity spinel nanopowders. The gelling system used AM and MABM as monomer and gelling agent. The influences of dispersant and PH on the rheological behavior of the MgAl₂O₄ slurries were investigated. The spinel slurry with low solids loading (25 vol%) and low viscosity (0.15 Pa s) was obtained by using 6 wt% Duramax-3005 (D-3005) as dispersant. After CIP, the green body had a relative density of 48% with a narrow pore size distribution. The influence of sintering temperature on densification and microstructure was studied, choosing 1500 °C as the sintering temperature. After HIP (1650 °C/177 MPa/5 h), transparent MgAl₂O₄ ceramic with the thickness of 3 mm was obtained, whose in-line transmittance was 86.4% at 1064 nm and 79.8% at 400 nm, respectively. The ceramic exhibited a dense microstructure with the average grain size of 23 μm. The Vickers hardness and flexure strength of the sample reached 13.6 GPa and 214 MPa, respectively.     

水热法合成SrAl2O4:Eu2+,Dy3+长余辉材料

研究了SrAl2O4：Eu^2 ，Dy^3 长余辉材料的一种新合成方法。首先利用水热法制备出该发光材料的前驱体，然后将此前驱体粉体在还原气氛下高温烧结，得亮度高，余辉时间长的洲SrAl2O4：Eu^2 ，Dy^3 超细长余辉材料，并对其发光性能进行了研究。并对水热法和复合沉淀法合成的此种材料进行了比较。     

Fabrication and laser operation of Yb:Lu2O3 transparent ceramics from co-precipitated nano-powders

In this article, 5 at.% Yb:Lu₂O₃ transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) posttreatment using co-precipitated nano-powders. The influence of precipitant molar ratio, ammonium hydrogen carbonate, to metal ions (AHC/M³⁺, R value) on the properties of Yb:Lu₂O₃ precursors and calcined powders was investigated systematically. It was found that the powders with different R value calcined at 1100°C for 4 hours were pure cubic Lu₂O₃ but the morphologies of precursors and powders behaved differently. The opaque samples pre-sintered at 1500°C for 2 hours grew into transparent ceramics after HIP posttreatment at 1750°C for 1 hour. The final ceramic with R = 4.8 showed the best optical quality with the in-line transmittance of 79.7% at 1100 nm. The quasi-CW laser operation was performed at 1034 nm and 1080 nm with a maximum output power up to 8.15 W as well as a corresponding slope efficiency of 58.4%.     

Unusual concentration induced antithermal quenching of the Eu2+ emission at 490 nm in Sr4Al14O25:Eu2+ for near ultraviolet excited white LEDs

Thermal quenching of phosphor is an important challenge for its practical application in phosphor-converted white light-emitting diodes (pc-WLEDs) and it usually becomes aggravated with the increase of activator concentration. Conversely, this work finds the thermal quenching of Eu²⁺ emission at 490 nm in Sr₄Al₁₄O₂₅:Eu²⁺ does not follow this in the temperature range of 300 to 480 K, and the rate of it is even slowed down as the concentration of Eu²⁺ increases. However, at the same time, the experiment on three heating-cooling cycles of Sr₄Al₁₄O₂₅:Eu²⁺ reveals that the thermal degradation of Eu²⁺ emission becomes improved. Once Eu²⁺ ions are doped into Sr₄Al₁₄O₂₅, they will prefer substituting for the 10- and 7-coordinated strontium sites Sr1 and Sr2, respectively. The emission centers Eu1 and Eu2, therefore, appear. The abnormal phenomenon is perhaps partly due to the enhanced energy transfer from the emission center Eu1 at 407 nm to the one Eu2 at 490 nm. It is also found interesting that the introduction of AlN can enhance the emission of Sr₄Al₁₄O₂₅:Eu²⁺ without leading to the deterioration of thermal degradation. In the end, a prototype of pc-WLED was fabricated with Sr₄Al₁₄O₂₅:Eu²⁺ to demonstrate the application of white lighting. This work is not only beneficial to the understanding of the relationship between concentration and thermal quenching, but also conducive to the design of the heavily doped phosphor for WLEDs with better resistance to thermal quenching.     

SrAl2O4:Eu2+发光材料的制备工艺及发光性能的研究

采用固相烧结法，在碳还原条件下合成了SrAl2O4：Eu^2 发光材料。研究了影响其发光性能的制备工艺及各种因素。探讨了SrAl2O4：Eu^2 发光材料的长余辉性能。     

发光材料SrAl2O4：Eu2＋的制备及XRD物相分析

采用高温固相法合成SrAl2O4：Eu2＋并用x射线粉末衍射仪进行表征。通过考察合成温度、原料配比的影响,找出了样品的最佳烧结温度及最佳原料配比。     

Ethyl vinyl acetate copolymer—SrAl2O4:Eu,Dy and Sr4Al14O25:Eu,Dy phosphor‐based composites: Preparation and material properties

New photoactive composite based on ethyl vinyl acetate (EVA) and SrAl₂O₄:Eu,Dy or Sr₄Al₁₄O₂₅:Eu,Dy were prepared by melt mixing or extrusion methodologies. The phosphorescent behavior and material properties of the polymer‐phosphor composites were studied. The morphology of the polymer and the composites were studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X‐ray spectroscopy (EDS). The SEM shows that the physical and chemical behavior of the matrix and the extrusion conditions were primarily responsible for the surface morphology. TEM and EDS show that the phosphor particles were uniformly dispersed in the EVA matrix. A broad band of ultraviolet (UV)‐excited phosphorescence of SrAl₂O₄:Eu,Dy and Sr₄Al₁₄O₂₅:Eu,Dy phosphors and the respective composites were observed at wavelengths of 516 nm and 490 nm, respectively. The photoluminescence (PL) spectra showed less intense phosphorescence but no shift in the wavelength of the emission peak for all the composites. The Hamburg wheel test was done on all the composites and the PL measurements before and after the test showed almost no change in the intensity of the emission. Thermal studies showed that the presence of the phosphors in the matrix slightly increased the crystallinity of EVA, which leads to higher melting enthalpies. Tensile testing shows very little change in the tensile strength and flexibility of the ethylene vinyl acetate copolymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and luminescence of SrAl2O4: Eu2+,Dy3+ phosphors coated with maleic anhydride

In this paper, maleic anhydride is directly coated on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ (SAO‐ED) phosphors by an interfacial coordination chemistry method. Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectra (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) methods are used to characterize the coating. The experimental result shows that a dense coating layer is consisting of maleic anhydride coordination with metal ions on the surface of the phosphors and the coating process does not destroy the crystal structure of the phosphors. It is also found that the introduction of maleic anhydride does not change the excitation and emission spectra of SAO‐ED phosphors, but decreases the luminous intensity, which is verified by the photoluminescence (PL) measurement. Afterglow delay curves show that the initial brightness of coated SAO‐ED phosphors decreases, but the afterglow decay rate of coated phosphors is slower than that of uncoated phosphors after they both are immersed into water for one month. This indicates that the coating layer protects the phosphors and the crystal structure of coated phosphors in water was not destroyed.     

掺钆的铝酸锶铕镝磷光体的发光特性及晶相分析

采用高温固相法在弱还原气氛下制备了掺入Gd3+的SrAl2O4:Eu2+,Dy3+磷光体.研究了Gd3+对SrAl2O4:Eu2+,Dy3+磷光体的发光性能的影响.结果发现:引入Gd3+以后,对SrAl2O4基质的晶体结构基本上没有影响,也并未改变磷光体的发光光谱,却使磷光体的初始亮度显著提高,并使余辉时间延长.其余辉强度随时间的变化由最初的快衰减过程和随后的慢衰减过程组成,符合t-1.1的双曲线规律.并初步探讨了Gd3+的作用机制.     

燃烧法合成长余辉发光材料SrAl2O4:Eu2+,Dy3+的研究

以尿素和硝酸盐溶液为反应介质，在600℃下用燃烧法一次制备出了Eu^2 ，Dy^3 掺杂的铝酸锶(SrAl2O4)磷光体。用SEM、XRD研究了所得磷光材料的形态、粒度和物相组成，用荧光分光光度计测定了磷光材料的发光性能。结果表明SrAl2O4：Eu^2 ，Dy^3 磷光材料的晶体结构属于单斜晶系结构。制备产物的形貌呈疏松多孔状，晶粒形状为针状，长度有200nm左右，直径在80nm以下。制备产物在520nm处有很强的发射峰，它的激发光谱是激发峰峰值290nm的宽带激发。并探讨了该材料发光性能的影响因素。     

Enhancing emission intensity and thermal stability by charge compensation in Sr2Mg3P4O15:Eu3+

Charge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr₂Mg₃P₄O₁₅:Eu³⁺ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R⁺ (R⁺ = Li, Na, and K), substituting Si⁴⁺ for P⁵⁺ and self‐compensation) were employed to solve the charge imbalance problem between Sr²⁺ and Eu³⁺. The results showed that emission intensity of Eu³⁺ was improved by 1.43 (Li⁺), 1.58 (Na⁺), 1.53 (K⁺), 1.61 (Si⁴⁺), and 1.30 (self) times than that of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺ to 55.69% (Li⁺), 61.62% (Na⁺), 58.98% (K⁺), 71.15% (Si⁴⁺), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor.     

Fabrication and laser performances of Yb:Sc2O3 transparent ceramics from different combination of vacuum sintering and hot isostatic pressing conditions

In this paper we report on the preparation and laser performance of transparent 3at.% Yb:Sc₂O₃ ceramics by reactive sintering of commercially available powders under vacuum followed by hot isostatic pressing (HIP). Combinations of different vacuum sintering temperatures (1650 °C and 1750 °C) and different HIP treatments (1700 °C and 1800 °C at 200 MPa) were tested in order to understand how these steps influence the microstructure and thus the optical and lasing properties of the ceramic samples. All the samples showed a good optical quality. The microstructure analysis and the laser tests showed that the vacuum pre-sintering temperature is the key factor determining the quality of the samples and the laser performances. The best values of slope efficiency i.e. η_L = 50 % and output power i.e. P_out = 6.62 W were obtained for the sample pre-sintered under vacuum at 1650 °C and hot isostatically pressed at 1800 °C.