Intense upconversion luminescence and energy‐transfer mechanism of Ho3+/Yb3+ co‐doped SrLu2O4 phosphor

A series of novel SrLu₂O₄: x Ho³⁺, y Yb³⁺ phosphors (x=0.005‐0.05, y=0.1‐0.6) were synthesized by a simple solid‐state reaction method. The phase purity, morphology, and upconversion luminescence were measured by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The doping concentrations and sintering temperature were optimized to be x=0.01, y=0.5 and T=1400°C to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the SrLu₂O₄:Ho³⁺, Yb³⁺ phosphors exhibit intense green upconversion (UC) emission band centered at 541 nm (⁵F₄,⁵S₂→⁵I₈) and weak red emission peaked at 673 nm (⁵F₅→⁵I₈). Under different pump‐power excitation, the UC luminescence can be finely tuned from yellow‐green to green light region to some extent. Based on energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the analysis of pump‐power dependence and luminescence decay curves. The energy‐transfer mechanisms for green and red UC emissions can be determined to be two‐photon absorption processes. Compared with commercial NaYF₄:Er³⁺, Yb³⁺ and common Y₂O₃:Ho³⁺, Yb³⁺ phosphors, the SrLu_1.49Ho_0.01Yb_0.5O₄ sample shows good color monochromaticity and relatively high UC luminescence intensity. The results imply that SrLu₂O₄:Ho³⁺, Yb³⁺ can be a good candidate for green UC material in display fields.     

Insight into a novel rare-earth-free red-emitting phosphor Li3Mg2NbO6:Mn4+: Structure and luminescence properties

Red phosphor is indispensable to achieve warm white light in the white light diode (WLED) application. However, the current red phosphors suffer from high cost and harsh synthesis conditions. In this study, an oxide-based rare-earth-free red-emitting phosphor Li₃Mg₂NbO₆:Mn⁴⁺ (LMN:Mn⁴⁺) has been successfully synthesized by a simple solid-state reaction method. The relationship between crystal structure and luminescence was investigated in detail. The site occupancy of the doping Mn⁴⁺ ion in the LMN host has been discussed from the point of bond valence sum. How the coordination environment of doping Mn⁴⁺ affects the energy level of doping Mn⁴⁺ ion has been illustrated via the Tanabe-Sugano energy-level diagram. Moreover, warm white light has been obtained using LMN:Mn⁴⁺ as compensator to the YAG:Ce³⁺.     

A novel pale-yellow Ba2ZnGe2O7:Bi3+ phosphor with site-selected excitation and small thermal quenching

A novel pale-yellow Ba₂ZnGe₂O₇:Bi³⁺ phosphor with site-selected excitation and small thermal quenching was synthesized by conventional solid-state sintering. The crystal structure and luminescence properties have been investigated in detail for the first time using XRD patterns, photoluminescence spectra, diffuse reflection spectra, decay curves, and temperature-dependent emission spectra. The results reveal that the excitation spectrum of Ba₂ZnGe₂O₇:Bi³⁺ phosphor locates in the near-ultraviolet region of 300-400 nm, and its emission shows an obvious site-selective excitation phenomenon since Bi³⁺ ions occupy two different crystallographic sites in the Ba₂ZnGe₂O₇ host. When excited under 360 nm, the phosphors show a pale-yellow emission in the range of 400-700 nm with the maximum peaking at 520 nm, while when excited under 316 nm, the phosphors show a blue emission in the range of 400-700 nm with the maximum peaking at 480 nm. In addition, the emission of Ba₂ZnGe₂O₇:Bi³⁺ can also be easily controlled by changing the Bi³⁺ concentration. The Ba₂ZnGe₂O₇:Bi³⁺ phosphor has small thermal quenching, and its emission intensity only decreases by 2% at 200°C. The results indicate that this novel pale-yellow Ba₂ZnGe₂O₇:Bi³⁺ phosphor could be conducive to the development of white light-emitting diodes.     

Li+掺杂浓度对Sr3ZnNb2O9:Eu3+荧光粉发光特性的影响

Li⁺作为电荷补偿剂可以提高Sr₃ZnNb₂O₉:Eu³⁺荧光粉的发光强度和热稳定性。本文通过高温固相反应成功制备了Sr₃ZnNb₂O₉:xEu³⁺,yLi⁺(0≤x≤0.5,0≤y≤0.5)荧光粉,为了鉴定和描述样品的物相、发光特性和热稳定性,进行了XRD和发光光谱测试。结果表明:Eu³⁺和Li⁺已经成功掺入到基质材料中,并取代Zn²⁺位点;Li⁺的最佳掺杂浓度为0.3(摩尔分数),浓度猝灭类型是在最近邻离子之间;掺杂Li⁺提高了荧光粉的热稳定性,活化能为0.193 eV,CIE色坐标为(0.651,0.349),非常接近国际照明委员会规定的标准色坐标。     

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.     

Preparation of MGF phosphor by O2 postannealing and impact on luminescence properties and crystal lattice

Mn⁴⁺-activated phosphors, Mg₂₈Ge₁₀O_48-δF_δ:Mn⁴⁺ (MGFs), can be obtained through an oxygen postannealing process. Analyses of the crystal structure and elemental composition by powder X-ray diffraction (XRD) and electron probe microanalysis (EPMA), respectively, indicated that under an O₂ atmosphere, oxygen atoms were substituted with fluorine atoms in the original MGF structure to leach the fluorine atoms with germanium atoms as GeF₄ by oxygen postannealing. The MGF phosphor annealed in O₂ exhibited ~1.3 times higher quantum efficiency (QE) than that annealed in ambient air. The Raman spectroscopy results suggested that an increase in the content of the [Mn⁴⁺O₆] octahedron led to an increase in the QE values. Additionally, the relaxation of lattice defects in the lattice interior and on the surface observed by XRD and X-ray photoelectron spectroscopy (XPS) measurements could explain the change in thermal quenching behavior between the different atmospheres, and the decrease in lattice defects increased the QE. The investigation of MGF phosphors prepared by different processes provides insight into the relationships among the surface and local structures, chemical composition, and photoluminescence properties. The optimized synthetic procedure increases the Mn⁴⁺ content and decreases the Mn²⁺ and Mn³⁺ contents in the phosphor, which drastically increases the luminescence efficiency.     

Deep‐red photoluminescence and long persistent luminescence in double perovstkite‐type La2MgGeO6:Mn4+

A novel non‐rare‐earth doped phosphor La₂MgGeO₆:Mn⁴⁺ (LMG:Mn⁴⁺) with near‐infrared (NIR) long persistent luminescence (LPL) was successfully synthesized by solid‐state reaction. The phosphors can be effectively excited using ultraviolet light, followed by a sharp deep‐red emission peaking at 708 nm, which is originated from ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. The luminescent performance was analyzed by photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The crystal field parameters were calculated to describe the environment of Mn⁴⁺ in LMG host. The LPL behaviors as well as the mechanisms were systematically discussed. This study suggests that the phosphors will broaden new horizons in designing and fabricating novel NIR long phosphorescent materials.     

On comparison of luminescence properties of La2Zr2O7 and La2Hf2O7 nanoparticles

Unveiling the underlying mechanisms of properties of functional materials, including the luminescence differences among similar pyrochlores A₂B₂O₇, opens new gateways to select proper hosts for various optoelectronic applications by scientists and engineers. For example, although La₂Zr₂O₇ (LZO) and La₂Hf₂O₇ (LHO) pyrochlores have similar chemical compositional and crystallographic structural features, they demonstrate different luminescence properties both before and after doped with Eu³⁺ ions. Based on our earlier work, LHO-based nanophosphors display higher photo- and radioluminescence intensity, higher quantum efficiency, and longer excited state lifetime compared to LZO-based nanophosphors. Moreover, under electronic O²⁻→Zr⁴⁺/Hf⁴⁺ transition excitation at 306 nm, undoped LHO nanoparticles (NPs) have only violet blue emission, whereas LZO NPs show violet blue and red emissions. In this study, we have combined experimental and density functional theory (DFT) based theoretical calculation to explain the observed results. First, we calculated the density of state (DOS) based on DFT and studied the energetics of ionized oxygen vacancies in the band gaps of LZO and LHO theoretically, which explain their underlying luminescence difference. For Eu³⁺-doped NPs, we performed emission intensity and lifetime calculations and found that the LHOE NPs have higher host to dopant energy transfer efficiency than the LZOE NPs (59.3% vs 24.6%), which accounts for the optical performance superiority of the former over the latter. Moreover, by corroborating our experimental data with the DFT calculations, we suggest that the Eu³⁺ doping states in LHO present at exact energy position (both in majority and minority spin components) where oxygen defect states are located unlike those in LZO. Lastly, both the NPs show negligible photobleaching highlighting their potential for bioimaging applications. This current report provides a deeper understanding of the advantages of LHO over LZO as an advanced host for phosphors, scintillators, and fluoroimmunoassays.     

Efficient red and broadband near-infrared luminescence in Mn2+/Yb3+-doped phosphate phosphor

In this work, we report a novel phosphor LSPO:Mn²⁺ that exhibits red emission at about 616 nm and pleasant broad near-infrared (NIR) emission at about 800 nm with a full width at half maximum (fwhm) of 112 nm. The structure and spectra show that the doped manganese ions occupy two kinds of Sc sites forming Mn1 and Mn2 emission centers, which are responsible for red and NIR emission, respectively. The XPS and low-temperature fluorescence spectra reveal that both red and NIR emissions come from the Mn²⁺ ions. Besides, NIR luminescence is improved by doping Yb³⁺ in LSPO:Mn²⁺, leading to the broadened NIR emission range (700-1100 nm) and enhanced luminescent thermal stability. Our results suggest that the prepared LSPO:Mn²⁺ and LSPO:Mn²⁺,Yb³⁺ phosphors offer the potential applications as red and NIR components in phosphor-converted white-light-emitting diodes (pc-WLED) and broadband NIR pc-LED. Meanwhile, this work provides a new way to design novel broadband NIR phosphors.     

Preparation,crystal structure and luminescence properties of red-emitting Lu3Al5O12: Mn4+ ceramic phosphor

A series of red-emitting Mn⁴⁺ doped Lu₃Al₅O₁₂ (LuAG) ceramic phosphors were successfully prepared by a simple solid-state reaction method in a high-temperature muffle. MgO was co-doped as sintering aids and Mg²⁺ ions helped to realize the charge balance. The relations between the luminescence properties, crystal structures and the microstructures were well established. Results indicated that MgO promoted the densification of the ceramics as the specimens’ relative densities were up to 99%. Moreover, the substitution of Al³⁺ with Mg²⁺ have changed crystal structures and further affected the luminescent properties. Overall, the obtained ceramic phosphors showed strong red-light emission under excitation of ultraviolet and blue light. By optimizing the Mg²⁺ and Mn⁴⁺ concentration, a quantum efficiency (QE) as high as 47.8% can be achieved under the excitation of 460 nm light, indicating that the LuAG: Mn⁴⁺ ceramic phosphors are promising candidates for WLEDs applications.     

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.     

Effects of Gd3+ substitution on the structure,photoluminescence, scintillation,and thermometric features of Pr3+:Lu2Zr2O7 phosphors

In this study, it is shown how the photoluminescence, scintillation, and optical thermometric properties are managed via the introduction of Gd³⁺ ions into Pr³⁺:Lu₂Zr₂O₇. Raman spectra validate that partial replacement of Lu³⁺ with Gd³⁺ can promote the phase transition of Lu₂Zr₂O₇ host from the defective fluorite structure to the ordered pyrochlore one. Upon 289 nm excitation, all the samples emit the 483 (³P₀ → ³H₄), 581 (¹D₂ → ³H₄), 611 (³P₀ → ³H₆), 636 (³P₀ → ³F₂), and 714 nm (³P₀ → ³F₄) emissions from Pr³⁺ ions, which are enhanced with the addition of Gd³⁺ ions due to the modification of crystal structure. Dissimilarly, the X-ray excited luminescence spectra consist of a strong emission located at 314 nm from Gd³⁺ ions (⁶P_7/2 → ⁸S_7/2), together with the typical emissions from Pr³⁺ ions, which exhibit different dependences on the Gd³⁺ concentration. When the luminescence intensity ratio between the ³P₀ → ³H₆ (611 nm) and ¹D₂ → ³H₄ (581 nm) transitions is selected for temperature sensing, Pr³⁺:(Lu_0.75Gd_0.25)₂Zr₂O₇ shows the optimal relative sensing sensitivity of 0.78% K⁻¹ at 303 K, which is higher than that of the Gd³⁺-free sample. Therefore, the developed Pr³⁺:(Lu, Gd)₂Zr₂O₇ phosphors have the applicative potential for optical thermometry, X-ray detection, and photodynamic therapy.     

Catalytic activity of Pt‐Re‐Pb/Al2O3 naphtha reforming catalysts

BACKGROUND: The main purpose of the naphtha reforming process is to obtain high octane naphtha, aromatic compounds and hydrogen. The catalysts are bifunctional in nature, having both acid and metal sites. The metal function is supplied by metal particles (Pt with other promoters like Re, Ge, Sn, etc.) deposited on the support. The influence of the addition of Pb to Pt‐Re/Al₂O₃ naphtha reforming catalysts was studied in this work. The catalysts were prepared by co‐impregnation and they were characterized by means of temperature programmed reduction, thermal programmed desorption of pyridine and several test reactions such as cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n‐heptane reforming. RESULTS: It was found that Pb interacts strongly with the (Pt‐Re) active phase producing decay in the metal function activity. Hydrogenolysis is more affected than dehydrogenation. Part of the Pb is deposited over the support decreasing the acidity and the strength of the most acidic sites. CONCLUSION: The n‐heptane reforming reaction shows that Pb modifies the stability and selectivity of the Pt‐Re catalysts. Small Pb additions increase the stability and greatly improve the selectivity to C₇ isomers and aromatics while they decrease the formation of low value products such as methane and gases. Copyright © 2011 Society of Chemical Industry     

Electrochemical Performance of PrBaCo2O5+δ and Sm0.5Sr0.5CoO3−δ Infiltrated Ce0.9Gd0.1O1.95 Cathodes

Cathodes with PrBaCo₂O_5+δ (PBC) and Sm_0.5Sr_0.5CoO_3−δ (SSC) infiltrated on Ce_0.9Gd_0.1O_1.95 (CGO) backbones are prepared using metal nitrates as precursors and ethanol as wetting agent. Electrochemical impedance spectra (EIS) are measured from cathode/CGO/cathode symmetrical cells in 400–650 °C under humidified air. The results indicate that interfacial area specific resistance (ASR) value decreases and then increases with infiltrate loading and minimum values occur at 50 wt.% loading (relative to sum of infiltrate and backbone) for both PBC and SSC infiltrates. ASR values of PBC infiltrated cathodes are lower than that of corresponding SSC infiltrated cathodes in general, and in particular ASR values as low as 1.36 × 10⁻² and 2.27 × 10⁻² Ω cm² are obtained at 650 °C in air for 50 wt.% PBC and 50 wt.% SSC infiltrated cathodes, respectively. Conductivity values of CGO electrolyte increase with infiltrate loading and agree with the reported values when the loading reaches 50 wt.%.     

聚丙烯酸钠包覆Fe3O4磁性交联聚合物的制备及其对Pb(Ⅱ)和Cd(Ⅱ)的吸附性能

采用溶液分散聚合和Ca²⁺表面交联制备了聚丙烯酸钠包覆Fe₃O₄的磁性交联聚合物（CPAANa@Fe₃O₄）,对其进行了XRD、FT-IR、SEM和TGA等表征。以CPAANa@Fe₃O₄为吸附剂研究了CPAANa@Fe₃O₄对水溶液中Pb²⁺、Cd²⁺的静态吸附,考察了溶液pH、吸附剂投加量、金属离子初始浓度对吸附的影响。结果表明：CPAANa@Fe₃O₄在pH 2～6范围内均具有较好的吸附性能,当吸附剂投加量分别为1.0 g·L^-1和1.6 g·L^-1时对初始浓度分别为200 mg·L^-1的Pb²⁺和100 mg·L^-1的Cd²⁺的去除率达到最大,可使Pb²⁺实现达标排放（GB 8978-1996）;CPAANa@Fe₃O₄对Pb²⁺和Cd²⁺的吸附动力学符合准二级模型,吸附等温线符合Langmuir模型,对Pb²⁺和Cd²⁺的最大吸附量分别为454.55 mg·g^-1和275.48 mg·g^-1。将CPAANa@Fe₃O₄用于处理实际电解矿浆废水,发现能有效吸附其中的Pb²⁺和Cd²⁺,具有潜在实用价值。     

A novel Eu3+‐ and self‐activated vanadate phosphor of Ca4La(VO4)3O with oxyvanadate apatite structure

Pure and Eu³⁺‐activated Ca₄La(VO₄)₃O phosphors were prepared via three‐step solid‐phase synthesis. The phase formation and structure were investigated by X‐ray diffraction (XRD) with Rietveld refinements. All the samples crystallized in an apatite‐type structure. The morphological properties were measured via by SEM and EDS measurements. Ca₄La(VO₄)₃O is a new vanadate optical material with a direct band feature and a band energy of 3.1 eV. The undoped Ca₄La(VO₄)₃O phosphor presents self‐activated yellow luminescence from 400 nm to 750 nm with a maximum wavelength of 525 nm originating from VO₄ groups. Luminescence characteristics of Ca₄La(VO₄)₃O indicate that the phosphor is not sufficient for practical applications. In Eu³⁺‐activated Ca₄La(VO₄)₃O, there is an efficient energy transfer from VO₄ to Eu³⁺ ions. The luminescence spectra, concentration quenching, decay curves, color chromaticity, and quantum efficiencies (QE) of Ca₄La(VO₄)₃O:Eu³⁺ were investigated. The phosphor presents optimal Eu³⁺ doping concentration of about 20 mol%. The dominant red emission in Ca₄La(VO₄)₃O:Eu³⁺ is 615 nm from electronic ⁵D₀→⁷F₂ dipole transitions. The quantum efficiency and the luminescence stability of the pure and Eu‐activated Ca₄La(VO₄)₃O were reported. The luminescence was discussed on the structural characteristics.     

Sr3B2O6∶Dy3+荧光粉的合成与发光性质

采用高温固相法合成了Dy3+掺杂的Sr3B2O6荧光粉,利用XRD、激发发射光谱以及色度坐标图等研究所制备荧光粉的相纯度、发光性能以及色度坐标位置。XRD测试表明在950℃下煅烧6 h制备的样品结构最佳,激发光谱表明在280～480 nm有一系列的激发峰,于350 nm处出现最强的吸收,发射光谱表明在477 nm和573 nm处分别有蓝光发射峰和黄光发射峰两部分,此系列荧光粉发光均呈白色,这种材料有潜力作为全色显示材料应用于三基色荧光灯中。     

B2O3-P2O5-SiO2系陶瓷的相组成和介电性能

讨论B2O3-P2O5-SiO2系低温共烧陶瓷的研究过程。该陶瓷用正交实验设计法安排试验,用单因素法设计陶瓷添加剂试验,用XRD分析其物相组成。从而获得了介电常数为4.1、介电损耗为5.0×10-4的低温共烧陶瓷。结果表明,该瓷料能满足1060℃共烧低介陶瓷的要求。     

Varistor,Dielectric, and Luminescent Properties of Pr6O11‐doped TiO2 Multifunctional Ceramics

A series of Pr₆O₁₁ (x = 0–0.70 mol%)‐doped TiO₂ ceramics were synthesized by the conventional solid‐state reaction method. The microstructure, electrical, and luminescence properties were systematically investigated. The results showed that the as‐prepared TiO₂ ceramics exhibited strong red emission at 606 nm at room temperature and the optimal photoluminescence were obtained at x = 0.30. In addition, the nonlinear coefficient was improved with the amount of Pr₆O₁₁ dopant, reaching the maximum value at x = 0.50. Therefore, Pr₆O₁₁‐doped TiO₂ ceramics, which simultaneously exhibited luminescent properties and good electrical properties, would be useful in novel multifunctional devices.     

硅质磷块岩去除水溶液中铅离子的研究

硅质磷块岩可以有效地降低水溶液中铅离子的浓度,其反应机理属于一种广义的吸附作用。当反应条件一定时,硅质磷块岩具有稳定的铅离子吸附量,而且其吸附量可以通过超细粉碎或改性活化作用得到显著提高。