Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Eu3+掺杂磷酸盐的燃烧法合成及发光性质

本文以磷酸盐荧光材料作为研究对象,采用燃烧法制备了不同基质的红色荧光粉,红色荧光粉可以改善光色、提高显色指数,一直是研究的热点.室温下用X射线衍射仪测定了其晶体结构,用F-4600测定了其光致发光性质.结果表明合成的Lu12P2O23∶ Eu3,YP5O14∶Eu3+与La3 PO7∶Eu3+均属单斜相结构,Eu3+在单斜结构基质中占据非对称性格位.在完全相同实验条件下,对不同基质下掺杂Eu3+离子的发光强度进行比较,同时还研究了不同的Eu3浓度对La3PO7发光性质的影响.     

Luminescence and temperature-sensing properties of Y4GeO8:Bi3+,Eu3+ phosphor

In this paper, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor with dual emission centers was elaborated via conventional solid-state reaction technology. Thorough research on the structure, morphology, and luminous properties of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor, the potential applications in optical thermometry were investigated by means of fluorescence intensity ratio and thermochromic techniques. Under 290 and 347 nm excitation, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor presents broadband emission from ³P₁ → ¹S₀ transition of Bi³⁺ ions and characteristic emission peaks from 4f–4f transition of Eu³⁺ ions. Outstanding temperature-sensing capabilities are acquired from Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor. The maximum relative sensitivity (S_r) can attain 1.51% K⁻¹ (λ_ex = 290 nm). With temperature raising (303–513 K), the emitted color of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor (λ_ex = 290 nm) shifts from faint yellow to red with a high chromaticity shift (0.180), which can be distinguished by the unaided eye clearly. Our results indicate that Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor has potential applications in optical temperature measurement and high-temperature safety marker.     

Crystal structure and luminescence mechanism of novel Fe3+-doped Mg0.752Al2.165O4 deep red-emitting phosphors

Nonstoichiometric alumina-rich spinel provides diverse and changeable local environments for transition-metal dopants. In this contribution, novel Mg_0.752Al_2.165−xO₄:xFe³⁺ deep red-emitting phosphors were designed and prepared by the solid-state reaction method. The red emission presents an unexpected shift from 735 to 770 nm by comparing with Fe³⁺-doped MgAl₂O₄. The excitation spectrum of Mg_0.752Al_2.165−xO₄:xFe³⁺ is broadened in the UV region with a new strong peak at 320 nm. The crystal structure refinement and NMR spectra fitting reveal that the cation vacancies and disorder increase with excess Al³⁺ entering the spinel crystal lattice. According to the results of EPR, NMR, and PL/PLE measurements, it was proposed that the Fe³⁺ ions locate at the distorted octahedral coordination. The changes of the local structure of Fe³⁺ ions promote the doublet state's involvement in the d−d transition. It was proposed that the new excitation peak at 320 nm in Mg_0.752Al_2.165−xO₄:xFe³⁺ is associated with the transitions from the ground state ⁶A_1g(⁶S) to the ⁴A_2g(⁴F)/T_1g(⁴P) and doublet states. The transition between the lower energy excited state of ²T_2g(²I) and ⁶A_1g(⁶S) mainly contributes to the deep red emission and the red-shifting effect.     

A novel Eu2+/Tb3+ co-doped phosphor with pyroxene structure applied for cryogenic thermometric sensing

Pyroxene-type phosphors were widely developed due to the advantages of high chemical stability, luminous efficiency, and low production cost. In this contribution, a series of Eu²⁺/Tb³⁺ co-doped Ca_0.75Sr_0.2Mg_1.05Si₂O₆ (CSMS) phosphors with pyroxene structure were successfully synthesized by the solid-state method. Under the 340 nm excitation, the emission peaks of the phosphor show a redshift with the increase of Eu²⁺ concentration. The emitting color of Eu²⁺/Tb³⁺ co-doped samples shows a redshift attributed to the energy transfer from Eu²⁺ to Tb³⁺. Simultaneously, acquired thermometer exposes superbly temperature-sensitive properties (S_a and S_r having maximum values 4.7% K⁻¹ and 0.6% K⁻¹, respectively) over the cryogenic temperature range (77–280 K). Furthermore, it has good stability and precision at cryogenic temperatures, indicating that CSMS:0.03Eu²⁺/0.03Tb³⁺ phosphor is a very promising fluorescent material suitable for cryogenic temperature sensing.     

A new parameter for characterizing Eu3+ distribution in mixed-valence Eu-doped cubic LaF3-based transparent glass-ceramics

Mixed-valence Eu-doped transparent oxyfluoride glass-ceramics containing cubic LaF₃ nanocrystals were fabricated by traditional melt-quenching technique and consequent annealing processes. Their structural and luminescent properties were systemically investigated by X-ray diffraction (XRD), transmission electron microscopy, absorption, excitation, emission spectra, and fluorescence lifetime measurements. Analyses of XRD patterns prove that the new precipitated nanocrystals disperse in glass-ceramics crystallize in cubic LaF₃. The spectroscopic investigations show that Eu²⁺ ions have been incorporated into the LaF₃ nanocrystals preferentially, while Eu³⁺ ions still remain in the glass phase after crystallization. Based on the spectral results, a new parameter was defined to describe the changes of the environments of Eu³⁺ before and after crystallization more straightforwardly and more sensitively, where R_PG and R_GC represent the integrated intensity radio of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ emissions of Eu³⁺ in PG and GC samples, respectively. Our investigation will not only enrich the understanding of fluoride nanocrystals-based oxyfluoride glass-ceramics, but also the distribution and luminescence behaviors of Eu³⁺ ions in them.     

Probing crystal structure and site-selective photo-physical properties of various Eu3+-doped niobates

Niobates of the formula Ba₂LaNbO₆ and BaLaM²⁺NbO₆ (M²⁺ = Mg, Ca) were synthesized by the conventional solid state route. Size dependence of M-cation on the bulk crystal structure of BaLaM²⁺NbO₆ was studied and compared with the Ba₂LaNbO₆ compound. X-ray diffraction study confirmed that BaLaMgNbO₆ compound has the rhombohedral () crystal structure as compared to the monoclinic (I2/m) in BaLaCaNbO₆ and Ba₂LaNbO₆. The change in the local structure of La cation among these compounds was investigated by carrying out Photoluminescence study on 2 atom% Eu³⁺-doped samples. PL study of BaLaMgNbO₆:Eu³⁺ sample indicates Eu³⁺ ions occupying the distorted 12-coordinated A-site, while in Ba₂LaNbO₆: Eu³⁺, Eu³⁺ is present at highly symmetric octahedral B-site. Upon excitation, the light emission of these compounds changes from reddish-orange to red to purple in the order Ba₂LaNbO₆:Eu → BaLaCaNbO₆:Eu → BaLaMgNbO₆:Eu³⁺, due to change in Eu³⁺-ions site occupancy. Lifetime study also confirmed the presence of two different Eu³⁺ components at two different lattice sites and their respective emission spectra were isolated by time resoled emission spectroscopy. Furthermore, this site selective lattice occupancy of Eu³⁺ ions also gave various new insights about its radiative and nonradiative properties at different lattice sites. This works presents a complete structural understanding of BaLaMNbO₆-based matrices and their versatile phosphor characteristics when doped with Eu³⁺ ion.     

红色荧光粉CaWO4:Eu3+,Gd3+的合成及其发光性能的研究

利用高温固相法合成了CaWO4:Eu3+,Gd3+红色荧光粉,通过X射线衍射、X射线光电子能谱和荧光光谱等对该荧光粉进行了表征。结果表明,CaWO4:Eu3+,Gd3+的荧光强度明显高于CaWO4:Eu3+,钆离子的最佳掺杂量为0.04。同时说明了钆离子引入到CaWO4:Eu3+中对其发光性能影响的机理以及不同浓度的钆对发光强度的影响。     

The composition engineering of red-emitting Eu3+-doped Ca10.5(PO4)7-type solid solution phosphors and application in LED

In this work, using Ca_10.5(PO₄)₇ as the structural model, a number of Eu³⁺-doped [Ca₉Na_3xY_1-x(PO₄)₇ (CNYP-I, 0 ≤ x ≤ 1/2) ← Ca_10.5(PO₄)₇ → Ca_9+yNa_3/2-y/2Y_(1-y)/2(PO₄)₇ (CNYP-II, 0 ≤ y ≤ 1)] phosphors were designed and synthesized through the heterovalent substitution of Y³⁺ and Na⁺ to Ca²⁺. The substitution mechanism, composition structure, luminescence performance, and thermal stability of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) as well as the solid solutions of CNYP-II (0 ≤ y ≤ 1), were discussed in detail. The morphology and element composition of CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) solid solutions were analyzed by SEM and EDS. The PL spectra of the specimens were containing the predominant red peak of emission at 612 nm caused via the transition of ⁵D₀-⁷F₂, indicating that Eu³⁺ occupies the low-symmetry center. Moreover, the site symmetry Eu³⁺ occupied changed with the x/y value. The luminous intensity of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) phosphors at 150°C maintained about 60% of room temperature. The representative compound CNYP-I (x = 1/3) was used as the red phosphor to prepare a near-UV based white LEDs along with Ra of 80.9 and CCT of 4100 K.     

YVO4:Eu3+,Bi3+荧光粉的制备及荧光性能研究

用溶胶凝胶法在较低温度下制备了YVO4:Eu3+,Bi3+荧光粉,采用X射线衍射仪(XRD),扫描电子显微镜(SEM)及荧光分光光度计测试,研究了合成产物的结构、表面形貌,分析了在Eu3+含量一定的情况下掺杂Bi3+的浓度的变化对发光性能的影响.结果表明,溶胶凝胶法合成的YVO4:Eu3+,Bi3荧光粉为单相结构、粒径在1 μm左右、无团聚现象;Bi3+对Eu3+离子有敏化作用,在一定浓度下使荧光粉的发射强度增加.     

Sr3Lu (VO4)3: Eu3+ red-emitting phosphors for warm white LEDs

A series of novel red emission phosphors Sr₃Lu_1-x(VO₄)₃:xEu³⁺(x = 0.007, 0.009, 0.02, 0.04, 0.06) were synthesized successfully by traditional high-temperature solid-state reaction. The results of X-ray diffraction (XRD) reveal the doped Eu³⁺ ions have replaced the lattice sites of Lu³⁺ ions. The diffuse reflectance spectra illustrate the energy gap of Sr₃Lu(VO₄)₃ host is 3.61 eV. The room-temperature steady-state fluorescence spectra show that these phosphors can be effectively pumped by the charge-transfer band (CTB) of the host in near ultraviolet (NUV) spectral region and then produce strong and pure red emission at 615 nm originated from ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺. The Commission Internationale de L’Eclairage (CIE) coordinates of Sr₃Lu_0.96(VO₄)₃:0.04Eu³⁺ are (x = 0.65, y = 0.35), which are very close to the red standard of National Television Standards Committee NTSC (0.67, 0.33). The fabricated warm white-light-emitting diodes (LED) demonstrate high color-rendering index Ra as 93. The results imply the red-emitting Sr₃Lu(VO₄)₃:Eu³⁺ phosphors could be potentially utilized in the fields of solid-state lighting.     

SrMoO_4：0.05Eu~（3＋）,0.05Gd~（3＋）的制备及发光性能研究

分别采用化学沉淀法、微波法、水热法制备了SrMoO4：0.05Eu3＋,0.05Gd3＋荧光粉,并通过X-射线粉末衍射（XRD）、荧光光谱和扫描电子显微镜（SEM）对其晶体结构、荧光光谱和形貌进行了表征。结果表明：SrMoO4：0.05Eu3＋,0.05Gd3＋的结构属体心四方晶系;其宽激发带由Eu3＋-O2-、Gd3＋-O2-电荷迁移带和Mo6＋-O2-基质吸收峰组成,荧光发光以在616nm处Eu3＋的5 D0→7 F2跃迁引起的红光发光最强;254nm紫外光激发时,化学沉淀法制备SrMoO4：0.05Eu3＋,0.05Gd3＋的发光峰比SrMoO4：0.05Eu3＋的相应发光峰强度增大,这是由于Gd3＋向Eu3＋的能量传递敏化增强了Eu3＋的发光。     

Trap distribution and photo-stimulated luminescence in LaSrAl3O7:Eu2+ long-lasting phosphors for optical data storage

Here, a green emission persistent luminescent phosphor LaSrAl₃O₇:Eu²⁺ which is chargeable by UV light, was synthesized by solid-state reaction method. Elemental mapping and fluorescence microscopy photoluminescence of the sample demonstrated the homogeneous distribution of La, Sr, Al, O, and Eu in the phosphor. Rietveld refinement shows that the as-prepared sample belongs to the tetragonal crystalline structure with space group of P42₁m. The Eu²⁺:5d-4f broad persistent luminescence with maximum emission peaking at 518 nm can be effectively obtained after irradiating in the UV light. A series of excitation temperature-dependent thermoluminescence measurements were conducted to gain some insight into the information of traps. Additionally, to verify its feasibility of optical data storage, specific information letters were encoded on the LaSrAl₃O₇:Eu²⁺ phosphor films using the laser of 405 nm, then the stored information could indeed be read out by thermal stimulation as expected. Meanwhile, NIR photo-stimulated red persistent luminescence was also obtained, which holds great potential for optical information storage. Finally, combined with the experimental and density functional theory calculation results, we proposed a tentative schematic diagram to account for the PersL and photo-stimulated persistent luminescence mechanism in LaSrAl₃O₇:Eu²⁺ phosphor.     

Luminescent properties of long‐lasting BaAlxOy:Eu2+,Dy3+ nanocomposites

BaAl_xO_y:Eu²⁺,Dy³⁺ blue‐green phosphor samples were synthesized by a combustion method at the low temperature of 500°C. Phosphor nanocrystallites with high brightness were obtained without significantly changing the crystalline structure of the host. The crystallite sizes determined from the Scherrer equation ranged between 34 and 41 nm. Different volume fractions of the BaAl_xO_y:Eu²⁺,Dy³⁺ powder were then introduced in LDPE polymer. The resulting composites were similarly analyzed and also thermally characterized by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). PL results indicate that the LDPE‐phosphor interface, which is considered to have an influence on the composite behavior, did not significantly change the spectral positions of the phosphor materials, whose major emission peaks occurred at about 505 nm. The improved afterglow results for the composites may have been caused by morphological changes due to increased surface area and defects. Thermal results indicate that the BaAl_xO_y:Eu²⁺,Dy³⁺ particles acted as nucleating centers and enhanced the overall crystallinity in the LDPE nanocomposite while preventing lamellar growth, hence reducing the crystallite sizes in LDPE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Optical transition and luminescence properties of Sm3+-doped YNbO4 powder phosphors

A series of YNbO₄: Sm³⁺ powder phosphors with different doping concentrations were synthesized by a traditional high-temperature solid-state reaction method. The crystal structure of the obtained samples was characterized by means of X-ray diffraction. Concentration quenching, energy-transfer mechanism, and luminescence thermal stability of YNbO₄: Sm³⁺ samples were studied through the fluorescence spectra and decays. It was concluded that electric dipole-dipole interaction was the dominant energy-transfer mechanism between Sm³⁺ ions according to both Van Uitert's model and Dexter's model. Using the Arrhenius model, crossover process was proven to be responsible for the luminescence thermal quenching of Sm³⁺. Moreover, a novel approach for evaluating the optical transition properties of Sm³⁺ ion in YNbO₄ powders using the diffuse-diffraction spectrum and fluorescence decay was examined in the framework of Judd-Ofelt (J-O) theory. It was confirmed that the J-O parameters Ω_λ (λ = 2, 4, 6) of Sm³⁺ in YNbO₄ powder were reliable by comparing the radiation transition rate with the measured emission results.     

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。     

Bi3+/Mn4+ co-doped dual-emission phosphors for potential plant lighting

Developing environment-friendly dual-emission phosphors of both blue–cyan and deep-red lights is desirable for the utilized indoor plant lighting research. Notably, the naked 6s and 6p Bi³⁺ ions are sensitive to the lattice sites, which emit from Ultraviolet (UV) to red lights in various crystal compounds. Meanwhile, the ²E → ⁴A_2g transition of Mn⁴⁺ ions promises its deep-red light emissions, which satisfies the demand for specific wavelength lights for plants growth. Hence, a Bi³⁺/Mn⁴⁺ co-doped Sr₂LaGaO₅: Bi³⁺, Mn⁴⁺ (SLGO:Bi³⁺:Mn⁴⁺) phosphor was finally synthesized. The phase, micromorphology and luminescent properties were systematically evaluated. Upon excitation at 350 nm light, dual emissions of both blue–cyan (470 nm) and deep-red (718 nm) lights were observed. Besides, due to the pronounced photoluminescence (PL) spectral overlap between Bi³⁺ and Mn⁴⁺ ions, a potential energy transfer process from Bi³⁺ to Mn⁴⁺ ions was confirmed. The relative PL intensities between Bi³⁺ and Mn⁴⁺ ions can be tuned just by adjusting the Mn⁴⁺ ion concentration. Besides, Li⁺ co-doping has been evidenced to improve the deep-red emissions (718 nm) of SLGO:0.005Mn⁴⁺ due to charge compensation and rationally designed lattice distortion, together with the improved thermal stability. Finally, the emissions of SLGO:Bi³⁺, Mn⁴⁺, Li⁺ phosphor suit properly with the absorption of the four fundamental pigments for plant growth, indicating that the prepared phosphorescent materials may have a prospect in plant light-emitting diodes lighting.     

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⁺.     

水热法对Eu3＋掺杂CaMoO4微纳米荧光体的制备及其发光性能

采用水热法成功的制得了不同形貌的CaMoO4：Eu3＋微纳米荧光体。实验结果表明,溶液的pH值在控制产物形貌上起了决定性的作用。用X射线粉末衍射（XRD）、场发射扫描电镜（FE—SEM）和荧光光谱（PL）等分析手段研究了荧光体的结构和光致发光性能。结果表明,CaMoO4：Eu3＋荧光体的激发光谱由两部分组成：1个宽的激发带（240～360nm）和属于Eu3＋的f—f跃迁的锐线谱（395nm、465nm）,它的发射光谱只出现常见的2个发射峰：592nm（5D0→F1）、615nm（5D0→7F2）,中5D0→7F2跃迁发射峰强度明显高于5D0→7F1跃迁发射峰强度,这表明Eu3＋在CaMoO4基质中处于无反演中心或偏离反演中心的格位上。本文还对造成发射峰强度变化的原因进行了分析,认为影响发射峰强度的原因有两个：表面积和对称性,材料的表面积越大,发光的猝灭越严重,荧光发射越弱;材料的结构对称性越差,跃迁戒律打破地越彻底,荧光发射越强。     

GdF3∶Eu3+和NaGdF4∶Eu3+发光粉的可控合成与发光性质

采用聚乙烯吡咯烷酮(PVP)辅助水热法合成了GdF3∶Eu3+和NaGdF4∶Eu3+发光粉。利用X射线衍射(XRD)、扫描电子显微镜和荧光光谱对样品的结构、形貌和发光性能进行了研究。XRD分析表明:GdF3晶相到NaGdF4晶相的转换可以通过改变初始溶液pH值、PVP加入量和NaF与稀土离子(Gd3+和Eu3+)摩尔配比等合成条件实现。NaGdF4∶Eu3+发光粉的形貌受合成条件的影响。荧光光谱研究表明:GdF3∶Eu3+发光粉主发射峰位于593nm处,来自于Eu3+的5 D0→7 F1磁偶极跃迁;NaGdF4∶Eu3+发光粉主发射峰位于616nm,来自于Eu3+的5 D0→7 F2电偶极跃迁。2个样品中Gd3+与Eu3+离子之间存在较好的能量传递,而NaGdF4晶格更有利于2种离子的能量传递。