Synthesis,structure and luminescence properties of a novel red fluorescent material Ba2MgB2O6:Eu3+

The crystal structure of Ba_2-xMgB₂O₆:xEu³⁺ phosphors, synthesized using a solid-state reaction, have been confirmed by X-ray diffraction analysis. This study focuses on the site occupancy preference of Eu³⁺ ions within the matrix, which was determined using bond energy theory, fluorescent spectra, and a consideration of energy transport and decay curves. The impact of Eu³⁺ ion concentration on luminescence has been assessed, and an optimal concentration (x = 0.22) identified. The critical distance, R_c was 9.6 Å, with a calculated θ value of 19.67, indicating that quadrupole-quadrupole interaction plays a critical role in the quenching Ba_2-xMgB₂O₆:xEu³⁺ phosphors. The Ba_2-xMgB₂O₆:xEu³⁺ phosphors exhibited a color purity of 99.26%, and a quantum efficiency of 49.68%. The activation energy Ea was determined to equal 0.2987 eV. The results have established Ba_1.78MgB₂O₆:0.22Eu³⁺ as a red fluorescent powder with high quantum efficiency and a millisecond fluorescence lifetime.     

Enhanced luminescence properties and energy transfer in Ce3+ and Tb3+ co-doped NaCaBO3 phosphor

A series of color-tunable NaCaBO₃: Ce³⁺, Tb³⁺ phosphors have been synthesized on the basis of efficient Ce³⁺→Tb³⁺ energy transfer. The photoluminescence emission and excitation spectra, the lifetime, and the effect of Tb³⁺ concentration are investigated in detail. The enhanced photoluminescence of Tb³⁺ with sharp emission lines could be obtained by the broad excitation band from the allowed 4f–5d absorption of Ce³⁺ ions. The intensity ratio of blue emission from Ce³⁺ and green emission from Tb³⁺ can be tuned by adjusting their concentrations. The energy transfer from Ce³⁺ to Tb³⁺ in NaCaBO₃ was found to be an electric dipole–quadrupole interaction.     

Color-tunable up-conversion emission in Y2O3:Yb3+, Er3+ nanoparticles prepared by polymer complex solution method

Abstract

Powders of Y₂O₃ co-doped with Yb³⁺ and Er³⁺ composed of well-crystallized nanoparticles (30 to 50 nm in diameter) with no adsorbed ligand species on their surface are prepared by polymer complex solution method. These powders exhibit up-conversion emission upon 978-nm excitation with a color that can be tuned from green to red by changing the Yb³⁺/Er³⁺ concentration ratio. The mechanism underlying up-conversion color changes is presented along with material structural and optical properties.

PACS

42.70.-a, 78.55.Hx, 78.60.-b     

Synthesis and luminescence characterization of Pr3+, Gd3+ co-doped SrF2 transparent ceramics

Pr³⁺, Gd³⁺ co-doped SrF₂ transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF₂ transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF₂ (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr³⁺: ³P₀ → ³H₄ and ¹D₂ → ³H₄, respectively. With the co-doping of Gd³⁺ ions, the emission intensity of the Pr:SrF₂ transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF₂ transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr³⁺ doping concentrations, whereas the lifetimes decreased dramatically with the Pr³⁺ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF₂ transparent ceramic is a promising material for visible luminescent device applications.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

Preparation and luminescence of Dy3+/Tm3+ co-doped Ca3NbGa3Si2O14 glass-ceramics for w-LED

In this work, a series of Dy³⁺ and Dy³⁺/Tm³⁺ ion activated Ca₃NbGa₃Si₂O₁₄ glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy³⁺/Tm³⁺. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm³⁺ and Dy³⁺ have intersections at 352 nm and 365 nm, which means that CNGS: Dy³⁺/Tm³⁺ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to ¹D₂ →³F₄, ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, ⁴F_9/2 → ⁶H_11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy³⁺ is Co-doped with a different amount of Tm³⁺, the luminous color can be adjusted by adjusting the doping amount of Tm³⁺ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm³⁺ doped glass and the excitation spectrum of Dy³⁺ doped glass, which indicates that there is energy transfer between Tm³⁺ and Dy³⁺. In addition, CNGS: Dy³⁺/Tm³⁺ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices.     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

Multifunctional Gd2O3:Tm3+, Er3+, Nd3+ particles with luminescent and magnetic properties

Development of novel materials with advanced properties is one of the main research directions of chemistry. New substances are not only crucial for many current technological applications but also should satisfy the needs of tomorrow. Industry often requires reliable, economically effective methods that can provide high quality reproducible results. Here we propose an inexpensive synthesis method that is suitable for synthesis of many types of particles. In this work we focused on Gd₂O₃:Tm³⁺, Er³⁺, Nd³⁺ particles with luminescence and magnetic properties. Based on the analysis of morphology, structural and optical properties of particles prepared by the standard Pechini methods and its variations, we found that the method with K₂CO₃ as additive yields particles with smaller sizes (down to tens of nm), higher crystallinity, and up to 1.7 times increased luminescence intensity. We also demonstrate that the unique combination of the particles’ characteristics, for example, the intensity ratio of the luminescent bands corresponding to different REI and the mass susceptibility, strongly depends on the composition, synthesis method, and structure. The variety of the combination of the properties makes these particles a promising candidate for safety markers applications.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Tunable single-phase white-light-emitting Ba2Mg(BO3)2:Ce3+, Na+, Tb3+, Eu2+ phosphor based on energy transfer

A series of white-light-emitting phosphors of single-phase Ba₂Mg(BO₃)₂:Ce³⁺, Na⁺, Tb³⁺, Eu²⁺ were synthesized by conventional solid-state reaction. The crystal structure of the host was characterized by X-ray diffraction and investigated by Rietveld refinement. Photoluminescence properties were studied in detail. The energy transfer from Ce³⁺ to Tb³⁺ in Ba₂Mg(BO₃)₂ host was investigated and demonstrated to be a resonant type via a quadrupole–quadrupole mechanism. White light with wavelength tunable was realized by coupling the emission bands peaking at 417, 543 and 626 nm attributed to Ce³⁺, Tb³⁺ and Eu²⁺, respectively. By properly tuning the relative composition of Ce³⁺(Na⁺)/Tb³⁺/Eu²⁺, optimized Commission Internationale de l׳Eclairage (CIE) chromaticity coordinates (0.363, 0.295), high color rendering index (CRI) 90 and low correlated color temperature (CCT) 3793 K were obtained from the phosphor of Ba_1.90Ce_0.04Na_0.04Eu_0.02Mg_0.94Tb_0.06(BO₃)₂ upon the excitation of 296 nm UV radiation. These results indicate that Ba₂Mg(BO₃)₂:Ce³⁺, Na⁺, Tb³⁺, Eu²⁺ phosphor has a potential application as an UV radiation down-converting phosphor in white-light-emitting diodes.     

Tb3+/Yb3+ co-doped Y2O3 upconversion transparent ceramics: Fabrication and characterization for IR excited green emission

Tb³⁺/Yb³⁺ co-doped Y₂O₃ transparent ceramics were fabricated by vacuum sintering of the pellets (prepared from nanopowders by uniaxial pressing) at 1750 °C for 5 h. Zr⁴⁺ and La³⁺ ions were incorporated in Tb³⁺/Yb³⁺ co-doped Y₂O₃ nanoparticle to reduce the formation of pores which limits the transparency of ceramic. An optical transmittance of ∼80% was achieved in ∼450 to 2000 nm range for 1 mm thick pellet which is very close to the theoretical value by taking account of Fresnel’s correction. High intensity luminescence peak at 543 nm (green) was observed in these transparent ceramics under 976 and 929 nm excitations due to Yb–Tb energy transfer upconversion.     

Influence of Gd content on the structural,Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe₂O₄ nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 10⁴ erg/cm³, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe_2-xGd_xO₄ magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.     

Up-conversion luminescence and temperature-sensing properties of Li+, K+ doped Na2Zn3Si2O8: Er3+ phosphors

In this work we detail the preparation of new luminescent Li⁺ and K⁺ doped Na₂Zn₃Si₂O₈: Er³⁺ up-conversion phosphors using the high-temperature solid-phase method. We investigate the phosphors phase structure, elemental distribution, up-conversion luminescence characteristics and temperature sensing properties. Our fabricated samples were found to be homogeneous and when excited using 980 nm light, they emitted wavelengths in the green and red visible wavelength bands, which correspond to two major emission bands of Er³⁺. Doping with Li⁺ and K⁺ increased the luminescence intensity of the Na₂Zn₃Si₂O₈: Er³⁺ phosphor at 661 nm by 36 and 21 times respectively. The highest relative temperature sensitivity (Sa) of the fabricated phosphor reached a value of 19.69% K^?1 and the highest absolute temperature sensitivity (Sr) reached 1.20% K^?1. These values are superior to other materials which utilize up-conversion by Er³⁺ ions as a tool for temperature sensing. We anticipate that these new phosphors will find significant application as components in optical temperature measurement systems.     

Photoluminescence,size and morphology of red-emitting Gd2O3:Eu3+ nanophosphor synthesized by various methods

Gd₂O₃:Eu³⁺ nanoparticles with doping concentration of 5% were prepared by urea-assisted combustion synthesis (UCS), carbohydrazide combustion synthesis (CCS), sucrose-aided combustion synthesis (SCS), glycine combustion synthesis (GCS) and by sol–gel (SG) synthesis. The nanopowders were postannealed at 1000 °C for 3 h to obtain nanocrystalline phosphor, which was confirmed by X-ray diffraction (XRD). Surface chemical groups were detected by Fourier transform infrared spectroscopy (FTIR). Particle size distribution and morphology images of the synthesized nanoparticles were obtained using transmission electron microscopy (TEM). Average particle size decreased exponentially with an increase in the amount of gases evolved during the synthesis method. Nanoparticles obtained by UCS showed the highest photoluminescence (PL) intensity, and absolute quantum yield (QY). A comparison of the factors affecting optical properties showed that PL intensity, QY and fluorescence lifetime were dependent on crystallite size.     

Laser synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

A laser melting method has been developed for the synthesis of highly luminescent, long-lasting SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors. The high temperature achieved in high-power density CO₂ laser irradiation of mixtures of SrCO₃, Al₂O₃, Eu₂O₃, and Dy₂O₃ enabled the one-step, fast synthesis of these phosphors in air at atmospheric pressure. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy characterization studies reveal that the produced materials consist of monoclinic SrAl₂O₄ grains extensively surrounded by rare-earth ion-enriched grain boundaries. The photoluminescence properties of laser-produced SrAl₂O₄:Eu²⁺, Dy³⁺ materials are discussed. The results reported here suggest that this laser melting method is a promising route for the synthesis of ceramic phosphors. It is presented as an alternative to the conventional sol–gel and solid-state methods, which require the use of high-temperature furnaces, flux additives, and reducing atmospheres.     

Improving the luminescence and afterglow properties of Mg3Y2Ge3O12:Cr3+ by co-doping Bi3+

Generally, the emission intensity and afterglow of the near infrared phosphors can be improved by co-doping the sensitizer. In this work, Bi³⁺ ions as sensitizer are introduced into the near infrared phosphor Mg₃Y₂Ge₃O₁₂:Cr³⁺, and the luminescence properties are investigated. According to the principle of radius adaptation, Bi³⁺ ions would occupy eight coordinates in the host instead of Y³⁺ and Mg²⁺. Through structural refinement, theoretical calculation and experimental phenomena, there are two kinds of luminescent sources for Bi³⁺ ions, which come from ³P₁ → ¹S₀ (441 nm) and MMCT (330 nm), respectively. In addition, the substitution of Bi³⁺ for Mg²⁺ will result in inequivalent substitution forming defects (Bi_Mg·), and the trap depth is 0.55 eV. For Bi³⁺ and Cr³⁺ co-doped Mg₃Y₂Ge₃O₁₂, there are two factors can that can affect the luminescent properties of Cr, which are energy transfer and defects. The samples are obtained with three times the original emission intensity with the introduction of defects. At the same time, Bi³⁺ ions capture electrons to form new electron traps Bi²⁺ (Bi³⁺ + e^-) and the trap depth is 0.81 eV. Therefore, under the action of two traps Bi_Mg· and Bi²⁺ (Bi³⁺ + e^-), the afterglow characteristics of the samples are improved and the time can reach 1.5 h.     

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.     

Dual-mode optical thermometry based on intervalence charge transfer excitations in Tb3+/Pr3+ co-doped CaNb2O6 phosphors

Self-calibrated temperature measurements combined with luminescence intensity ratio (LIR) and luminescence lifetime are more accurate. A dual-mode self-calibration optical thermometer was designed based on CaNb₂O₆: Tb³⁺/Pr³⁺ phosphor. The obtained sample has excellent sensitivity, with the maximum values of absolute sensitivity (S_a) and relative sensitivity (S_r) being 0.69 K^-1 at 612 K and 2.50% K^-1 at 532 K for LIR mode, and 0.0059 K^-1 at 475 K and 2.62% K^-1 at 535 K for luminescence lifetime mode, respectively. These results indicate that CaNb₂O₆: Tb³⁺/Pr³⁺ phosphor has valuable potential application for self-calibration optical temperature measurement.     

Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics

Transparent Eu³⁺-doped (0.05–0.15 at. %) alumina ceramics with fine-grained microstructure were prepared and studied in terms of optical properties and photoluminescence (PL). The light transmission through ceramics up to dopant concentrations 0.125 at. % is dominated by birefringence scattering at grain boundaries. As confirmed by HRTEM/EDS element mapping, high photoluminescence intensity was achieved as the result of the dopant segregation at grain boundaries. The PL emission spectra of Al₂O₃:Eu³⁺ ceramics exhibited red light emissions with the highest intensity (394 nm excitation) for material containing 0.125 at. % of Eu³⁺. The luminescence decay was single-exponential with a lifetime ～1.5 ms. The post-sintering reduction of Eu³⁺→Eu²⁺ under an H₂ atmosphere (at 1300 °C) was difficult. Two simultaneously coexisting Eu²⁺ emitting PL centers were identified, one emitting blue light with average decay constant of 150 ns, and the other green light (more intense) with average decay constant of 1.3 μs.     

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.