VUV-excited luminescence properties of Tb3+ activated BaGdB9O16

The single phase of BaGd1-xTbxB9O16(0.05≤x≤0.3) was prepared by the solid-state reaction.Their photoluminescence properties were investigated under vacuum ultraviolet(VUV) excitation.Monitored by 541 nm emission,the excitation spectrum of BaGd0.75Tb0.25B9O16 consisted of one broad band centered at about 148 nm and some bands in 163 to 282 nm.The former was assigned to the overlapped absorptions among borate groups,charge transfer bands(CTBs) of O2-→Ln3+(Ln=Tb,Gd) and the f→d transition of Gd3+.The bands in ...     

Effect of gadolinium incorporation on optical characteristics of YNbO_4：Eu~（3＋） phosphors for lamp applications

Eu3+-doped (Y,Gd)NbO4 phosphor was synthesized by solid-state reaction for possible application in cold cathode fluorescent lamps. A broad absorption band with peak maximum at 272 nm was observed which was due to the charge transfer between Eu3+ ions and neighboring oxygen anions. A deep red emission at the peak wavelength of 612 nm was observed which could be attributed to the 5D0→7F2 transition in Eu3+ ions. The highest luminance for Y1-x-yGdyNbO4:Eux3+ under 254 nm excitation was achieved at Eu3+ concentration of 18 mol.% (x=0.18) and Gd3+ concentration of 8.2 mol.% (y=0.082). The luminance of Y0.738Gd0.082NbO4:Eu3+0.18 was higher than that of a typical commercial phosphor Y2O3:Eu3+ and the CIE chromaticity coordinate was (0.6490, 0.3506), which was deeper than that of Y2O3:Eu3+. The particle size of the synthesized phosphors was controlled by the NaCl flux and particle size as high as 8 μm with uniform size distribution of particles was obtained.     

Synthesis and photoluminescence studies of Ba(Gd,Ln)B9O16:Eu3+(Ln=La,Y) phosphors for n-UV LED lighting and display devices

BaGdB9O16:Eu3+ and Ba(Gd,Ln)B9O16:Eu3+(Ln=La, Y) phosphors were synthesized by solid state diffusion method. The X-ray diffraction, scanning electron microscopy(SEM) and photoluminescence properties were investigated. The as-synthesized BaGdB9O16:Eu3+ and Ba(Gd,Ln)B9O16:Eu3+(Ln=La, Y) phosphors showed strong red emission under ultraviolet light excitation. By partially substituting Gd3+ by La3+ and Y3+ ions in the host BaGdB9O16:Eu3+ materials, the maximum emission intensity was observed for the optimum composition of BaGd0.91La0.8B9O16Eu0.01 phosphor. The experimental results indicated that the Eu doped BaGdB9O16 and Ba(Gd,Ln)B9O16(Ln=La, Y) phosphors were promising red phosphors, which might find potential applications in near-UV excited LED lighting as well as display devices. Comparison of as-synthesized phosphors with standard phosphor used in CFL(compact fluorescent lamp) was also done. Energy transfer mechanism of Gd3+ to Eu3+ was also discussed in this paper.     

Luminescence properties of a single-host phosphor Bal.8-wSrwLi0.4SiO4： cea＋,Eu2＋,Mn2＋ for WLED

In order to obtain a single-host-white-light phosphor,a series of Ba1.8-w-x-y-zSrwLi0.4-xCexEuyMnzSiO4(BSLS:Ce3+,Eu2+,Mn2+)powder samples were synthesized via high temperature solid-state reaction.The structure and photoluminescence properties were investigated.Under ultraviolet excitation,the emission spectra contained three bands:the 370-470 nm blue band,the 470-570 nm green band and the 570-700 nm red band,which arose from the 5d→4f transitions of Ce3+ and Eu2+,and the 4T1→6A1 transition of Mn2+,respectively.The excitation spectra of the emissions of Ce3+ and Mn2+ ions showed the energy transfer from Ce3+ to Mn2+.White light emission was obtained from the tri-doped samples of appropriate doping concentration under 310-360 nm excitation.     

Cooperative energy transfer in Eu3+,Yb3+ codoped Y2O3 phosphor

Under 980 nm laser excitation,red emission(5D0-7FJ(J=0,1,2)) of Eu3+ was observed in cubic Y2O3 codoped with Eu3+ and Yb3+.The dependence of the upconverted emission on doping concentration and laser power was studied.Yb3+ emission around 1000 nm(2F5/2-2F7/2) was reported upon excitation of Eu3+ ions.The decay curves of 5DJ(J=0,2) emission of Eu3+ under excitation of 266 nm pulse laser were examined to investigate the Eu3+→Yb3+ energy transfer process.Cooperative energy transfer process was discussed as the possible mechanism for the visible up-conversion luminescence of Eu3+ and near-infrared down-conversion emission of Yb3+.     

Properties of red-emitting phosphors Sr2MgSi2O7:Eu3+ prepared by gel-combustion method assisted by microwave

Novel red-emitting phosphors Sr2MgSi2O7:Eu3+ were prepared by gel-combustion method assisted by microwave. The phase struc-ture and luminescent properties of as-synthesized phosphors were investigated by XRD and fluorescence spectrophotometer, respectively. The results showed that the as-synthesized sample was Sr2MgSi2O7 with tetragonal crystal structure. The excitation spectrum of Sr2MgSi2O7:Eu3+ was composed of two major parts: one was the broad band between 200 and 350 nm, which belonged to the charge transfer of Eu3+-O2-; the other consisted of a series of sharp lines between 350 and 450 nm, ascribed to the f-f transition of Eu3+. The emission spec-trum consisted of two emission peaks at 593 and 616 nm, which was attributed to 5D0→7F1 and 5D0→7F2 of Eu3+, respectively. The concen-tration of Eu3+ (x) had great effect on the emission intensity of Sr2-xMgSi2O7:Eu3+x. When x varied in the range of 0.04-0.18, the intensity of emission peaks at 593 and 616 nm increased gradually with the concentration of Eu3+ increasing. It was interesting that no concentration quenching occurred. Moreover, the luminescent intensity could be greatly enhanced with incorporation of charge compensator Li+ ions.     

Photoluminescence studies of Eu2+-Yb3+ co-doped BaMgAl10O17 phosphor synthesized by the combustion method

BaMgAl10O17:Eu2+,Yb3+ was investigated as a possible quantum cutting system to enhance solar cells efficiency. Phosphors were synthesized by combustion method and composed of nanorods. Photoluminescence spectra showed that Eu in the sample was reduced to bi-valence while Yb remained trivalence. Through a cooperative energy transfer process, the obtained powders exhibited both blue emission of Eu2+ (around 450 nm) and near infrared emission of Yb3+ (around 1020 nm) under broad band excitation (250-410 nm) originating from 4f→5d transition of Eu2+. Energy transfer phenomenon between the sensitizer Eu2+ and the activator Yb3+ was investigated via the lumines-cent spectra and the decay curves of Eu2+ with different Yb3+ concentrations. Results indicated that energy transfer efficiency from Eu2+ to Yb3+ was not high. The poor efficiency can be explained by the long distance between rare earth ions.     

Hydrothermal synthesis and luminescence properties of Eu3＋ and Sm3＋ codoped BiPO4

Eu3+/Sm3+codoped BiPO4 phosphors were synthesized via a facile hydrothermal method with surfactant-free environment. The X-ray diffraction analysis demonstrated that the samples possessed the standard BiPO4 monoclinic structure. Scanning electron microscopy images showed that all samples composed of well-dispersed, micrometer-sized crystals with shuttle-like shape. Energy transfer from Sm3+to Eu3+was confirmed by the luminescence spectra and the decay processes of Sm3+ 4G5/2 →6H5/2 emission. Orange-red luminescence could be obtained in Eu3+/Sm3+codoped BiPO4 phosphors. The average lifetime of Sm3+ 4G5/2 →6H5/2 emission decreased from 2.70 ms in BiPO4 :0.03Sm3+to 2.37 ms in BiPO4 :0.03Sm3+,0.05Eu3+. The strong and wide absorption band around 395 nm, originating from both7F0 →5L6 transition of Eu3+and6H5/2 →4K11/2 transition of Sm3+, endowed BiPO4 :Eu3+,Sm3+ phosphors with the potential application in the fields of near UV-excited white-light-emitting diodes.     

Energy transfer between Gd^3＋ and Tb^3＋ in phosphate glass

The phosphate glass doped with Gd3+,Tb3+ and Gd3+/Tb3+ were prepared by high temperature melting.The photo-luminescence behavior of Gd3+ and Tb3+ in phosphate glass were investigated by absorption,excitation,and emission spectroscopy.Energy transfer between Gd3+ and Tb3+ in phosphate glass was studied,and it was found that there were two energy transfer mechanisms between Gd3+ and Tb3+ in phosphate glass: one was from 4f7 level of Gd3+ to the 4f8 level of Tb3+,and the other was from 5d level of Tb3+ to 4f7 level of Gd3+.The new findings would be beneficial for the study of Tb3+-doped scintillating phosphate glass.     

Spectral variations of Ca3Sc2Si3O12:Ce phosphors via substitution and energy transfer

The luminescence intensity of emission peak at around 525 nm decreased in the Ce3+ and Er3+ co-doped Ca3Sc2Si3O12 phosphors. Mg2+ ion, which was likely incorporated into the Sc3+ position of the host crystal, was co-doped to adjust the crystal field and compensate for the excess positive charge due to the doping of Ce3+. The green emission belonged to the 5d→4f transition of Ce3+ moved toward longer wavelength by addition of Mg2+ in Ce3+ and Er3+ co-doped Ca3Sc2Si3O12 phosphor, which could increase the brightness of the phosphor. However, the position of weakening of luminescence intensity at around 525 nm remained basically unchanged by increasing the amount of Mg2+. The results showed that the weakening of luminescence intensity at around 525 nm caused by the absorption of Er3+, which had little influence on the environment of the crystal field.     

Synthesis and luminescent properties of BaGd2O4:Eu3+ phosphors with highly efficient red-emitting

The BaGd_(2-2 x)Eu_(2 x)O_4(BG, x = 0.01-0.09) phosphors were successfully synthesized via the sol-gel method,and BaY_(2-2 y)Eu_(2 y)O_4(BY, y = 0.005-0.07) phosphors were included for comparison. The pure phase BG phosphors with the ordered CaFe_2 O_4-type structure are obtained by annealing at 1300℃ for5 h. The phosphors with uniform particle size of 120 nm and good dispersion display typical Eu~(3+)emission with the strongest peak at 613 nm(~5 D_0→~7 F_2 transition of Eu3+) under optimal excitation band at 262 nm(CTB band). The presence of Gd~(3+) excitation bands on the PLE spectra monitoring the Eu3+emission directly proves an evidence of Gd~(3+)-Eu~(3+) energy transfer. Owing to the concentration quenching, the optimum content of Eu3+ addition is 5 at%(x = 0.05), and the quenching mechanism is determined to be the exchange reaction between Eu3+. All the BG samples have similar color coordinates and temperature of(0.64 ± 0.02, 0.36 ± 0.01) and 2000 ± 100 K,respectively. The lifetime value of BaGd_(1.9)Eu_(0.1)O_4 for 613 nm is fitted to be 2.19 ± 0.01 ms, and the Eu~(3+) concentration does not change the lifetime significantly. Owing to the Gd~(3+)-Eu~(3+) energy transfer, the luminescent intensity of the BaGd_(1.9)Eu_(0.1)O_4 phosphor is better than BY system. The BG system served as a new type of phosphor is expected to be widely used in lighting and display areas.     

Synthesis and luminescent properties of Ba3Y3.88Gd0.12O9:Eu3+ phosphors with enhanced red emission

In this work, the Gd³⁺/Eu³⁺ activated Ba₃Y₄O₉ (BYO) phosphors were successfully synthesized via coprecipitation method at 1400 °C. The precursor composition, crystal structure stability, microscopic morphology, photoluminescence (PL)/photoluminescence excitation (PLE) spectra and fluorescence attenuation analysis of the phosphors are discussed in detail. The chemical composition of the precursor was determined by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG) analysis; According to field emission-scanning electron microscopy (FE-SEM) analysis, it is found that the particle size of phosphor is uniform and the agglomeration is few. According to PL/PLE spectra analysis, Ba₃Y_3.28Eu_0.6Gd_0.12O₉ phosphors has the strongest excitation band at 260 nm and the strongest emission band at 614 nm, and the fluorescence intensity of Ba₃Y_3.28Eu_0.6Gd_0.12O₉ is higher than that of Ba₃Y_3.4Eu_0.6O₉. The quenching concentration of Eu³⁺ in Ba₃Y_3.88–4xEu_4xGd_0.12O₉ phosphors is x = 0.15 and the mechanism of quenching concentration of Eu³⁺ is electric dipole-quadrupole type interactions. The lifetime value of Ba₃Y_3.88–4xEu_4xGd_0.12O₉ (x = 0.15) phosphors is 0.686 ms and decreases with the increase of Eu³⁺ content. In addition, the CIE chromaticity diagram of Ba₃Y_3.28Eu_0.6Gd_0.12O₉ phosphors is (0.66, 0.34). Finally, the lamp beads assembled with Ba₃Y_3.28Eu_0.6Gd_0.12O₉ phosphors have an ideal luminous effect. Therefore, the Ba₃Y_3.88–4xEu_4xGd_0.12O₉ phosphors designed in this work may hopefully meet the requirements of various lighting and optical display applications.     

Synthesis and luminescence properties of Tb3+/Eu3+ co-doped GdAlO3 phosphors with enhanced red emission

The(Gd_(0.97-x)Eu_xTb_(0.03))AIO_3(x= 0.005-0.07) phosphors were synthesized by the co-precipitation method,using ammonium bicarbonate as a precipitant.The combined technologies of FT-IR,XRD,FESEM,PLE/PL and photo luminescence decay analysis were used to study the phase evolution,morphologies and luminescent properties.The phosphors with good dispersion exhibit strong vivid red emission located at 617 nm(~5 D_0-~7 F_2 transition of Eu~(3+)) under the optimal excitation wavelength of 275 nm(~4 f~8-4 f~75 d~1 transition of Tb~(3+),~8 S_(7/2)→6~I_J transition of Gd~(3+)).The presence of Gd~(3+) and Tb~(3+) excitation bands on the PLE spectra monitoring the Eu~(3+) emission directly gives an evidence of Tb~(3+) → Eu~(3+) and Gd~(3+) → Eu~(~(3+)) energy transfer,The emission intensity varies with the Eu~(3+) amount,and the quenching concentration is ～5 at% which is close to the calculated value.The quenching mechanism is determined to be the exchange reaction between Eu~(3+).The temperature-dependent PL analysis indicates that the best(Gd_(0.92)Eu_(0.05)Tb_(0.03))AlO_3 sample possesses good thermally stable properties.All the(Gd_(0.97-x)Eu_xTb_(0.03))AIO_3 phosphors in this work have similar CIE chromaticity coordinates and color temperatures,which are(0.65 ± 0.02,0.35 ± 0.02) and ～2558 K,respectively.Fluorescence decay analysis shows that the lifetime for～617 nm emission decreases with the content of Eu~(3+) and temperature increasing.Owing to the Tb~(3+)→ Eu~(3+) energy transfer,the luminescent properties of the(Gd_(0.92)Eu_(0.05)Tb_(0.03))AlO_3 phosphors are superior to the single Eu~(~(3+)) doped sample(Gd_(0.95)Eu_(0.05))AlO_3.As a result,the prepared phosphors may be widely used in solid-state display and light emitting devices.     

Enhanced afterglow performance of CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors by co-doping Gd~(3+)

In order to effectively improve the afterglow properties of CaAl_2 O_4:Eu~(2+),Nd~(3+) phosphors,a series of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)phosphors belong to monoclinic CaAl_2 O_4,without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4 f~65 d→4 f~7 transition of Eu~(2+) ions.Doping with appropriate amount of Gd~(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd~(3+) induces the fluorescent quenching.The doping of moderate Gd3+changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.     

Luminescent ionic lattice occupation and wide tunable emission spectra of La2MgZrO6:Bi3+,Eu3+ double perovskite phosphors for white light LED

La₂Mg_1-x/2Zr_1-x/2O₆:xBi³⁺(x=0.01-0.035,abbreviated as LMZ:Bi³⁺) and La_2-yMg_0.99Zr_0.99O₆:0.02Bi³⁺,yEu³⁺(y=0.1-0.11,abbreviated as LMZ:Bi³⁺,Eu³⁺) double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi³⁺(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range be...     

Vacuum ultraviolet excited photoluminescence properties of Gd2O2CO3：Eu^3＋ phosphor

The Gd2O2CO3：Eu^3＋ with type-Ⅱ structure phosphor was successfully synthesized via flux method at 400 ℃ and their photoluminescence properties in vacuum ultraviolet （VUV） region were examined. The broad and strong excitation bands in the range of 153-205 nm owing to the CO3^2- host absorption and charge transfer （CT） of Gd^3＋-O2^- were observed for Gd2O2CO3：Eu^3＋. Under 172 nm excitation, Gd2O2CO3：Eu^3＋ exhibited strong red emission with good color purity, indicating Eu^3＋ ions located at low symmetry sites and the chromaticity coordination of luminescence for Gd2O2CO3：Eu^3＋ was （x=0.652, y=0.345）. The photoluminescence quenching concentration of Eu^3＋ excited by 172 nm for Gd2O2CO3：Eu^3＋ was about 5%. Gd2O2CO3：Eu^3＋ would be a potential VUV-excited red phosphor applied in mercury-free fluorescent lamps.     

Ce3+ sensitized Tb3+ and Dy3+ photoluminescence in β-LaB5O9 prepared by sol–gel method

Rare earth (RE) pentaborates, both α- and β-polymorphs, are good candidates for photoluminescent hosts suitable for various RE activators. Ce³⁺ acts not only as an activator itself, but also as a sensitizer to other rare earth activators, like in the case of commercial green phosphor CeMgAl₁₁O₁₉:Tb³⁺. In this work, two solid solutions of β-La_0.9–xCe_0.1Tb_xB₅O₉ (0 ≤ x ≤ 0.15) and β-La_0.9–yCe_0.1Dy_yB₅O₉ (0 ≤ y ≤ 0.07) were prepared by sol–gel method with high crystallinity, and the phase purity was confirmed with careful analyses on powder X-ray diffraction patterns. Energy transfers are expected due to the overlapping of Ce³⁺ emission with the Tb³⁺/Dy³⁺ excitation. Indeed, the steady photoluminescence spectra indicate the decrease of the Ce³⁺ emission and the increase of the Tb³⁺/Dy³⁺ emission, and the fluorescence decay curves exhibit the decrease of the average lifetime of Ce³⁺. The energy transfer efficiency is estimated to be 60% at x = 0.15 and 55% at y = 0.07, respectively. The mechanism is likely through the dipole–dipole electric interactions for both cases. With this rationale, the Tb³⁺ and Dy³⁺ emissions are greatly enhanced, in particular, the white emission of Dy³⁺ in β-La_0.85Ce_0.1Dy_0.05B₅O₉ is enhanced by 20 times.     

Red-emitting CaWO4:Eu3+,Tm3+ phosphor for solid-state lighting: Luminescent properties and morphology evolution

CaWO₄:xEu³⁺,yTm³⁺crystals were obtained by facile synthesis at low temperature by the microwaveassisted hydrothermal method(MAH).The phase formation,morphology,luminescent properties and ene rgy transfer were investigated.The X-ray diffraction(XRD)re sults show the formation of a scheelitelike tetragonal structure without the presence of secondary phases.The growth mechanism of hierarchical micro structures based on self-assembly and Ostwald-ripening processes was evaluated,obtaining different types of morphologies.The luminescence spectra of CaWO₄:Eu³⁺,Tm³⁺at 325 nm excitation show the predominance of red emission at the 5 D0→7 F2(Eu³⁺)transition at 624 nm.This feature signals dominant behavior of the electric dipole type.The presence of Tm³⁺is notably evident in the absorption spectra by the related excitation transitions:3 H6→1 G4,3 H6→3 F3 and 3 H6→3 H4.Color parameters are discussed to characterize CaWO₄:Eu³⁺,Tm³⁺emission.The study of the emission spectrum as a function of the concentration of Eu³⁺(x mol%)and Tm³⁺(y mol%)indicates that the CaWO₄:Eu³⁺,Tm³⁺phosphors show stronger red emission intensity and exhibit the CIE value of x=0.63 and y=0.35.The photoluminescence results show 97%high color purity for CaWO₄:4 mol%Eu³⁺,a high CRI(92%)and a low CCT of 1085 K.These results demonstrate that the CaWO₄:Eu³⁺,Tm³⁺red phosphors are promising as color converters for application in white light-emitting diodes and display devices.     

Spectral properties and Judd–Ofelt analysis of novel red phosphors Gd2InSbO7:Eu3+ with high color purity for white LEDs

Gd₂InSbO₇:Eu³⁺ red phosphors were successfully synthesized via high-temperature solid–state reaction. The phase purity, particle size, and luminescence properties of obtained phosphors were measured and analyzed in detail. The Gd₂InSbO₇ lattice possesses cubic structure with F_d-3m (227) space group. The phosphors emit bright red emission at 628 nm under 393 nm excitation, and this phenomenon is attributed to the ⁵D₀–⁷F₂ transition. The Judd–Ofelt parameters (Ω₂, Ω₄), transition ratio, and branching ratios (β) of Eu³⁺-doped Gd₂InSbO₇ phosphor were calculated on the basis of the emission spectra and decay lifetimes. The optimal content in Gd₂InSbO₇:xEu³⁺ is identified to be 15 mol%. The thermal quenching of Gd₂InSbO₇:Eu³⁺ is found to be over 500 K, and its activation energy is 0.26 eV. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of Gd₂InSbO₇:15%Eu³⁺ are (0.629, 0.371), which are close to ideal red chromaticity coordinates (0.670, 0.330). The fabricated w-LED exhibits good color rendering index (R_a) (86), correlated color temperature (CCT) (6997 K), and CIE chromaticity coordinates (0.302, 0.330). The obtained results demonstrate that Gd₂InSbO₇:Eu³⁺ phosphors have potential applications in white LEDs.