Nearly monodisperse,regular-shaped and well oil-dispersible tetragonal BaYF5:0.2Yb3+/0.02Er3+ nanocrystals(NCs) were synthesized in water-ethanol-oleic acid-sodium oleate system.The as-obtained NCs exhibited bright upconversion(UC) fluorescence under the 980 nm excitation.Blue(2H9/2-4I15/2),green((2H11/2,4S3/2)-4I15/2) and red(4F9/2-4I15/2) transitions were observed.The results indicated that the relative intensity of green to red increased gradually with increasing power density,which were seldom in the previous work.Therefore,the UC properties and mechanism were studied in detail.
Micro-and nanocrystals cubic-phase SrF2:Yb3+/Er3+ upconversion luminescence phosphors were synthesized via a facile hydro-thermal route in the presence of different surfactants.The samples were characterized with X-ray diffraction (XRD),Fourier transform infra-red spectra (FT-IR),scanning electron microscopy (SEM),transmission electron microscopy (TEM),and upconversion emission spectra.As-prepared products showed a variety of morphologies,such as cubic-shaped microcrystal,hierarchical structure microspheres,spheri-cal-shaped nanocrystals and nanosheets.The intrinsic structural feature of cubic-phase SrF2 and two important external factors,namely,the surfactants in the reaction solution and fluoride sources,were responsible for shape determination of SrF2:Yb3+/Er3+.The possible formation mechanisms for products with various architectures were presented.A systematic study on the photoluminescence of Yb3+/Er3+-doped SrF2 samples with cubic shape,microspheres,spherical and nanosheets shapes showed that the optical properties of these products were strongly dependent on their morphologies and size.
Different lanthanide ions (Yb3+/Ho3+/Er3+/Tm3+) codoped KGd(WO4)2 phosphors were prepared by high-temperature solid-state reaction. The upconversion luminescence properties of two-ion and three-ion co-doped KGd(WO4)2 phosphors were investigated in detail. The concentration quenching effect of the two-ion co-doped KGd(WO4)2 phosphors was studied, and the optimum concentration of Ho3+, Er3+ and Tm3+ are 2 mol.%, 2 mol.% and 3 mol.%, respectively. The Yb3+/Ho3+/Tm3+ co-doped KGd(WO4)2 sample is the best white upconversion luminescence material among three-ion co-doped KGd(WO4)2 phosphors. The CIE coordinates for the samples were calculated, and chromaticity coordinates were close to white light regions. The upconversion luminescence mechanism of the samples was discussed. The upconver-sion luminescence of Ho3+ and Er3+ was both produced through two-photon process. The emissions of Ho3+ at 546 and 654 nm originated from the transition of Ho3+ (5S2→5I8 and 5F5→5I8), while those of Er3+ at 530 and 551 nm were attributed to the transition of Er3+ (2I11/2→4I15/2 and 4S3/2→ 4I15/2). The upconversion luminescence mechanism of Tm3+ was a three-photon process. The blue emission of Tm3+ was due to the transition of Tm3+ (1G4→3H6).
Yb3+,Tm3+co-doped Gd6 Mo O12phosphors with different morphologies are prepared by the hydrothermal method.The dendrites present different morphologies(including hexagonal prisms,spindles,and spheres) after changing the p H value and edetate disodium(EDTA) usage.It is found that each of the two factors plays a crucial role in forming different morphologies.The up-conversion(UC) luminescence is studied.Under 980-nm semiconductor laser excitation,relatively strong blue emission and weak red emission are observed.Finally,the effect of pumping power on the UC luminescence properties and the level diagram mechanism of Gd6 Mo O12:Yb3+/Tm3+phosphor are also discussed.
Hexagonal NaYF4:Yb3+,Er3+ (β-NaYF4:Yb3+,Er3+) nanoparticles supported on TiO2 nanobelts were prepared using two-step pro- cedures of ion-exchangeable process and hydrothermal treatment: layered titanate nanobelts were first ion-exchanged with Y3+, Yb3+ and Er3+ cations to produce titanate nanobelts with these cations, and then, the product nanobelts in NaY solution were treated under hydrothermal con- dition to transform into anatase TiO2 nanobelts supported with β-NaYF4:Yb3+,Er3+ nanoparticles. The final products were characterized by various measurement techniques. Many preparation conditions, e.g., the content of added precursors, reaction time and pH value, were optimized to obtain nanocomposites including relatively uniform nanoparticles with strong upconversion (UC) emission intensity. The measurement results showed that the anatase TiO2 nanobelts, supported by the large number of β-NaYF4:Yb3+,Er3+ nanoparticles with 30–70 diameter range and very strong UC emission, could be achieved under suitable preparation condition. The UC emission intensity of the nanoparticles with the concentrations of Yb3+ and Er3+ closer to 20 mol.% and 1 mol.% was the strongest.
A series of new red-emitting BaCa1-2xBO3F:xEu3+, xM+ (M=Li, Na, K) phosphors were synthesized by the solid-reaction method. X-ray diffraction (XRD), diffuse reflection (UV-vis) and photoluminescence spectra were utilized to characterize the crystallization process, structure and luminescence properties of the as-synthesized phosphors. The XRD results indicated that the sample began to crystallize at 800 oC, and single-phase BaCaBO3F was fully obtained after annealing at 1000 oC. The charge compensated behaviors were investigated in this paper by considering different cations like Li+, Na+ and K+ acting as the charge compensator. The as-prepared phosphors had better emission properties, and the two characteristic emission lines peaking at 590 and 615 nm could be obtained upon 394, 463 and 532 nm excitation with the chromaticity coordinates of (0.596, 0.391), which were due to 5D0-7F1 and 5D0-7F2 transitions of Eu3+ ions. Further, the concentration quenching and corresponding luminescence mechanisms of BaCa1-2xBO3F:xEu3+, xNa+ phosphors were also discussed.
Trivalent rare-earth ions (La3+,Pr3+,Nd3+,Sm3+,Gd3+,Tb3+,Dy3+,Ho3+,Er3+,Tm3+,and Yb3+) were investigated as the codoped auxiliary sensitizer for the electron trapping materials SrS:Eu2+ in order to enhance the fluorescence properties.It was found that Sm3+ and Tb3+ had the best photoluminescence stimulated luminescence (PSL) effect among the selected trivalent rare-earth ions.All the SrS:Eu2+ samples doped by different trivalent rare-earth ions could be stimulated by 980 nm laser after being exposed to the conventional sunlight,and they emitted PSL with the peak located at 615 nm.The result also indicated that some co-doped rare earth ions could increase fluorescence intensities of the traditional electron trapping materials SrS:Eu2+.
The strong yellow upconversion (UC) light emission was observed in Ho3+/Yb3+ co-doped Gd2Mo3O9 phosphor under the excitation of 980 nm diode laser. The phosphors were synthesized by the traditional solid-state reaction method. The structures of the samples were characterized by X-ray diffraction (XRD). Under 980 nm excitation, Ho3+/Yb3+ co-doped Gd2Mo3O9 exhibited strong yellow UC emission based on the green emission near 541 nm generated by 5F4 , 5S2 → 5I8 transition and the strong red emission around 660 nm generated by 5F5 → 5I8 transition, which assigned to the intra-4f transitions of Ho3+ ions. The doping concentrations of Ho3+ and Yb3+ were determined to be 0.01 mol Ho3+ and 0.2 mol Yb3+ for the strongest yellow emission. Then the dependence of UC emission intensity on excitation power density showed that the green and red UC emissions were involved in two-photon process. The possible UC mechanisms for the strong yellow emission were also investigated. The result indicated that this material was a promising candidate for the application in the yellow display field.
Novel Sr3Gd(1–x)DyxNa(PO4)3F(SGNP:x Dy3+, x=0.01, 0.03, 0.05, 0.07, 0.09, 0.11) phosphors were synthesized by a conventional solid-state reaction method at different compositions. The X-ray diffraction results confirmed that the as-prepared samples were pure phase. The phosphor had two intense emission bands centering at 481 and 574 nm which could be attributed to the 4F9/2→6H15/2 transition and the 4F9/2→6H13/2 transition, respectively. The chromaticity coordinates(x, y) of this phosphor were calculated to be(0.3054, 0.3354) located on the region of white light region when excited at 350 nm. The concentration quenching mechanism of Dy3+ was ascribed to the dipole-dipole interaction. The current research suggested that the phosphors might be potential application in the w-LEDs.
Green-emitting Sr2LiSiO4F:Eu2+ and blue-emitting Sr2MgSi2O7:Eu2+ phosphors were synthesized by the conventional high temperature solid-state route, respectively. Their structures and photoluminescence properties were comparatively investigated. It was found that the mixture phases of Sr2MgSi2O7 and SrF2 were obtained when a part of Sr2+ in Sr2LiSiO4F was replaced by some amount of Mg2+ in order to design the possible SrMgLiSiO4F:Eu2+ phosphor. Based on the photoluminescence analysis, Sr2LiSiO4F:Eu2+ phosphor exhibited a green broad emission band of main peak at 513 nm under the excitation of 365 nm, while the Sr2MgSi2O7:Eu2+ and SrMgLiSiO4F:Eu2+ phosphor showed blue emission centered at 467 nm. The temperature dependent photoluminescence properties and room temperature decay time for the three kinds of phosphors were also discussed in this paper.
