Du Haiyan

Hydrothermal synthesis of SrF2:Yb3+/Er3+ micro-/nanocrystals with multiform morphologies and upconversion properties

Abstract Micro- and nanocrystals cubic-phase SrF 2 :Yb 3+ /Er 3+ upconversion luminescence phosphors were synthesized via a facile hydrothermal route in the presence of different surfactants. The samples were characterized with X-ray diffraction (XRD), Fourier transform infrared 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, spherical-shaped nanocrystals and nanosheets. The intrinsic structural feature of cubic-phase SrF 2 and two important external factors, namely, the surfactants in the reaction solution and fluoride sources, were responsible for shape determination of SrF 2 :Yb 3+ /Er 3+ . The possible formation mechanisms for products with various architectures were presented. A systematic study on the photoluminescence of Yb 3+ /Er 3+ -doped SrF 2 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.

Preparation of Non-Grinding Long Afterglow SrAl2O4: Eu2+, Dy3+ Material by Microwave Combustion Method

Abstract The non-grinding long afterglow material SrAl 2 O 4 :Eu 2+ , Dy 3+ was prepared by combustion method in home microwave oven directly, after dispersant, frother, comburent, and mineralizer were added into the reacting system. XRD analysis showed that the powders were nearly pure SrAl 2 O 4 phase with few other phases, and the size of the grain was 41.1 nm. Fluorescence spectrum results indicated that there were 2 excitation peaks located at 345 and 400 nm, and the emission peak located at 516 nm, afterglow lasted up to 30 min or more. The microwave combustion method has advantages of less time, low temperature and no grinding process, and the material made by the method has good luminescent property.

Upconversion luminescence of Yb3+/Ho3+/Er3+/Tm3+ co-doped KGd(WO4)2 powders

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 upconversion 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).

Luminescence properties of a new red emitting Eu3+-doped alkaline-earth fluoborate phosphor: BaCa(1-2x)BO3F:xEu3+, xM+ (M=Li, Na, K)

Abstract A series of new red-emitting BaCa 1-2 x BO 3 F: x Eu 3+ , x M + (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 °C, and single-phase BaCaBO 3 F was fully obtained after annealing at 1000 °C. 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 5 D 0 - 7 F 1 and 5 D 0 - 7 F 2 transitions of Eu 3+ ions. Further, the concentration quenching and corresponding luminescence mechanisms of BaCa 1-2 x BO 3 F: x Eu 3+ , x Na + phosphors were also discussed.

Effect of trivalent rare earth ions doping on the fluorescence properties of electron trapping materials SrS: Eu2+

Abstract Trivalent rare-earth ions (La 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , and Yb 3+ ) were investigated as the co- doped auxiliary sensitizer for the electron trapping materials SrS: Eu 2+ in order to enhance the fluorescence properties. It was found that Sm 3+ and Tb 3+ had the best photoluminescence stimulated luminescence (PSL) effect among the selected trivalent rare-earth ions. All the SrS: Eu 2+ 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: Eu 2+ .

Preparation and characterization of upconversion nanocomposite for β-NaYF4:Yb3+,Er3+-supported TiO2 nanobelts

Abstract Hexagonal NaYF 4 :Yb 3+ ,Er 3+ (β-NaYF 4 :Yb 3+ ,Er 3+ ) nanoparticles supported on TiO 2 nanobelts were prepared using two-step procedures of ion-exchangeable process and hydrothermal treatment: layered titanate nanobelts were first ion-exchanged with Y 3+ , Yb 3+ and Er 3+ cations to produce titanate nanobelts with these cations, and then, the product nanobelts in NaY solution were treated under hydrothermal condition to transform into anatase TiO 2 nanobelts supported with β-NaYF 4 :Yb 3+ ,Er 3+ 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 TiO 2 nanobelts, supported by the large number of β-NaYF 4 :Yb 3+ ,Er 3+ 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 Yb 3+ and Er 3+ closer to 20 mol.% and 1 mol.% was the strongest.

Combustion synthesis and luminescence properties of blue NaBaPO4:Eu2+ phosphor

Abstract The blue-emitting phosphor NaBaPO 4 :Eu 2+ was prepared by the combustion method. The phase structure and microstructure of the as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Under the excitation wavelength of 360 nm, the emission spectrum exhibited only one blue band centering at 435 nm, which was ascribed to the 4f 6 5d 1 →4f 7 transition on Eu 2+ ions. Compared with the phosphor obtained by solid-state reaction method, the relative emission intensity of sample obtained by combustion method increased slightly. The decay times and the temperature dependence luminescence intensities (25–300 °C) were discussed in order to further investigate the potential applications. Furthermore, Eu 2+ -doped NaBaPO 4 phosphor showed higher thermally stable luminescence comparable to commercially available Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) phosphor. All the investigated suggestions that NaBaPO 4 :Eu 2+ is a good phosphor candidate applied in white light emitting diode.

Luminescence properties of SrB4O7:Sm2+ for light conversion agent

Abstract A deep red-emitting SrB 4 O 7 :Sm 2+ phosphor for light conversion agent was synthesized by the conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation of SrB 4 O 7 :Sm 2+ materials. Results of luminescence properties showed that the phosphor could be efficiently excited by the UV-vis light region from 250–500 nm, and it exhibited deep red (685 nm) emission corresponding to 5 D 0 → 7 F 0 transition of Sm 2+ . The critical quenching concentration of Sm 2+ in SrB 4 O 7 :Sm 2+ phosphor was about 0.05, and the corresponding concentration quenching mechanism was verified to be the dipole-dipole interaction according to the Dexters theory. The decay times had few alterations with different concentrations in SrB 4 O 7 : x Sm 2+ phosphor.

Phase structure and temperature dependent luminescence properties of Sr2LiSiO4F:Eu2+ and Sr2MgSi2O7:Eu2+ phosphors

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.

Near-infrared downconversion in Eu2+ and Pr3+ co-doped KSrPO4 phosphor

A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4:Eu2+, Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KSrPO4 host. With broadband near-ultraviolet light excitation induced by the 4f→5d transition of Eu2+, the characteristic NIR emission of Pr3+, peaking at 974 nm and 1019 nm due to 3P0→1G4 and 1G4→3H4 transitions, is generated as a result of the energy transfer from Eu2+ to Pr3+. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2+ prove the energy transfer from Eu2+ to Pr3+. This Eu2+ and Pr3+ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.