Synthesis and spectral characteristics of La2MoO6：Ln3＋ （Ln=Eu, Sm, Dy, Pr, Tb） polycrystals

The novel phosphors of La 2 MoO 6 activated with the trivalent rare earth Ln 3+ (Ln=Eu, Sm, Dy, Pr, Tb) ions were synthesized by solid state reactions at high temperature in air atmosphere, and their phase impurities and luminescent properties were studied. The photoluminescence (PL) excitation and emission spectra, and decay curves were employed to study their luminescence properties. The lifetimes of the characteristic emissions from Ln 3+ ions were in the order of millisecond except Pr 3+ ions. (LaEu 1-x ) 2 MoO 6 was a promising phosphor for practical application and the optimum concentration was x=0.075. The concentration quenching mechanism of Eu 3+ was also discussed by theoretical fitting using Burshtein model.     

Synthesis and luminescence properties of BaWO4：Pr^3＋ microcrystal

BaWO4:Pr3+ (hereafter BWO:Pr) microcrystals were prepared via a hydrothermal route, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra. The as-prepared products with different morphologies of egg-shape rod, olive-like, and quasi-sphere were obtained by the addition of the surfactants and chelating agents. The emis-sion spectra of BWO:Pr microcrystals showed the strong red emission (642 nm) assigned to the Pr3+ ions of 3P0→3F2 transition with blue ex-citation (484.6 nm, 3H4→3P0).     

Energy transfer and frequency upconversion in Er~（3＋）-Yb~（3＋） codoped oxy-fluoro-tungstosilicate glasses

Er3+-Yb3+ codoped oxy-fluoro-tungstosilicate glasses with infrared-to-visible frequency upconversion luminescence were prepared by melting quenching in air.The effects of Er3+ doping on the optical properties of the samples were measured by means of techniques such as optical absorption spectra and photoluminescence spectra.The results showed that intense green and red signals centered at 546 and 665 nm,corresponding to the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ by a multiphoton stepwise phonon-assisted excited-state absorption process,respectively,were simultaneously observed by exciting the samples with a diode laser operating at 980 nm at room temperature.The upconversion process was found very sensitive to Er3+ content at a constant Yb2O3 content of 5 mol.%.With the increase of Er3+ content from 0.5% to 1.5%,the upconversion intensity increased gradually.Further increasing of Er3+ content to 3.0% resulted in a significant fluorescence quenching.Moreover,the possible upconversion mechanisms were discussed based on the energy-matching conditions and the quadratic dependence on excitation power.     

Hydrothermal synthesis and luminescence properties of YW2O6（OH）3：Tb^3＋ green phosphors

YW2O6(OH)3:Tb3+ green phosphors were synthesized at different pH values via a facile hydrothermal method. The structure and optical properties of as-synthesized samples were studied by X-ray diffractometer (XRD), scanning electron microscopy (SEM), photolumi-nescence spectra and luminescence decay curve. The results showed that pure monoclinic YW2O6(OH)3:Tb3+ green phosphors could be ob-tained at pH 2-5. Uniform spherical micro-phosphors of ~5 μm in diameter with narrow size distribution could be prepared at pH 5. pH value had dramatic influence on morphologies, which could be ascribed to the various spatial configurations of different poly-tungstates existing at different pH values. The emission spectra under 261 nm excitation exhibited dominant green emission at 546 nm. The green emission inten-sity reached the maximum value at pH 5 due to the high packing density of the obtained phosphor.     

Investigation on luminescence properties of Ln^3＋ doped Sr3EuMgSi2O8 （Ln=Dy, Er, Ho）

The luminescent properties of Sr2.97MgSi2O8:Eu2+0.01 phosphors were investigated with different Ln3+0.02(Ln3+:Dy3+,Er3+,Ho3+) co-dopants. The co-dopants had no influence on both the structure of the lattice and the position of the emission peak. However, the afterglow properties of samples were enhanced with different co-dopants. The afterglow duration of the Dy3+ co-doped sample was longer than that of the others. Furthermore, the co-doping samples had stronger thermoluminescence (TL) intensity and therefore longer afterglow duration. At last, the self-reduction of Eu3+→Eu2+ was observed in an silicate compound of Sr3-xMgSi2O8:xEu phosphor in air condition. This is the first time to show a blue long afterglow phosphor synthesized avoiding reducing atmosphere.     

Influence of concentration and sintering temperature on luminescence properties of Eu^3＋：SnO2 nanocrystallites

The nanopowders of SnO2 doped with different Eu3+ concentrations were synthesized using the modified Pechini method. The Eu3+ concentrations were high above solubility limit. The average size of crystallites was controlled by the sintering temperatures. The structure and the morphology of obtained powders were examined using the XRD (X-ray diffraction) and TEM (transmission electron microscopy) analyses. The Eu2Sn2O7 phase separation was observed at relatively high concentration of Eu3+ ions. The ZnS:Ag micropowders were mixed with the Eu3+:SnO2 powders and their normalized emission was used to measure a relative efficiency of Eu3+:SnO2. The photoluminescence spectra of mixed powders were measured in function of Eu3+ concentration and average size of nanocrystallites. The reference peak method was used for comparison of intensities of the samples and selection of optimal one. The influence of the average grain size and Eu3+ concen-tration on the phosphor’s efficiency was discussed. The presented results confirmed the rightness of synthesis of the Eu3+:SnO2 in form of nanocrystalites with relatively high Eu3+ concentration.     

Synthesis and luminescence properties of Sr3-z（AlxSi1-x）O5-xFx：zCe^3＋phosphors

Sr3-z(Alx,Si1-x)O -5-xFx:zCe3+ phosphors were synthesized by high-temperature solid-state reaction.The structure and luminescence properties of phosphors with various Al/Si ratios and Ce3+ concentrations were characterized using various methods such as X-ray diffraction,photoluminescence excitation and photoluminescence spectra.XRD result displayed that a complete solid solution between Sr3AlO4F and Sr3SiO5 was formed.With the increasing of x value,a broader excitation band and stronger absorption appeared in the blue light region.Moreover,the emission band shifted to a shorter wavelength and the emission intensity reached a maximum at x=0.6.By adjusting the concentration of Ce3+,a widely tunable range of emission wavelength under the excitation of 460 nm was obtained from the green to yellow regions.In addition,the concentration and thermal quenching were also discussed.     

Synthesis and luminescence properties of SrAleO4：Eue＋,Dy3＋ hollow microspheres via a solvothermal co-precipitation method

SrAl2O4:Eu2+,Dy3+ hollow microspheres were successfully prepared through a facile and mild solvothermal co-precipitation combining with a postcalcining process.The structure and particle morphology were investigated by X-ray diffraction(XRD),scanning and transmission electron microscopy(SEM and TEM)pictures,respectively.The mechanism for the formation of spherical SrAl2O4:Eu2+,Dy3+ phosphor was preliminary presented.After being irradiated with ultraviolet(UV)light,the spherical phosphor emitted long-lasting green phosphorescence.Both the photoluminescence(PL)spectra and luminance decay,compared with that of commercial bulky powders,revealed that the phosphors had efficient luminescent and long lasting properties.It was considered that the SrAl2O4:Eu2+,Dy3+ hollow microspheres had promising long-lasting phosphorescence with potential scale-dependent applications in photonic devices.     

Preparation and luminescent properties of MgTiO3：Eu3＋ phosphor for white LEDs

A novel red phosphor Eu3+ doped magnesium titanate (MgTiO3) was synthesized via sol-gel method. The X-ray diffraction patterns (XRD) revealed that a pure MgTiO3 phase was obtained. Its excitation spectrum consisted of a broad band (<350nm) and a series of narrow bands in the long wavelength, and the strongest excitation peak at 465nm might be exited by GaN-chip to emit red light for white LED. The phosphors showed strong emission at 614nm which could be attributed to the 5D0→7F2 emission of Eu3+ . The emission intensity of MgTiO3:Eu3+ phosphor reached the maximum at the Eu3+ concentration of 3.5mol.%. The luminescent properties (such as emission intensity and decay times) were further improved by introducing Al3+ as a charge compensator, demonstrating potential applications in white LED.     

Luminescence properties of Eu3＋ and Ho3＋ in SreTiO4

Eu3+ and Ho3+ doped Sr2TiO4 were synthesized by using solid-state reactions. Samples sintered at 1300 oC for 6 h could be indexed to Sr2TiO4 with a single phase. Eu3+ in Sr2TiO4 emitted orange light under the excitation at 365 nm in a broad band which was coupled well with the strongest emission of high pressure mercury vapor lamps. Ho3+ in Sr2TiO4 emitted yellow light under blue excitation from 450 to 460 nm which agreed well with the emission of blue InGaN-based light-emitting diodes. The present results indicated that Sr2TiO4 was a promising host for high pressure mercury vapor lamps or white light-emitting diodes.     

Photoluminescence properties and effect of Bi~（3＋） dopant of Eu~（3＋） and Dy~（3＋） co-doped Sr_3V_2O_8

Photoluminescence properties of Sr 2.5 Dy 1/3-x Eu x V 2 O 8(x=0,0.06,0.12,0.18,0.24,0.33) were investigated.The excitation spectra included a broad band in the short wavelength region and several sharp lines in the longer wavelength region,and the spectral origin were discussed.The emission spectra were measured in two different exciting ways,i.e.,exciting the VO 4 group at 270 nm and the Eu 3+ ion at 398 nm,respectively,and the energy transferring process was reasonably suggested.Furthermore,multi-color emission could be achieved in Sr 2.5 Dy 1/3-x Eu x V 2 O 8,indicating that the studied samples had potential applications in the white light emitting diodes.Further investigation showed that reducing the concentration of Eu 3+ and Dy 3+ and introducing Bi 3+ as a sensitizer ion greatly enhanced the emission intensity.     

Effect of trivalent rare earth ions doping on the fluorescence properties of electron trapping materials SrS：Eu~（2＋）

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+.     

Facile sol-gel combustion synthesis and photoluminescence enhancement of CaZrO3：Sm3＋ nanophosphors via Gd3＋ doping

CaZrO3:Sm and CaZrO3:Sm,Gd nanophosphors were synthesized by a facile and efficient sol-gel combustion method. Their structure and optical properties were studied. The photoluminesce (PL) results showed that the phosphor could be efficiently excited by irradiation at wavelengths in the visible light region (350-430nm). The CaZrO3:Sm nanophosphor exhibited strong yellow-green, orange and red emissions with peak wavelength centered at 565nm (4G5/2→6H5/2), 601nm (4G5/2→6H7/2) and 645nm (4G5/2→6H9/2), respectively. The incorporation of Gd3+ ions could greatly improve the luminescence intensity. The highest emission intensity was observed with 2mol.% Gd3+ doped CaZrO3:3mol.% Sm powder. The material had potential application in the development of materials for LED’s and other optical devices in the visible region.     

Luminescence properties of Tm^3＋/Yb^3＋, Er^3＋/Yb^3＋ and Ho^3＋/Yb^3＋ activated calcium tungstate

CaWO4 phosphor activated by the Tm3+/Yb3+,Er3+/Yb3+ and Ho3+/Yb3+ ions were synthesized by a traditional high-temperature solid-state method.The crystal structures and morphologies of the products were characterized by X-ray powders diffraction method(XRD) ,infrared spectra(FT-IR) and scanning electron microscopy(SEM) .The samples were found to show up-conversion luminescence properties.CaWO4 doped with Tm3+/Yb3+ showed blue luminescence characteristic of Tm(III) ion in the range of 460-485 nm,corresponding to the 1G4→3H6 electronic transition.CaWO4 doped with Er3+/Yb3+ showed strong green luminescence at 510-565 nm(2H11/2,4S3/2→4I15/2) and weak red luminescence at 640-685 nm(4F9/2→4I15/2) of Er(III) ion.CaWO4 doped with Ho3+/Yb3+ phosphor emitted green luminescence at 525-560 nm(5S2,5F4→5I8) and red luminescence at 630-670 nm(5F5→5I8) and at 730-770 nm(5S2,5F4→5I7) ,which is the characteristic of Ho(III) ion.     

Preparation and luminescence properties of Ce3＋/Dy3＋-codoped fluorosilicate glass ceramics

The Ce3+and Dy3+ co-doped fluorosilicate glass and glass ceramics containing SrF2 or CeF3 nanocrystals were prepared under re-ducing atmosphere. The precipitated nano-crystalline phase shifted from cubic SrF2 to hexagonal CeF3 gradually with the heat treatment tem-perature increasing from 620 to 680 °C. The glass and glass ceramics emitted white light, deriving from a combination of the Ce3+ blue and the Dy3+ yellow light. The CIE coordinates could be tuned by adjusting the ratio of Ce3+/Dy3+ concentration. The luminescence could be en-hanced significantly by annealing the samples at the temperatures lower than 640 °C.     

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.     

Fabrication and photoluminescent characteristics of one-dimensional La202S：Eu3＋ nanocrystals

One-dimensional La2O2S:Eu3+ nanowires(NWs) were fabricated with a simple hydrothermal method.The structures were characterized by X-ray diffraction and transmission electron microscopy(TEM).The photoluminescent properties including excitation and emission spectra were studied.The results indicated that in excitation spectra there existed charge transfer(CT) absorption of both O2-→Eu3+ and S2-→Eu3+,and f-f transitions absorption in NWs and corresponding sub-meter materials(SMs).The relative intensity of CT absorption of O2-→Eu3+ to S2-→Eu3+ in both samples clearly changed.The strong yellow and red emissions of Eu3+ ions in NWs were observed.     

Preparation and upconversion luminescence of monodisperse Gd2O3：Ho^3＋,Yb^3＋ nanocrystals

Gd2O3:Ho3+,Yb3+ nanocrystals were synthesized via solvothermal method.X-ray diffraction(XRD),transmission electron microscopy(TEM),absorption and upconversion spectra were employed to characterize the synthesized nanocrystals.The results of XRD and TEM showed that obtained Gd2O3:Ho3+,Yb3+ nanocrystals were cubic in crystal structure and uniform spherical in morphology.The average crystallite size was calculated to be 7.5 nm.Green and red up-conversion emissions corresponding to(5F4,5S2)→5I8 and 5F5 → 5I8 transition were observed upon 980 nm excitation at room temperature.The results indicated that both green and red luminescence were based on the two-photon processes.Laser power and doping concentration dependence of the upconverted emissions were studied to understand the upconversion mechanisms.Excited state absorption and energy-transfer processes were discussed as the possible mechanisms for the visible emissions.     

Synthesis and fluorescence properties of Eu（Ⅲ）, Tb（Ⅲ） and Sm（Ⅲ） with β-diketone and 2,2＇- bipyridine

Three new rare earth ternary complexes,RE(PPP)3bpy(RE=Sm 3+ ,Eu 3+ ,Tb 3+ ),were synthesized by the reaction of 1-phenyl-3-(p-phenylethynylphenyl)-1,3-propanedione(HPPP)and 2,2′-bipyridine(bpy)with rare earth chloride RECl3,respectively,in alcohol solution. The compositions were characterized by means of infrared(IR)spectra,chemical analysis,elemental analysis,and thermodynamic analysis.Luminescent properties of the three complexes were studied.At room temperature,under UV light excitation,the Sm 3+ ,Eu 3+ and Tb 3+ complexes exhibited characteristic emission of the central ions.The fluorescence spectra showed that the fluorescence emission intensity of Eu 3+ complex was the strongest.The narrow strongest emission band of Eu 3+ complex was considered to be a valuable material with bright red fluorescence.