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 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.     

Luminescence properties of Mn2） ions doped Lu2CaMg2Si3O1） garnet phosphors

Yttrium aluminum garnet structure phosphors Lu2CaMg2Si3O12:Mn2+ were synthesized by conventional high temperature solid-state reaction in reductive atmosphere. The structure and optical properties of samples were characterized by application of powder X-ray diffraction (XRD) and photoluminescence spectroscopy. Results of X-ray diffraction (XRD) analysis showed that the phosphors mainly presented garnet structure with a few weak peaks of impurity phases. Lu2-xCaMg2Si3O12:xMn2+ (x=0.01-0.8) phosphors showed a broad emission band peaking at around 590 nm under ultraviolet (UV) light of 408 nm when Mn2+ concentration was less than 0.08 mol. With an increase in the Mn2+ concentration (above 0.08), another broad emission band peaking at 720 nm besides 590 nm was observed, which may be due to manganese ion having different valence and occupying different host lattice. The critical quenching concentrations of manganese ion in the wavelength of 590 and 720 nm were about 0.06 and 0.2 mol, respectively. With 408 nm excitation wavelength, emission color of the samples had a red shift trend as the Mn2+ concentration increased. All the results indicated that the Lu2CaMg2Si3O12:Mn2+ phosphors could be applicable to n-UV based white LEDs.     

Luminescent properties of MMgP_2O_7：Eu~（3＋）（M=Ca,Sr,Ba） phosphor

A series of red phosphors Eu3+-doped MMgP2O7(M=Ca,Sr,Ba) were synthesized by solid-state reaction method.X-ray powder diffraction(XRD) analysis confirmed the formation of pure CaMgP2O7,SrMgP2O7 and BaMgP2O7 phase.Photoluminescence spectra of MMgP2O7(M=Ca,Sr,Ba):Eu3+ phosphors showed a strong excitation peak at around 400 nm,which was coupled with the characteristic emission(350-400 nm) from UV light-emitting diode.The CaMgP2O7:Eu3+,SrMgP2O7:Eu3+ and BaMgP2O7:Eu3+ phosphors showed strong emission bands peaking at 612,593 and 587 nm,respectively.Due to the difference of the ion sizes between Ba2+(0.142 nm),Sr2+(0.126 nm),Ca2+(0.112 nm),Mg2+(0.072 nm) and Eu3+(0.107 nm),Eu3+ ions were expected to substitute for different sites in CaMgP2O7,SrMgP2O7 and BaMgP2O7 lattice.     

用于白光LED的荧光粉Sr3MgSi2O8:Eu2+的发光特性

使用高温固相法制备不同NH4Cl(作为助熔剂)加入量和不同Eu2+浓度的Sr3MgSi2O8:Eu2+,并研究其成相和发光性质.研究结果表明:NH4Cl加入量为24%时,样品为纯相,发光最强.Sr3MgSi2O8:Eu2+样品在近紫外区存在强激发带(250～400 nm),谱峰位于366 nm相应的发射谱带位于蓝光区(420～500nm),为一个不对称宽带,谱峰位于457 nm,该发射带由两个发射峰组成,其位置较接近,因此不能复合出白光,Sr3MgSi2O8:Eu2+仅适合作为紫外LED芯片激发的蓝光荧光粉.     

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.     

Effect of alkali metal oxides R2O （R=Na, K） on 1.53 μm luminescence of Er3＋-doped Ga2O3-GeO2 glasses for optical amplification

This paper reported the thermal stability and spectroscopic properties of Ga2O3-GeO2-Na2O-K2O (GGNK) glasses doped with Er3+. The GGNK glasses were characterized by differential scanning calorimetry (D...     

Effect of RO （R=Ca, Sr, Ba, Zn or Pb） component on spectroscopic properties of Eu3＋ in RO-B2O3 glasses

Eu3+-doped binary borate glasses with different metal oxide components RO (R=Ca, Sr, Ba, Zn or Pb) were prepared by meltquenching technique. The fluorescent spectral properties of Eu3+in these glasses were experimentally studied. The analysis on the phonon sidebands (PSBs) indicated that RO component did not cause obvious change of the electron-phonon coupling constant (EPC). By inspecting the optical absorption edges it was found that RO could greatly affect the band gap energy, and the glass with PbO component revealed the smallest band gap energy, the glasses with ZnO, BaO and SrO showed similar band gap energy. The optical transition intensity parameters of Eu3+in all studied glasses were calculated, it was found that for each sample its value of2 was larger than that of 4 and 6, and the sample with PbO component exhibited the smallest2, but the λ values for ZBE, CBE, BBE and SBE were very similar. These results might be helpful for the design of borate glasses.     

Improvement of conversion efficiency of silicon solar cells using up-conversion molybdate La_2Mo_2O_9：Yb,R （R=Er, Ho） phosphors

The goal of this work was aimed to improve the power conversion efficiency of single crystalline silicon-based photovoltaic cells by using the solar spectral conversion principle, which employs an up-conversion phosphor to convert a low energy infrared photon to the more energetic visible photons to improve the spectral response. In this study, the surface of multicrystalline silicon solar cells was coated with an up-conversion molybdate phosphor to improve the spectral response of the solar cell in the near-infrared spectral range. The short circuit current (Isc), open circuit voltage (Voc), and conversion efficiency (η) of spectral conversion cells were measured. Preliminary experimental results revealed that the light conversion efficiency of a 1.5%-2.7% increase in Si-based cell was achieved.     

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 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 luminescence properties of a novel red Sr3Bi（PO4）3：Sm^3＋ phosphor

A series of Sr3Bi1-x(PO4)3: xSm3+phosphors were prepared by solid state method at 1250 °C for 4 h. X-ray diffraction (XRD) indi-cated that the sample was of a pure phase of Sr3Bi(PO4)3. The main excitation peaks were located at 343 (6H5/2→4H9/2), 360 (6H5/2→4D3/2), 373 (6H5/2→6P7/2), 400 (6H5/2→4F7/2), 414 (6H5/2→6P5/2) and 467 nm (6H5/2→4I13/2). The main emission were located at 563 (4G5/2→6H5/2), 599 (4G5/2→6H7/2), 646 (4G5/2→6H9/2) and 708 nm (4G5/2→6H11/2). The intensest emission was excited by 400 nm. We studied the effect of differ-ent doping concentrations of Sm3+ activator on the luminescence properties and found that the luminescent intensity first increased with Sm3+ concentration increasing, and then decreased. The luminescent intensity had the best value when x=0.04. The chromaticity coordinates of the sample Sr3Bi0.96(PO4)3:0.04Sm3+ were (x=0.57, y=0.36), and the lifetime was 2.12 ms.     

Eu2+、Er3+共掺杂Sr3MgSi3O10高亮度蓝色荧光粉的制备及性质研究

采用凝胶-燃烧法在活性炭弱还原气氛下成功合成了高亮度蓝色发光材料Sr3 MgSi3 O10:Eu2+,Er3+.用X射线粉末衍射仪、荧光分光光度计对样品的物相结构和发光性质进行了分析和表征.结果表明,所合成的Sr3 MgSi3O10:Eu2+,Er3+的晶体结构与Sr2 MgSi2 O7的相似,属四方晶系.样品激发光谱是位于250 nm～450 nm的宽带,最大激发峰位于357 nm处;发射光谱也是一宽带,最强的发射峰位于466 nm处,属于Eu2+典型的4f65d1→4f7跃迁,呈蓝光发射.根据光谱测定结果和Van Uitert经验公式,推断Eu2+进入Sr3 MgSi3 O10基质后占据八配位Sr的格位.研究发现,共掺杂Er3+能有效敏化Sr3 MgSi3 O10基质中Eu2+的发光,当Er3+的掺杂摩尔分数为0.04时,样品发光强度最大,约为单掺Eu2+样品发光强度的3.3倍.     

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.     

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.     

A comparison of Ce~（3＋） luminescence in X_2Z（BO_3）_2（X=Ba,Sr;Z=Ca,Mg） with relevant composition and structure

The VUV-UV spectroscopic properties of Ce3+ in Ba2Mg(BO3)2,Ba2Ca(BO3)2 and Sr2Mg(BO3)2 were compared,and the relation between the energy of the 4f→5d transition of Ce3+ and the coordination environments of substituted alkaline earth ions was discussed.The chromaticity coordinates of Ce3+ activated X2Z(BO3)2(X=Ba,Sr;Z=Ca,Mg) phosphors were changeable from blue to whitish and further to green range by varying the doping concentration of Ce3+ or the types of substituted alkaline earth ions upon 172 nm excitation.     

Influences of phase composition on Sr3SiOs：Eu2＋ luminous performance

α’-Sr2SiO4 :Eu2+ phase always coexists with the Sr3SiO5:Eu2+ phase when it is synthesized by a high-temperature solid-state method. This may affect the luminescent properties of the Sr3SiO5:Eu2+ phosphors. We investigated the decomposition reaction of Sr3SiO5 during the cooling process with the quenching method. The results indicated that Sr3SiO5 was a stable compound above 1250 ℃. The Sr3SiO5 phase decomposed into α’-Sr2SiO4 and SrO below 1250℃. The α’-Sr2SiO4 :Eu2+ phase would coexist with the Sr3SiO5:Eu2+ phase because of the decomposition reaction of Sr3SiO5 , making the luminescent wavelength of coexistence sample move to the short-wavelength compared with the luminescent wavelength of Sr3SiO5:Eu2+. Pure phase Sr3SiO5:Eu2+ could be obtained by the rapid cooling method to suppress Sr3SiO5 decomposition. When the cooling rate was 20℃/min, nearly pure phase Sr3SiO5:Eu2+ could be produced.     

Factors affecting afterglow properties of red-emitting phosphor MgSiO3：Mn^2＋,Nd^3＋ for luminescent fiber

With stable physical properties,the rare-earth silicate phosphor of MgSiO3:Mn2+,Nd3+ is one of the suitable luminescent materials used in preparing functional fibers.In order to promote the afterglow properties of red-emitting phosphors,we prepared it by means of solid-state reaction,and the effect of manufacturing elements including H3BO3 and environmental factor of calcining temperature,type of flux on its luminescence property were investigated through evaluating their afterglow properties.The results showed that with the concentration of Nd 3+ increasing,the amounts of H3BO3 doping and calcining temperature,the afterglow time and initial brightness of the rare-earth silicate phosphor increased and then decreased gradually.The afterglow properties of different flux concentration were different from one to another as:H3BO3 >Na+>K+>No flux.     

Effect of different dopants on the long lasting phosphorescence behavior of CaTiO_3：Pr~（3＋）

In order to improve the luminescence properties of CaTiO3:Pr3+, a series of CaTiO3:Pr3+, such as CaTi0.97Nb0.03O3:Pr3+, Ca0.8Zn0.2TiO3: Pr3+, Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ and B3+-doped Ca0.8Zn0.2Ti0.97Nb0.03O3: Pr3+ were prepared through conventional solid state reaction method. The results of the photoluminescence excitation and emission spectra showed that all the samples emitted red phosphorescence at 612 nm originating from 1D2 to 3H4 emission of Pr3+ under the 337 nm excitation. When examined by the X-ray diffraction (XRD), all the samples presented a predominant phase of CaTiO3 (JCPDS# 42-423) except Zn2+-doped samples which also revealed another phase of Zn2Ti3O8 (JCPDS# 73-579). The results of the afterglow decay curves showed that co-doping Zn2+ ions, Nb5+ ions or adding a small amount of B3+ into Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ were effective in improving the photoluminescence properties of CaTiO3:Pr3+ phosphor. Thermoluminescence results showed that the trap existing in all the samples was the same as in CaTiO3:Pr3+ and doping singly Nb5+ or Zn2+ hardly changed the trap depth but co-doping Nb5+ and Zn2+ could modify the trapping level from 0.63 to 1.26 eV distinctively. In addition, adding a certain amount of B3+ into CTO-PZN could also deepen the trap depth.     

Yellow upconversion luminescence in Ho3＋/yb3＋ co-doped Gd2Mo3O9 phosphor

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 soli...