Synthesis and Luminescence Properties of Gd2O3：Eu^3＋ Phosphors

Gd2O3: Eu^3 phosphors were prepared by urea homogeneous precipitation with different surfactant and sol-gel method. XRD patterns show that all the obtained samples are in cubic Gd2O3, and the results of FTIR and fluorescent spectra conformed that OP is a good surfactant for preparing the Gd2O3:Eu^3 phosphors. The SEM photographs show that the particles prepared by urea homogeneous precipitation method are all spherical and well-dispersed, and grain morphology can be controlled by different surfactant. XRD and SEM indicate that the particle sizes prepared by sol-gel method are in the range of 5-30 nm, and the grain sizes increase with increasing of heated temperatures. Luminescence spectra indicat that the main emission peaks of all samples are at 610 nm, the intensities are different from samples prepared with different surfactant and the luminescence intensities increase with increasing of annealed temperatures.     

Adjustable Luminescence of SrAl2O4：Eu^2＋ , Dy^3＋ Assembled in Zeolite

Capsulating guest into the nanometer yoids of zeolites is a effective way to form novel host-guest material. In our work, stoichiometric SrAl2O4: Eu^2 , Dy^3 sol guest was prepared by sol-gel method and assembled into the nanometer channels of zeolite ZSM-5 host through mechanical mixing, hydrothermal reaction and microwave heating reaction, respectively. After being reduced and diffused in a microwave muffle, the fluorescence spectra of the host-guest materials exhibit remarkable blue shifts in comparison of that of SrAl2O4 : Eu^2 , Dy^3 . Some interesting phenomena in the assembled hostguest materials are that the after-glow emission spectra exist two bands at about 400 nm and 517 nm and the relative strengths of these two bands can be adjusted by changing the assembly methods and the assembly concentration. These are attributed to the fact that the phosphor was capsulated into the voids of zeolite ZSM-5 and generated the quantum size effect and the host-guest effect.     

Long-Lasting Properties of Rare Earth-Doped Y2O2S Phosphors

The aim of this presentation is to report a new result of afterglow materials. The Y2O2S:Ln^3 (Ln = Sm, Tm)phosphors show bright reddish orange and orange-yellow colors when excited by UV or visible light. The main spectroscopic characterizations of Sm^3 and Tm^3 in yttrium oxysulfide and their long-lasting phosphorescence were measured and discussed in this presentation. Their long-lasting phosphorescence can be seen by the naked eyes clearly for about one hour in the dark room after the irradiation light sources were removed. XRD and photoluminescence (PL) spectra as well as the luminance decay were used to characterize these long-lasting phosphorescence phosphors. The results of XRD indicate that the products synthesized through the flux fusion method under 1050℃ for 6 h have a good crystallization without any detectable amount of impurity phase. Both the PL spectra and luminance decay results reveal that these phosphors have efficient luminescent and good long-lasting properties. We believe that the experimental data gathered in our present work will be useful in finding some new long-lasting phosphors with different colors.     

Study on Luminescence Properties and Crystal-Lattice Environment of Eu^2＋ in Sr4-xMgxSi3O8Cl4：Eu^2＋ Phosphor

According to the Van Uitert experimental equation, crystal-lattice environment of Eu^2 in the Sr4Si3O8C14 crystal was discussed. By adding Mg^2 to the host lattice, Sr4-xMgxSi3O8C14:Eu^2 was synthesized and the emission peak shifted from blue-green (488nm) to blue-violet (411nm) with the increase of amount of the magnesium which replaced the strontium. By analyzing the spectra of Sr4-xMgxSi3O8C14:Eu^2 the two Eu^2 emission centers were found because of the change of crystal-lattice environment in the host and the crystal structure was obtained by X-ray diffraction data.     

Preparation and Long Persistence Red Luminescence of M0.2Ca0.8TiO3 ： Pr^3＋ （M = Mg^2＋ , Sr^2＋ , Ba^2＋ , Zn^2＋）

M0.2Ca0.8TiO3 : Pr^3 (M = Mg^2 , Sr^2 , Ba^2 , Zn^2 ) long persistence red phosphors were prepared by solid state reaction. The influence of the partially replacing Ca^2 in CaTiO3 with Mg^2 , Sr^2 , Ba^2 , Zn^2 on the excitation spectra, the emission spectra and the long persistence properties were studied. The results suggest that certain quantity of Mg^2 , Sr^2 , Ba^2 , Zn^2 which partially replace Ca^2 can enhance the luminescent intensity and prolong the afterglow persistence of the samples. The intensity of Mg0.2Ca0.8TiO3: Pr^3 is above all of the samples. Take Mg0.2Ca0.8TiO3:Pr^3 as the basic sample, the influence of Pr^3 concentrations (C (Pr^3 )) on the long afterglow properties were also studied.The results suggest that when the C (Pr^3 ) is 0.10% (tool fraction) the intensity of the sample is the highest. The excitation spectra of all these samples show broad band spectra ranging from 300 - 500 nm peaking at about 342 nm. The emission spectra also exhibit a broad band peaking at 613 nm (CaTiO3: Pr^3 is 612 nm). XRD research indicates that the crystalline phases change due to the replacement of divalent metal ions. The research on the thermoluminescence spectra of Mg0.2Ca0.8TiO3:Pr^3 indicates that the peak is at 107.35℃ and the depth of the trap energy is about 0.852 eV.     

Effects of Doping Trace Sm^3＋ and Gd^3＋ on Luminescent Character of Y2O2S：Eu^3＋

After trace Sm^3＋ ions and Gd^3＋ ions doping, the emission intensity of red phosphors Y2O2S： Eu^3 ＋ was enhanced and the voltage character （relation between emission intensity and excitation voltage） was improved while the other properties of physics and chemistry were not changed. The origins of enhancement and improvement are discussed. Probably the distortion and the defect of crystals are decreased by the substitution of Gd^3＋ for Y^3＋ instead of Eu^3＋ for Y^3＋ , and thus the Eu^3＋ crystal field is improved, and radiationless process and energy loss resulted from crystal defect are weakened, which leads to increased luminescence intensity and voltage character improvement. The overlapping fluorescent spectra of Y2O2S： Sm^3＋ emission and Y2O2S：Eu^3＋ excitation as well as Eu^3 ＋ excitation spectra transitions spectra lead to energy transfer from Sm^3 ＋ sensitization of Sm^3＋ ions fectively. containing Sm^3＋ excitation the possibility of resonance ions to Eu^3＋ ions, and the to Eu^3＋ ions is achieved effectively.     

Preparation of Non-Grinding Long Afterglow SrAl2O4 ：Eu^2＋ , Dy^3＋ Material by Microwave Combustion Method

The non-grinding long afterglow material SrAl2O4：Eu^2＋ , Dy^3＋ was prepared by combustion method in home mierowave oven direetly, after dispersant, frother, eomburent, and mineralizer were added into the reacting system. XRD analysis showed that the powders were nearly pure SrAl2O4 phase with few other phases, and the size of the grain was 41.1 nm. Fluoreseenee speetrum results indieated that there were 2 exeitation peaks loeated at 345 and 400 nm, and the emission peak loeated at 516 nm, afterglow lasted up to 30 min or more. The mierowave eombustion method has advantages of less time, low temperature and no grinding process, and the material made by the method has good luminescent property.     

Study on Luminescence Properties of High-Density Phosphors BiTaO4：Pr^3＋ and BiTaO4

The photoluminescence properties of BiTaO4:Pr^3 and BiTaO4 at room temperature were studied, and the infrared transmission and diffusion reflection spectra of BiTaO4 were measured. The photoluminescence spectrum of BiTaO4 peaks at about 420, 440 and 465nm. There has an obvious excitation band from 330 to 370nm. The photoluminescence spectrum of BiTaO4:Pr^3 consists of the characteristic emission of Pr^3 , and its main peak is at 606 nm from ^3P0→^3H6 transition of Pr^3 . Its excitation spectrum consists of the wide band with maximum at 325nm, the wide band in the range of 375-430nm, and the characteristic excitation of Pr^3 .The bands at 325nm and 375-430nm may be from the absorption of the charge transfer transition of the tantalate group and defect energy levels in its forbidden band, respectively.There is energy transfer from host to Pr^3 . Because both the host density and photoluminescence peak intensity of BiTaO4:Pr^3 are superior to PbWO4, BiTaO4:Pr^3 may be a potential heavy scintillator.     

VUV Spectroscopy of GdPO4： Eu^3＋ and GdBO3： Eu^3＋

The emission and the excitation spectra of GdPO4 ： Eu^3＋ and GdBO3： Eu^3 ＋ prepared by solid state reaction method were investigated using the synchrotron radiation source of SUPERLUMI station of HASYLAB. The energy transfer between Gd^3＋ and Eu^3＋ was discussed with the probability of quantum cutting process. In the excitation spectra monitoring the red emission from Eu^3＋ , the distinct lines corresponding to the intraconfigurational 4f-4f transitions from Gd^3＋ were observed for both samples, indicating an efficient energy transfer from host Gd^3＋ ions to the doped Eu^3＋ ions. The efficient energy transfer is necessary for the quantum cutting process based on the two-step energy transfer from Gd^3＋ to Eu^3＋ . However, the overlapping of the lines corresponding to Gd^3＋ ：^8S7/2→^6GJ and the broad excitation band （180 - 270 nm） due to Eu^3＋- O^2- charge transfer states （CTS） around 200 nm cause excitation energy on ^6GJ levels to dissipate into CTS by direct energy transfer, unfavorable to the cross relaxation energy transfer between Gd^3＋ and Eu^3＋, thus unfavorable to the quantum cutting process. With the help of the general rules governing the energy positions of Eu^3＋-O^2- ：CTS, the suggestions concerning searching suitable oxide hosts for Gd^3＋-Eu^3＋ quantum cutting were made.     

Luminescence Properties of （ Y, Gd） Al3 （BO3） 4 ： Eu^3＋ under VUV excitation

(Y, Gd)Al3 (BO3)4:Eu^3 samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd^3 mole concentration in the range of 0.15 to 0.85 mol (and Eu^3 mole concentration, 0.02 to 0. 1 mol). The correlative data show that the concentration quenching occurs when the Eu^3 mole concentration ranges from 0.02 to 0.1 mol, and the Gd^3 →Gd^3 , Gd^3 →Eu^3 and host→Eu^3 , Gd^3 energy transfers exist, and Gd^3 mole concentration influences Eu^3 emission.     

Luminescence Properties of Eu^2 ＋ and Mn^2 ＋ Co-Doped CasMg（SiO4）4Cl2

The green phosphor for white LED, Ca8Mg(SiO4)4C12:Eu^2 , Mn^2 , was synthesized by high temperature solid state reaction under reducing atmosphere. During the process of the phosphor prepared, the excess CaC12 can improve the intensity of emission. The experimental results indicate that there is an effective energy transfer from Eu^2 to Mn^2 in Ca8Mg(SiO4)4Cl2 host. This kind of energy transfer may be due to resonance transfer, and this energy transfer is limited     

Preparation of CaS：Eu^2＋ , Sm^3＋ by Solid Reaction Method and Its Photostimulated Luminescence

The CaS:Eu^2 , Sm^3 powders were prepared by high-temperature solid method in a reducing atmosphere. The influences of temperature and fired-time on properties of samples were studied. XRD analysis shows that crystal structure of CaS has formed at 700℃. Spectrum analysis results show that the samples which were stimulated by 980 nm laser after excited by ultraviolet lamp emit red luminescence peaking at 649 nm.     

Study on UV Excitation Properties of Eu^3＋ at S6 Site in Bulk and Nanocrystalline Cubic Y2O3

Increases of emission intensities for Eu^3 at the S6 site relative to that at the C2 site were observed as UV excitation wavelength decreases from 300 nm to 200 nm in both bulk and nanocrystalline cubic Y2O3:Eu^3 . Decomposition of excitation spectra shows that the charge transfer band of Eu^3 at the S6 site lies in the high-energy side of that at the C2 site, resulting in that the energy transfer from the host prefers to the S6 site. Detailed emission and excitation spectral characteristics were analyzed and discussed. In addition, spectral red-shift were found in both charge transfer bands in nanocrystalline Y2O3: Eu^3 compared to the bulk material. The number ratio of S6 sites to C2 sites is also smaller in nanocrystalline Y2O3:Eu^3 than that in the bulk one.     

Preparation and characterization of flower-like SrAIeO4：Eu^2＋,Dy^3＋ phosphors by sol-gel process

A flower-like Eu²⁺ and Dy³⁺ co-doped SrAl₂O₄ long-lasting phosphorescent (LLP) phosphor was synthesized via the inorganic- salt-based sol-gel method. The crystal structure, morphology and optical properties of the composite were characterized. X-ray diffraction diffusion (XRD) data and DSC-TG curves of the phosphor revealed that the SrAl₂O₄ crystallites have been formed after the precursor was calcined at 900 °C and to be single-phase SrAl₂O₄ at 1100 °C. The SEM photographs indicated that the sample exhibited a universal flower-like morphology with crystallite size of about 1-2 μm. After being irradiated with ultraviolet (UV) light, the flower-like phosphor emitted long-lasting green phosphorescence with an excitation peak at 365 nm and emission peak at 500 nm which was ascribed to the characteristic 5d-4f transition of Eu²⁺. Both the PL spectra and the luminance decay curve revealed that this phosphor exhibited efficient luminescence and long lasting properties.     

Luminescence Properties of Green-Emitting Phosphor （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ for White LEDS

The （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ green-emitting phosphors were synthesized by conventional solid-state reaction in a CO-reductive atmosphere, and their luminescent properties were investigated. The XRD data show that the Ba/Sr ratio not only affects the lattice parameters, but also influences the emission peak. The excitation spectra indicate that this phosphor can be effectively excited by UV light from 370 to 470 nm. The emission band is due to the 4f^65d^1→4f^7 transition of the Eu^2＋ ion. With an increase in x, the emission band shifts to longer wavelength and the reason was discussed. The emission spectra exhibit a satisfactory green performance under different excitation wavelength（380,398,412,420,460 nm）. （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ is a promising phosphor for green white-lighting-emission diode by ultraviolet chip.     

Preparation and Luminescence Properties of the New Long Phosphorescent Phosphors Ba_(1-x)Ca_xAl_2O_4∶Eu ~(2 ), Dy~(3 )

Inrecentyears ,SrAl2 O4 ∶Eu2 ,Dy3 ,CaAl2 O4 ∶Eu2 ,Nd3 [1～ 8] andBaAl2 O4 ∶Eu2 ,Dy3 [9]havebeenconsideredasusefulblueandgreenphos phorsbytheirlongdurationphosphorescence .Howev er ,toourknowledge ,thephosphorBa1-xCaxAl2 O4 ∶Eu2 ,Dy3 hasnotbeeninvestigated .TheluminescenceofEu2 isverystronglydepen dentonthehostlattice ,whichcanoccurfromtheul traviolettotheredregionoftheelectromagneticspec trum .Itiswellknownthatthepersistentluminescenceisduetothetrappingofenergyinthed…     

Synthesis of Long Afterglow Phosphors MAI204：Eu^2＋ , Dy^3＋ （M=Ca, Sr, Ba） by Microemulsion Method and Their Luminescent Properties

Long afterglow phosphors MAl2O4：Eu^2＋ , Dy^3＋ （M = Ca, Sr, Ba） were synthesized by microemulsion method, and their crystal structure and luminescent properties were compared and investigated. XRD patterns of samples indicate that phosphors CaAl2O4：Eu^2＋, Dy^3＋ and SrAl2O4 ： Eu^2＋, Dy^3＋ are with monoelinie crystal structure and phosphor BaAl2O4：Eu^2＋ , Dy^3＋ is with hexagonal crystal structure. The wide range of excitation spectrum of phosphors MAl2O4： Eu^2 ＋ , Dy^3＋ （M = Ca,Sr, Ba） indicates that the luminescent materials can he excited by light from ultraviolet ray to visible light and the maximum emission wavelength of phosphors MAl2O4：Eu^2＋ , Dy^3＋ （M = Ca, Sr, Ba） is found mainly at λem of 440 nm （M = Ca）, 520 nm （M = Sr） and 496 nm （M = Ba） respectively, the corresponding colors of emission light are blue, green and eyna-green respectively. The afterglow decay tendency of phosphors can he summarized as three processes： initial rapid decay, intermediate transitional decay and very long slow decay. Afterglow decay curves coincide with formula I = At^ - n, and the sequence of afterglow intensity and time is Sr 〉 Ca 〉 Ba.     

（Zn, Ca） Solid-Solution Behavior and Its Effect on Luminescence Properties in Ca1-x Znx TiO3 ： 0.002Pr^3＋ Phosphors

Nominal composition of Ca1-xZnxTiO3 ： 0. 002Pr^3 ＋ （x = 0. 000 - 0. 200） phosphors were prepared by conventional solid reaction route. XRD and PL measurements were used to investigate the solid-solution structure and luminescence properties of Zn-doped Ca1-xZnxTiO3：0.002Pr^3＋ phosphors. The effect of solid-solution structure formed by substitution between Ca^2 ＋ and Zn^2＋ ions on the luminescent properties was analyzed. The results reveal that, with the increase of Zn substitution content below 0.010, lattice parameters and the intensity of excitation peak at both 260 and 330 nm as well as the corresponding 610 nm emission intensity are monotonously decreased quickly in a similar tendency. Also, the evolution of luminescence intensity and crystal cell parameters against Zn doping concentration are in good agreement. Above results are closely related with the structure change within Ca1- xZnxTiO3：0.002Pr^3＋ solid-solution phase formed by the Zn ions substitution for the Ca sites. Present study reveals that the solid-solution structure formed by substitution between Ca^2＋ and Zn^2＋ ions has significant effect on the luminescence properties of single phase Ca1-xZnxTiO3：0.002Pr^3＋ phosphors.