Synthesis of Long Afterglow Phosphors MAl_2O_4∶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.

Synthesis of SrAl_2O_4:Eu^(2+),Dy^(3+) phosphors by the coupling route of microemulsion with coprecipitation method

Nano-sized SrAl2O4：Eu^2＋,Dy^3＋ phosphors with good monodispersity and narrow size distribution were synthesized by the coupling of water-in-oil （W/O） microemulsion with coprecipitation method. The phase composition, morphology, crystallinity, excitation spectra, emission spectra, and afterglow decay of SrAl2O4：Eu^2＋,Dy^3＋ nanophosphors were measured. It was found that the amount of surfactant that was used had an important effect on the shape and average size of the phosphor particles. SrAl204 phase of the phosphors showed an increase with the increase in calcination temperature. When the calcination temperature reached 1150℃, the fine crystal of SrAl2O4 was formed and the long afterglow luminescence could be obviously observed. In comparison with the samples prepared by the high-temperature solid-state method, the calcination temperature showed an obvious decrease and a dear blue shift occurred in the excitation and emission spectra of the sample. The afterglow time could be more than 8 h.

SrAl_2O_4∶Eu^(2+),Nd^(3+) and Dy^(3+) Long Afterglow Phosphor

The SrAl 2O 4∶Eu 2+ , Nd 3+ and SrAl 2O 4∶Eu 2+ , Dy 3+ long afterglow phosphor were synthesized. Their excitation and emission spectra at different excitation and afterglow characteristics were analyzed after the excitation power was taken off. The effects of Eu 2+ , Dy 3+ , Nd 3+ mole concentrations on phosphorescence characteristics were also discussed. It is crucial to have trapping levels located at a suitable depth related to the thermal release rate at room temperature. The incorporation of Nd 3+ ions as an auxiliary activator into the SrAl 2O 4∶Eu 2+ system causes very intense and long phosphorescence. The response time of SrAl 2O 4∶Eu 2+ , Dy 3+ phosphors is quicker than that of SrAl 2O 4∶Eu 2+ , Nd 3+ . Phosphorescence characteristics of SrAl 2O 4∶Eu 2+, Nd 3+ is much better than those of SrAl 2O 4∶Eu 2+ , Dy 3+ . The integrate area of the excitation spectrum of SrAl 2O 4∶Eu 2+ , Nd 3+ phosphor is larger than that of SrAl 2O 4∶Eu 2+ , Dy 3+ phosphor within the range of 250～360 nm. For phosphorescence characteristics to the system of SrAl 2O 4∶Eu 2+ , Nd 3+ phosphor, the optimum concentration of Nd 3+ trivalent rare earth ions is 0.05 mol.

Quenching Study on Iron Impurity in Eu^(2+), Dy^(3+) Doped Strontium Aluminate Phosphor Prepared by Nano-Coating Process

A series of long afterglow phosphors, Eu2+, Dy3+, with different iron content were prepared by nano-coating process. The resulted precursors were characterized by Transmission Electron Microscope (TEM), which suggested that the precursor particles had nanometer size distribution. The optical quenching of iron impurity on the phosphor powders were investigated by X-Ray powder Diffraction (XRD) and photoluminescence methods. The XRD indicates that a pure monoclinic SrAl2O4∶Eu2+, Dy3+ was formed at 1200 ℃ and iron impurity up to 296.36×10-4% had no effect on the SrAl2O4∶Eu2+, Dy3+ phase structure. However, the luminescence intensity were strongly dependent on the trace iron impurity, which might be explained that iron displace the aluminium and form Fe-O bond, which competed energy with Eu2+ and transfer red them to infrared sites.

Interaction of Rare Earth Ions in Sr2MgSi2O7：Eu^2＋,Dy^3＋ Material

To discuss the function of Eu and Dy and their interaction in Sr2 Mg Si2O7：Eu^2＋,Dy^3＋ long afterglow material,the Eu and Dy single doped and their co-doped Sr2 Mg Si2O7：Eu^2＋,Dy^3＋ were prepared.The samples were characterized by X-ray diffraction（XRD）,decay curves,photoluminescence（PL）,and thermoluminescence（TL）.The results indicate that Sr2 Mg Si2O7：Eu has afterglow properties,and the doping of Eu ion in Sr2 Mg Si2O7：Eu^2＋,Dy^3＋ can lower the depth of traps.Eu ion can not only serve as luminescence center,but also produce traps in the matrix,meanwhile,it also exerts certain influences on the traps produced by Dy in Sr2 Mg Si2O7：Eu^2＋,Dy^3＋.The Dy ion can not act as luminescence center but relates to the change of the traps in the Sr2 Mg Si2O7 matrix.

Enhancement of luminescence and afterglow in Ca_(0.8)Zn_(0.2)TiO_3:Pr^(3+) by Nb^(5+) substitution for Ti^(4+)

Nb5＋ doped Ca0.8Zn0.2TiO3：Pr3＋ red long afterglow phosphors were synthesized by solid-state reaction methods. X-ray diffraction, photoluminescence spectroscopy and thermally stimulated spectrometry were used to investigate the effects of Nb5＋ content on the crystal characteristics and luminescent properties of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors. The results showed that the addition of a small quantity of Nb5＋ had negligible effect on the crystal characteristics of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋, but it could change the trapping parameters （the depth of trap, frequency factors and the concentration of trapped charges at t=0） of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors, and then led to the enhance-ment of red fluorescence and phosphorescence at 612 nm originating from 1D2→3H4 transition of Pr3＋. Both of the red fluorescence intensity and afterglow time reached the largest values in the sample of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ with x=0.05. The afterglow time of Ca0.8Zn0.2Ti0.95Nb0.05O3：Pr3＋ phosphors lasted for over 24 min （≥1 mcd/m2） when the excited source was cut off.

A novel long lasting phosphor Sr5 （PO4）3FxCll_x：Eu2＋,Gd3＋ prepared in air condition

A series of blue long afterglow mixed halide-phosphate phosphors Sr5 （PO4）3 FxCll-x：Eu2＋,Gd3＋ were synthesized in air by traditional solid-state reaction routte. The crystal structures, photoluminescence, thermolurninescenee properties and afterglow proper- ties of the phosphors were characterized systematically using X-ray diffraction （XRD）, luminescence spectrophotometer, microcom- puter thermoluminescence dosimeter and single photon counter, respectively. Under 280 nm excitation, the broadband emissions of Eu2＋ ions were observed at 445 nm （blue） due to the 4f7→4f65d transition. It was demonstrated that there existed the self-reduction of the Eu3＋ to Eu2＋ ions in this special halide-phosphate matrix in air condition. The addition of Gd3＋ ions obviously enhanced the after- glow properties of the single doped Eu2＋ ions in the halide-phosphate phosphors. And the content of the fluoride anions also had sig- nificant influence on the afterglow properties. All results indicated that Srs （PO4）3 FxCI1-x：Eu2＋,Gd3＋ might be potential phosphors for long lasting phosphorescence （LLP） materials.

Investigation on luminescence properties of Ln^(3+) doped Sr_3EuMgSi_2O_8 (Ln=Dy,Er,Ho)

The luminescent properties of Sr2.97MgSi2O8：Eu^2＋0.1 phosphors were investigated with different Ln^3＋0.02（Ln^3＋： Dy^3＋, Er^3＋, Ho^3＋） 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 Dy^3＋ co-doped sample was longer than that of the others. Furthermore, the co-doping samples had stronger thennolmninescence （TL） intensity and therefore longer afterglow duration. At last, the self-reduction of Eu^3＋→Eu^2＋ was observed in an silicate compound of Sr3 xMgSi2Os：xEu phosphor in air condition. This is the first time to show a blue long afterglow phosphor synthesized avoiding reducing atmosphere.

Synthesis and characterization of Ca0.9Mg0.1TiO3：Pr3＋,Ag＋ phosphor

Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observed by X-ray powder diffractometer（XRD）, transmission electron microscope（TEM）, photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~＋ can diminish in the crystal particle sizes of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）. Because Ag＋ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ is 2.3 times as high as that of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）at the same preparation condition. The effect of Ag＋ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_（0.9）Mg_（0.1）TiO_3 to Pr^（3＋）. The persistent afterglow properties of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ are better than those of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋） at the same preparation condition. In conclusion,Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphor with molar ratio of Ag~＋to Pr^（3＋） 3：1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.