Electron migration in BaFCl:Eu2+ phosphors

Here we report the electron migration by photo- or thermostimulation in BaFCl:Eu2+. Electrons released from F centers may be trapped by other defect sites to form F aggregates or another type of F center and vice versa. This migration reduces the photostimulated luminescence efficiency, lowers the imaging plate sensitivity, and causes the difference between the optical absorption and photostimulation spectra of color centers. (C) 1997 American Institute of Physics.

Photoluminescence and photostimulated luminescence of BaFBr:Eu2+,Eu3+

In the photoluminescence (PL) of BaFBr:Eu2+,Eu3+, the emissions of Ea(2+), carrier electron-hole (e-h) recombination, and Eu3+ are observed, while in the photostimulated luminescence (PSL) only the emission of Eu2+ is exhibited. This disappearance of e-h recombination in PSL is considered to be caused by carrier migration during photo-stimulation. (C) 1997 American Institute of Physics.

Photostimulated luminescence of BaFBr:Eu2+ phosphors

After x-irradiation for 10 s, luminescence from BaFBr:Eu2+ phosphors by photostimulation of longer wavelength than F absorption bands was observed and assigned to the surface states or intrinsic defects of the powders. It is found that the luminescence by photostimulation into F bands can be reduced via electron migration from F centers into the surface states or intrinsic defects, thus reducing the x-ray storage or image stability. Surface passivation can lower these defects and improve the phosphors or imaging plate quality. (C) 1996 American Institute of Physics.

BaFi:Eu���2������������������������������������������

���2010-11-23������������

BaFI:Eu���2������������������������������������

������������������������,������������������������������������������

Reduction of Eu3+ to Eu2+ in MAl2Si2O8 (M = Ca, Sr, Ba) in air condition

In general, the reduction of Eu3+ to Eu2+ in solids needs an annealing Process in a reducing atmosphere. in this paper, it is of great interest and importance to find that the reduction of Eu3+ to Eu2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl2Si2O8 (M = Ca, Sr, Ba) just in air condition. The Eu2+-doped MAl2Si2O8 (M = Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong hand emissions of 4f(6)5d(1)-4f(7) from Eu2+ were observed at 417, 404 and 373 nm in air-annealed CaAl2Si2O8, SrAl2Si2O8 and BaAl2Si2O8, respectively, under ultraviolet excitation although the Eu3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu2+-doped MAl2Si2O8 also shows strong blue or ultraviolet emission corresponding to 4f(6)5d(1)-4f(7) transition.

Luminescent properties of a new blue long-lasting phosphor Ca2P2O7:Eu2+, Y3+

A new pyrophosphate long-lasting phosphor with composition of Ca1.96P2O7:0.02Eu(2+), 0.02Y(3+) is synthesized via the high-temperature solid-state reaction method. Its properties are systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphor emits blue light that is related to the characteristic emission of Eu2+ due to 5d-4f transitions. For the optimized sample, bright blue long-lasting phosphorescence (LLP) could be observed by naked eyes even 6 h after the excitation source is removed. The TL spectra show that the doping of Y3+ ions greatly enhanced intensity of 335 K peak and created new TL peak at about 373 K that is also responsible for the blue LLP. Based on our study, Y3+ ions are suggested to act as electron traps to improve the performance of the blue phosphorescence of Eu2+ such as intensity and persistent time.

novel blue-emitting long-lasting proyphosphate phosphor Sr2P2O7:Eu2+, Y3+

By introducing the Y3+ into Sr2P2O7:Eu2+, we successfully prepared a kind of new phosphor with blue long-lasting phosphorescence by the high-temperature solid-state reaction method. In this paper, the properties of Sr2P2O7:Eu2+, Y3+ were investigated utilizing XRD, photoluminescence, luminescence decay, long-lasting phosphorescence and thermoluminescence (TL) spectra. The phosphor emitted blue light that was related to the 4f(6)5d(1)-S-8(7/2) transition of Eu2+. The bright blue phosphorescence could be observed by naked eyes even 8 h after the excitation source was removed. Two TL peaks at 317 and 378 K related to two types of defects appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.61 and 0.66 eV. Also, the mechanism of LLP was discussed in this report.

Sr3Al2O5Cl2:Ce3+,Eu2+: A potential tunable yellow-to-white-emitting phosphor for ultraviolet light emitting diodes

The Sr3Al2O5Cl2:Ce3+,Eu2+ phosphors were prepared by solid state reaction. The obtained phosphors exhibit a strong absorption in the UV-visible region and have two intense emission bands at 444 and 609 nm. The energy transfer from the Ce3+ to Eu2+ ions was observed, and the critical distance has been estimated to be about 24.5 A by spectral overlap method. Furthermore, the developed phosphors can generate lights from yellow-to-white region under the excitation of UV radiation by appropriately tuning the activator content, indicating that they have potential applications as an UV-convertible phosphor for white light emitting diodes.

Preparation of SrAl2O4:Eu2+, Dy3+ fibers by electrospinning combined with sol-gel process

One-dimensional SrAl2O4:Eu2+, Dy3+ fibers were fabricated by a simple electrospinning combined with sol-gel process. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence were used to characterize the fibers. The results show that the phase structure of SrAl2O4:Eu2+, Dy3+ belongs to a monoclinic one, the composite fibers and fibers calcined at high temperature remain the original one-dimensional texture, and the SrAl2O4:Eu2+, Dy3+ was a green emission. (C) 2010 Elsevier Inc. All rights reserved.

Long lasting phosphorescence of Eu2+ in reduced SrO-B2O3 glasses

The blue long-lasting phosphorescence (LLP) phenomenon was observed for Eu2+-doped SrO-B2O3 glasses prepared in the reducing atmosphere. The phosphorescence peaks at about 450 nm due to the 4f5d -> 4f transition of Eu2+. With the doping of different amounts of Eu2+, the concentration-quenching phenomenon was observed for both the LLP and photoluminescence of the glasses, and the critical concentration for the two cases was same, i.e., 0.02 mol% Eu2+. And by the investigation of the TL curves, the content of Eu2+ had an effect on the trap depth of the samples. At last the possible mechanism of the LLP of the samples was suggested.

Study on stimulated emission of Eu2+ in crystal KMgF3 : Eu2+

The line emission peak of Eu2+ ion in crystal KMgF3 is at 360 nm. The probability of stimulated emission on 4f(7) (P-6(7/2))-> 4f(7)(S-8(7/2)) transition was predicted with a four-level decay model of Eu2+6P7/2 excited states proposed by the authors. Optic gain and net gain coefficient (g = 11.4 +/- 3.2)cm(-1) of 360 nm emission in crystal KMgF3 : Eu2+ were measured by ASE method, and the predication was proved by experiment. The net gain coefficient can be increased by annealing or doping crystal KMgF3 : Eu2+ with Gd3+ or Ce3+.

Reduction from Eu3+ to Eu2+ in BaAl2O4 : Eu phosphor prepared in an oxidizing atmosphere and luminescent properties of BaAl2O4 : Eu

A reduction phenomenon of Eu3+ -> Eu2+ was observed for the first time when Eu3+ ions were doped into an AlO4-tetrahedron-containing compound BaAl2O4 in an oxidizing atmosphere of air by high-temperature solid-state reaction. X-ray powder diffraction patterns and photoluminescent spectra are used to confirm the compound structure and detect the simultaneous existence of both divalent and trivalent europium ions, respectively. The abnormal Eu3+ -> Eu2+ reduction is explained by a charge compensation model. Spectroscopic properties of BaAl2O4:Eu are discussed and Eu2+ emission spectrum shows consistence with the results reported by Katsumata et a]. [J. Cryst. Growth 198/199 (1999) 869.] and Lin et al. [Mater. Chem. Phys. 70 (2001) 156.].