Crystal structure, photoluminescence and cathodoluminescence of Ba1-xCaxAl2O4 doped with Eu2+ (original) (raw)
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Crystal structure, photoluminescence and cathodoluminescence of Sr1-xCaxAl2O4 doped with Eu2+
Optical Materials Express
The crystal structure, photoluminescence and some cathodoluminescent spectra of Sr 0.99−x Ca x Eu 0.01 Al 2 O 4 (Eu 2+) are described. Five different phases have been found: three different monoclinic phases, one hexagonal and one cubic phase. Based on the cathodoluminescence of SrAl 2 O 4 :Eu 2+ at low temperature and photoluminescence of Sr 1−x Ca x Al 2 O 4 :Eu 2+ at 0 ≤ x ≤ 0.1, we consider an alternative explanation for the origin of the 440 nm peak in the low temperature spectrum of SrAl 2 O 4 :Eu 2+ , namely that it can be attributed to the emission from Eu 2+ ions situated on the alkaline earth sites of the monoclinic P2 1 /n structure that generate the 440 nm emission of CaAl 2 O 4. However, this alternative hypothesis has been eliminated by XRD analyses of SrAl 2 O 4 at low temperature.
Persistent luminescence of Eu 2+ and Dy 3+ doped barium aluminate (BaAl 2O 4:Eu 2+,Dy 3+) materials
Optical Materials, 2009
Polycrystalline Eu 2+ and Dy 3+ doped barium aluminate materials, BaAl 2 O 4 :Eu 2+ ,Dy 3+ , were prepared with solid state reactions at temperatures between 700 and 1500°C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500°C follow the formation of BaAl 2 O 4 composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu 2+ band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu 2+ ) and co-dopant (Dy 3+ ) concentrations affect the crystallinity and luminescence properties of the materials.
Synthesis and Photoluminescence of Eu3+-activated Ca3La2 (BO3)4 Phosphor
Polycrystalline Ca3La2(BO3)4 phosphor doped with rare-earth ions (Eu3+) were prepared by conventional solid state reaction method and the samples were sintered at 1200°c for 8 hours in air atmosphere. The structural characterisation was carried out by X-ray diffraction method (XRD). The Photoluminescence (PL) spectra investigated. The PL spectra indicate that the main emission peak at 611 nm under UV excitation due to 5D0→7F2 transition of Eu3+ ions. PL peak intensity was found to increase with increase in the dopant concentration. These phosphors may provide a new kind of luminescent material for light emitting diodes under uv excitation.
X-ray excited optical luminescence of Ce-doped BaAl2O4
Journal of Luminescence, 2012
The luminescence properties of Ce 3 þ in BaAl 2 O 4 are reported. The results of simultaneous measurements of XEOL and XAS in the X-ray energy range that includes the Ba L II,III-edges and Ce L III edge are shown. The XEOL yield increases as the energy of the photons increases. The radioluminescence spectra, taken from 200 to 1100 nm, showed broad emission bands corresponding to 5d 1-2 F 5/2 , 2 F 7/2 transitions of Ce 3 þ when incorporated into two nonequivalent Ba sites. The lifetime of the light emission was also measured using the single bunch operation mode at the Brazilian National Synchrotron Laboratory (LNLS), and BaAl 2 O 4 :Ce 3 þ showed single exponential decay time component of about 44.3 ns.
Journal of Luminescence, 2013
Sr 3 B 2 O 6 :Eu 2+ yellow phosphor was prepared by the combustion method. The crystalline structure, photoluminescence and thermoluminescence properties of Sr 3 B 2 O 6 :Eu 2+ were investigated extensively. The X-ray diffraction result indicates that the Sr 3 B 2 O 6 :Eu 2+ phosphor exhibited a rhombohedral crystal structure. The emission spectra under a 435 nm excited wavelength showed an intense broad band peaking at 574 nm, which corresponds to the 4f 6 5d 1 → 4f 7 transition of Eu 2+ ion. There were two different sites of Sr replaced by Eu in host lattice. The concentration quenching process between Eu 2+ ions is determined and the corresponding concentration quenching mechanism was verified as dipole-quadrupole interaction. The glow curve under 3 Gy βray irradiation had the glow peak at 160°C and the average activation energy was defined as about 0.98 eV.
Optical Materials Express
In this article the photoluminescence (PL) and cathodoluminescence (CL) of undoped BaAl 2 O 4 and BaAl 2 O 4 doped with 500 ppm and 3 mol% Eu 2+ is described. The most important results from the CL measurements are: (1) Undoped BaAl 2 O 4 manifested intrinsic CL at 460 nm, which increased at low temperature and did not change significantly upon exposure to the e-beam; (2) Doping BaAl 2 O 4 with Eu 2+ changed the character of the intrinsic luminescence band: it became more sensitive to temperature variations and the band experienced a blue shift to ∼425 nm; (3) electron beam (e-beam) exposure of Ba 0.97 Eu 0.03 Al 2 O 4 at low temperature increased the 425 nm band strongly while the Eu 2+ emission at ∼500 nm decreased by about 70%. The Eu 2+ emission band was symmetric, indicating that BaAl 2 O 4 :Eu has changed to the P6 3 22 phase upon e-beam exposure at low temperature; (4) We have identified the 460 nm band in undoped BaAl 2 O 4 and the 425 nm band in BaAl 2 O 4 :Eu 2+ with F-centre luminescence, corresponding to the F-centre emission in α-Al 2 O 3. The evidence for the assignment of the 425 nm band in BaAl 2 O 4 :Eu 2+ is the spectacular increase of the spectral radiance at 425 nm by e-beam exposure at 200 keV and low temperature. A preliminary model is presented that explains the results. The PL from BaAl 2 O 4 :Eu 2+ quenched at the rather low temperature of 140°C; this observation is explained in terms of thermal ionization of the Eu 2+ ion.
PHOTOLUMINESCENCE OF CaxBa1–xGa2S4 SOLID SOLUTIONS ACTIVATED BY Eu2+ IONS
We have studied the photoluminescence (PL) of CaxBa1–xGa2S4 solid solutions (x = 0.1, 0.2, 0.3, 0.4, and 0.5) activated by ions of the rare-earth element Eu2+ in the temperature range 10–300 K, due to 4f65d → 4f7 transitions in the Eu2+ ions. The photoluminescence spectra of CaxBa1–xGa2S4:Eu are located in the blue-green – green regions, and their maxima are shifted from 506 nm for x = 0.1 to 531 nm for x= 0.5. We show that the long-wavelength shift as Ca content increases is due to the increasing crystal fi eld, in the resence of which the 5d orbitals of the europium ions are split and consequently the energy of the recombination transitions decreases. We observed high temperature stability of the position of the photoluminescence spectra and the integrated intensity (decreasing by 13% for all x) in the temperature range 10–300 K. We have established that an increase in the Ca content in CaxBa1–xGa2S4:Eu leads to a decrease in the thermal shift of the photoluminescence, and for x = 0.5 there is no shift.
The structural and luminescence properties of chalcogenide semiconductor CaxBa1-xGa2S4 solid solutions (x = 0.1 – 0.9) doped with 7 at.% of Eu2+ ions were studied at room temperature. It was found, that the crystal structure of CaxBa1−xGa2S4 solid solutions varies with the amount of Ca2+ cations and phase transition from cubic to orthorhombic takes place with increase of x value. CaxBa1-xGa2S4:Eu2+ solid solutions exhibit intense photoluminescence in cyan to yellow spectral region depending on x due to 5d → 4f electron-dipole transitions in Eu2+ ions. The peak position of the emission band shifts from 506 nm for x = 0.1 to 555 nm for x = 0.9 and the full width at half maximum of the emission band varies from 62 nm to 72 nm depending on the symmetry of the crystal lattice. The PL excitation spectrum of CaxBa1-xGa2S4:Eu2+ covers the range at half maximum from 310 nm to 480 nm for x = 0.1 and to 520 nm for x = 0.9. It was shown that long-wavelength shift is caused by influence of the growing crystal field strength on Eu2+ ions.
Synthesis and characterization of BaAl 2O 4:Eu 2+ co-doped with different rare earth ions
Physica B-condensed Matter
Combustion method was used in this study to prepare BaAl2O4:Eu2+ phosphors co-doped with different trivalent rare-earths (Re3+=Dy3+, Nd3+, Gd3+, Sm3+, Ce3+, Er3+, Pr3+ and Tb3+) ions at an initiating temperature of 600 °C. The phosphors were annealed at 1000 °C for 3 h. As confirmed from the X-ray diffraction (XRD) data, both as prepared and post annealed samples crystallized in the well known hexagonal structure of BaAl2O4. All samples exhibited bluish-green emission associated with the 4f65d1→4f7 transitions of Eu2+ at ∼500 nm. Although the highest intensity was observed from Er3+ co-doping, the longest afterglow (due to trapping and detrapping of charge carriers) was observed from Nd3+ followed by Dy3+ co-doping. The traps responsible for the long afterglow were studied using thermoluminescence (TL) spectroscopy.
Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+
Physica B: Condensed Matter, 2014
The R 3 þ (rare earth) co-dopants may have a surprisingly important role in persistent luminescenceenhancement of up to 1-3 orders of magnitude may be obtained in the performance of these phosphor materialsdepending strongly on the R 3 þ ion, of course. In this work, the effects of the R 3 þ co-dopants in the BaAl 2 O 4 :Eu 2 þ ,R 3 þ materials were studied using mainly thermoluminescence (TL) and synchrotron radiation XANES methods. In BaAl 2 O 4 , the conventional and persistent luminescence both arise from the 4f 7-4f 6 5d 1 transition of Eu 2 þ , yielding blue-green emission color. The former, in the presence of humidity, turns to more bluish because of creation of an additional Eu 2 þ luminescence centre which is not, however, visible in persistent luminescence. The trap structure in the non-co-doped BaAl 2 O 4 :Eu 2 þ is rather complex with 4-5 TL bands above room temperature. With R 3 þ co-doping, this basic structure is modified though no drastic change can be observed. This underlines the fact that even very small changes in the trap depths can produce significant modifications in the persistent luminescence efficiency. It should be remembered that basically the persistent luminescence performance is controlled by the Boltzmann population law depending exponentially on both the temperature and trap depth. Some mechanisms for persistent luminescence have suggested the presence of either divalent R 2 þ or tetravalent R IV during the charging of the Eu 2 þ doped materials. The present XANES measurements on BaAl 2 O 4 :Eu 2 þ ,R 3 þ confirmed the presence of only the trivalent form of the R 3 þ co-dopants excluding both of these pathways. It must thus be concluded, that the energy is stored in intrinsic and extrinsic defects created by the synthesis conditions and charge compensation due to R 3 þ co-doping. Even though the effect of the R 3 þ co-dopants was carefully exploited and characterized, the differences in the effect of different R 3 þ ions with very similar chemical and spectroscopic properties could not be explained in a satisfactory manner. More work isand perhaps a completely new approach may beneeded.